CEF speed contest Design Discussions (2014)

I am thinking Spitfire as well. I hope so anyway. It's my favorite WW2 bird.

OTOH it has some non Spit features..... 

Hawker Typhoon?

Mike,

Very impressive work!

Very impressive Mike. You are going to leave the rest of us behind on the looks of that plane.

Good to see all the pices Ian. I also am thinking Spitfire.

Theo

In my schooldays woodwork classes, we were taught two things:-

1. Measure twice, cut once
2. Don't tell anyone what you are making until it is finished

(That way - you can cover up your mistakes and change your mind. Start off making a rocking horse, end up with a rocking donkey!)

Rocking donkey <<<<>>>>that's a good one Ian1954.... this time I am going to get the engine right before I start building (what ever it is )   Floats like a rock stings like a bee  Getgack

ian1954 wrote:In my schooldays woodwork classes, we were taught two things:-

1. Measure twice, cut once
2. Don't tell anyone what you are making until it is finished

(That way - you can cover up your mistakes and change your mind. Start off making a rocking horse, end up with a rocking donkey!)

From this point forward Ian's plane will be referred to as "The Rocking Donkey". 

No wonder Youtube was slow tonight!

Would any of you guys be willing to divulge how much fuel you found was needed to complete a qualifying flight? I did a search and didn't really find anything, so I hope it hasn't been discussed to death somewhere and I just missed it!

I know there will be variables from engine to engine, etc., but I'm getting ready to make up some tanks for the Conquest Bearcat, or deciding if it would have room for a bladder. Actually, I have no experience at all with bladders and don't have a clue how much space is required, but logic would suggest that it varies significantly with the amount of fuel, so back to the beginning...

I have plenty of room for fuel, I expect, but I don't want to have to spin that fast for any longer than I need to!

Any insight appreciated!

Thanks!

Mike

Hi Mike. I used about about a half ounce in the pressure bladder, but I just eyeballed it. Then after a few backward starts and walking to the handle, it flew 19 laps, the last 3 of which were starting to shut off.
Rusty

Mike Mulligan wrote:Would any of you guys be willing to divulge how much fuel you found was needed to complete a qualifying flight? I did a search and didn't really find anything, so I hope it hasn't been discussed to death somewhere and I just missed it!

I know there will be variables from engine to engine, etc., but I'm getting ready to make up some tanks for the Conquest Bearcat, or deciding if it would have room for a bladder. Actually, I have no experience at all with bladders and don't have a clue how much space is required, but logic would suggest that it varies significantly with the amount of fuel, so back to the beginning...

I have plenty of room for fuel, I expect, but I don't want to have to spin that fast for any longer than I need to!

Any insight appreciated!

Thanks!

Mike

Mike, Some contestants finished with 5cc tanks (stock Babe Bee size) if that helps you. That's considerably less than 1/4 oz. if my calculations are correct. I built 3 different size tanks to test; a 4.61cc (.156 oz.) tank.. a 7.7cc (.26 oz.) tank.. but settled on a 6.15cc (.208 oz.) "conservative/middle of the road" size just to play it safe.. because I was running that large venturi and Tee Dee piston/cylinder combination. It was.. and "still is" unfamiliar territory for me. Like Rusty said; you have to allow for how long the engine runs (starting/needling etc.) until the model is airborne.. and you give the signal (raising your hand) to start the timing. If you're all tuned/warmed-up and have a good pit-man, that might only be 15 seconds in duration. No sense in carrying the weight of extra fuel that you don't need, to complete the 10 laps.

I musta' had a thirsty engine. Maybe I'm overestimating how much it was.

Mike,
I used a bladder with about 1/3oz. and flew for WAY to long.

Jim

Finally found time to cut some wood for round two:

Great choice Jim, one of my all time favorite airplanes. The outlines and proportions look to be really accurate. Did you scale it or is it just eyeballed?

Thanks Mark!

Mike Mulligan wrote:Great choice Jim, one of my all time favorite airplanes. The outlines and proportions look to be really accurate. Did you scale it or is it just eyeballed?

Mike,
I generally do a google search for three view drawings of the plane I'm going to model.  I print 'em off and enlarge them at kinkos/fed ex to use as patterns.

Hi Guys. I need some help.

This is the first time I am doing something like this and need some advice.

I would like to try and build a nemesis. If I scale the 3 view to a 15inch wingspan, I only have 31square inches of wings. So I need to go to 45squares.

So If I extend the wingspan to 19inches and make it a little bit wider, I get to the 45squares.

Is this a good way to go? What is better to do: add length or make the wing wider?

I would appreciate the help.

Also, as the wings are not as wide at the tips, how do you accurately calculate the area?

Theo

Theo,

For my model, I blew up the wing as it is, so it becomes bigger but keeps the same shape.

To determin the surface, cut out your wing or half the wing out of a piece of paper and use the negative. put it onto an imperial cutting math and count the squares, half squares and so on:



Lieven

Theo,
I have no background in aerodynamics but it is my understanding that a long thin wing is faster than a short wide wing. Maybe someone with a better understanding of the subject will chime in.

Jim

JPvelo wrote:Theo,
I have no background in aerodynamics but it is my understanding that a long thin wing is faster than a short wide wing. Maybe someone with a better understanding of the subject will chime in.

Jim

That is VERY generally true. A long, thin wing tends to be more efficient, meaning that for a given area and a given amount of lift, the thinner wing will generate less drag, all else being equal.  I say this is very generally true, because as you can guess, the variables are almost infinite. One of those variables is the shape (planform) of the wing.

Theo, if the Nemesis you are looking to build is the version in the drawing, the shape of the wing is excellent for what we are trying to do. From my figures, it looks like if you were to increase the span to 17", make the chord (width) 3.25" and make the shape as close as possible to the original (especially the tips) you would have a very nice wing shape and be just a little over 45 sq. inches. The Nemesis wing shape is very efficient and the extra span will probably be slightly less of a drag penalty than the extra width would be.  

Looking at the drawing, it looks like it would be pretty easy to enlarge the top view drawing until the wing chord at the fuselage  was 3.5", then measure 8.5" in from the tip and use that as your wing pattern. Of course sanding in a good airfoil shape with a nice thin trailing edge is the most important thing. Worth spending a bit of time to get that right!

Hope this helps...

Mike