encan

Hello,

I am only thinking to try a design of my own and have couple of questions.

Whats the role of a planes nose lenght? By this i mean from the LE of the wing to the prop. Comparing an air liner and a J3 cub may seem weird but in terms of the nose lenghts of these planes what characteristics change? If we take this J3 cub and just stretch the nose longer (all else being same) what would be different other than making it so ugly?

http://www.modelaircraft.org/insider/07_05/itch.htm

In this web site the author suggests %16,875 of the fuselage is ideal for the nose lenght. But then he also gives an example at the end. He says the total lenght of the fuselage is 38,5 inches and the nose lenght is 8,7 inches. However, %16,875 of 38,5 does not make 8,7 inches when i calculate.

So what is the real ratio for it. 8,7 is about %22,9 of 38,5. Am i confused?

thanks in advance.

HighPlains

My Feedback: (1)

You are correct, his numbers don't work out in his example. However there are a few good ideas in the article.
This is how most convential designs has been done over the decades and still works. Pick a model close to what you want, and make changes.
The author didn't follow his own advice, other wise he would have written the nose length as 17% instead of 16.875%. Either number is pretty much pure bunk. The purpose of having any distance at all on the nose is to make the airplane balance.
You ask a pretty good question. The airliner is like stuffing sausage, the longer the tube, the more meat it can carry. So their fuselage is designed as a long tube full of paying meat. When they want to carry more, the tube is made longer in front of the wing and behind in proper proportions to maintain balance.

As to the difference in proportions, what most people don't realize about airplanes, is that the propeller in a tractor instillation is destabilizing. (Tractor instillation means the prop is in front of the airplane). So you need a larger vertical surface for the plane to have stability. The size required is proportional to the diameter of the prop and distance ahead of the CG.

Back to the airliner, no props, so the nose proportion can be much longer on jets.

Really, about the only proportion you need is 1/3, 2/3 for most prop models. About 1/3 of the fuselage is in front of the CG, and 2/3 behind.

P-40 DRIVER

Nose lenth as a practical matter is cosmetic for a scale airplane or a matter of balance. What will it take to get the airplane to balance with all the components installed. adjusting nose lenth ie where the engine is can save alot of lead.

Danny Baker

My Feedback: (2)

Nose lenght in sport planes (full scale), warbirds (full scale) and all others (full scale) was determined by whatever the engine weight was to balance the plane. That's why most warbirds have such a short nose, very heavy engines in those days on the full scale version.

Tall Paul

The nose -length- on the Gentle Lady glider for example, is too short!
Proper balance requires adding ballast to the nose, which contributes zero to the flight performance.
Extending the nose about 2'' over the kit length gives room to put the receiver battery further forward without having to add ballast.
Not fixing the nose length until all the equipment is located can pay off in needing the least amount of nose weight.
Kit GL vs follow-on built to use the same wing and tail length...

All Day Dan

My Feedback: (5)

Encan, Send me your E-mail addrress. I have some design information in PDF format that I am unable to upload. Dan.

vertical grimmace

My Feedback: (1)

Also, it depends on the type of flying you want your model to do. A Pattern type aircraft have always had long moments for added stability in the pitch axis. This adds smoothness. While Combat models have short moments so they can turn quickly. Keeping the weight closer to the CG is how the combat models benefit here.
When I have designed my models, I always started out with how I wanted the plane to fly. Then I decided on engine. I will set my nose length first and then adjust the tail moment to get my CG.
Interesting to look at 1\2 A models. They have very long noses as the engines are much lighter than say a .40 size engine. (relative to their power) One trick you see here to minimize a really long moment with the 1\2 A models is to add sweep to the wing. This allows the CG to be further aft and allows you to have a somewhat longer tail moment. Look at a modern CL Combat model for an example here.

encan

Thank you very much for the responses. It is getting clearer in my head now.

Dan,

I would appreciate having the files you have. Thank you verymuch. I am sending a pm.