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CEF speed contest Design Discussions

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CEF speed contest Design Discussions

Post  ian1954 on Mon Jun 23, 2014 4:00 pm

I have started
 

 
All the big bits cut out to make one of these thin slab profile thingies that will spin in a circle.

Shouldn't need to say what it is supposed to be!
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Re: CEF speed contest Design Discussions

Post  Mike Mulligan on Mon Jun 23, 2014 4:17 pm

Spit'? Looks like a good start!
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Re: CEF speed contest Design Discussions

Post  batjac on Mon Jun 23, 2014 7:54 pm

Mike Mulligan wrote:Spit'? Looks like a good start!

I was thinking de Havilland Caterpillar.... Very Happy 

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Re: CEF speed contest Design Discussions

Post  Cribbs74 on Mon Jun 23, 2014 8:47 pm

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

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

Hawker Typhoon?
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Re: CEF speed contest Design Discussions

Post  Cribbs74 on Mon Jun 23, 2014 10:25 pm

Mike,

Very impressive work!
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Re: CEF speed contest Design Discussions

Post  Theo Kleynhans on Tue Jun 24, 2014 3:07 am

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
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Re: CEF speed contest Design Discussions

Post  Oldenginerod on Tue Jun 24, 2014 3:17 am

Cribbs74 wrote:

Hawker Typhoon?

Looking at pictures of the Typhoon, I'd suggest they have fairly straight leading & trailing edges, nothing like the beautiful elliptical shape of a Spifire wing.  I'm betting a British plane from a British builder.

Rod.
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Re: CEF speed contest Design Discussions

Post  ian1954 on Tue Jun 24, 2014 4:13 am

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!)
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Re: CEF speed contest Design Discussions

Post  getback on Tue Jun 24, 2014 7:15 am

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 )  Smile Floats like a rock stings like a bee lol! Getgack
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Re: CEF speed contest Design Discussions

Post  JPvelo on Tue Jun 24, 2014 7:30 am

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". lol!
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Re: CEF speed contest Design Discussions

Post  batjac on Thu Jul 10, 2014 9:12 pm

Well, I test flew my September Fury after retrofitting the PeeWee on it instead of the .049. As I was thinking, it's a bit of a dog with the .020. Since I designed it around the .049, I had to add some weight to balance it out with the lighter engine. You can see it struggling at first to get some bite in the air. I was using the 2-bladed prop on it, so I'll swap that out for a 3-bladed prop and see if I can get some more oomph out of it. Otherwise, this'll be just a straight roundy-roundy plane. It still looks cool, and it got some favorable comments at the field on its looks.



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Re: CEF speed contest Design Discussions

Post  RknRusty on Thu Jul 10, 2014 9:42 pm

No wonder Youtube was slow tonight!

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Fuel capacity requirement...

Post  Mike Mulligan on Fri Jul 11, 2014 1:07 pm

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
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Re: CEF speed contest Design Discussions

Post  RknRusty on Fri Jul 11, 2014 1:38 pm

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.
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Re: CEF speed contest Design Discussions

Post  roddie on Fri Jul 11, 2014 5:08 pm

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.
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Re: CEF speed contest Design Discussions

Post  RknRusty on Fri Jul 11, 2014 6:08 pm

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

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Re: CEF speed contest Design Discussions

Post  JPvelo on Fri Jul 11, 2014 8:57 pm

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

Jim
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Re: CEF speed contest Design Discussions

Post  JPvelo on Tue Jul 15, 2014 7:38 pm

Finally found time to cut some wood for round two:

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Re: CEF speed contest Design Discussions

Post  Mike Mulligan on Wed Jul 16, 2014 12:14 am

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?
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Re: CEF speed contest Design Discussions

Post  batjac on Wed Jul 16, 2014 12:22 am

JPvelo wrote:Finally found time to cut some wood for round two:


Looks awesome. Caint wait to see the finished product.

The Waitin' Mark
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Re: CEF speed contest Design Discussions

Post  JPvelo on Wed Jul 16, 2014 12:43 am

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.
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Re: CEF speed contest Design Discussions

Post  Theo Kleynhans on Wed Jul 23, 2014 7:44 am

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

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Re: CEF speed contest Design Discussions

Post  OVERLORD on Wed Jul 23, 2014 8:17 am

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
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Re: CEF speed contest Design Discussions

Post  JPvelo on Wed Jul 23, 2014 3:47 pm

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
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Re: CEF speed contest Design Discussions

Post  Mike Mulligan on Wed Jul 23, 2014 8:21 pm

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

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