Laminar flow aircraft

Now, you're talking delta wings. Nothing seems to have just beneficial effects. You always have to pay the piper. You're not talking funny(ha,ha) but funny(twilight zone).


True that. All aircraft design is a compromise between different strengths and weaknesses.
 
"Meredith effect" was not well known as such, until relatively recently, since not too many read RAE papers from the thirties. The heat exchanger installation on the original North American P-51 was originally laid out by Art Chester, a racing pilot and aircraft designer on loan from Menasco Corp. He may have read the report. By early post war, many knew of the ramjet and understood the addition of heat in a divergent duct with an appropriate exit nozzle could produce some thrust when in motion. The relatively long wingtip ramjet heat exchangers on the 1949 Thompson Trophy Mustang "Beguine" were reportedly good for +20 MPH, relative to the original under-fuselage setup. Even model airplane magazines had articles by Bob Wood of Bell Aircraft, and Roy Marquardt on cowling the engine cylinders on control line speed models to recover some of the drag (I built and flew them then). Can't offer any explanation of the German wind tunnel anecdote, which I've heard from several sources.

The outer wing panels on the Me 262 were swept back because the CG was too far back.- The engines were heavier and the center section couldn't be relocated.

Dynasoar
 

longsword14

Banned
I really doubt it is possible to actually have such a practical wing that operates through various Reynolds number outside of a lab (it is barely possible inside a lab). Schlichting and Co. I believe did analyse P 51 wings and came to the conclusion that no, it in fact did not have a laminar wing.

People could discuss the strength of turbulent wake of such wings but it is impossible to remove the issue of turbulence altogether.
 
I really doubt it is possible to actually have such a practical wing that operates through various Reynolds number outside of a lab (it is barely possible inside a lab). Schlichting and Co. I believe did analyse P 51 wings and came to the conclusion that no, it in fact did not have a laminar wing.

People could discuss the strength of turbulent wake of such wings but it is impossible to remove the issue of turbulence altogether.

But yet Progress were made as I read it. Laminar flow on parts of the wing is beneficial and the increased thickness may be as well? You can mayve save 10% on drag and store 10% more fuel and your range is up a good 20% and speed by 20 km/h?

Its worth taking into account just as an engine upgrade.
 

longsword14

Banned
But yet Progress were made as I read it. Laminar flow on parts of the wing is beneficial and the increased thickness may be as well? You can mayve save 10% on drag and store 10% more fuel and your range is up a good 20% and speed by 20 km/h?

Its worth taking into account just as an engine upgrade.
The use of the word "laminar" gives people the wrong idea.
Getting wings with very little parasitic drag is something that any/all of the powers could have done.
Do a google search for "P 51 wing laminar", the first result has this conclusion which follows after some discussion about how skepticism was shown by aeronautical scientists about a "laminar wing":
"Concluding you can say that the performance of the Mustang could not be attributed to its laminar flow airfoil. It was the overall low drag design of this aircraft with clean surfaces including the careful design of the radiator that was the key of its good performance. Edgar Schmued succeeded to build an aircraft as clean as the wind tunnel model - a remarkable aircraft and a remarkable designer."
Ask any person in aero sciences, and he would refuse to believe that laminar flows are possible for any aerofoil at any practical Reynolds number. It seem the P 51 had low drag because it was well designed, so that it had in reality drag close to that found in tunnel testing.
 
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I find this interesting that a failed attempt still gives the desired result. I guess the uniqueness is relative so that the perceived need yielded efforts that resulted in generally accepted benefits.
Is that all? Not even part of the wing achieving what was sought after?
 
. Schlichting and Co

I did a quick google of Schlichting and Company. Is that the coal and gas, sauerkraut and pickles or tax company? GmBH. We are sinking in a cesspool of semantics here. Perhaps you would prefer "laminar" be called NACA 6-series or the British EC airfoils which feature low drag for high speed. They are intended to increase the degree of laminar flow and decrease the drag. I wouldn't want to be super-critical.
 

longsword14

Banned
I did a quick google of Schlichting and Company. Is that the coal and gas, sauerkraut and pickles or tax company? GmBH. We are sinking in a cesspool of semantics here. Perhaps you would prefer "laminar" be called NACA 6-series or the British EC airfoils which feature low drag for high speed. They are intended to increase the degree of laminar flow and decrease the drag. I wouldn't want to be super-critical.
It is not really a corporation but refers to the famous aerodynamics scientist Hermann Schlichting (he wrote a standard text on boundary layers used by many undergrads) and people with him.
At the speeds mentioned the region occupied by laminar flows will not be sufficient to effect drag to such an extent that we may call it a "laminar wing".
There would be other reasons for the low form drag experienced. Not trying to be super-critical here, but if we keep in mind that wings at that high Re simply do not have great laminar flows at all, then the low drag wing could be replicated by other teams without trying to get laminar flows.
 
I find this interesting that a failed attempt still gives the desired result. I guess the uniqueness is relative so that the perceived need yielded efforts that resulted in generally accepted benefits.
Is that all? Not even part of the wing achieving what was sought after?

IMO - people at NACA did came out with a wing profile that offered significant drag reduction. NAA designed the aircraft with wing based on that profile, that management and workers managed to manufacture true to the design.
We can compare the Mustang with perhaps the most similar design, the Ki-61. Wing thickness was in the ballpark in percentage points, Ki-61 sports a bit smaller wing, both don't have much of the weapon- or undercarriage-related drag. On about the same horsepower, the Mustang I was faster than the Ki-61 by as much as 35 mph. Or Mustang I vs. Yak-9 (smaller wing; lighter) with VK-105 - up to 25 mph.
 
At the speeds mentioned the region occupied by laminar flows will not be sufficient to effect drag to such an extent that we may call it a "laminar wing".

It is a matter of semantics as much as science, but Teddy von Karman, another Prandtl graduate, called it a laminar-flow airfoil. If he can play fast and loose with terminology, so can we.

I used the term "super-critical" as another word-play. It's an airfoil, but is it really super-critical or just moderately critical?
 
The best laminar wings maintain smooth boundary layers back to 35 maybe 40 percent of chord. Aft of that, boundary layers become turbulent.
However, that is still an improvement on earlier airfoils that went turbulent 25 percent aft of the leading edge. That worked fine on fabric-covered wings.
The other reason Mustang flew faster was detail design. Mustang was the first airplane designed from the skin in. That meant lots of flush butt joints and flush rivets that helped reduce parasitic drag.
The pitot inlet on the Mustang radiator helped prevent that turbulent boundary layer air from blundering around inside the radiator duct. Meredith Effect has rarely produced more thrust in practice. In practice, the best most designers aim for is zero cooling drag.
Later British designs (Mosquito, Vampire, Sea Fury, etc.) used wing leading edge inlets to avoid ingesting slow, turbulent boundary layers.
 
The other reason Mustang flew faster was detail design. Mustang was the first airplane designed from the skin in. That meant lots of flush butt joints and flush rivets that helped reduce parasitic drag.
A fair judge of an aircraft's streamlining is its Zero Lift Coefficient of Drag, that is, the dimensionless value of the amount of drag produced by the airframe without producing lift. The Bf.109G was about 0.023. The P-38L was a high 0.0268.

The P-51D was at 0.0163 :eek:
 
A fair judge of an aircraft's streamlining is its Zero Lift Coefficient of Drag, that is, the dimensionless value of the amount of drag produced by the airframe without producing lift. The Bf.109G was about 0.023. The P-38L was a high 0.0268.

The P-51D was at 0.0163 :eek:

I've seen .0174 for the F4U-1D.
Amazing what wing root oil coolers, spot welding and no wing fillets did
 
Thread highjack alert.:openedeyewink:
Dan Gurney used some boundary layer tech/principles in one of his Eagle Indy car designs, until that avenue was written out of the rules.
You mean designer Len Terry, don't you? (Formerly of Lotus, IIRC.) Didn't Terry also use the rad outlets to manipulate the BL flow?
Thus, the Delta-Wing.
AIUI, the delta gets the benefit by effectively going to an extremely long chord, so flow doesn't separate.

If the links are right, it wouldn't matter if Germany did get laminar flow, because the wing as built would never sustain it, because fit & finish were so poor...:eek:

A thought: couldn't the Me-109 &/or P-51 have turned the rad horizontal & fed it with a flush BL scoop? Would turning the outlet ducting sacrifice thrust from the hot air?

Another: if reducing drag is the goal, what about reducing tip vortices? I understand the modern winglets make a big difference; was there a way to do that in the '40s? Tip fences? Do winglets, or fences, actually eliminate the vortices, or just move them around? Is there an actual way to eliminate vortices? (I've read a paper suggesting there is, but I really didn't understand it....:openedeyewink:)
 
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Another: if reducing drag is the goal, what about reducing tip vortices? I understand the modern winglets make a big difference; was there a way to do that in the '40s? Tip fences? Do winglets, or fences, actually eliminate the vortices, or just move them around? Is there an actual way to eliminate vortices? (I've read a paper suggesting there is, but I really didn't understand it....:openedeyewink:)

USAF noticed it where P-80s with wingtip tanks flew better when empty than dropping them
 

longsword14

Banned
AIUI, the delta gets the benefit by effectively going to an extremely long chord, so flow doesn't separate.
From what I remember from my 1st year class, it is the formation of strong vortices over the top of the wing that allow it to go for very high angles of attack without suffering from separation.
Do winglets, or fences, actually eliminate the vortices, or just move them around?
They sort of change the local strength of the vortices.
https://en.wikipedia.org/wiki/Helmholtz's_theorems
You can't kill the vorticity of the flow (that would contradict the first part of Helmholtz Theorems), but you can change its distribution reducing the induced velocity vector.
So why not use obstructions, however crude, to do this ?
Got to do something with directional stability. I remember the glider in our department not being used in wind conditions at the peak of summer while some other planes were.
Had to do something with winglets on the long wings of the glider and cross winds that made directional control problematic.
Hope it helps.
 
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They sort of change the local strength of the vortices.

You can't kill the vorticity of the flow (that would contradict the first part of Helmholtz Theorems), but you can change its distribution reducing the induced velocity vector.
...Hope it helps.
It sure does. Thx.:) Even reducing would be good (in this case); tbh, tho, I was thinking of F1 rear wings & reduced turbulence for following cars.;)
 
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