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I am experimenting with different aircraft designs. The one I am trying right now is a canard (horizontal stabilizer at the front) and the main wings are quite far back. I wondered if it would be of any use to put the vertical stabilizers at the tip of each wing as a winglet, but that would not have much direction control effect as the wings are rectangular (not swept back).

The other and best option for me would be to put the vertical stabilizers at the tip of the horizontal stabilizers as a winglet, as shown in the picture.

Problem is, as I said before, the horizontal stabilizers are at the front and this then means the vertical stabilizers would be at the front as well.

Are there any disadvantages to putting them at the front? Would it even work properly?

Thanks in advance and have a great dayenter image description here

Unusual Edit:

As a canard design could sweeping the wings back a little add enough yaw stability to make small forward flying rudders feasible? (Pterodactyl inspired).

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  • $\begingroup$ It is supposed to be an electric aircraft. I want the cockpit to be at the front and the batteries at the back. Batteries are really heavy, that is why I put the main wings at the back to support the weight. Because of that, I had to put the horizontal stabilizers at the front $\endgroup$
    – Vincent Cerowski
    Jun 9, 2021 at 12:04
  • $\begingroup$ Turn it around and you have a Lockheed Electra. Wing fairings look great! There is no reason at all why the battery and cockpit CG cannot be forward. You then have a fairly classical (and much safer) design. Just put 2 engines on the wings. $\endgroup$
    – Robert DiGiovanni
    Jun 9, 2021 at 15:35
  • $\begingroup$ @RobertDiGiovanni It is also a matter of space in the aircraft. The whole thing including the fuselage is made of airfoils, that means I do not have much space at the front. I have made calculations, and if the results are right, I cannot really place any batteries inside the actual cockpit, or there will not be enough headroom (for example). I could swap the placement (putting the cockpit at the back and batteries at the front), but the visibility would then be worse. $\endgroup$
    – Vincent Cerowski
    Jun 9, 2021 at 15:54
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    $\begingroup$ We have not one but two questions here which cover the subject adequately. I vote to close it. $\endgroup$
    – Peter Kämpf
    Jun 9, 2021 at 17:34
  • $\begingroup$ @Vincent Cerowski Any fuselage "airfoil" will not be as efficient as a wing (but will be very stylish looking). The wing fairings are good, but let the wing do the lifting. A fuse can be very pedestrian as long as it does its job. It need only have a low Coefficient of Drag. $\endgroup$
    – Robert DiGiovanni
    Jun 9, 2021 at 18:04

2 Answers 2

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Putting vertical surfaces at the front is pretty much trying to make the plane fly backwards in the yaw axis. Remember that it is just a weathervane. It will want to switch ends same as a weathervane would if you reverse it to the wind direction and let it go. If you tried to fly a plane configured like that, you'd crash as soon as you got airborne, unless you had some fancy FBW electronics and servos actively controlling the surfaces to force artificial stability in the extremely unstable configuration, and what's the point of that?

The vertical neutral point, the aerodynamic center of yaw forces, has to be somewhere aft of the CG for the weathervane effect to work. So the fin and rudder needs to be at the back to place the vertical neutral point where it needs to be.

The closer to the CG, the larger the surface needs to be, so you can put them at the end of the existing fuselage if you make the fin and rudder big enough. Jim Marske's flying wings do that; fin and rudder at the flying wing's trailing edge, made very large because the moment arm is so short.

Or you can sweep the wings and place the fins/rudders at the tips of the swept wings, as Rutan did with the "Eze" airplanes. This provides the smallest surfaces due to the generous moment arms, and is aerodynamically most efficient.

Or you can add a little stinger sort of tail extension to place the fin/rudder farther aft. That's what Rutan did with the Solitaire motorglider, where sweeping the long wings wasn't really feasible.

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  • $\begingroup$ I have thought of doing it exactly like the "Eze", but I am not sure if the benefits of placing the stabilizer there outweigh the cons of having swept-back wings (stalling at the tip and other worse low speed characteristics). $\endgroup$
    – Vincent Cerowski
    Jun 9, 2021 at 15:48
  • $\begingroup$ "If you tried to fly a plane configured like that, you'd crash as soon as you got airborne", not necessarily, Rutan did try this front rudder configuration. It was not so good, but it was not stupid either. However the rudder was more like a keel, below the wing not to cause lift loss. $\endgroup$
    – mins
    Jun 9, 2021 at 17:44
  • $\begingroup$ But not a front stabilizer configuration; he just put the rudder surface there. The yaw neutral point still has to be aft of the CG, so large tip fins are required, larger than otherwise, to compensate for the destabilizing effect of the forward rudder, and you're back where you started. If you sawed off the wing tip stabilizers, it would immediately crash. $\endgroup$
    – John K
    Jun 9, 2021 at 18:21
  • $\begingroup$ If you want to keep the wings straight, then you'd go the Solitaire or Marske route. I'd probably go the Solitaire route and try a carbon boom to move the fin a few feet back, to the extent you can deal with the tail clearance issues. You could also try a large fixed fin aft and moveable rudder forward as @mins mentioned, and deal with some probably odd characteristics (like dynamically unstable reactions to rudder inputs since a fixed yaw input results in ever increasing rudder AOA as it yaws). $\endgroup$
    – John K
    Jun 9, 2021 at 18:28
  • $\begingroup$ John, I agree, there is a difference between horizontal and vertical front control surfaces due to lack of wing equivalent in the vertical plane. $\endgroup$
    – mins
    Jun 9, 2021 at 19:00
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Would it even work properly?

Depends on your definition of "properly".

Would it steer the aircraft like a tail one would? In principle yes.

Would it be as easy to use as a tail one? Not by a long shot.

Putting the vertical fin in the front will not make it act as a stabilizer any longer: any small deviation in sideslip angle will get amplified by said surface (instead of corrected). And the reason is that now the surface is ahead of the CoG, instead of behind.

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  • $\begingroup$ Well, I think the only feasible option now is to put it in the center at the very back of the aircraft and move the main wings a bit forward (to increase its distance from the CoG - I will make it later so that the CoG is where the wings are, as it is now, by moving the inside components - should have some margin). Thanks for the help! $\endgroup$
    – Vincent Cerowski
    Jun 9, 2021 at 12:29
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    $\begingroup$ @VincentCerowski Calculate your CG properly. Use ecalc.ch/cgcalc.php. The size and position of horizontal stabilizers will change the correct CG position. The usual advice of 1/3 or 1/4 wing chord only applies to normal planform with "regular" tail sizes. The more you deviate from it the more that advice is wrong. You are building a canard - something VERY different from "normal" planes. $\endgroup$
    – slebetman
    Jun 9, 2021 at 13:48
  • $\begingroup$ It's like driving a car in reverse .. doable but much harder !! $\endgroup$
    – Mr R
    Jun 9, 2021 at 22:33

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