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I have found a paragraph in the 1904 British patent of the Wright brothers (see the citation below) and it seems, from what they explain, that the two inventors believed the front rudder could have recovered the plane from a stall in any situation.

The question is, why were they so sure that after a stall the plane would have started to fall nose down, would have accelerated and the front rudder would have been able again to control the pitch of the flying machine?

If the main wings (and also the front rudder) had stalled their glider/airplane could have started to fall sideways or tail first.

"Contrary to the usual custom, we place the horizontal rudder in front of the main surfaces or “wings” at a negative angle, and use no horizontal tail at all. By this arrangement we obtain a forward surface which is almost free from pressure under ordinary conditions of flight, but which, even if not moved at all, becomes an efficient lifting surface whenever the speed of the machine is accidentally reduced very much below the normal, and thus largely counteracts that backward travel of the centre of pressure on the main surfaces or wings which has frequently been productive of serious injuries by causing the machine to turn downward and strike the ground head on." Wright brothers, “British Patent No. 6732, A.D. 1904 – Improvements in Aeronautical Machines”, Date of Application: 19th Mar., 1904, Accepted: 12th May, 1904. enter image description here Wright glider

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    $\begingroup$ Even though they called it a "horizontal rudder" it's probably clearer if you call it an elevator or stabilizer. $\endgroup$ – fooot Jan 4 at 2:24
  • $\begingroup$ Note the raised rear Vstab position (not only helps prevent tail strike but also) gives a little "top drag", which, along with more forward set CG, improves static stability. This helps avoid stalling. Now move forward apparatus to the rear (could be on top of the Vstab!) and ... now where do we put the high by-pass turbofans ... er ... um ... oh! ... propellers! $\endgroup$ – Robert DiGiovanni Jan 4 at 14:00
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No, it would not have helped by itself.

What could prevent a stall or recover the aircraft from an incipient stall would be a counteracting movement of that canard surface, but that would need to be commanded by the pilot. It makes little difference if that control surface is ahead or behind the wing as long as it has enough lift potential left to produce the desired pitch down moment.

The way we understand stability today is that the aircraft will correct a deviation from the desired pitch attitude without pilot intervention. Using this definition, the Wright Flyers were unstable. Only by active and permanent corrections could straight flight be maintained. This is rather stressful and makes longer flights very tiring. Flying faster also can be ruled out because the speed of deviations goes up with flight speed, such that the human reaction time delays corrections too much and can even make them counterproductive.

The Wrights were correct that an unloaded surface gives them the highest control authority and, when moved in a correct and timely manner, helps to prevent a stall. However, placing that surface ahead of the wing comes with several disadvantages, loss of stability being only one of several. On the other hand, placing that lightly loaded surface at the rear results in a stable aircraft with better performance.

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  • $\begingroup$ I will click to accept your explanation in about two weeks if no better answer is posted until then. Something else, I asked a different question (see: aviation.stackexchange.com/questions/73054/…) and a user (Robert Werner) attempted an answer. Because you appear to have quite a lot of experience in aeronautics, I will dare to ask you whether his explanation seems valid or it is flawed. (Only if you have time to take a look at his answer, there is no emergency, no rush.) $\endgroup$ – Simplex11 Jan 4 at 19:27
  • $\begingroup$ @Simplex11: Robert knows much more about the Wrights than I, so I trust his explanations. The Wrights certainly were the first who successfully controlled an aircraft in all three axes; before them all elements had been developed already but not used in a practical application. Lilienthal already discussed wing warping, elevators and rudders with his fellow pioneers but his glider designs tied his hands (literally), so he stayed with weight shifting. Wolfmüller, one of those pioneers, put those ideas into a glider which is now on display in a museum. (tinyurl.com/yx4xtpzy). $\endgroup$ – Peter Kämpf Jan 4 at 22:36
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They are describing the Flyer's canard configuration. The canard surface is the "horizontal rudder". The wing airfoils they and others were using at the time had very strong pitching moments at stall AOA (due to the constant curvature or arc of the profile as you can see in the sketch), that would overpower the downforce of a horizontal tail, or even cause the tail itself to stall, and pitch the plane over violently.

The Wrights found that an up lifting surface at the front could deal with this (that is, resist the pitching moment of the main wing) better than a down lifting surface at the tail. It was a solution to a problem they faced caused by the airfoil they were using.

The price of this was a very twitchy craft to fly in pitch because the canard had little in the way restorative forces itself due to the way it was mounted, so it had to be consciously held at a desired position, which they lived with and got used to. Like with wing warping, they had little stability, but lots of control (too much in the pitch mode, you could say, as as result of making the canard big enough to resist the wing's pitching moment), which is what wowed observers, who were impressed with the control while unaware of the pilot's struggle with pitch stability when it was flying.

Later development of airfoils with better managed pitching moments (by moving most of the camber forward) made aft tails less problematic and the advantages of the aft down-lifting tail won out. The canard faded from the scene, only to reappear occasionally, with mixed success.

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  • $\begingroup$ Several errors in your answer. 1:”the up force of a horizontal tail”; you probably meant horizontal stabilizer however the force is down ant not up. Is meant to pitch the plane up, which is not the same thing. 2:”down lifting surface at the front”; what is down lifting? You probably meant down pitching as pitching the nose down. 3:”down-lifting tail”, I have never heard of such a thing. Would you care to explain yourself? $\endgroup$ – WindSoul Jan 4 at 5:21
  • $\begingroup$ "Up lifting force at the front... better than a down lifting surface at the tail". A canard surface at the front lifts UP. A regular tail at the back lifts DOWN. What is the problem with that? I don't understand what you are confused about. $\endgroup$ – John K Jan 4 at 5:30
  • $\begingroup$ The problem is that the canard pitches the nose down, otherwise the wing would pitch up and stall. This makes the basics of canard. The exact opposite of what you state. You can not say “lifts UP” because lifting mean getting something up and lifting up is redundant. You also say “a regular tail lifts DOWN”. Lifting something down is nonsensical because lifting means bringing up and down is the exact opposite. I hope you understand now. $\endgroup$ – WindSoul Jan 4 at 5:37
  • $\begingroup$ A canard is an up lifting surface that supports perhaps 20% of the total weight of the machine. The horizontal tail on a conventional aircraft makes "lift" in the aerodynamic sense, not lift as in away from gravity; the "lift" is downward. A canard aircraft is like a 4 leg table with most of the weight on two legs at one end and a minority of weight at the other. A conventional aircraft is a see saw with the C of G on one side of the pivot and someone pushing DOWN on the other side of the pivot. He's not "lifting" in pushing down,but the force he is applying is "lift" in the aerodynamic sense. $\endgroup$ – John K Jan 4 at 5:50
  • $\begingroup$ We’re talking about the Wright brothers. The forward stabilizer had a negative angle and pitched the craft nose-down. As for canard, if you think dassault rafale is supported 20% by nose stabilizer, then I don’t agree. $\endgroup$ – WindSoul Jan 4 at 6:03
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What they had was a further called canard configuration with the horizontal stabilizer ahead of the wing. They stated that the stabilizer is angled negatively and not loaded in normal conditions.

The center or pressure is located 1:3 of the wing cord towards the leading edge. For this reason in flight the wing has a tendency to tilt up, pitching the nose of the craft towards the sky. If left uncompensated by the horizontal stabilizer, the wing will fly at high angle of attack, will loose speed and stall.

To avert that situation, they devised the forward stabilizer meant to forcibly keep the nose down. Situation in which the wing gains speed, lift increase, the wing pitches (the nose) up, the drag increases, the wing slows down, the lift decreases, the nose pitches down. They must have optimized the design to the point where these nose oscillations were canceled at least in normal flight.

About horizontal stabilizers

The positive angle of the aft stabilizer contributes to maintaining the nose down after the wing stalled. This must have been known by Wright brothers.

The negative angle of the forward stabilizer used by Wright brothers maintains the nose down before the wing stalled, practically inviting the wing to speed up. However the wing would pitch up while speeding, which in the event of overcoming the forward stabilizer, will lead to higher drag and slow down.

As long as the wing was not able to change speeds too fast, the self control of the pitch worked way better with the forward stabilizer.

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    $\begingroup$ What you say is correct only if the speed of the plane/glider is above what the Wrights called "normal". "Whenever the speed of the machine is accidentally reduced very much below the normal [I quoted them]", which means stall, the front elevator will also stall and will no longer be able to control the pitch of the flying machine. The plane can stall while following an ascendent course, while climbing. The nose is evidently up and the front elevator in stall. How can the glider be recovered? $\endgroup$ – Simplex11 Jan 4 at 4:17
  • $\begingroup$ The glider can’t recover from any stall. The reason is that there are stalls outside the flight envelope. The stall they were referring to is in level flight where the speed can’t sustain lift. If the speed is above normal but still in the envelope, there is no stall. Since the forward stabilizer is angled negatively it won’t allow high pitch, however if high pitch stall is met, I don’t think Wright brothers had a solution for it. $\endgroup$ – WindSoul Jan 4 at 4:44
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NO, the Wright British Patent No. 6732 appears to deal with post stall control of the aircraft.

Though 1904 A.D. is a long time ago, a modern wings center of lift still shifts backwards to the center of the wing after it stalls. Even their curiously proto laminar/Davis design thin undercambered wings had a center of lift further forward at lower AOA "unstalled".

Notice you don't see an airspeed indicator on that aircraft. At this early stage, stalling was a frequent occurrence, and, at low altitudes, would result in a ground impact.

The design only had value in perhaps softening the blow from a nose in to a belly flop post stall impact, but actually hindered stall recovery.

As designers began to better understand proper relationships of center of pressure to center of gravity, then they came to realize that this post stall pitching down behavior actually helped unstall the wing faster, helped even more by placing the horizontal stabilizer in the back of the aircraft, as the Wrights did on their successful Model B.

This lead to the modern solution to deal with stalling: avoid it at low altitudes with airspeed and AOA instruments, and pitch down to unstall your aircraft, which works at altitude. Simply do not accept even controlled crashing as part of your flight envelope.

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