Flying wing as cheap and simple option for basic fun flying.

HomeBuiltAirplanes.com

Help Support HomeBuiltAirplanes.com:

rotax618

Well-Known Member
Joined
Oct 31, 2005
Messages
835
Location
Evans Head Australia
If you are considering low aspect ratio wing, a rectangular planform is the least efficient, circular, semi-circular, elliptical, Zimmerman and inverse Zimmerman are better with regard to slow speed stability, and low drag. It is not a great deal more difficult to build a curved low aspect wing because with the short span you need few ribs.
 

cluttonfred

Well-Known Member
HBA Supporter
Joined
Feb 13, 2010
Messages
7,300
Location
World traveler
In that case you might want to take a look at this Australian side-by-side, two-seat plank glider derived from Al Backstrom’s EPB-1. Something similar with a motor and lower AR wing might work well.

 

Sockmonkey

Well-Known Member
Joined
Apr 24, 2014
Messages
1,840
Location
Flint, Mi, USA
Sockmonkey yes you’re getting to the final stage I believe. What if you integrate de rudder into the turtledeck and give the wingtips a Hoerner style shape?!
Turtledeck rudder wouldn't have enough leverage. Would Hoener tips reduce drag more than endplates on a LAR wing like this?
 

Victor Bravo

Well-Known Member
Joined
Jul 30, 2014
Messages
7,291
Location
KWHP, Los Angeles CA, USA
Tip fins and tip rudders were found to be less desirable, by Backstrom himself. That's why the last EPB plank (the good looking white one which there are very few photos of) had a central tail.
 

Sockmonkey

Well-Known Member
Joined
Apr 24, 2014
Messages
1,840
Location
Flint, Mi, USA
Tip fins and tip rudders were found to be less desirable, by Backstrom himself. That's why the last EPB plank (the good looking white one which there are very few photos of) had a central tail.
Those had a much higher aspect ratio though. I think a stubby wing needs those endplates.
 

Victor Bravo

Well-Known Member
Joined
Jul 30, 2014
Messages
7,291
Location
KWHP, Los Angeles CA, USA
Yes, you are right about the aspect ratio. Yaw control is probably best done at the wingtips, but I would still guess yaw stability is not helped at all by tip rudders on a straight (unswept) plank..
 

Sockmonkey

Well-Known Member
Joined
Apr 24, 2014
Messages
1,840
Location
Flint, Mi, USA
Yes, you are right about the aspect ratio. Yaw control is probably best done at the wingtips, but I would still guess yaw stability is not helped at all by tip rudders on a straight (unswept) plank..
That's a tough one. I can't say for sure if they give enough stability on their own. Would enlarging them help?
 

cluttonfred

Well-Known Member
HBA Supporter
Joined
Feb 13, 2010
Messages
7,300
Location
World traveler
Yes, as I remember Al Backstrom's comments from the SHA flying wing symposium at Elmira back in the 90s, the final incarnation of his plank used a single central rudder and elevons inset slightly from the wing tips (maybe 1/4 chord?) to keep them clear of the tip votices.

He also had drawings of (though I don't think he had flown) a version with extended-chord elevons projecting beyond the wing trailing edge to reduce their span while retaining the same effect and therefore lower the stall speed (or reduce wing area for the same stall speed) by washing out less of the wing surfaces with the up elevons in slow flight.

That is not to say that there wouldn't be value in tip rudders, including as air brakes, but for a simple fun flyer the single rudder is much simpler to build and actuate. I wonder how hard it would be to do a single central rudder that can split to serve as an air brake? I could see a single teleflex cable operating such an arrangement for a very handy way to control approach angle without impacting the wing in any way.
 

Sockmonkey

Well-Known Member
Joined
Apr 24, 2014
Messages
1,840
Location
Flint, Mi, USA
Yes, as I remember Al Backstrom's comments from the SHA flying wing symposium at Elmira back in the 90s, the final incarnation of his plank used a single central rudder and elevons inset slightly from the wing tips (maybe 1/4 chord?) to keep them clear of the tip votices.

He also had drawings of (though I don't think he had flown) a version with extended-chord elevons projecting beyond the wing trailing edge to reduce their span while retaining the same effect and therefore lower the stall speed (or reduce wing area for the same stall speed) by washing out less of the wing surfaces with the up elevons in slow flight.

That is not to say that there wouldn't be value in tip rudders, including as air brakes, but for a simple fun flyer the single rudder is much simpler to build and actuate. I wonder how hard it would be to do a single central rudder that can split to serve as an air brake? I could see a single teleflex cable operating such an arrangement for a very handy way to control approach angle without impacting the wing in any way.
Well, a split central rudder brake could work like so.

Push left or right pedal for yaw, push both for brake. The pedals would have to be mounted independently.
Tip drag rudders would use a similar system, shut by a spring, and pulled open by a single cable, but they would only be a pop-out panel on the outside of each fin.

So, here's the latest iteration of the Possum.

Cleaned it up a bit to make it look as sexy as possible.
 

Victor Bravo

Well-Known Member
Joined
Jul 30, 2014
Messages
7,291
Location
KWHP, Los Angeles CA, USA
I'm thinking that the tip fin/rudders would be almost de-stabilizing in yaw, more or less canceling each other out in some way.

In a right-yaw upset, the starboard tip fin would create almost as much drag (pulling aft on that wingtip) as the port fin creates on the other (corrective) side.

And the length of the arm on which these forces are acting is of course longer than if it were a central fin.
 

Sockmonkey

Well-Known Member
Joined
Apr 24, 2014
Messages
1,840
Location
Flint, Mi, USA
I'm thinking that the tip fin/rudders would be almost de-stabilizing in yaw, more or less canceling each other out in some way.

In a right-yaw upset, the starboard tip fin would create almost as much drag (pulling aft on that wingtip) as the port fin creates on the other (corrective) side.

And the length of the arm on which these forces are acting is of course longer than if it were a central fin.
Oh, they don't both act at the same time. To yaw right, only the right drag rudder opens up, and only the outside half moves. Think of a vertically mounted spoiler. A spring shuts it so you only need a single pull cable on either rudder.
 

rotax618

Well-Known Member
Joined
Oct 31, 2005
Messages
835
Location
Evans Head Australia
Te builder of the Aussie plank said that it flew perfectly co-ordinated turns without rudders, the nosewheel was castering with spring biased attached to the rudder pedals.
 
2
Top