Variable Geometry Control Surfaces

[JUSTNUZZA]

This is interesting.

 

 

 

[Birdseye]

Seems just to be hinge-less flaps so far. Other than through shorter take offs and steeper climbs, I fail to see how it will make aircraft quieter.

 

A truly variable wing would be something quite different and of much greater value.

 

 

[Deskpilot]

Quite right Birdseye. Cover any wing with a rubber membrane and you have the same thing. When they come up with a completely morphing wing, then they'll have something to shout about.

 

 

[facthunter]

Birds don't have sealed surface wings. They have exotic surfaces and slats. Better boundary layer control. Slots VG's and blown surfaces can achieve things I doubt anything else can , Nev

 

 

[Marty_d]

Birds don't have sealed surface wings. They have exotic surfaces and slats. Better boundary layer control. Slots VG's and blown surfaces can achieve things I doubt anything else can , Nev

True, but then birds don't cruise at .8 mach either.

 

 

[facthunter]

Not the point. They (birds) CAN fly at 30,000 feet and some go very fast in a dive, and are more efficient than anything we will ever build, but we are talking about flaps and ailerons. Most jets use spoilers (coupled with ailerons) for lateral control. I can't see boundary layer control addressed with the concept here. You won't get the high lift coefficient at low speeds with high wing loadings without multi slotted flaps and leading edge devices to match. Crude but I'm skeptical of anything else working.

 

Scale effect makes bigger wings work better. A jumbo sized bumblebee wouldn't get off the ground.

 

Laminar flow wings were all the go once but had problems.. Once you get tot he M crit speeds (High subsonic) the design has to address localised areas of high velocity. airflow. In this area we haven't advanced much in the last 50 years as far as higher subsonic cruise speeds (with economy) are concerned. Nev

 

 

[Marty_d]

Interesting article here http://www2.hesston.edu/Physics/WingDesign/research.htm - includes what you mention about "exotic surfaces" Nev.

 

 

[facthunter]

The problem of inefficient flaps and ailerons and other controls is secondary with our type of fun aircraft where control "authority" and neutral or other stability questions are more important. You can dirty it up when coming down to get extra lift at the lower speeds. Steepen the approach path or do a powered approach. I've owned planes with no flaps. I'm certainly no advocate of complexity. Shielded rudder and poor airflow (boundary layer control/ separation)Turbulent airflow equals efficiency loss stuff, and often control authority/ response. We can improve these things and have better to fly aeroplanes.

 

I've been pondering for years a design concept with a blown wing and thrust from a pressurised plenum which is part of the structure and enclosed mid mounted engine, with centrifugal compressor. Mass in the middle where it should be. Nev

 

 

[Marty_d]

When you say "blown wing", are you referring to blowing the flaps or the leading edge (boundary layer enhancement) or both?

 

It'd be interesting but the plumbing would be complex.

 

 

[facthunter]

Top wing surface mainly and provide thrust Plumbing built into composite structure. Part of it (load bearing) large x sectional area for minimum fluid friction. Nev.

 

 

[AVOCET]

The problem of inefficient flaps and ailerons and other controls is secondary with our type of fun aircraft where control "authority" and neutral or other stability questions are more important. You can dirty it up when coming down to get extra lift at the lower speeds. Steepen the approach path or do a powered approach. I've owned planes with no flaps. I'm certainly no advocate of complexity. Shielded rudder and poor airflow (boundary layer control/ separation)Turbulent airflow equals efficiency loss stuff, and often control authority/ response. We can improve these things and have better to fly aeroplanes.I've been pondering for years a design concept with a blown wing and thrust from a pressurised plenum which is part of the structure and enclosed mid mounted engine, with centrifugal compressor. Mass in the middle where it should be. Nev

When do we start Nev?

 

Ill clear a spot on the calendar !

 

Mike

 

 

[facthunter]

I've had this concept for about 20 years. It's not the first time I've mentioned it here, but you are the first one to respond, avocet

 

The efficiency of the thrust concept has to be determined. You could boost it by burning fuel in a couple of the ducts for take off. it would be classified as a jet then, but perhaps we don't have to go there.

 

Perhaps a university might come on board? Nev

 

 

[ToniT]

Seems to me that a variable thickness and wing shape is easy to achieve mechanically. But every piece adds weight. I can create mechanisms to transition from one NACA airfoil to another (STOL to Cruiser), but the materials double the weight of the wing.

 

But let's say I have a revelation and am able to create a lightweight variable geometry wing.

 

What other aircraft structural considerations need to be considered to double Vne?

 

I am particularly interested in a variable geometry airfoil for the CH 701. But it only has a 550 # useful load before modification.

 

 

[facthunter]

Cost, weight complexity and reliability are your enemies. Going fast is another problem with flutter and extra strength of the structure needed.. Blown aerofoils combined with pressurised plenum thrust is simpler, safer too as there's no prop to be damaged and the undercarriage can be shorter, and mass located better. Nev

 

 

[nomadpete]

Nev, you have got me hanging in a string, waiting for the next installment.

 

I'm acutely aware of my limited knowledge. And Totally intrigued with the concepts of which you speak. Concepts which I can only barely conceptualise. I do understand that there is a large amount of R&D that goes between your description an an actual flying machine, and there is high probability of some ideas turning out to be dead ends, but I'd love to somehow be along for the ride. Just don't tell bexy. He's got enough projects.

 

 

[facthunter]

It's a high volume low pressure system. I need some efficiency figures for thrust. Use a centrifugal impeller and the plenum and some ducting is structural. Nev

 

 

[facthunter]

The post repeated, so deleted. While I can, luckily. Nev

 

 

[onetrack]

Gee, Nev, you need to catch up with Duan Phillips, the Phillips helicopter designer.

 

He's 20 years in front of you, and he only needs a few thousand dollars more, to get airborne!

 

duan phillips flying saucer - Google Search

 

 

[Marty_d]

Seems to me that a variable thickness and wing shape is easy to achieve mechanically. But every piece adds weight. I can create mechanisms to transition from one NACA airfoil to another (STOL to Cruiser), but the materials double the weight of the wing.But let's say I have a revelation and am able to create a lightweight variable geometry wing.

 

What other aircraft structural considerations need to be considered to double Vne?

 

I am particularly interested in a variable geometry airfoil for the CH 701. But it only has a 550 # useful load before modification.

Hi Toni,

 

I'm currently building a 701. Agree that the weight limitations don't offer much scope for extras. Besides that though, the 701 is a boxy "built-in-headwind" design with draggy struts, rivet heads, thick wing & tailplane - to get full benefit of variable geometry you probably want to start with a much cleaner aircraft, drag-wise.

 

 

[facthunter]

One track.. Nothing so radical. Blown aerofoils are nothing new, the principle is proven. It's thrust efficiency and structure concerns I have.. Fairly conventional looking , tailfeathers controlled. NO conventional propeller. Outlets in the wings. Nev

 

 

[ToniT]

Blown aerofoils combined with pressurized plenum thrust is simpler, safer too as there's no prop to be damaged and the undercarriage can be shorter, and mass located better. Nev

I've seen many RC models that use pressurized plenum airfoils. Some use a virtual plenum to create an external chamber around an otherwise non-airfoil.

 

Flying Pipe

 

 

These would be more suited to making a fast aircraft stall at a slower airspeed. So like Marty_d said, start with a plane like a Pulsar XP that cruises at 180 mph, and use a pressurized plenum to provide STOL performance.

 

I can imagine a hinged leading edge and a squirrel cage blower under it, that opens automatically when airspeed and blower pressure are compatible at slower air speeds. "Potentially" reducing the 49 mph stall speed of the Pulsar XP to some significantly lower air speed.

 

Instead of using the pressurized plenum to increase air speed, use it to lower the stall speed of a fast air foil.

 

 

[ToniT]

Imagine, you are on final approach on a gravel bar. At 55 mph the blower starts and leading edge opens. The stall speed dropping to lets say 30 mph (but 15 mph is not too far fetched). The difference in landing roll out of 50 mph versus 30 mph is significant.

 

A CH 701 lands within 80 feet at 30 mph. A Pulsar XP currently lands with a stall speed of 50 mph at 800 feet; 10 times further.

 

Pushing the concept further, could the pressurized plenum provide for near VTOL performance at slow air speeds, and a different reuse of the same blower, increase cruising air speeds.

 

 

[onetrack]

It's interesting to see the RC models flying, thus proving that Anton Flettner was correct with his theory of the Magnus Effect wing.

 

However, translating the theory into the practical, working, safe, full-size product, is where it gets difficult.

 

It is obvious that any wing that relies on lift from a powered, spinning cylinder, is totally dependent on the cylinder power source for lift.

 

Any power source failure results in a massive reduction in lift and little glide ability. That definitely sucks, as power sources fail, as sure as the sun rises.

 

Then we have the gyroscopic forces problem, relating to spinning cylinders on the wing.

 

These forces would almost certainly, negatively impact on aircraft controllability.

 

Essentially, if the arrangement could be made to work and provide an adequate level of safety, then someone would have done it by now.

 

The U.S. military carried out a study on the Magnus Effect wing and deemed it impractical - and the only full-size aircraft ever built utilising spinning wing cylinders, crashed, and was wrecked, after only one flight.

 

What are the advantages of a Spinning Wing (Magnus Effect) and why haven't any been commercially produced?

 

 

[facthunter]

Not interested on anything like rotating cylinders, just improving the laminar flow at higher angles of attack by blowing the boundary layer to stop separation occurring for longer. This isn't rocket science but the plane will be propelled by the same feature. At low angles of attack you don't have a problem with separation. That's when it will provide more thrust. Nev

 

 

[Old Koreelah]

Fascinating discussion, people! I believe one version of the C-130 Herc blew air out slots in the wings, presumably into the flaps gap.

 

This snippet about laminar flow comes from my first book about flight, published 1966: