Streamlining principles

[Old Koreelah]

Perhaps someone can help me. Yonks ago I happened on some principles of streamlining aircraft, but now that I need the info, I cannot find it.

 

From memory most appendages (wings, empennage, undercarriage struts) should be followed by streamlining at a ratio of 3:1 to their thickness. If within the prop wash, 4 or even 5:1 ratio was needed.

 

Can anyone confirm this?

 

 

[facthunter]

They would be rough rules of thumb. If you look at a modern jet fuselage you will notice that flush rivets are only used for the first 1/2 approx. of the length. The boundary layer is deep enough to make the round headed rivet protrusions of little consequence. Don't forget a dimpled golf ball travels further than a plain surface one. Fairings are used on some planes and not on others but MUST be an advantage done properly.. At low speed you get away with a lot. Look at the drag caused by flying wires. Nev

 

 

[turboplanner]

Have a look on Amazon for some books OK. (Newer ones)

 

As Facthunter has said there's a lot of new knowledge around.

 

One base principle I've used in the transport industry with multi million dollar success is reducing frontal area, since air resistance is exponential with speed, and streamlining what's left has a much smaller effect.

 

 

[Mick]

I was told that having the widest point of the fuselage at the trailing edge of the wing negates the need for significant fillets at the fuse / wing intersection. It was pointed out to me as that is how my Skylark is.

 

 

[Sapphire]

A round wire or tube has ten times the drag than if it is shaped similar to an aerofoil. Or, a thin wire say quarter inch dia. has the same drag as an aerofoil shape with a cross section two and a half inches. All those insignificant looking thin wires on a wire braced a/c are real big drag. Think again when an exhaust pipe sticks way out.

 

 

[djpacro]

Everything to know is in the book by Hoerner: Fluid Dynamic Drag. You should be able to find the relevant chapter online. e.g. Me109 drag breakdown is here. http://www.wwiiaircraftperformance.org/me109/Hoerner-Me_109.pdf

 

 

[corvairkr]

Perhaps someone can help me. Yonks ago I happened on some principles of streamlining aircraft, but now that I need the info, I cannot find it.From memory most appendages (wings, empennage, undercarriage struts) should be followed by streamlining at a ratio of 3:1 to their thickness. If within the prop wash, 4 or even 5:1 ratio was needed.

 

Can anyone confirm this?

Everything to know is in the book by Hoerner: Fluid Dynamic Drag. You should be able to find the relevant chapter online. e.g. Me109 drag breakdown is here. http://www.wwiiaircraftperformance.org/me109/Hoerner-Me_109.pdf

I can highly recommend this book,i got a copy for research into my modified KR build.

I have it in front of me now and it says the optimum length ratio of fairings put around two dimensional obstacles is 3.7 ....smaller and you will induce flow separation which equals drag....and larger you will create unnecessary friction drag.

 

Jason

 

 

[Old Koreelah]

...the optimum length ratio of fairings put around two dimensional obstacles is 3.7 ....smaller and you will induce flow separation which equals drag....and larger you will create unnecessary friction drag.Jason

Thanks for these great replies, people. Looks like I will be replacing the old U/C fairings (1:3) with 1:3.7. If I get the time and energy to built spats, they might have to comply with the same ratio. My wheels are 6", so that means fat, ugly, long wheel fairings.

 

Everything to know is in the book by Hoerner: Fluid Dynamic Drag. You should be able to find the relevant chapter online. e.g. Me109 drag breakdown is here. http://www.wwiiaircraftperformance.org/me109/Hoerner-Me_109.pdf

Loved this, although the maths made my eyes glaze over. Presumably a post war analysis without the aid of modern computers, it shows the painstaking attentions to detail of old-school designers. Reminded me of a book about 617 (the Dam Busters) squadron. Those fliers were given the time and equipment to develop incredibly accurate bombing: within 25 yards from 18,000 feet. Their American analogue bomb sight took account of every conceivable factor- even heat bleed from a temperature probe via aluminium skin to the frozen air outside.

 

 

[djpacro]

I use wheel fairings just to keep mud off the undersurface of the wing. To reduce drag needs that same painstaking attention to detail esp gaps, brake lines etc.

 

 

[rgmwa]

Me109 drag breakdown is here. http://www.wwiiaircraftperformance.org/me109/Hoerner-Me_109.pdf

Not that I understood it, but the conclusion was very interesting. The Me109 looks quite streamlined, but appearances can obviously be deceiving. It would be fascinating to know how other contemporary aircraft like the Spitfire and Mustang would have compared.

 

rgmwa

 

 

[Old Koreelah]

Well before the Spitfire was conceived, the Germans were building very streamlined aircraft, such as the Heinkel 70. The Bf-109 shares design principles with the VW bug: simplicity to allow mass- production.

 

The P51's designers saw the radiator as an assett rather than a source of drag. During flight it was moved up and down via cables according to engine cooling needs, and contributed significant amounts of thrust. The laminar flow wing sure helped efficiency, but its stall characteristics would have required intensive training... and very long concrete runways! Those runways were built all over the place during the war and must have been a major factor in the decline of Flying Boats after the war.

 

 

[rgmwa]

A bit off-topic: Ironically, Edgar Schmued who designed the Mustang was born and educated in Germany. The book `Mustang Designer' by Ray Wagner is a fascinating read if you can get hold of a copy.

 

rgmwa

 

 

[Old Koreelah]

A bit off-topic: Ironically, Edgar Schmued who designed the Mustang was born and educated in Germany. The book `Mustang Designer' by Ray Wagner is a fascinating read if you can get hold of a copy.rgmwa

Who cares about thread drift? Must get a copy. I love the efficiency of the Mustang design, but somehow the earlier shape looks more appealing to me.

 

The term "German Scientist" appears so much, that the stereotypical mad professor has to have a German accent. I've read that, like the Scots who also produced more than their share of innovators, the Germans poured resources into technical education centuries ago. They still turn out engineers and scientists at rates orders of magnitude greater than we do.

 

 

[Neil_S]

... like the Scots who also produced more than their share of innovators, ....

I think that's down to a few wee drams of Scotch, Jimmy.....

 

 

[rgmwa]

Here you go: http://www.amazon.com/MUSTANG-DESIGNER-Edgar-Schmued-P-51/dp/1560989947

 

rgmwa

 

 

[Old Koreelah]

I think that's down to a few wee drams of Scotch, Jimmy.....

Is that what I'm missing...which label would you recommend?

 

 

[Neil_S]

Is that what I'm missing...which label would you recommend?

Personally I would go for Glenfiddich....hoots!

 

 

[kaz3g]

The term "German Scientist" appears so much, that the stereotypical mad professor has to have a German accent. I've read that, like the Scots who also produced more than their share of innovators, the Germans poured resources into technical education centuries ago.

As a young student of chemistry in the early 1960s, I had to learn scientific German as a compulsory unit. This was when Bohr and Rutherford were still working out their atomic molecular theories and a great many scientific papers were only available in German.

 

Ironically, perhaps, most of the budding nuclear physicists (and medical researchers) were Jews and it was Hitler's blind hatred of them that sent the survivors to the USA where they helped make the bomb that ended the war against the Axis.

 

kaz

 

 

[Neil_S]

As a young student of chemistry in the early 1960s, I had to learn scientific German as a compulsory unit. This was when Bohr and Rutherford were still working out their atomic molecular theories and a great many scientific papers were only available in German.Ironically, perhaps, most of the budding nuclear physicists (and medical researchers) were Jews and it was Hitler's blind hatred of them that sent the survivors to the USA where they helped make the bomb that ended the war against the Axis.

 

kaz

Yes, it's enough to make you believe in karma....(well, almost.....as it's so unscientific )....

 

Cheers

 

Neil

 

 

[Yenn]

The secret appears to be to have a round leading profile and a tapering trailing profile. That keeps the air attached beyond the widest part and reduces drag

 

I have an old kitplanes mag somewhere where a WW2 fighter type was completely cleaned up and then the protruberances were added one by one with the resulting drag numbers

 

Some very small things can have big drag consequences.

 

 

[Ultralights]

this is interesting, actual testing starts at about 1 minute.

 

 

 

[Old Koreelah]

Here you go: http://www.amazon.com/MUSTANG-DESIGNER-Edgar-Schmued-P-51/dp/1560989947rgmwa

Thanks for the link; Amazon delivered my copy after a few weeks. Like so many American histories, it focuses on the personalities and the awesome productivity of US industry. There are only passing references to design details, and the engine cooling system (the main reason I bought the book) gets a paragraph. It was a good read, however and it was fascinating to find out the impact Schmued had on design well into the jet age.

 

 

[rgmwa]

Yes, it's not technical reference, more a biography with a technical focus, but I found the story of what Schmeud and his team did and how they did it very interesting.

 

rgmwa