Why the Trim Tab on a Racer Matters So Much

Courtesy: EAA Chapter 1000

Video and still photos clearly show the trim tab on Jimmy Leeward’s modified P-51 air racer Galloping Ghost breaking off before the tragic crash sequence began at the Reno Air Races last week. Reliable eyewitnesses also saw the trim tab depart. Why is the trim tab failure such a potentially important piece of evidence in the search for a probable cause of the accident?

Trim systems are important on any airplane because they are used to neutralize control forces across the airspeed operating range of the airplane. Trim is also used to compensate for forces caused by various CG locations, and to remove control force caused by an out of balance condition such as more fuel in one wing than the other. Extension and retraction of wing flaps also generates pitch force changes in most airplanes.

The various types of trim tabs. Courtesy: Infoinhand.com

But pitch trim takes on an even greater importance in a racing airplane because the airplane is flying at the edge of, or more likely beyond, its original design airspeed.

Among the many decisions an airplane designer must make is setting the angle of incidence of the wing. The angle of incidence is the angle of the wing compared to the centerline of the fuselage, and more importantly, compared to the angle of the horizontal stabilizer.

Since a wing produces lift by flying at a positive angle of attack, most airplanes have a positive angle of incidence for the wing. With the wing angled up compared to the fuselage, the fuselage can remain close to level in cruise while the wing is flying at a positive angle of attack.

Because stability requires the center of lift of a wing to be located forward of the center of the wing chord, an increase in lift causes the wing to pitch up. To compensate for the up pitching moment created by wing lift, the horizontal tail is angled to create a down force to keep the airplane in balance.

As airspeed increases, so does lift. Additional lift creates more nose-up pitching force, so the horizontal stabilizer must generate more down force to keep the airplane in balance or in trim, as pilots would say. If the stabilizer is fixed and non-moving, the only way to generate more down force is to push the trailing edge of the elevator down. It is the function of the elevator trim tab to push the elevator down to compensate for the added wing lift of increasing airspeed.

Trim tabs work opposite of their adjoining control surface, helping to relieve control forces for the pilot. Their function becomes even more important at high speeds.

At high airspeeds the pilot moves the trim system to deflect the trim tab up, which generates the force to push the elevator down. When an airplane is flying within its original design airspeed envelope there is enough force from the trim system to balance pitching forces from the wing.

But when an airplane is flying at the extreme fast limit of its design, the trim system is operating at its limits to push the elevator down and keep the wing from pitching the airplane up.

If a trim tab fails when the airplane is flying at high airspeed, all of the force the tab was generating would be instantly transferred into the flight controls, slamming the stick back with extreme force. The result would be a violent nose-up pitching of the airplane.

Nobody knows yet what caused Jimmy Leeward’s airplane to go out of control at Reno, but that’s why possible failure of the pitch trim system is being examined so closely.

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84 Responses to Why the Trim Tab on a Racer Matters So Much

  1. Roger says:

    The importance and even lethality of the trim tab is not limited to “the big iron” or even hot rod home builts. Pilots have lost their lives due to trim tabs even in planes like the Cessna 182.

    But…several examples: A couple of friends were on their way to Sun-n’-Fun some years back in a relatively fast and slippery home build. The elevator trim tab broke in level cruise. This was followed abruptly by what was described as roughly a 6G pull up. Quite a thrill when you are not expecting it and worse if you don’t have the skill (or strength) to handle it. The pilot was able to easily handle the situation.

    When I land I know I did it right because the trim will be “full nose up” . You just continuously keep easing in nose up trim on final, but you also carry a fair amount of power. Power on landings are about 10 knots slower than power off and use a lot less runway. However, if you have a balked landing and go full power (ease it in) that Debonair will want to stand on its tail. It takes a lot of force to hold the nose down while trimming.

    The Deb, it’s descendants, and the Cessna 182 will go into a very steep climb and stall if the nose is not held down in the balked landing situation. More than one pilot has “bought the farm” when they were unprepared for that sudden nose high attitude, or they were physically incapable of holding the nose down.

    The 172, 182, and Bonanzas are all capable of being landed using only the elevator trim. It’s an interesting exercise to do although doing it with an instructor along the first few times is more than advisable.

  2. Jim Gombold says:

    Roger said, “When I land I know I did it right because the trim will be “full nose up” . You just continuously keep easing in nose up trim on final, …………..”

    Ok, I do not know if you are kidding about this, or just trying to make a point. To keep trimming nose up on final is an invitation for disaster in two ways:

    1. As you mentioned above, in making a go around.

    2. The second though is a more subtle way of inviting trouble. I am talking about forming a bad habit in early years, and letting it carry through to larger aircraft. On a transport aircraft, if you keeping trimming during the flare, it is very easy to have a tail strike during landing.

    I am not telling you how to fly, but an airplane trimmed for hands off flight on final at the proper speed, is a safe bet. Using a bit of back pressure for the flare, instead of the trim, and being able to release it once on the ground, makes for a safe landing. The go around is much easier managed as well.

    The aerodynamics of flight haven’t changed since Orville and Wilbur took to the skies, we just need to understand and respect them. Be careful out there.

    Jim

    • John in Brisbane says:

      A couple of times my instructor made me take my hands (just) off the controls on final to see if I had it trimmed to proceed nicely down towards the numbers …

    • Walter says:

      A C-!82 needs to be trimmed somewhat nose up on final,or the stick forces,in particular during flare get unbearably high. But not trimming all the way UP, helps during a balked landing, where the 182 an others need a healthy push and a few quick slabs UP on the trim wheel. It is all about beeing prepared and avoiding the extreme. In racing,my unexperienced humble opinion, is probably to hold some small up-trim avoid inadvertantly hitting the ground. It might als o help the stick pull around the pilons.

  3. Roger says:

    No, you don’t trim through the flare, if you trim hands off with the proper power settings and full flaps the trim will reach full up well before you reach the flare. The flare will be exactly as you describe it. Just finger tip pressure. That is what we were taught in the Air Safety Foundation Bo Specific training. This results in a final with a speed (depending on model) considerably slower than most Bo pilots fly. In the Deb it’s a tad under 80 MPH. They complained that most Bo pilots land wayyyy too fast. BTW years back I had an instructor who had me land a 172 the same way. We do have to remember that each aircraft is an individual.

    As for the go-around and particularly the balked landing, we just have to remember to hold the nose down until the plane is properly trimmed.

    If you touch down like this which I prefer to hold it off until it stalls on, you let the nose down for a short field landing, get on the brakes and pull back on the yoke. That puts more pressure on the mains plus gives aerodynamic braking. The older Bo has about the same wing loading as a Cherokee 180 or about 17# per sq ft. Flown by the book it is a very good short field airplane and can match or beat most 172′s. Remember the older Bonanzas and Debonairs are a lot lighter than the newer ones so they can get in and out of very short fields and particularly so if they have had larger engines installed which a lot of the older ones have.

  4. Jim Gombold says:

    I just never thought of “doing it right” as a position of the trim tab after landing. Guess I just never noticed it too much. Outside of resetting the trim in the cockpit for takeoff for the next pilot, and seeing the position of the trim tab during the walk around before takeoff, I never thought about it too much.

    Jim

  5. Roger says:

    I never did either until I had it pointed out after a landing at the proficiency training.
    The early Debs had a very coarse trim with the trim wheel being up behind the Panel. You have to know where it is because you can’t see it although there is a white stripe painted on the front of the panel to show you where it’s hidden<:-)). A 1/4" movement of the wheel is enough to lift you right out of the seat or push you down. They changed it to a more modest change after about the first 60 planes. Ball had the number listed in his book.

  6. Thomas Boyle says:

    Mac,

    Oh, dear. This stuff is complicated and some of it is counterintuitive, and you’ve gotten your aerodynamics in a knot. Your conclusion – that the trim tab is needed to deflect the elevator downward in high-speed flight – is correct, but how you get there is all mixed up.

    Without getting too deep into the details, let me take a shot at fixing it for you.

    “Because stability requires the center of lift of a wing to be located forward of the center of the wing chord, an increase in lift causes the wing to pitch up. To compensate for the up pitching moment created by wing lift, the horizontal tail is angled to create a down force to keep the airplane in balance.”

    Stability requires that an increase in wing lift will pitch the nose down, not up. If, as you describe it, an increase in wing lift caused the wing to pitch up, it would further increase the wing lift and cause the wing to pitch up more, creating an (unstable) runaway pitch condition.

    Complicating matters, a conventional, cambered wing “wants” to pitch nose-down because of the camber (it has a “negative pitching moment”). Without a tail the only way to balance the aircraft would be to put the center of lift ahead of the center of gravity, to provide the required balancing nose-up effect. The aircraft would be balanced like this, but it would be unstable balance – like a pencil balanced on its point. If the lift should increase for any reason (flying into a vertical gust, say), it would push the nose up, increasing the lift further, and of course that’s unstable. (Vice versa, too – the nose could run away downward as easily as upward.)

    Fixing this requires a tail. The downforce on the tail offsets the nose-down tendency by adding a “positive pitching moment”, allowing the aircraft to be balanced even with the lift center located aft of the center of gravity, as required for stability.

    “As airspeed increases, so does lift. Additional lift creates more nose-up pitching force, so the horizontal stabilizer must generate more down force to keep the airplane in balance or in trim, as pilots would say. “

    No – if additional lift created more nose-up pitching force, not only would the aircraft be unstable, but the horizontal stabilizer would need to create less downforce, not more.

    Actually, when the speed increases the pilot lowers the nose to maintain lift equal to the weight of the aircraft. No change there, really. But, the downforce on the tail increases at the higher speed, and now it’s bigger than it needs to be. As a result, the airplane “wants” to raise its nose and bleed off speed to get back in balance – and that’s what we want, in a stable airplane.

    “At high airspeeds the pilot moves the trim system to deflect the trim tab up, which generates the force to push the elevator down. When an airplane is flying within its original design airspeed envelope there is enough force from the trim system to balance pitching forces from the wing.”

    On this part, you’re right (for the wrong reasons, above). To get the airplane balanced at the higher speed, the pilot needs to reduce the downforce on the tail. To do that, the pilot pushes the elevator downward – or the trim tab upward (which pushes the elevator downward, which reduces the downforce on the tail).

    And that’s why we need nose-down trim at high speed.

    • Mike says:

      yes, what tom said……………

    • Jeff Schlueter says:

      I’m glad Thomas wrote this, because I was thoroughly confused by Mac’s description as well. It seemed to me he had things totally backwards, talking about how a downward force on the horizontal stab was needed to prevent the nose from pitching up. I’m no professional, but I know that the downward force on the stab is REQUIRED to pitch the nose up. Or did I miss something in primary training?

    • Dan says:

      Thanks Thomas, Mac’s aerodynamics is backwards, hope he doesn’t ever try and design an airplane.

    • Walter says:

      Exactly right !!

  7. Mac says:

    Sorry about the confusion. The down force is applied to the trailing edge of the elevator by the trim tab to push the elevator down. So if the tab were to fail the elevator would rise allowing the nose to pitch up.

    Mac Mc

    • Dan says:

      That may be so…but your explanation of how you got to that point is all backwards as has already been explained above.

    • Richard says:

      “Yes, but…”

      Although it is improbable that an aircraft can be designed to be “in trim” across its entire flight regime without the use of a trim tab, it seems to me that the practice of using very substantial (excessive?) trim tab adjustment at race airspeed is a band aid for an aircraft that is essentially out of trim at the most critical flight speed where control forces and loads are the greatest.

      Whether the failure of the trim tab was the result of flutter, shock loading from wake turbulence or other factors will be investigated and perhaps determined. It failed and a failure mode effects analysis seems rather obviously to suggest that something need be done to change things as this is the second instance of such a failure. There may even have been other instances where damage occurred, but was not reported. What is very different between the Galloping Ghost mishap and the Voodoo Chile mishap is the roll vector. Perhaps the difference was a matter of differences in the configuration of the two aircraft.

      While many presume to discount the potential effect of an aft CG condition (I have no knowledge of the actual CG of Galloping Ghost), it is well known that an aft CG condition can cause serious problems. At the very least, it may exaggerate the trim issues when an aircraft is loaded up rounding a pylon.

      I think that all concerned should be examining their own practices. Who knows, there might even be a performance advantage to having the aircraft in better trim at racing speeds.

      As a side note, it is not uncommon for clipped wing aircraft to require substantial balance adjustments. For example, Bevo Howard’s clipped wing cub had a weight added to the tail to get it in balance for his aerobatic routines.

  8. Thomas Boyle says:

    Now I’ll throw in a small point that almost no-one covers in ground school, which is that it is actually possible to design an aircraft so that in normal flight there is an upload on the tail! In fact, it’s normal to design gliders so that they have an upload on the tail at speeds lower than best glide (best L/D) speed.

    In my description above I started by assuming a download on the tail, then described how it would get bigger at higher speeds. But, I could have started by assuming a small amount of lift on the tail (or no load at all); at higher speed the angle of attack of the main wing and tail are reduced, so the lift on the tail gets smaller or goes negative, which leaves the aircraft with a net nose-up change in the pitching moment, as required for stability.

    While it seems to be more difficult for most of us to imagine this, rather than the “tail always has a download” mental picture, there is a familiar unconventional layout where it’s easy to see that it always has an upload on the tail: the canard. Of course, in that case the tail is very big, too!

  9. golly. says:

    A photo now made public shows that Jimmy’s seat was not in the cockpit, seconds before it crashed: http://www.dailymail.co.uk/news/article-2039871/Reno-air-crash-2011-Pilots-chair-broken-moments-impact.html

    I’m wondering if the trim-tab came off first (do we know when it came off?), the plane nosed up radically, and he (and seat) were subjected to G-forces which broke the seat off forcing him back from the controls, at which point the plane rolled and nose-dived? Just speculation. We’ll get the details soon enough.

    • jack irwin says:

      the back of the seat was up against a bulkhead, could not have gone back.. On board telemetry said Jimmy pulled ten and a half G’s when the trim tab let loose. He was pulling 100 inches map at that time, and that is what GG was pulling at impact.

    • Bob says:

      The picture that shows the trim tab missing also seems to show the top or back of a helmet forward in the cockpit when enlarged.

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  11. Don Hull says:

    I would be interested to know if any of the Unlimited Air Racers at Reno use a stabilator, i.e., a movable horizontal stabilizer. I’ve been to the Reno Air Races twice but must confess I did not take the time to notice. I’m not saying it would be a solution to this problem, but it must be recognized that the stabilator is commonly used in high speed aircraft. It would seem to me that a stabilator on an Unlimited Reno Racer MIGHT result in less drag than a horizontal stabilizer and elevator with a trim tab set for significant down pitch to the aircraft. I’m sure it’s been attempted and there must be at least one good reason why they are not commonly used at Reno. One would have to say that’s a significant amount of down trim if it’s sudden release results g-loading on the order of 10 g’s. It’s been mentioned that Bob Hannah experienced a similar event several years ago in Voodoo when his trim tab failed during a Reno race. In his case the P-51 climbed high enough for him to “come to” and regain control before declaring a Mayday and landing. As in other tragedies, I really hope a truly safer design results from this event. It may be too early to start re-designing the pitch trim system on the Unlimiteds, but one must admit the photographic evidence supports the notion that the trim tab failed and separated suddenly.

  12. Speed says:

    With no change in angle of attack, as airspeed increases lift increases.

    As airspeed increases the angle of attack must be reduced to maintain level flight. The pilot does this by pushing the stick forward which pushes the elevator down. The pilot may use elevator trim to reduce the force necessary to maintain level flight. He will trim “nose down” which is “trim tab up” to do this.

    If the elevator trim tab comes off, the “nose down” trim is no longer there, the elevator moves up, the angle of attack increases, lift increases and the airplane climbs.

  13. Niko says:

    So what about the roll and dive on the top? Any speculation on what caused that? Since the same thing happened to Voodoo but it just climbed I wonder why GG didn’t do that.

    • Jim Oeffinger says:

      Regarding the difference in Voodoo’s and GG’s post failure behavior: I’ll give it a shot, but not with all of the technical talk about pitching moments, etc., that no one seems to be able to keep straight. A simple POSSIBILITY, straight and level, pull back on the stick and you go straight up. Pull back on the stick in a turn what happens? You go up and over, right? Might be more complicated than that, but maybe not. Voodoo’s issue also bent the torque tube. You can find the pictures online pretty easily.

      • Walt Woltosz says:

        In all likelihood, Voodoo was also in a turn, because these planes are almost never straight and level in the races. So why would one roll over and the other one didn’t? Maybe it has to do with engine torque. Taking off in a P-51, you can’t jam the throttle forward all at once or the torque will spin you around – the roque produced by the prop has to be countered, just like a helicopter needs a tail rotor to keep the fuselage from rotating in the opposite direction of the main rotor. Pulling power off rapidly would have the opposite effect (just as it does in a helicopter – pedal is needed whenever you change power). If the sudden pitch up caused the pilot’s arm to pull back on the throttle rapidly, a roll would inevitably ensue. Maybe the Voodoo pilot was lucky that his hand wasn’t gripping the throttle too tightly when the pitch-up occured and it slipped off, and maybe Leeward was not so lucky.

        Just a theory.

        • Jim Oeffinger says:

          As I said, a POSSIBILITY. Turns vs. “straight and level” is relative, but it is not a circle. Unlimiteds do use the long course and this does produce somewhat of a straightaway. Regarding power, see Jack Irwin’s comment. 100 inches mp all the way.

  14. Speed says:

    Something I haven’t seen discussed (and with good reason — it’s all speculation right now) is structural damage that may have occurred due to overstress from the sharp pull up. The NTSB has ways of discovering such things.

  15. maradamx3 says:

    “Since a wing produces lift by flying at a positive angle of attack,….” ???
    Doesn’t a wing produce lift by the airflow over the top and bottom surfaces, regardless of AoA?

    • Roger says:

      Sometime take an afternoon and attend a model air show. Usually someone will be flying Snoopy’s Dog House. All flat planks with Snoopy in silhouette on top for lateral surface. None of the Bernoulli stuff.
      A wing generates lift by hurling air “downward;” the quotes because down is not necessarily towards the earth.

  16. Gordon Arnaut says:

    Yes, Mac got some things mixed up…but Thomas’s correction didn’t get it right either…

    Thomas your explanation is correct for the most part, but the part about less downforce on the tailplane as airspeed increases is backward…let’s start from square one…

    The wing pitching characteristics are a function of the airfoil camber, as you said…positive camber is where the concave side is facing down and this will create a nose-down pitching moment, or negative pitching moment, which is what we want because it is stabilizing…

    But airfoil pitching moment is not all there is to it…a symmetric airfoil has zero pitching moment, but that does not mean that there will be no pitching moment on the airplane…because the airplane’s pitching moment is a function of all forces and moments about the airplane’s center of gravity…

    This includes the moment created by wing lift multiplied by the distance from the point at which the lift acts (center of lift or aerodynamic center, usually about the quarter chord point) to the airplane center of gravity…

    A symmetric airfoil may have zero moment but it still makes a pitching moment due to lift force times the moment arm to the CG…so it still needs a tail…

    Likewise we could have a reflexed wing (typically at the trailing edge) that will produce a nose-up pitching moment (as in Mac’s scenario) but the airplane can still have an overall nose-down pitching moment, provided the CG is far enough forward of the wing center of lift that the lift-moment arm product is greater than the nose up pitching moment of the wing itself…

    We can also have an airplane with a tail that produces lift instead of downforce…if the CG is aft of the wing center of lift then the lift-moment arm product will produce a nose-up pitching moment and if this nose up moment is greater than the nose down moment from the cambered airfoil, then the tail will need to make up lift to balance it…

    We can also do away with the tail altogether… let’s say we have a wing with a reflexed trailing edge that produces a nose-up moment…now we can put the CG forward of the center of lift and the lift-moment arm product will balance the airfoil nose-up moment…now we have a flying wing like the B2…

    So it is important to remember that the nose up or nose down pitching characteristics of the airfoil are not the whole story by any means…we have to keep in mind the total moment about the CG which is strongly influenced by the product of wing lift x moment arm to the CG…

    Where we place the CG in relation to wing lift and tail lift is also important…but here we need not worry about the wing center of lift, but the airplane’s overall center of lift which will be quite a bit farther aft of the wing center of lift…

    This is called the neutral point and is the point on the airplane through which all forces act…the airplane’s aerodynamic center…

    For stability in a wing-tail conventional configuration it is important to place the CG ahead of the neutral point…although we can place the CG aft of the wing center of lift…and we often do…

    Now trim requirements change with speed…at lower speeds the tail might need to make up lift to balance the airplane…while at high speeds it will need to make a down force…and at some point in between the tail will make zero lift as this is most efficient since there is no induced drag when there is no lift…

    I will try to explain this but a drawing would be most helpful…here is the reason why trim changes with airspeed…it is basically because the only thing that changes with speed is the airfoil pitching moment…it gets bigger with increasing airspeed…just like lift and drag get bigger with increasing airspeed…

    Now let us walk through what happens when we are flying at our design speed for best lift/drag ratio…let us assume that the wing airfoil is of positive camber and has has a nose-down pitching moment…

    Let us assume that the CG is aft of the wing center of lift but sufficiently forward of the airplane center of lift (neutral point) that we have a good static stability margin…

    With CG being aft of the wing center of lift, the lift-moment arm product creates a nose up pitching moment (positive moment, like Mac’s scenario)…but this is balanced by the airfoil nose-down pitching moment which is due to camber…

    So we have a tail that needs to do nothing…the airplane moments are perfectly balanced and the airplane is in trim…and that is the ideal situation because this means zero trim drag and maximum aerodynamic efficiency…but the tail is still there in case there is a pitch excursion and it will right the airplane to its trimmed state…

    Now what happens when we slow down but still continue to fly level?…well the wing lift x moment arm product always remains the same in level flight because weight remains constant and so does CG location (more or less on both)…so all that changes is the amount of pitching moment we get from the airfoil…

    Remember that the airfoil pitching moment coefficient, unlike the lift and drag coefficients, remains constant at any angle of attack…so the total airfoil pitching moment is purely a function of airspeed… more airspeed more pitching moment…less airspeed, less pitching moment…

    So now at the lower speed we have less nose down pitching moment from the airfoil and the lift-moment arm product (nose-up) is overpowering the airfoil pitching moment (nose down) and our tail must make up lift in order to trim the airplane…

    Is this more efficient than down force on the tail?..yes but still not as efficient as no lift on the tail because any lift also comes with induced drag…

    Now let us look at what happens when we take the plane into high speed…again the lift-moment arm product (nose-up) remains the same…but the nose down moment due to the airfoil increases, being dependent strictly on airspeed…

    Now we have the reverse situation where the airfoil pitching moment is overpowering the lift-moment arm product…now the tail must obviously push down in order to balance the airplane and maintain trim…

    Now in a race airplane the question is whether you want a lot of downforce on the tail to begin with?…any downforce on the tail means you need more lift on the wing in order to hold the airplane up against its weight plus the downforce on the tail…but more lift on the wing comes with more induced drag, which, in turn, requires more thrust…thereby decreasing speed…

    For best speed the tail should be set up as close to zero lift (and zero trim drag) as possible…and I would think the racers would do this…by setting the tailplane incidence to provide zero lift at the airplane’s race speed…although this would require that CG be considerably aft of the wing center of lift…

    that way the wing lift x moment arm product would produce a nose-up moment that would exactly balance the heavy nose down moment caused by the airfoil at such high speed…

    So little trimming should be required to fly the course…and this may be why only one trim tab was functional on the accident Mustang, the other one not movable at all…

    So my question is why would the airplane be trimmed for so much tail down force to begin with?…perhaps the very steep turns require so much back stick that the pilots dial in a lot of nose up trim? And then they are pushing forward stick on the straightaways…?

    Or maybe the entire assumption that the departed trim tab cause the violent pitch up is wrong?

    • Thomas Boyle says:

      Hi Gordon,

      Well, you can see why I started off with a brief disclaimer,

      Without getting too deep into the details…

      :-D

      You’re absolutely right that the aerodynamic pitching moment on a cambered wing increases with airspeed; it increases like the square of the airspeed. I did skip over that.

      I didn’t say that there was a need for less downforce on the tail at high speed. I said that if nothing is changed, the tail will automatically generate too much downforce at high speed (or too little upforce). There is still more downforce on the tail at high speed than at low speed.

      If you use a symmetric airfoil and put the cg at the aerodynamic center, you can create an airplane that doesn’t “need” a tail. Unfortunately it will be neutrally pitch stable (not a lot of fun to fly). But, aerobatic aircraft approximate this condition by having symmetric wings and quite small pitch stability margins. They can hold a nice 45 degree dive line because the airplane doesn’t try very hard to pitch up.

      Likewise we could have a reflexed wing (typically at the trailing edge) that will produce a nose-up pitching moment (as in Mac’s scenario) but the airplane can still have an overall nose-down pitching moment, provided the CG is far enough forward of the wing center of lift that the lift-moment arm product is greater than the nose up pitching moment of the wing itself…

      That’s true, but the aircraft will dive and fly faster until the pitch-up moment of the reflexed wing is enough to balance the forward cg. That’s what defines its trim speed.

  17. Gordon Arnaut says:

    Oops, I got things a little backward myself…

    Okay, let’s make things simple…we design the airplane for stability at both low and high speeds…at low speed we want the airplane to lower its nose and avoid a stall, which means an UP lift on the tail…

    At high speed we want the airplane to pitch up by itself and bleed off excess speed…and that is what it will do…let’s say we nose the airplane over and head straight down…as our speed increases it will take more and more stick forward force to keep the plane’s nose pointed down…

    So the airplane will start with tail down force at low speed, and increasing tail UP lift as as we increase speed…not the other way around…

    • Thomas Boyle says:

      Gordon,

      You had it right the first time! You need the forward stick at high speed, not because you need a net lift force on the tail, but because you need to reduce the excessive amount of downforce it is generating.

      If the airplane is pitch stable and you try to fly it faster than its trim speed, the tail will generate excess downforce and pull the nose up. To prevent that, you have to change its trim speed by reducing the downforce on the tail. You either re-trim the tail incidence to reduce the downforce, or you push forward on the stick. However, the net downforce remains higher at high speed than it was at low speed.

      Like I said, it’s counterintuitive, and confusing!

  18. Walt Woltosz says:

    I’ve been told by someone close to Rare Bear that these guys trim for about 40 lb of forward force to hold the nose level, so that if anything happens, just relaxign the forward pressure takes them up – away from the ground. If that’s correct, losing the trim tab could make that 40 lb turn into something very much higher in an instant – more than the pilot can overcome, driving the stick back, and resulting in the high-G pitch-up. If the pilot is gripping the throttle tightly, he might also pull back on it rapidly, inducing a roll (see my earlier comment above). If the videos are good enough, the NTSB should be able to see where the controls went and maybe even tell if the throttle was rapidly decreased by resolving the position-vs-time of the airplane with the thrust, drag, and gravity forces that would have been acting at each instant to cause its trajectory.

  19. Don Hull says:

    I’d still like to know if any of the Unlimited Air Racers at Reno use a stabilator instead of a horizontal stabilizer and elevator. I’m guessing none of you theoretical guys know. One way or the other, I’m gonna find out. :-)

    • derbyrm says:

      Good question. I once spent quite a bit of time (I’m a poor machinist.) taking the play out of the bell crank connection on a Thorp T-18 I owned. I was later told by an aerodynamicist I respect that play there was stabilizing with a stabilator; and no, I can’t explain the logic.
      A stabilator should have significantly less drag since it doesn’t incorporate two opposing forces, each with its own induced drag.
      If one is cutting up an F-15 to shorten the fuselage and the wings, substituting a stabilator seems like a minor mod. At a distance, the structural loads on the airframe should be the same.

  20. Felix Finch says:

    Wouldn’t the roll be accounted for by losing just one trim tab? Or are the elevators joined so well that they would not react separately? And if they are that well joined, is there still enough differential effect from one missing trim tab to roll the airplane?

    • Wm says:

      Galloping Ghost only had one trim tab on the left side. Jimmy’s plane was modified from the original design in that respect, as the factory P-51 had two, one on each side.

  21. Afterburner says:

    I have a question that is separate from all this talk about trim tabs.

    In one of the videos, someone pulled a single frame just before the aircraft impacted the tarmac. In that frame you can clearly see the tailwheel extended. Why is the tailwheel extended? How does the retract mechanism on the tailwheel work? Did the departure of the trim tab cause other damage that caused the tailwheel to extend? Or was it simply a matter of the excessive g’s mentioned previously that overpowered the locking mechanism? Could any of this be related to the fact that the fuselage had been shortened by 3 feet?

    Could there have been other failures inside the aircraft that caused the trim tab to depart and the tailwheel to extend?

  22. D Rant says:

    SABOTAGE! Because, as we all know, trim tabs seem to always be just, falling off.

  23. Dan Winkelman says:

    A business associate was at this race when Leeward went down. He described seeing the tail flutter as Leeward lost control. This is still all speculative: if the tail surfaces began to flutter severely enough that it was visible from the ground, that could have caused the trim tab to part company with the aircraft, compounding his control problems.

    We won’t know the real causes and effects until a thorough investigation is completed, and even then it may be inconclusive.

    Fly safe, everyone.

  24. Michael R. Gallagher says:

    Two aspects of the tragic mishap have not drawn much attention:
    1) Could the pilot suffered a broken neck from the sudden application of 10-11 g’s. A 74 year old neck supporting both a head and a helmet might not have been up to the load.
    2) Why no post impact explosion? Perhaps not much fuel on board and the vaporization from the impact did not creat a combustible fuel air mixture?

  25. Corrie says:

    Afterburner,
    I’ve been told that on a P-51, high G’s can cause the tailwheel to extend.

    Felix,
    There’s not enough surface area difference between a solid elevator and one missing a square foot of trim tab to have enough roll authority to roll a P-51. The roll was probably the gyro effect of the prop accelerating in three dimensions.

    Walt,
    I’ve read that military show pilots roll in a lot of nose-down trim so they’re always pulling hard. Trim tab failure due to high-sped flutter would slam the stick back resulting in immediate pitch-up and accelerated stall. At that point Isaac Newton and God are flying the airplane. Isaac doesn’t know how to fly, and God is busy looking up the pilot’s name in The Big Book.

    Don,

    Most Unlimited racers are converted WW2 (or immediately postwar) piston types designed in the 1940s for much lower airspeeds than are being flown at Reno today. You simply don’t need a trimmable horizontal stab or stabilator at those speeds. (The first few generations of F4U Corsairs had fabric-covered control surfaces!) Retro-fitting a trimmable stab on a warbird would be a major undertaking.

    Perhaps this accident will have some racers considering it.

    • Richard says:

      I had heard a number of stories about forward stick pressure and so on about the Blue Angels’ (legacy) F-18s (not the Super Hornet), but FAQ #15 on the web site says that there is a 35 pound spring installed to minimize the opportunity for “uncommanded aircraft movements”. http://www.blueangelsalumni.org/bafaq.htm

      While I don’t know about the trim of the Thunderbirds’ F-16s I do note that they use a side stick controller (“electric jet”) rather than a conventional control system as used in the F-18. Unless there has been a change of policy, the Thunderbirds fly aircraft that vary from line aircraft only in paint scheme and smoke systems so that the aircraft could be quickly restored to operational status.

  26. Eric Foy says:

    “But when an airplane is flying at the extreme fast limit of its design, the trim system is operating at its limits to push the elevator down and keep the wing from pitching the airplane up.”
    …No, I don’t think so, though this might be true in the case of a very poorly trimmed aircraft.

    The really bad thing about losing a trim tab is that typically the reason it comes off is because its linkage has failed. When a trim tab linkage fails it usually starts to oscillate. The oscillation causes the control surface to oscillate. The motion compounds and builds to catastrophic levels within tenths of seconds. Usually the whole tail structure is destroyed in flight, which makes this case somewhat unique in that the airframe appeared intact before impact. What you can’t see, however, is the probable internal damage to the control system. It could have easily torn cable pulley mounts loose, buckled push rods, etc. It’s possible that the trim tab shook itself off before the airframe was destroyed, but after the control system was rendered inop.

  27. Gordon Arnaut says:

    Thomas, I did have it backward…

    Forward stick means down elevator, which makes UP lift on the tail and nose down on the airplane…if Leeward had a lot of forward trim dialed in, the loss of the tab would have slammed the stick back and pitched the nose up…as others have pointed out…

    But why would you dial in nose down trim when you are 50 ft agl at 500 mph?…if you let go of the stick you go straight in…if anything what you want is nose-up trim so that if you let go, you go up, away from the ground as Walt pointed out…plus it will make pulling through those steep turns easier…

    Anyway in my explanation I did leave out the contribution of the tail lift to the overall equation as you pointed out…

    Here goes…if we shove the nose over and go straight down we have no lift, but we need to have maximum positive pitching moment (nose up) in order to right the airplane…

    This is done by setting the tail incidence with the leading edge pointing down, in order to make a tail DOWN force and the positive pitching moment that goes with it (nose up)…

    the increasing speed over the tail increases the down force and makes the nose want to pitch up more the faster we go…that’s why it is impossible to hold stick down in a dive…even with two guys pushing on the stick you will not be able to do it for long…

    That’s the part I left out, the tail incidence angle…the rest is okay but I got the lift directions reversed because I did not take the tail lift into consideration…

    So that is the aerodynamics of it…airfoil camber, wing lift and moment arm AND the tail lift (either down or up) and the moment arm…all of these forces and moments act right at the CG…when the airplane is in trim there is zero moment about the CG…

    I would assume Leeward had nose-up trim dialed in so he would have to push forward…if he encountered tail flutter that could easily yank the stick from your grip and up you go…

    • Thomas Boyle says:

      I think we’re in violent agreement but are having a terminology problem. We need to clarify whether we’re talking about absolute lift and trim, or relative.

      To try to clarify, let me call the tendency of the aircraft to pitch nose-up or nose-down its “absolute” trim. However, if the elevator is trimmed to a non-neutral position (i.e., where it would trail if there were no trim tab), let’s call that its “relative” trim. Trim tab up -> elevator down is a nose-down relative trim. At the same time, if the aircraft if flying level with no tendency to deviate, it is in neutral absolute trim.

      Forward stick means down elevator, which means UP lift on the tail relative to what it would have been otherwise. At high speed there may be a downforce on the tail in absolute terms even with (some) forward elevator – just not as much as there would have been without the forward elevator.

      But why would you dial in nose down trim when you are 50 ft agl at 500 mph?…if you let go of the stick you go straight in

      Indeed, if you dial in absolute nose-down trim then the nose would go down. However, what I believe people commonly understand by “nose-down trim” is what I’m calling relative trim. You would dial in nose-down trim as speed increases, to keep the nose level at neutral stick pressure and maintain neutral absolute trim.

      At high speed, the normal condition is neutral (or slightly nose-up) absolute trim, achieved with substantial nose-down relative trim. If the trim tab fails, the elevator will adopt the free-trail position (neutral relative), leaving the aircraft now having a strong pitch-up trim condition in an absolute sense.

      Trimming for modest absolute nose-up doesn’t change the fact that it may require considerable relative trim that, on failure, could leave the aircraft with a strong absolute up-trim condition.

      Cheers!

  28. lloyd says:

    you guys have way to much time on your hands, i think it should be left to the FAA.

  29. Dennis Karoleski says:

    If you Google “VooDoo racer” the site explains Bob Hannah’s pitch-up was due to incorrectly rigged flaps. That required the tab to be extended further than normal into the airstream, causing it to flutter and depart the aircraft.

  30. Roger says:

    Lloyd:

    Humans have an innate need to know and to ignore it would be unnatural and extremely frustrating. Also there is a lot of expertise available in this group and much of the speculation is based on actual information available from images, data, and previous accidents that were similar in nature. As time goes on the gaps are slowly filling in. Certainly we are not privy to all the information the FAA has but most of it seems to be made available.

    If you want to see “off the wall” speculation from “those in the know” who apparently have never set foot in an airplane, go to the national news blogs which abound with misinformation. Pilots with thousands of hours and those “who were there” are ignored and disparaged as “know it alls” by “experts” who appear to know nothing about flying airplanes. Nor do they know anything about “crowd lines” at air shows.

    One point that needs to be made though and that is the claim that this was an air race and not a air show. Unfortunately it was advertised as an “Air Race and show” if you look at their Internet site, although the show part really doesn’t resemble a typical air show.

  31. John Johnston says:

    Thanks Mac and to all that posted for the educated information. The talking heads on TV think elevators only go to the top floor. I was there and saw what happened…so once again thanks for the educated speculation and explanation.

  32. Eugene says:

    It is the most interesting discussion,I’ve ever heard and the refreshing course of aerodinamics! Thank you folks! Many issues were touched upon here which stay live in the memory for long years. Let me briefly dwell on some. So happened,I’ve caught all of sudden G=11.3 and have had my neck slightly displayed for two weeks. It was during the tests of the fighter. The throttle was fully under control. The cause of G overshooting was the unforeseen sharp unloading of the backforces on the stick. Somewhat about 17 kg desappeared but hand muscles tension stayed frozen for a bit. It was enough to G jump from planned 9 to not desired at all 11.3 Just the habit to fasten the harness tightly saved my face from the control stick head.Later we found out that the cause was the wrong methodology when we haven’t taken in account the work of automatic. So to procced from the assumption that the G numbers could move the hand with a throttle to the idle automatically-I don’t think so. I am also happened to take part in the tests where we were reseaching the possibility to complete safety flight with primary control failure by one separate channel in small aircraft. The brief conclusion is: to master by skill of landing without control stick one is in need to do it step by step at first at the altitude with experienced instructor and train it regularly. Someday it may save your life. As for trim, when close to terrain or on glideslope in IMC, I use to leave some push forces on the stick-de bene esse

    • derbyrm says:

      Aircraft designed for catapult launches; e.g. the A-6, have a T-handle fixed to the fuselage structure forward of the throttle so the pilot can wrap his fingers around it and prevent the acceleration of the launch resulting in a power off “climb” from the carrier.
      G forces aren’t just vertical.

  33. Gordon Arnaut says:

    Eugene, absolutely agree with the push forces on the stick when close to terrain…

    This means if you lose your grip or take an unexpected nap the plane will go up not down…

    Thomas, I think I understand what you are saying…but it doesn’t matter…Look let’s make it simple…a race airplane SHOULD be rigged with its tailplane incidence so it is in perfect trim at race sped…

    This means no trim tab deflection and no elevator deflection and lift or downforce or moment on any kind on the tail…which is just along for the ride and to bring things back if there is a pitch excursion…

    The reason is that this is the most aerodynamically efficient configuration and you will be flying with less drag (the tailplane making lift to push the nose down comes with plenty of induced drag) and more speed for a given engine thrust…

    The stock airplane would be designed to make all kind of nose-up pitching moment at that speed because it is part of its requirement for longitudinal stability…a race plane has no such need…it only needs to go fast…and re-rigging the tailplane is a simple matter…

    Now if you are concerned about the hard ground 50 feet beneath your wings you can add a little bit of nose up trim so you have to push on the stick in order to stay level…

    You lose a little speed but it might be worth it…

    Now let’s say you don’t reset your tailplane incidence and leave it completely stock…which is pretty bizarre considering you have shortened the fuselage by several feet and lopped 10 feet of your wing…

    Now you do have to crank in some nose down trim but you don’t go all the way to where you are in trim hands free…you still leave a little nose up moment in there and push on the stick…

    In no circumstance would you put in excess nose down trim so you have to hold the stick back in order to fly the airplane…

    Now which is the more likely scenario? I would say the neutral tailplane incidence and this is supported by the fact that one trim tab was disconnected as unnecessary…

    So in this situation the loss of a trim tab does not do much, it will not yank the stick out of your hand because the airplane is basically in trim without the tab…

    The most likely scenario is that flutter occurred BEFORE the tab let go…this is usually how it works…the flutter would have ceratinly yanked the stick out of the pilot’s hands and if there was a bit of up trim there the plane would have gone up…

  34. Evan Mortenson says:

    I believe that Mr. Arnaut had the aerodynamics correct the first time around. The key is the aerodynamic pitching moment of the wing itself.

    The pitching moment coefficient remains almost constant over a wide range of angles of attach, and is negative for airfoils with positive camber. Also, the pitching moment itself is a function of velocity squared. Some airfoils are famous for having very low moment coeficients (e.g. NACA 23000-series), but most of the early laminar flow airfoils (such as those used on the Mustang) had relatively high moment coeficients.

    Mr. Arnaut is correct in describing the requirements for basic stability, which can be summarized as requiring the airplane CG to be forward of the neutral point. This can (and does) lead to situations where an airplane is completely stable while carrying a significant up load on the tail. Generally, the possibility of carrying a large up load on the tail is greater when the tail size relative to the wing is large, because this moves the neutral point aft.

    As speed increases, so does the nose down pitching moment produced by the wing, even though wing lift stays almost constant. It is this change in pitcing moment with increasing airspeed that calls for more down load from the tail to balance the airplane. For airplanes with very high pitching moment coefficients the V-dive condition can produce the critical loads for the horizontal tail, just to balance the airplane in level flight.

    The problem for the race airplane is dealing with the extremes of the speed range. The tail down load will be maximum at high speeds, just to balance and maneuver the airplane. At low speeds the high pitching moment disappears, and the tail plane may be carrying an upload. The race pilot can reduce the tail down load at high speed by moving the CG aft before takeoff, but at some point the stability will become unacceptably low (and dangerous).

    It is also important to point out that the load developed on the horizontal tail is not strictly a function of elevator angle. The tailplane has its own incidence angle relative to the fuselage and wing, and the wing creates downwash into the tail that influences the effective angle of attack of the tailplane. With the right tailplane incidence conditions it is quite possible for the elevator to be deflected downward even though the tail as a whole is generating a huge down load. In this situation the trim tab would be up, holding the elevator down. If the tab pushrod were to fail allowing the tab to move to the trail position, the elevator would move up, causing an even greater down load on the tail (and a large pitch up excursion).

    Although Mac may have messed up in describing the aerodynamics of the wing, he got the trim tab’s contribution right. We use the trim tab to relieve the pilot stick forces, but there can be a lot of load on the trim tab and elevator (pushing against one another) to produce this situation, and if the tab were suddenly to fail or depart the airplane, the force that it was supplying to make the pilot’s job managable suddenly goes away.

  35. Mac says:

    Thanks All for the comments.

    The loads on trim tabs at high speed are well known, and that is one of the reasons most jets move the stabilizer leading edge up and down to trim the airplane. This change in the angle of incidence of the stab puts most of the load on the stab structure not on the elevator and a tab on its trailing edge. A trimmable stab also gives an airplane more trim authority so it can operate over a very wide airspeed range and also adjust for big trim loads caused by large wing flaps and leading edge devices.

    If you were going to design an airplane today to fly at the speeds of a Reno racer you would probably trim the stab, not the elevator. But the airplanes at Reno were designed about 70 years ago.

    Mac Mc

  36. Kevin Baird says:

    “which is pretty bizarre considering you have shortened the fuselage by several feet and lopped 10 feet of your wing…”

    The wing clip information is correct, however I don’t recall reading or hearing anything about the fuselage of G.G. being shortened. I’m interested as to where you got this info.

    Kevin

  37. Kevin Baird says:

    “Could any of this be related to the fact that the fuselage had been shortened by 3 feet?”
    Again, where did you get your facts? Leeward Air Ranch website gives length of G.G. as 32′ 3″. The same as a stock P-51.

    Kevin

  38. Don Hull says:

    All this discussion has been based on flying straight and level. Gentlemen, as you know, the racers at Reno spend a lot more time banked between 60 and 90 degrees than they do in straight and level flight. When an airplane is banked, does it take some up elevator to “hold the nose up?” Do you think the pilots might crank in some “up trim” to help them as they bank around the course? I do. What we need here is a former (or current) Unlimited race pilot to speak up about how elevator trim is typically used at Reno. I can understand if they don’t want to discuss this right now. I only hope this whole sad scenario will result in safer racing at Reno in the future.

    • Don Hull says:

      I retract my “up trim” statement I made on Sept. 26. I have since become convinced that the removal of the radiator and air scoop on the bottom of GG resulted in less drag and a nose down moment at racing speeds.

      • Don Hull says:

        Correction…I intended to say that the removal of the air scoop and radiator on the bottom of GG’s fuselage should result in less drag and a nose UP moment, thus requiring more nose down trim. All of this is assuming Mr. Leeward didn’t change incidence angles of the wing and horizontal stab. I must say I really do like the lines of GG after the removal of the scoop and the installation of the Formula I canopy. Perhaps someone will take his ideas and further refine another P-51. Such a shame…such a tragedy.

  39. Don Hull says:

    Thanks Mac Mc,
    Looks like I overlooked your comment about trimmable stabs on high speed aircraft. Someone up above (Corrie) said “Retro-fitting a trimmable stab on a warbird would be a major undertaking.” Compared to the other modifications they make, I would not consider this a “major undertaking.” These guys want to be the fastest, and they are willing to spend the “mostest” to go the “fastest.”

    Back to the trim tab discussion, as someone pointed out above, GG had only one trim tab on the elevator. At the speeds he was running, it appears to me that the GG’s one trim tab would have more aerodynamic load on it than would two trim tabs, which apparently is the stock P-51 configuration. Is it true someone advised Leeward not to run just one elevator trim tab? I have an unverified email that states that. It also says GG incurred 11g’s, loss of fuel flow, intermittent power loss with engine re-start at the top of the arc and 105 inches of MP on the way down.

    • Richard says:

      I had read the same thing as your email on a web posting on a competitive shooting forum. (A fair number of competitive shooters are air race fans, too.) I am unable to verify the information, but here is the link. You can judge it for yourself.

      http://www.jouster.com/forums/showthread.php?22857-Galloping-Ghost-P51-piloted-by-Jimmy-Leeward-crashes-at-reno-Air-show/page4

      Apparently Voodoo Chile (Voodoo) had the same modification (single trim tab) at the time of her incident. Another post referred to a friend who worked on Pegasus before she became Voodoo Chile indicating that the pilot had experienced elevator flutter, though the configuration of Pegasus at that time was not stated. Elsewhere, it was reported that the rivets on Voodoo Chile’s trim tab were found to have sheared after its incident.

      Stiletto is reported to have had an electric trim system as a part of its weight reduction program so it is not improbable to believe that a different trim system was known to be within the capability of the unlimited race community.

      There have been discussions elsewhere about adjusting the angle of incidence of the wing to optimize its performance and trim at race speeds (which also reduces drag). Using the original angle of incidence is reported to be associated with the need to use a lot of elevator trim at race speed.

      I have yet to see a reference to the weight and balance of either Voodoo Chile at the time of her incident or GG prior to the mishap. It is known that, in military configuration, 85 gallons of fuel in the tank behind the pilot caused handling issues because of the aft CG.

      I do not know what the exact configuration of Voodoo Chile or GG may have been, but I have seen some reports that boil-off systems typically use 60 gallons of boil-off fluid which might be water or a water/alcohol mixture in the same general location as the military fuel tank behind the pilot.

      60 gallons of water would weigh about 480 pounds and 85 gallons of gasoline would weigh about 510 pounds so that there is a question to be answered about what effect this may have had upon the aircraft’s handling characteristics in flight and trim issues.

      As far as loss of fuel flow goes, I do not know that the aircraft would have suffered fuel starvation during the positive G pull up and roll. I am sure someone will conduct an analysis of the cause of the roll vector in the GG mishap as compared to the Voodoo Chile incident which was a vertical climb. Perhaps the difference is, as one individual opined, just dumb luck.

  40. Pingback: Reno Airplane Races and Air Shows - Page 2

  41. derbyrm says:

    If there was flutter in the tail surfaces, then all bets are off as to what forces are controlling the flight path. A video shown at Oshkosh some decades ago showed a B-727 fuselage in a wind tunnel with flutter induced in the tail. The entire tail was twisting some ten or twenty degrees relative to the wing stubs.
    A routine part of stability and control design for military size aircraft includes measuring the fuselage flexibility. The structure bends and reduces the control effectiveness; e.g. the pitch loop gain goes down.
    The X-wing fighter (test aircraft) used forward swept wings so that their flexibility increased the roll gain and enhanced maneuverability.
    SPOs being conservative, we’ll probably not see forward swept wings except on drones.

    • Richard says:

      The problem with forward swept wings is mostly structural. It was not until relatively recently that it was practicable to construct wings with sufficient stiffness and strength to keep them from being ripped off during heavy maneuvering, which is where the potential aerodynamic benefits could be achieved.

  42. derbyrm says:

    Yep! Ain’t carbon fiber wonderful?

  43. RHalstead says:

    BUT the forward swept wing is inherently unstable presenting a divergent, positive feedback. IOW with a slight pitch up the wing wants to pitch up even more, but that slight increase adds even more divergence. Hence the “fly by wire” with 3 computers figuring out what to do to prevent the plane from going backwards while squashing the pilot in the transition. Again, the pilot becomes the limiting factor in maneuverability.

  44. derbyrm says:

    Yes he is.

    We once calculated how much more effective the F-16 would be if we could remove the canopy, the ejection seat, the multiple displays, the climate controls, oxygen systems, etc.;
    BUT PILOTS BUY AIRPLANES.

    They also want to be fighter pilots which is why the F-22 is not the B-22. Before 1948, planes that carried their weapons inside the fuselage were called bombers.

    There are poles in the right half plane of most air superiority aircraft, not just the X-wing.

    Don’t count too much on that triple redundancy. They put all three computers in the same box with one fat cable feeding it where one 20 mm shell (or magic BB or stray compressor blade) can kill all three channels in an instant.

    • Richard says:

      The F-16 voting system has gone through some evolutions. The way it starts is everybody votes (A, B, C & D). Anyone who comes up with a different answer is voted off the island in the current vernacular. Where the original system had problems was if it got down to two systems and their answers were different. The system was caught in a paradox so one of the first iterations was that the main system simply took command and that was that. I don’t recall whether a fan blade can get into the FCS or not. I think not, but might be mistaken.

      There were enough early birds that lost fan blades without getting into it that I think it is a fairly low order of probability. In glider mode you will not be flying the aircraft for long in any event. There were some test stand runs with F-111 engines which were intentionally fodded out to examine the practicability of attempting to shroud the engine in some way to contain fan blades. I saw the video which was rather dramatic as the engine ripped itself out of the test stand and danced around the room. Needless to say, the idea got dropped.

      If you take a 23mm or 37mm shell in the FCS you are going to have a bad day. That’s about all there is to say except the Aces II is a great seat.

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  49. Rich Hensch says:

    When flying airplanes,
    The reason we “trim” an aircraft is so that the our brains can use “fine” motor skills of our fingers and hands vice our “course” motor skills of our bicep muscles. If we have the acft trimmed, we can merely use fine motor skills to control it, or if not, we must use our course motor skills as well. As a pilot with 46 years accident free, here is the key: Speed is life!! Altitude is life insurance! And all landings must be nose up, especially on floats, and flying floats is highly addictive!!

  50. Rich Hensch says:

    Instead of USA paying with our taxpayer money, $160Million per acft for new F-35′s, why not dust off a few of the military jets that I used to fly, like A-4 Skyhawks and A-7 Corsair II’s, and the government instead of spending $160Million could spend a few hundred thousand $$, and have the old jets reconfigured with cheap GPS avionics that are available and laser bombing sights. Then rent these machines to wealthy USA pilots who would gladly pay just to have the priviledge of flying them!! This would save $$Millions of taxpayer dollars!!

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