Help Scaling Focke Wulf
 

Attention model aviation experts; I am scratch-building a scale Focke Wulf FW190 German WWII fighter, and need advice on weight and sizing. I am designing the model in AutoCAD 2007 in order to get everything perfect, and then getting the parts laser cut some time in the near future. I have already purchased the engine for the model, the Saito 170 3-Cylinder Radial, linked here:

http://www.horizonhobby.com/Products...odID=SAIE170R3

I intend to design my model around this engine, and since I am using AutoCAD, I can scale the model to any size I want. Here lies my dilemma. The engine is rated for 2 HP (1.70 cu in (27.8 cc)), and can swing a 16x8 prop at 8400 rpm, but it weighs 46 ounces. With such a heavy engine, I am not sure of the correct procedure for scaling my aircraft around it. It should be noted here that I intend to include retracts, flaps, it will be covered in balsa sheeting and then fiber glassed, and loaded with detail.

Given the diameter of the engine, the minimum cowl diameter could be 8 inches on the model. This would correspond to a 71 inch wingspan according to the ratio of cowl diameter to wingspan, which I calculated using AutoCAD. A cowl diameter of 9 inches would correspond to a wingspan of 80 inches. My Eagle 2 has a wingspan of 70 inches and it weighs slightly more (all inclusive, engine, wing, radio equipment) than JUST the Saito Radial! My Four-Star 40 Weighs about the same as the Saito engine I just purchased, and has a wingspan slightly less than 70 inches. I am therefore assuming that if the Focke Wulf is to fly, the wingspan (and thus wing useful wing loading area to provide adequate lift) must be increased to a reasonable amount. My problem is I don’t know just how large it should be.

I found a site that lists other scale Focke Wulf models, found here: http://rcwarbirds.com/fockewulfpage.htm

I am comparing some of the models with their respective engines, and these are some of the results:

Example #1: Wingspan: 84 inches
Engine: Zenoah G45, 3.8 HP, 74 ounces

Example #2: Wingspan: 88 inches
Engine: Desert Aircraft DA-100 twin, 9.8 Hp, 100cc, 5.8lbs
Total Weight: 38 lbs

Example #3: Wingspan: 83 inches
Engine: Zenoah G38, 2.5 HP, 71 ounces
Total Weight: 21 lbs

Judging from these examples, it doesn’t even seem likely that the engine I have chosen will fly the plane adequately, even with a 70 inch (smallest) wingspan. It’s depressing when you buy an expensive 4-stroke radial engine expecting insane performance from it and then finding out cheaper gas engines are much more powerful. But anyways, that’s why I need your help.

I’m afraid that if I make the model too small, the nose will be too heavy and the plane will be off-balance and extra weight wouldn’t be a good thing to add. On the other hand, if I make the plane too big to begin with, it might not even get off the ground.

If any of you could help me reason this out I would be highly appreciative. Perhaps giving me some stats with your own personal aircraft, such as weight and wingspan with an engine comparable to the Saito radial, would really help me. Thanks in advance.

RE: Help Scaling Focke Wulf
 

The F-w 190 series, in general, seems to be a hot topic over at RCSCALEBUILDER the past two months. Have you been there?

I worked on plans for a model version a good ten years ago. All I can remember from that time was that the aft control surfaces were too small for direct scale to model. They need to be a bit larger, or you get some lack of control.

Wm.

RE: Help Scaling Focke Wulf
 

That is interesting; when I was designing the tail the other day I noted how large the elevator and rudder control surfaces were, and was trying to work out the maximum deflection I'd need. I will re-assess this area based on your comment. I am indeed talking to the guys at rcscalebuilder.com and they have been quite helpful so far. I've learned that a high wing load is acceptable, that is, if I made my model with a 71 inch wingspan and it weighs under 15 pounds I should be good.