Karl Nickel's Falter 1 tailless aircraft

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Aerowerx

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.... But the Hoerner PUL-10 ....
Hmmm. For some reason it won't let me edit my own post, so I had to reply to it with a quote.

I meant Horten PUL-10, not Hoerner.

[Edit] I guess if you log out and then back in, you loose the ability to edit??
 

danmoser

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I guess I have fumbled the ball on this, since I promised to post my idea on how the control system might work.

Sometimes reality gets in the way of having fun! (By the way, if anyone is low on stress, I have plenty to pass around.:nervous:)

Anyway, I have been thinking about the problem, and came across this diagram of the KasperWing control hookup:



Not, the same scheme as the Falter 1, since the KasperWing uses tip rudders, but I see several mixers in there. And this is just one wing. This would be duplicated on the other side. I believe the Kasper wing uses the tip rudders along with elevons. But there appears to be something on this diagram that looks like flaps.

Hold on a bit...

Took another closer look at the diagram. There are 4 horizontal control surfaces. Starting from the tip and working inwards, my guess is that they are: Aileron, elevator, "flaperator", "flaperator", and flap.

I am intrigued by the possibility of a tailless design, similar to the Mitchel B-10, KasperWing, or Nickel's Falter 1. Except with a rigid wing and pod. LSA size. Two seats preferably side-by-side, if the change in CG with 2 people can be accommodated. Otherwise, it would have to be tandem. But the Hoerner PUL-10 is side-by-side, so I know it is possible.
The triangle tip surface has been called an "elevator" in other Kasper documents I've seen.
This is not the BKB or BEKAS design control layout.
Perhaps it's one of Kasper's other GA aircraft designs like the "Mighty Mouse" (?) .. the link Henryk posted above seems to confirm this.

My interpretation of the picture:
Purple rod is rudder, individually deflected outward only (both left & right can be opened simultaneously)
Green rod is elevator and/or pitch trim (triangle tip surface)
Brown rod is elevon (no sign of the notoriously ineffective anti-yaw tab in the picture)
Red rod is split flap (supposedly vortex-enhancing)

BKB test flight evaluation: Falvy 37
Severe adverse yaw reported with aileron application, but turning with tip rudders only worked beautifully.
Kasper's claims of low sink rate mush and sustained vortex lift were not confirmed.

My conjecture is that the Falter 1 had the elevon/elevator control surface at mid-span, the ailerons at the tip. The rudders are individually actuated, mixed into aileron & elevator/elevon such that that "rudder open" command on one side consists of down elevator and up aileron on that same side, producing a yaw moment without significant roll & pitch moments.
But I'm far from certain about this.. we need to find out for sure how Ali Schmidt & Karl Nickel did this. ;)
 

Aerowerx

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Thanks, Henry, for the pictures.

I just thought that the Falter 1 and KasperWing would have a similar control set up. Except the Falter 1 uses cables instead of push rods.

Instead of aileron/rudder/flaps/elevator, the Falter 1 would use aileron/elevator/rudder. Probably eliminate the tip rudders and flapsnof the Kasper, and instead hook the rudder pedals to the elevon surfaces somehow.
 

John Newton

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Intriguing, I haven't come across this before, anyone able to translate the German? I am guessing that the adjacent inboard and outboard portions open in opposite directions (diferentially) to give rudder/yaw control ?
 

Aerowerx

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.... anyone able to translate the German?
I could if I had a dictionary in my lap. If you could actually read the fuzzy picture you could use Google translate.

I am guessing that the adjacent inboard and outboard portions open in opposite directions (diferentially) to give rudder/yaw control ?
Exactly right.
 

Aerowerx

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I have been thinking some more on this.

If you want a steerable nose wheel you are going to have a problem with the scheme as shown on the Falter 1 or KasperWing. This is because each rudder pedal is independent, and hooking them to the steering will negate this. One solution is to have springs to hold the rudders so that they work in only one direction, allowing the rudder pedals to work as in a 'normal' plane. Personally, I don't like the idea of springs.

Another solution is to use tip rudders, as in this page from Nickels book:
Page155.jpg
Note that both tip rudders are displaced, but one is more so than the other. This can be achieved by a differential bellcrank, like is used for differential ailerons. This would allow the rudder pedals to be coupled together and tied to the steering.

What would be interesting is to investigate whether such a system could be used on the Falter 1 style drag rudders, and what is the minimum movement that could be achieved on the 'undesired' rudder movement.
 

danmoser

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If you want a steerable nose wheel you are going to have a problem with the scheme as shown on the Falter 1 or KasperWing. This is because each rudder pedal is independent, and hooking them to the steering will negate this. One solution is to have springs to hold the rudders so that they work in only one direction, allowing the rudder pedals to work as in a 'normal' plane. Personally, I don't like the idea of springs.

Another solution is to use tip rudders, as in this page from Nickels book:
View attachment 30858
Note that both tip rudders are displaced, but one is more so than the other. This can be achieved by a differential bellcrank, like is used for differential ailerons. This would allow the rudder pedals to be coupled together and tied to the steering...
Another steering possibility is connecting rudder pedals to left & right wheel brakes .. Steering with the brakes and and letting the nosewheel caster freely .. perhaps not the most elegant, but many planes use this arrangement effectively.

Note the force vector from the left tip rudder in the picture is almost aligned with the CG, so it is not producing much of a yaw moment at all .. the right tip rudder does all the "heavy lifting" by producing a much greater yaw moment, due to increased lift/drag forces combined with a resultant force vector direction that provides a much longer lever arm from the CG.

Tip rudders can be very effective for yaw control, but one of the main motivations for the Falter 1 design was the elimination of vertical surfaces, potentially reducing drag & inertia.
 
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Aerowerx

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Note the force vector from the left tip rudder in the picture is almost aligned with the CG...
I'm not sure, but I believe this is just a conceptual drawing to illustrate his main point. So I don't think you can draw any conclusions from the relative size and direction of the arrows.

Tip rudders can be very effective for yaw control, but one of the main motivations for the Falter 1 design was the elimination of vertical surfaces, potentially reducing drag & inertia.
I think it would certainly reduce drag and inertia---no 'potential' about it.
 

Aerowerx

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=remember=TUCK possibility!!!
I don't remember the details at the moment, but Nickel discusses this problem, what causes it, and how to avoid tuck. I think it has something to do with the CG being too far to the rear, IIRC, but don't hold me to that.
 

danmoser

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I'm not sure, but I believe this is just a conceptual drawing to illustrate his main point. So I don't think you can draw any conclusions from the relative size and direction of the arrows.
Conceptual, yes, but the Frise nose feature he is describing creates much greater drag when deflected outwards than when deflected inwards.
EVERY hang glider or ultralight equipped with vertical tip rudders I have ever seen has had them arranged to be actuated independently, and only opening outwards .. usually creating extra drag as well, as in the Frise nose arrangement.
This is both highly effective and mechanically simple.
And as a bonus: this provides the capability to use both rudders simultaneously as approach control spoilers while maintaining good directional stability and control.


I think it would certainly reduce drag and inertia---no 'potential' about it.
Not necessarily .. it's not as easy as simply eliminating vertical surfaces .. you have to replace them with something else that performs the same function.
To get the same directional stability as a vertical surface, you must make some other wing design compromises, such as greater sweep angle, taper or non-optimal washout .. this can lead to some other problems: poor stall properties, poor span efficiency, lower CL,max, etc. .. tailless aircraft design is a complex maze of compromises with pitfalls everywhere.
Some compromises are particular poor, and can easily result higher drag and higher inertia on the wing as a whole.

Nickel's Falter 1 was a demonstration aircraft that seems to have had a particularly good combination of features .. they might work out well in a more modern aircraft design too .. ;)
 

henryk

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I don't remember the details at the moment, but Nickel discusses this problem, what causes it, and how to avoid tuck. I think it has something to do with the CG being too far to the rear, IIRC, but don't hold me to that.
-yes,in "Tailless aircraft" it is discussion about longitudal stability...

and two phrases about BKB1-A glider="BKB is only tuck resistant tailless wing..."\from memory\.

http://www.nurflugel.com/Nurflugel/Papers/Dr_Nickel_Paper/body_dr_nickel_paper.html

=BTW...

+ many,many links=
http://aeroexperiments.org/links.shtml
 
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Aerowerx

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-can anybody finde short info about BKB1 stability in "Tailless aircraft" book\page circa 200-230?\
Is this in the chapter on hang gliders?

I skimmed through what I had and could not find it, but I did not scan in all the chapters.
 

henryk

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Is this in the chapter on hang gliders?

I skimmed through what I had and could not find it, but I did not scan in all the chapters.
=in the chapter on "longitudal stability"...

23. "Tailles Aircraft", by K, Nickel, M. Wohlfahrt, 1990 pp. 213 214.
 

Aerowerx

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Dan and HenryK:

I thought you might find this of interest. It is talking about the EH 3.0/12.0 airfoil for tailless aircraft, but it would probably apply to any reflexed airfoil.

Scroll down to the 4th paragraph. I tried to copy and paste, but it did not work.

It says that you should put turbulators on the bottom of the wing at the 65% chord point, particularly in front of a control surface. Also at 15% chord on the top of the wing. By 'turbulator', I guess they mean 'vortex generators'?
 
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