18

Wikipedia says that the control surfaces were locked.

What does this mean, and if the control surfaces cannot be moved, how did the aircraft get into the air in the first place?

FreeMan
  • 16,245
  • 16
  • 87
  • 166
user2927392
  • 2,359
  • 2
  • 20
  • 37

2 Answers2

15

The prototype aircraft had small "blocks" (more like wedges) which were used to prevent the control surfaces moving in the wind and potentially damaging the control surfaces, or even moving the aircraft on the ground. A bit like putting chocks under the wheels to stop the aircraft rolling.

These were not removed when the aircraft was taken on a test flight, so the control surfaces could not move. Essentially, they were "fixed" in an approximately neutral position. Imagine if you couldn't move your steering wheel in your car because someone had put wedges next to your front wheels to prevent them turning: that's basically the situation the pilots were dealing with, but unlike you they can't just hit the brakes and stop once the aircraft is in the air.

The Boeing 299 / B-17 are "taildragger" aircraft.

As you can see in this photograph which I won't link directly due to the size, the aircraft's nose is pointing quite sharply "up" when on the ground.

Here's a B-17, which isn't identical to the Type 299 but is close enough that it makes no difference. Hopefully this gives you the visual to see why the aircraft will lift off at a high enough speed.

B-17

When accelerating the nose being pointed slightly up gives a positive angle of attack for the wings. This means that once the aircraft gets above stall speed, it will naturally lift off into the air. Essentially, the aircraft is already pitched slightly up before any control surfaces are moved.

That also means that when the aircraft takes off, it will climb - at least initially. With the locked elevators, there is no way to change the pitch angle of the aircraft, and the aircraft will either pitch up or down naturally - there is almost no chance that the aircraft would be perfectly trimmed by accident.

In this case, the position the elevators were locked caused the aircraft to continue pitching up until it stalled. The crew had no way to correct this and the aircraft stalled out, rolled and crashed into the ground.

Jon Story
  • 10,417
  • 1
  • 48
  • 62
  • 12
    This has absolutely nothing to do with being a tail-dragger! As the aircraft picks speed and the wings start to generate lift, the aircraft will pitch down, since the centre of lift is behind the main wheels. If it is trimmed for low speed (nose up), it will remain nose up and lift off, but if it is trimmed for high speed (nose down), it will happily continue rolling on the main wheels with tail raised. – Jan Hudec Apr 11 '16 at 17:45
  • Similarly a tricycle gear aircraft if trimmed for low speed will raise the nose wheel (centre of lift ahead of main gear there) and lift off while if trimmed for high speed, it will happily continue rolling on all three wheels. In fact the standard procedure for A320 warns against lifting the nose prematurely and recommends making the take-off roll with forward pressure on the stick when heavy (wing-mounted engines shift the empty CoG forward, so heavy also means CoG at aft limit). – Jan Hudec Apr 11 '16 at 17:50
  • The A320 is affected somewhat by the fact the wings are under the engines - not an issue in the B-17. The B-17 doesn't raise it's tail much naturally like a lighter taildragger, it lifts off almost (but not quite) in a 3-point-landing stance https://www.youtube.com/watch?v=PgpWuxYLhLU&nohtml5=False – Jon Story Apr 11 '16 at 17:53
  • So the problem was that the aircraft was trimmed for speed just above stall speed so it lifted off on its own, climbed a bit in ground effect and stalled as it left the ground effect and slowed down in the upper part of the phugoid cycle. It would have happened if it had a nose wheel too. – Jan Hudec Apr 11 '16 at 18:04
  • 3
    Yes, low mounted engines cause a pitch-up moment when running. But while that makes the problem worse, it does not create it. If the trim speed is above stall (in ground effect) and within what the plane can reach on the ground, it will lift off without control input and whether it has tricycle or conventional gear does not matter. – Jan Hudec Apr 11 '16 at 18:08
  • 1
    If B-17 lifts off in almost 3-point attitude, it is because it corresponds to the appropriate angle of attack. But if you trimmed it nose-down, it would still raise the tail and continue rolling on the ground and not lift off. Whether it lifts off depends on the trimmed speed, not type of gear. – Jan Hudec Apr 11 '16 at 18:12
  • I think you're missing the fundamental point - most B-17's will take off naturally with a neutral stick position. That's why the aircraft took off and, more importantly, why the pilots didn't notice prior to takeoff... They would have no major need to touch the yoke (or is it a stick in the B-17?) perhaps I should make the answer slightly more B-17 specific in that regard – Jon Story Apr 11 '16 at 18:14
  • 1
    I admit there is one difference, but it is in when the crew could notice something is wrong. In tail-dragger the crew is waiting for the tail to raise before doing anything, so they won't realize it is going to lift off early before the wheels are off the ground. In a tricycle, the crew expects the aircraft to only start rotating on positive control input, so when it starts raising the nose early, they will try to keep it on the ground and thus get a chance to cut the engines before they gain altitude. Still, it does not make the situation exclusive to tail-draggers, merely more dangerous. – Jan Hudec Apr 11 '16 at 18:19
  • 1
    @JonStory The pre-takeoff checklist is a pretty good reason to touch the yoke before takeoff. :) That Flight Controls: Free and Clear part is pretty important. – reirab Apr 11 '16 at 18:24
  • 1
    No, I am not. B-17 will take off naturally with neutral stick position. That was contributing factor in the accident. What I am saying is that it is not a consequence of it being a tail-dragger, but a consequence of how it is trimmed and that a tricycle aircraft trimmed the same way would lift off naturally with neutral stick position as well while if B-17 was trimmed differently, it would not lift off with neutral stick position. – Jan Hudec Apr 11 '16 at 18:25
  • 2
    @reirab this accident was one of the main catalysts for the introduction (or at least increased use) of the pre-takeoff checklist. – Jon Story Apr 11 '16 at 18:25
  • And I even see a reason to trim a tail-dragger nose-up while tricycle nose-down. In both cases, you want to keep the third wheel on the ground as long as possible to maintain directional control—and prop engines cause significant yawing moment during take-off roll so you definitely don't want the tail off the ground too early in B-17. But is still makes being a tail-dragger only an indirect reason for being trimmed to lift off with neutral stick. – Jan Hudec Apr 11 '16 at 18:31
10

If you follow through the links to the one on Ployer Peter Hill the B-17 (Model 299) test pilot, it says this about his death:

On October 30, 1935, Ployer Peter Hill died as a result of injuries received from the crash of the Boeing experimental aircraft Model 299 at Wright Field. The crash occurred because the crew neglected to remove the devices intended to keep the control surfaces from moving when the plane was on the ground. This aircraft was the prototype of what would later become the famous B-17 Flying Fortress of World War II. Major Hill was buried in Newburyport, Massachusetts, on November 3, 1935.

So basically they forgot to remove the gust-lock devices. Yet another case for doing a thorough pre-flight check and control check before taking off.

I can't find any evidence or anything to suggest the aircraft ever left the ground, however its possible for the aircraft to become airborne just through the amount of lift generated at higher speeds. Many airplanes will fly even with slight nose-down attitudes. Its also possible that the gust locks still allowed enough elevator movement to get off the ground. The link that Federico provided seems to suggest that the elevator was in the up position and allowed the aircraft to climb into a stall, but still not completely clear since most tail-draggers require some down-elevator to get the tail up, then up elevator to climb.

Ron Beyer
  • 36,182
  • 7
  • 126
  • 154
  • 7
    also: Yet another case for doing a thorough pre-flight check and control check before taking off. pre-flight checks were not a thing at the time. and, to say it all, they became a thing because of this accident: http://www.thisdayinaviation.com/30-october-1935/ As a direct result of this accident, the “check list” was developed, now required in all aircraft. – Federico Apr 11 '16 at 15:03
  • @Federico I modified the answer to respond to how it can fly. I understand that check-lists and pre-flights weren't around then, I was just commenting on the need for them now because even military test pilots can forget to check things. – Ron Beyer Apr 11 '16 at 15:08
  • 1
    Worth noting that a tail-dragger aircraft like the B-17 will generally lift off naturally when accelerating due to the nose-up attitude. This source suggests that the aircraft did indeed lift off before stalling: http://code7700.com/mishap_boeing_model_299.html – Jon Story Apr 11 '16 at 15:32
  • 1
    Please don't click on this link unless you understand that it shows an actual aircraft crash in which people died. This video is a particularly horrific example of what happens when the gust locks are not removed. – Simon Apr 11 '16 at 17:29
  • 1
    @JonStory, tail-draggers will often be trimmed to lift off naturally, because they are trimmed to keep the tail on the ground until they pick up enough speed for the rudder to be efficient. But the nose-up attitude is only reason indirectly by motivating that default trim setting. Any aircraft will assume the trimmed attitude before lifting off. – Jan Hudec Apr 11 '16 at 18:38
  • (The accident in the video was on an air strip in Gimli, the same place where a 767 once landed after gliding from 12.500 m without fuel.) / Following check list is inportant: http://news.aviation-safety.net/2015/09/09/ntsb-series-of-errors-by-flight-crew-caused-fatal-gulfstream-g-iv-crash/ – cvr Apr 11 '16 at 18:49
  • 6
    To be more precise, it was this accident that caused WRITTEN checklists to become universal. Pilots did preflight checks before this accident, but they relied on memory to tell them what to check, and this particular pilot had a brainfade on that particular day, with bad results. – John R. Strohm Apr 11 '16 at 20:38