Very low aspect ratio planes?

HomeBuiltAirplanes.com

Help Support HomeBuiltAirplanes.com:

berridos

Well-Known Member
Joined
Oct 10, 2009
Messages
916
Location
madrid
Off course, but its supposed to be a travel machine. The original design has a cruise of 120 kts and loosing on that front would be painful. The engeneering is superb and minimalist. I believe in composites it will be heavier.
The vertical fin fairings (Arnold lessons), the laminar surface and the cooling drag can be definitly improved in composites without any research. If that would allow for a tad more of S while keeping cruise constant.....??? However again, matching his weight i see highly difficult (210kg). It could be achieved without problem with a rotax rick, but travelling at 120 decibel is a bit of a nightmare (and then the 2 stroke reliability). By the way, the rotax is significantly lighter and much more powerful. His specs are with a 50 hp subaru.
On the other hand i believe the Verhees has disregarded the basic devices and rules of vortex lift. His sweep is not high enough and the leading edges arent sharpened at the roots. Maybe theere is a source of improvement.
Regarding the double delta approach iw onder if i should target vortex lift on both wing section or taarget vortex lift at the root section and normal lift at the less swept section. Maybe worth to explore.
 
Last edited:

berridos

Well-Known Member
Joined
Oct 10, 2009
Messages
916
Location
madrid
The tractor engine is the corner stone of that design. Reduces induced drag, favors vortex lift and requires a tiny landing gear. We would be talking about a completely different design.
But obviously, that one looks amazing if you have got a 100 million budget.
 
Last edited:

Johan Fleischer

Active Member
Joined
Aug 24, 2019
Messages
25
Thank you ("looks amazing") :) But it should not be more expensive to build than a Velocity, or other Rutan-type canards the only difference being more aesthetic curves (and abscence of canards)
I admit, I have not enough knowledge to evaluate if pusher configuration can work with deltawings, but it seems to work fine with the canard aircrafts (and a lot of deltawing drones without canards)
 

TopherJA

Active Member
Joined
Mar 14, 2004
Messages
37
Location
Osceola WI
Full disclosure – I love goofy, weird airplanes with bookshelfs to prove it. Low-aspect-ratio (LAR) wings just have no real place on non-goofy general aviation airplanes. Sure, there are structural advantages and “look what I built” pride of the builder. However, these are not compelling reasons to design a LAR light airplane.

Reasons you might want to have a LAR airplane include:

  • Launch into space and reentry into the atmosphere (lifting bodies and shuttle orbiter)
  • Fit into the bomb bay (XF-85) or on a MIR or TIR (JDAM kitted Mk 82’s)
  • Fly faster than the speed of sound (gobs of delta-winged jets)
  • You need improved body lift to maneuver (Standard Missile)
My guess is that you won’t be doing those things.

The opposite of LAR wings is HAR wings – like sailplanes and (wait for it) helicopters.

We all know that sailplanes are efficient (low induced and profile drag). What about helicopters? Long skinny, twisty, droopy HAR blades work much better than short, wide LAR blades having the same blade area. That’s because a key figure of merit in a helicopter rotor is disk area – not blade area. Helicopters barely fly with those HAR blades and will not work with the short, wide LAR blades.

I don’t wish to be a Debbie Downer on LAR wings, I just can’t find a use for them on light airplanes. Jimstix
Powered lift aircraft that do not need to generate large lift coefficient at low speed make great use of LAR wings.
 

berridos

Well-Known Member
Joined
Oct 10, 2009
Messages
916
Location
madrid
It would be very helpful to test a prototype of the inverted zimmerman planform with rounded le at the low swept root section and sharp at the highly swept tip section. According to my basic understanding of vortex lift, only the tip sections are producing vortex lift and therefor should be sharpened (Dyke Delta).
 

berridos

Well-Known Member
Joined
Oct 10, 2009
Messages
916
Location
madrid
I bet the tip devices henryk shared in this thread should have interesting consecuences for LAR planes. Most deltas hav enormous drag in manouveures due to extrme induced drag. Therfor they have to fly in very large radius. Maybe those tips could be a complement to ailerons and facilitate yaw at negative dihedrals.
On the other hand they could deviate the direction of the vortex whirl spanwise along the leading edge instead of chordwise. Dont know if that is a desired effect.
Third, in order to reduced induce drag i see potential if the axis of this winglet aileron is not vertical, but leaned forward, extending artificially the wing span. Strangely the patent leans the axis backwards, sending the airstream downwards, what will increase the interaction with the airflow below the wing and theoretically increase induce drag.

An interesting problem is, if at high angles of attack, this vertical aileron gets blanketed and looses its effect.
Worth some basic experiments to get a feeling for this device.
Anyway, has to exert enourmous forces on the wingtip spar end.US3831885-drawings-page-4(1).png
 
Last edited:

Mavigogun

Well-Known Member
Joined
May 29, 2016
Messages
74
Location
Progressive Texas
According to my basic understanding of vortex lift, only the tip sections are producing vortex lift and therefor should be sharpened (Dyke Delta).
Can you qualify that understanding by citing a reference? As I recall, the entire sharp leading edge conspires to spawn stable vortices within a set of conditions- not just the outboard/tip sections.
 

berridos

Well-Known Member
Joined
Oct 10, 2009
Messages
916
Location
madrid
The vortex lift starts at a sweep of 50º and is strongest at about 60º. Has been reviewed and cited in this thread several times between aircar and danmoser. The center section hasnt enough sweep i would guess. Sharpness without sweep doesnt produces eddys
 
Last edited:

lr27

Well-Known Member
Joined
Nov 3, 2007
Messages
3,822
Is really HAR more efficient?
When people say a high aspect ratio wing is more efficient, they usually or often fall back and cite the classic induced drag coefficient:

Cdi = Cl^2/(pi*aspect ratio* efficiency factor)

And skip two underlying assumptions:
  • Constant wing area.
  • Evaluated at the same speed.
That is, wings with the same area are compared at a fixed speed. Now, instead of keeping area constant, keep the wing span constant. You will find that with fixed wing span and evaluated at the same speed, the Cdi rises with increasing aspect ratio. Then what do that tell us about aspect ratio and efficiency?
Yes. If you preclude using the advantage of having a high aspect ratio, then a high aspect ratio doesn't look so good. Similarly, if you require a long span, a low aspect ratio doesn't look so good.

The aircraft with the highest L/D's have long, skinny wings. That should tell you something.

For a given span, lift, and speed, and equivalent lift distribution, the wing area doesn't affect actual induced drag, although the Cdi changes. Remember that you have to multiply by wing area to get the actual drag. Or, at least, that's what the theory we use for moderate and high aspect ratio wings that are straight says. Try the calculations and see what I mean.
 
Last edited:

cluttonfred

Well-Known Member
HBA Supporter
Joined
Feb 13, 2010
Messages
7,282
Location
World traveler
Himat and lr27 and all, I'd like to explore this a little further. In my own back-of-the-envelope, that-looks-about-right, check-it-with-a-basic-spreadsheet type of design exercises, I usually have four relatively fixed parameters:

1) span (because of workshop or hangar limitations, or to facilitate folding or removable wings);
2) stall speed (trying to suit LSA or Part 103 or European microlight rules);
3) gross weight (because of those same rules and to achieve the mission); and
4) power (because I am usually designing around a particular engine for cost and availability and personal preference).

Stall speed and weight give me a required wing area, which combined with the span gives me the aspect ratio, and then the power goes in to tell me if the climb rate and cruise are acceptable. I keep doing that until I find something that seems like a good balance.

When this all falls apart is that the spreadsheets and approximations that work for "normal" light aircraft aspect ratios (say >4) do not take into account the unique conditions of very low aspect ratios.

I would love to see someone with the right mathematical skill and aeronautical knowledge create table combining conventional design techniques and low aspect ratio to show the impact of aspect ratio (say AR = 8/6/4/2/1) but keeping span, power, stall speed, and gross weight constant. Bonus points for a very rough approximation of the impact of aspect ratio on structural empty weight and therefore useful load.

Like I said, I have seen this sort of thing before but never in a way that included and accounted for the special behavior of very low aspect ratio and I do not, personally, have the chops to do it.

Cheers,

Matthew
 

BJC

Well-Known Member
HBA Supporter
Joined
Oct 7, 2013
Messages
11,056
Location
97FL, Florida, USA
If you preclude using the advantage of having a high aspect ratio, then a high aspect ratio doesn't look so good.
Within the speed range where most sport aircraft operate, there is no advantage to a high AR. There is an induced drag advantage to a greater span, which, coupled with a constant area, also produces a disadvantagous reduction in Reynolds number.

A classic design tradeoff: choose what is important.

BJC
 

lr27

Well-Known Member
Joined
Nov 3, 2007
Messages
3,822
Stall speed doesn't give you a wing area unless you're constrained to one particular airfoil, or airfoil and flap combination.

There may be a graph helpful to you in one of Hoerner's books. Given your level of enthusiasm, I recommend both of them to you if they're within your budget and you don't have to pack light when moving.

Once you've got a fuselage involved, things may get a bit complicated for really short spans, especially if you take advantage of the long chords involved by burying things in the wing.
 

rotax618

Well-Known Member
Joined
Oct 31, 2005
Messages
824
Location
Evans Head Australia
LAR planform and available power dictate the minimum flying speed - they don’t stall in the conventional sense - the airfoil seems to only effect the cruise drag, that is why faceted airfoils and even flat plates work for LAR.
 

berridos

Well-Known Member
Joined
Oct 10, 2009
Messages
916
Location
madrid
Reviewing my comment of the facet (i confused with dykedelta by the way) the sweep of the central section sweep looks strong, in the recommended ballpark that is dictated by the papers mentioned in this thread. Rotax618, maybe you remeber the degrees of the sweep? Looks like the sweep is stronger in the extensions and therefor forming a second stronger vortex over the extension, benefiting control at lower speed or already when the inner vortex has already burst.
It would be really interesting to see your model flying with out the winglets vs a central fin.
Dont you need a fin to counter the P moment of the engine at takeoff?
 
Last edited:

Sockmonkey

Well-Known Member
Joined
Apr 24, 2014
Messages
1,812
Location
Flint, Mi, USA
There's a question I asked a while back that nobody seemed to know the answer to. What if you went super-low-aspect and made the wing in a surfboard shape with sharp edges so you had almost nothing but vortex lift?
 
2
Top