Low aspect ratio sport plane ideas

Homebuilt Aircraft & Kit Plane Forum

Help Support Homebuilt Aircraft & Kit Plane Forum:

cluttonfred

Well-Known Member
Supporting Member
Joined
Feb 13, 2010
Messages
9,523
Location
World traveler
That seems like a design that could be a lot more acceptable with a cosmetic makeover. I can't imagine that the airfoil shape of the forward fuselage actually does much for performance. Give it a sexy fuselage nose and sweep the end plates up at the trailing edge to make Rutan-style winglet rudders. Maybe also find some landing gear that doesn't look like it was salvaged from a WWII Luftwaffe experiment. "Simplicate and add lightness" but pay a little attention to the looks and you might have a winner.
 

Urquiola

Well-Known Member
Joined
Aug 23, 2013
Messages
297
Location
Madrid, Spain
If you go with the full underslung cockpit, you can taper the rear of the fuselage into a rudder.
Having the rudder below the wing and engine means that it won't create adverse roll, and may in fact roll you into the turn without needing to use ailerons.
Using a straight leading edge extends the wing root structure forward to allow mounting the engine further ahead of the COL.
IrpeNxX.png

It's basically a "paper airplane" configuration.
The effective dihedral caused by the sweepback and high mounting of the wing would make it stable enough in roll that you may only need an elevator and no ailerons.
I found the attached Flying Wing document in my files, perhaps it's interesting for someone. Blessings +
 

Attachments

  • Flying Wings-Lifting Fuselages NASA.pdf
    1.7 MB · Views: 29

Bigshu

Well-Known Member
Supporting Member
Joined
Jun 7, 2020
Messages
1,292
Location
KCMO, midwestern USA
I need to review my last remarks about this airplane. If you look at the following pictures you will see that the distance between trailing edge and control surfaces are not that small. Could be it will not be a problem in that case. But ... i start to wonder ... what is the distance between prop tips and those outside wingpanels?
View attachment 126521 View attachment 126522
I'm gonna have to swear off this thread! Just when I think I'm out...you pull me back in again! Now I have to seek out a copy of this issue.
 

nestofdragons

Well-Known Member
Joined
Jun 8, 2016
Messages
717
Location
Near Antwerp, Belgium
I would not be me if i did not try to place a pilot on his belly in a low aspect ratio. I just took my latest wingshape and tried to see how a pilot would fit in. I have to admit ... he fits in nicely! only needs a small canopy. I could make him fit in ever completely but he would then have to be totally flat in wing. And i want to give him some better comfort.
Major disadvantage now is that the engine which i always put in front of the wing in the previous proposals is right in the way of his view. I could place the engine higher, but that would create a pitch down moment which the elevons might not compensate due to short moment arm.
At this moment i just draw it without engine or prop. And than it hit me. ****, would it not be great to make it electric and put a few engines on the trailing edge like in the BWB-designs of NASA. Or maybe a few engines along the leading edge. If placed at trailing edge, CG could be be corrected by placing batteries in front of CG. I admit ...it would create a very spread out weight. I would prefer engines at front. Maybe something like in Cri-Cri but then electric.
Would it be possible to create it as a glider with starter help? Or ... would it be possible to create it as hangglider whatso ever??? Yep, i drew one with his legs out like in the Horten HXa glider. If glide ratio would be good enough ... why not???
Largest change in my proposal is the use of more conventional elevons instead of my split V-tail. Reason for this change: if i would really consider it as a hangglider, it needs to be very light. The need for extra reinforcements in the wing to keep the wingtips rigid enough to handle the split V-tail would add a lot of weight.
Enough talk ... here are the drafts. ;)
LAR0001.png LAR0002.png LAR0003.png LAR0004.png LAR0005.jpg LAR0006.jpg
In the last draft there are two lines. One is the horizontal line parallel to the main line of the root airfoil. The other is at 15 degrees of that line and shows that the legs would be possible to use when landing at 15 degrees.
 

cluttonfred

Well-Known Member
Supporting Member
Joined
Feb 13, 2010
Messages
9,523
Location
World traveler
I would not be me if i did not try to place a pilot on his belly in a low aspect ratio. I just took my latest wingshape and tried to see how a pilot would fit in. I have to admit ... he fits in nicely! only needs a small canopy. I could make him fit in ever completely but he would then have to be totally flat in wing. And i want to give him some better comfort.
Major disadvantage now is that the engine which i always put in front of the wing in the previous proposals is right in the way of his view. I could place the engine higher, but that would create a pitch down moment which the elevons might not compensate due to short moment arm.
At this moment i just draw it without engine or prop. And than it hit me. ****, would it not be great to make it electric and put a few engines on the trailing edge like in the BWB-designs of NASA. Or maybe a few engines along the leading edge. If placed at trailing edge, CG could be be corrected by placing batteries in front of CG. I admit ...it would create a very spread out weight. I would prefer engines at front. Maybe something like in Cri-Cri but then electric.
Would it be possible to create it as a glider with starter help? Or ... would it be possible to create it as hangglider whatso ever??? Yep, i drew one with his legs out like in the Horten HXa glider. If glide ratio would be good enough ... why not???
Largest change in my proposal is the use of more conventional elevons instead of my split V-tail. Reason for this change: if i would really consider it as a hangglider, it needs to be very light. The need for extra reinforcements in the wing to keep the wingtips rigid enough to handle the split V-tail would add a lot of weight.
Enough talk ... here are the drafts. ;)
View attachment 127115 View attachment 127116 View attachment 127117 View attachment 127118 View attachment 127119 View attachment 127120
In the last draft there are two lines. One is the horizontal line parallel to the main line of the root airfoil. The other is at 15 degrees of that line and shows that the legs would be possible to use when landing at 15 degrees.

Koen, I like the simpler single-fin arrangement very much.

I would tweak the thickness ratio of the airfoil at each rib (they all have to be different anyway) to provide a constant thickness at the elevon spar and also eliminate that dip in the center. Alternatively you could carry the two center bays all the to the trailing edge and then start the elevons from there. That would make building and rigging your elevons and much simpler.

I know you like the prone pilot position and it is certainly aerodynamic and attractive but it makes me very uncomfortable from both a safety and, well, confort point of view..
 

nestofdragons

Well-Known Member
Joined
Jun 8, 2016
Messages
717
Location
Near Antwerp, Belgium
Koen, I like the simpler single-fin arrangement very much.

I would tweak the thickness ratio of the airfoil at each rib (they all have to be different anyway) to provide a constant thickness at the elevon spar and also eliminate that dip in the center. Alternatively you could carry the two center bays all the to the trailing edge and then start the elevons from there. That would make building and rigging your elevons and much simpler.

I know you like the prone pilot position and it is certainly aerodynamic and attractive but it makes me very uncomfortable from both a safety and, well, confort point of view..
No worries, i will return to seated position. It needs to be acceptable by many to be a good design. Being a low aspect ratio is already very special. And yes ... i see the advantages of having that central fin as well. It is super easy. It has no questionable function as my own split V-tail. But ... i admit ... that idea of me still triggers me to know if it would work, yes or no.
 

Riggerrob

Well-Known Member
Joined
Sep 9, 2014
Messages
2,769
Location
Canada
....

I know you like the prone pilot position and it is certainly aerodynamic and attractive but it makes me very uncomfortable from both a safety and, well, confort point of view..
Probably comfortable enough if he "borrows" a prone harness from a Rogallo hang-glider.
 

Sockmonkey

Well-Known Member
Joined
Apr 24, 2014
Messages
2,318
Location
Flint, Mi, USA
If you're going prone and electric you can just stick motors along the leading edge of the wing if you use a reverse delta.
e07brZx.png
Still very flying wing-ish, and batteries could be housed in a hollow main spar.
 

Aesquire

Well-Known Member
Joined
Jul 28, 2014
Messages
3,259
Location
Rochester, NY, USA
Re: footlaunch.

L/D ratio isn't the limitation on foot launch. Stall speed is.

Yes, if the glide path is steeper than your slope, you can't take off, you just run until exhausted, fall, or hit whatever at end of slope. Usually trees, locally, but certainly something with sharps or Really Hard objects. Occasionally, a cliff.

I've done no wind take offs where I was in ground effect for over 50 yards before the slope got steeper and I had more than 6 feet clearance over brush with stickers. Wild roses S$%&.

Stall speed is less of a problem when you cliff launch or have a steep slope to dive for airspeed. On level ground for a powered UL there is some assistance as the wings take the weight off but if you can't keep up with leg speed, you face plant.

Which leads to...

Re: prone position

You need to be able to stand up to run with a flying thing. Your back can't take much weight when your upper torso is bent over, and you have to support the mass Somehow. On a typical hang glider, it's the arms supporting the weight until airflow takes the weight of the wing. Then you need pitch control for the rest of the take off run, to minimize drag, and smoothly take the load of the pilot's weight.

Plus, the center of gravity of the pilot shifts when transitioning from upright-ish running, to prone. ( Or supine ) Typical human males have a CG around the bottom of the breast bone. Females lower. A harness supporting your weight at the hips, upright, has to support at hips and ( typically ) shoulders, reclined, so the main hip support has to move back as you lean forward. Or you get a large CG displacement.

It's obvious if you watch videos of hang glider take offs. With a SWIFT & it's supine parallel cage, the pilot's butt slides forward as he is transitioning from upright to supine.

It's even more fun when the LOADED CG and the empty CG of the air thing are different. Then you need to leverage the nose up or down while carrying it to get the proper AOA. The Manta Fledgling & some others were notably tail heavy for ground handling. And that tail heaviness changed to zip as you accelerated on take off & the wings began to lift.

Finally, human legs are fragile and wimpy, although with a sophisticated shock absorbing system. & You can't carry the wing and work pedals for the rudder simultaneously.
 
Top