Low aspect ratio sport plane ideas

[nestofdragons]

Had some time to test a idea. I was a bit worried about my 14% thick wing. Especially about the elements of the spar that needed to pass under and over the pilots legs. And i wanted to give the pilot enough room for his feet. Not all pilots have small feet like me (eur: 42, usa: 9).
So i went back to thinking about thicker airfoil. But this time only for the center section. Later i will test with a even smaller section at higher thickess (half of center section).
Here are the pictures.
Thickness center section goes from 14 to 22 in center. Front glazing not done yet.

More internal space to make retracting front wheel possible. Pilot still can see sideways over wing.

The canopy is a lot smaller that pure 14% thickness wing of course. I still like the looks of the fatter wing.
In this picture you can see where i am currently planning to place spars. There are three lines visible. Just forget the most rearwards line. Those two first lines are supposed to be spars. I will connect them in such a way they will become a very rigid structure. Front leading edge D-tube will be not as strong as possible due to the glazing in the leading edge. This spar-structure should help to keep it all very rigid.


The picture above gives a bit of a idea how much of the leading edge needs to be transparent for good view on the airfield while landing.

This picture gives a idea of the transit from 14 to 22% thickness.

 

[Tiger Tim]

Your little flying wing is somewhat reminiscent of Northrop’s earlier testbeds. At least one of them (perhaps the N-1?) had adjustable dihedral wing tips to explore what worked best for stability and control. I bet there’s a NACA report or similar on their findings. All this to say I don’t think your wide split V-tail will be the answer you want.

 

[nestofdragons]

Your little flying wing is somewhat reminiscent of Northrop’s earlier testbeds. At least one of them (perhaps the N-1?) had adjustable dihedral wing tips to explore what worked best for stability and control. I bet there’s a NACA report or similar on their findings. All this to say I don’t think your wide split V-tail will be the answer you want.

Thanks for guiding me to possible test reports. I will try to find them.

 

[Aesquire]

The Northrop testing with ground adjustable anhedral cranked wings ended up with straight wings mostly to get acceptable amounts of dihedral / roll stability. The amount of apparent dihedral from sweep was enough that a straight wing worked.

My guess is the wide butterfly surfaces will work well If you look at the Vought V-173, for pitch & roll control. Like every V tail design, you need bigger area vs. Conventional tails, and might run out of travel to get acceptable control in all 3 axis. Adding a vertical fin behind the cockpit, like the Verhees Delta might be needed.

I do like the looks!

if you look at the wing structure on the B-58 or the UFO, there's no singular wing spar. Or lots of thin ones.

 

[Riggerrob]

Dear NestofDragons,
Great sketches.
Please keep them coming.
May I suggest off-setting the nose wheel to outboard of the rudder pedals? This minor asymmetry will free up space along the center-line for simple rudder pedal installation.
Like A-10 Warthog, you will probably not notice the asymmetry while taxiing.

 

[Tiger Tim]

My guess is the wide butterfly surfaces will work well If you look at the Vought V-173, for pitch & roll control.

My concern is this: picture which way that wide split V-tail would have to move to roll right. Now instead picture which way those same surfaces would move to yaw left. Uh oh. It looks to me like roll and yaw are forever tied together with those controls but acting opposite to one another. Roll will carry an enormous amount of adverse yaw and yaw will bring adverse roll. It may even be uncontrollable.

This is where a quick RC foamie or X-plane simulated proof of concept would pay off well, IMO. Not to prove out any performance figures, because that’s hard, but just to explore the configuration.

 

[Sockmonkey]

My concern is this: picture which way that wide split V-tail would have to move to roll right. Now instead picture which way those same surfaces would move to yaw left. Uh oh. It looks to me like roll and yaw are forever tied together with those controls but acting opposite to one another. Roll will carry an enormous amount of adverse yaw and yaw will bring adverse roll. It may even be uncontrollable.

This was my thinking as well. Anhedral tips would give you the good kind of yaw/roll coupling.

 

[rotax618]

Anhedral tips present another set of design challenges, for a very light single seat LAR, it’s best to stick with the KIS principle - keep it simple. I would ditch the tips, use a central fin and rudder, either a high mounted horizontal stabiliser or Junkers elevons. Look how well Rowe’s UFO flies, maybe just copy his arrangement - the control surfaces are big but if kept light they should be OK.
You certainly don’t need fighter plane like roll, for you machine to be pleasant to fly the roll needs to be well dampened, a wide chord ensures that pitch control wont be too sensitive.

 

[nestofdragons]

I guess i would need to testfly a RC model of this configuration to see if it would have the mentioned instability. Sadly ... i suck at RC modelling. I crash each model i make. I am used to sit in cockpit. Not seeing a cockpit fly towards me. One turn and ... CRASH.
The idea of a assymetrical front wheel is one that i will probably follow. For two reasons. Closer to a strong rib and better chance of installing a window for landing approaches.

 

[nestofdragons]

A maybe last attempt to keep the split V-tail controls. What if i only use the control surface at the inside of the turn? If that one goes up, it looses lift. So that wing drops. Good. Now ... the airfoil gets deformated due to the deflection. Due to the AoA of that area the frontal area will increase if the elevon goes up. Right? More drag. That wingtip drags more than the non-activated wingtip. Proverse yaw????? Possible ?? Or am i toooootally getting it wrong? Probably.

 

[cluttonfred]

Of interest for those thinking about round wings in this context...a new clip from Ed Nash that came out just yesterday.

 

[Kavin]

Nestofdragons, from looking at it you have a wonderful design minus the outboard Vtail for the reasons everyone has stated. Vertical winglets with elevons on the wing are what you want here I'd say. Testing a model would be very simple, here is the YouTube I run, I am offering to make and test a model out for you if you would like: https://m.youtube.com/channel/UCMZkAT1Vf7CPSNcTzZkK_qQ

 

[nickec]

If you build an RC model, you will find it easy to find an RC pilot nearby who will fly it for you. Just find the local club, if there is one, or use RCGroups: Remote Control, Radio Control Planes, Drones, Cars and Boats to locate a pilot.

Consider making two or three. Batch building goes quickly. You then have spares to modify and compare.

 

[U+fly]

A maybe last attempt to keep the split V-tail controls. What if i only use the control surface at the inside of the turn? If that one goes up, it looses lift. So that wing drops. Good. Now ... the airfoil gets deformated due to the deflection. Due to the AoA of that area the frontal area will increase if the elevon goes up. Right? More drag. That wingtip drags more than the non-activated wingtip. Proverse yaw????? Possible ?? Or am i toooootally getting it wrong? Probably.

Lippisch had an evolution of the wing end plate position on his Storch tailless gliders, from vertical up to
partially sticking down (like Rutan's Long Ez) to the wing end plates going down (anhedral) on his later Delta development. If you try your design in X-plane, you will see how "wabely" it is in roll compared to lippisch configuration, flying on rail. The RC glider "Stromburg-E" has proven that gull wings are right.

 

[WonderousMountain]

So I'm just going to breakout into my suggestions.

Go ahead and droop the footbox airfoil section. This
Should alleviate the vascillating thickness conjecture.
Suddenly you and sasquatch will fit & have visibility.

Take the forespar straight into the main spar regardless
of aft tie-in. Not that it matters, can't recall a single time
LAR wing failed from flight forces.

Retracting front wheel, would like to see that drawn up.

Final proposition,

Put my Canted tails along the edge of your main Cabin
section, you can clamp the outer wing modules to tails.
Which ruins the whole tailless thing, but retains short AR.

 

[nestofdragons]

Nestofdragons, from looking at it you have a wonderful design minus the outboard Vtail for the reasons everyone has stated. Vertical winglets with elevons on the wing are what you want here I'd say. Testing a model would be very simple, here is the YouTube I run, I am offering to make and test a model out for you if you would like: https://m.youtube.com/channel/UCMZkAT1Vf7CPSNcTzZkK_qQ

I feel deeeeeply honored with this proposal. Somebody offered me a bit of help with getting the design a bit more tested in simulation. Once i have some results, i surely will contact you again. It might have better chances after the design became edition 2.0 . Give me a month time.
By the way ... impressive tests you already did.

 

[rotax618]

From my experiments, tip fins did not work all that well, they tended to interfere with the formation of the vortex. The models appeared to have increased L/D without the fins.

 

[nestofdragons]

Happy news. I am getting help to tinker some more on this project. So ... keep following this adventure, because ... it is a adventure.

First a question i have after seeing some data a contact send to me.

He showed me this flow result of a similar wing. Airfoil is different and thickness too, but that doesn't matter yet. I want to get your attention to the flow at the bottom and the top of the wingtip. There are vortexes at both places! And ... that made me remind of something i wrote in the past.

BirdWing - Nest of Dragons

In that very old (i guess it is 15-20 years old) page of my website i talk about how vortexes dissolve when they are close to each other. You can easily test it in your tub at home.
Now back to the drawing. I see two vortexes. Would they be close enough to dissolve each other? Would that decrease induced drag? If yes ... would that be a advantage or disadvantage when it happens on a Low Aspect Ratio? Seems that some of the lift on those wings is generated by the vortexes.

At this moment i still want to see those split V-tails tested. But i realise it might be better to keep ailerons and elevators seperated. Just ailerons in the wingtips and elevators in the second step of the wing. Elevators might even be splitting controls like the elevons on the B-2. It seems not so hard to make such control surfaces.

 

[U+fly]

Happy news. I am getting help to tinker some more on this project. So ... keep following this adventure, because ... it is a adventure.

First a question i have after seeing some data a contact send to me.
View attachment 125234
He showed me this flow result of a similar wing. Airfoil is different and thickness too, but that doesn't matter yet. I want to get your attention to the flow at the bottom and the top of the wingtip. There are vortexes at both places! And ... that made me remind of something i wrote in the past.

BirdWing - Nest of Dragons

In that very old (i guess it is 15-20 years old) page of my website i talk about how vortexes dissolve when they are close to each other. You can easily test it in your tub at home.
Now back to the drawing. I see two vortexes. Would they be close enough to dissolve each other? Would that decrease induced drag? If yes ... would that be a advantage or disadvantage when it happens on a Low Aspect Ratio? Seems that some of the lift on those wings is generated by the vortexes.

At this moment i still want to see those split V-tails tested. But i realise it might be better to keep ailerons and elevators seperated. Just ailerons in the wingtips and elevators in the second step of the wing. Elevators might even be splitting controls like the elevons on the B-2. It seems not so hard to make such control surfaces.

On that nice simulation of the airflow, can you make it fly a little "crabwise" to see a strong (or not) changes in lifts between the right and left wing ? Because that would be the roll "wable" I was writing about earlier.

 

[nestofdragons]

On that nice simulation of the airflow, can you make it fly a little "crabwise" to see a strong (or not) changes in lifts between the right and left wing ? Because that would be the roll "wable" I was writing about earlier.

The mix of anhedral of the main wing and the dihedral of the smaller wingtips makes it very interesting indeed to see what will happen when the airplane crabs in the air.