CEF speed contest Design Discussions

andrew wrote:Question for Phil and Mark ---

Since you both have chosen a similar approach in mounting the engine, I'm sure there is a viable reason.  

With the engine mounted to the right of the centerline, it seems that it would have a tendency to turn the plane into the circle.  Aside from simplifying fuel flow, was there a particular reason for outboard mounting rather than inboard?  I don't know how much impact outboard vs. inboard would have, which is why I'm asking.

andrew

Andrew, I used this engine mounting scheme for the empirically derived and scientifically proven reason that "it looks good". It's a profile plane, so I thought it should look authentic from the side. Besides, I figured that if I tried to mount a round cowl over the engine, I'd most likely get it out of alignment and increase the total drag of the model. As for the asymmetrical thrust from the engine on the outboard side of the fuse, I doubt that it makes any real difference. The location of the leadout guide and engine offset would have more effect on the inward/outward turning. I just guessed where to put the leadout guide on the inner wing, probably making it too far aft for minimum drag, but I didn't want to spend a bunch of time experimenting with the best placement. I was more interested in ensuring the plane wouldn't turn in towards me as it flies. I'm not putting in any left thrust on the engine. We'll see how things go after the test flight.

The Good Looking Mark

pkrankow wrote:

ian1954 wrote:Nail polish is usually nitro cellulose in a butyl actetate or more commonly ethyl actetate solvent.

I think it should be fuel proof but it can become quite brittle. It can be removed using its solvent - butyl or ethyl actetate - but even more rapidly with acetone.

Sounds like it will be perfect, depending on my fuel bath test tomorrow with my test sticks.

Phil

Decidedly NOT fuel proof. The fuel simply washed the nail polish away in mere seconds.

I don't know what I will do. Maybe use clear fuel-proof dope over it? Maybe see if black Rustoleum comes in 1/2 pint cans?

Phil

pkrankow wrote:

pkrankow wrote:

ian1954 wrote:Nail polish is usually nitro cellulose in a butyl actetate or more commonly ethyl actetate solvent.

I think it should be fuel proof but it can become quite brittle. It can be removed using its solvent - butyl or ethyl actetate - but even more rapidly with acetone.

Sounds like it will be perfect, depending on my fuel bath test tomorrow with my test sticks.

Phil

Decidedly NOT fuel proof.  The fuel simply washed the nail polish away in mere seconds.

I don't know what I will do.  Maybe use clear fuel-proof dope over it?  Maybe see if black Rustoleum comes in 1/2 pint cans?

Phil

I was just reading somewhere that paint can be mixed into epoxy for colored epoxy. Maybe try that thined with alcohol?

Jim

I use Testors paint pens all the time for touchups and painting prop tips. I press on a hard surface until the paint flows, and it gets plenty wet to do some marking before you have to press to reload. The paint comes off the props when I aggressively clean with alcohol, so I go easy on it. And I haven't tried spraying Lustrekote over it or painting anything critical in the engine area. It sticks to the existing paint around touchups better than on the plastic prop, and I can see it on my cleaning rag, but I haven't ever rubbed it all off. I think the red stays on the prop tips better than the white. And it looks cool too.

Rusty

I drew my wing last night. Boy, scaling a plane from random pictures pasted from the internet is a pain. I had to crank out a bunch of percentages with all the different angles on the P-51 wing. My fuse is exactly 12", making my wingspan 14.76". Since that's below minimum, I'll stretch it to exactly 15". I should have made the fuse longer if I wanted exact scale, but I know it isn't an issue here.

I'm undecided about whether to use an airfoil or just a flat surface. I'm thinking of sanding a thin flat bottomed foil out of a 1/4" sheet. It seems like for speed, a little bit of lift to float the plane would be helpful rather than using so much energy to brute force it through the air. The root chord is 3.1", so a Sig 1/4"x3" symmetrical airfoil is an option. On the other hand a flat slat with a couple of degrees of + incidence might serve the same purpose, but I would guess it may also introduce enough drag to counter the lift, or worse. Decisions decisions... any thoughts on lift vs. brute force?

Rusty

If you need to calculate percentages, go to Kirt's site. You fill in the length you've got and the length you want to obtain. The % is given right away!:


http://www.airplanesandrockets.com/resources/plans-scale-calculator.htm

Lieven

RknRusty wrote:I drew my wing last night. Boy, scaling a plane from random pictures pasted from the internet is a pain. I had to crank out a bunch of percentages with all the different angles on the P-51 wing. My fuse is exactly 12", making my wingspan 14.76". Since that's below minimum, I'll stretch it to exactly 15". I should have made the fuse longer if I wanted exact scale, but I know it isn't an issue here.

I'm undecided about whether to use an airfoil or just a flat surface. I'm thinking of sanding a thin flat bottomed foil out of a 1/4" sheet. It seems like for speed, a little bit of lift to float the plane would be helpful rather than using so much energy to brute force it through the air. The root chord is 3.1", so a Sig 1/4"x3" symmetrical airfoil is an option. On the other hand a flat slat with a couple of degrees of + incidence might serve the same purpose, but I would guess it may also introduce enough drag to counter the lift, or worse. Decisions decisions... any thoughts on lift vs. brute force?

Rusty

I used 3/16 sheet with a 3/16x1/16 basswood L.E. cap sanded to a symmetrical airfoil. I got the trailing edge as thin as possible and then reinforced it with light glass. Not do much brute force as "slicing through the wind".

Jim

RknRusty wrote:I drew my wing last night. Boy, scaling a plane from random pictures pasted from the internet is a pain. I had to crank out a bunch of percentages with all the different angles on the P-51 wing. My fuse is exactly 12", making my wingspan 14.76". Since that's below minimum, I'll stretch it to exactly 15". I should have made the fuse longer if I wanted exact scale, but I know it isn't an issue here.

I'm undecided about whether to use an airfoil or just a flat surface. I'm thinking of sanding a thin flat bottomed foil out of a 1/4" sheet. It seems like for speed, a little bit of lift to float the plane would be helpful rather than using so much energy to brute force it through the air. The root chord is 3.1", so a Sig 1/4"x3" symmetrical airfoil is an option. On the other hand a flat slat with a couple of degrees of + incidence might serve the same purpose, but I would guess it may also introduce enough drag to counter the lift, or worse. Decisions decisions... any thoughts on lift vs. brute force?

Rusty

If you're gonna try to make the wing shape scale, you're going to run into the same problem I had.  At 15" wingspan, I couldn't make a scale wing shape.  If your root chord is only 3.1", you're not going to be able to taper the wing.  It'd have to be 2.9" at the tip to maintain the 45 square inch rule for the wing area.  To make my wing scale, the root would have been just at 3 1/4", so my tip couldn't have been any less than 2 3/4" to meet the 45 sq.in. rule.  I went ahead and made my root 4" and then scaled the taper to make as scale-like a wing as I could and still maintain 45 sq.in.  Or, you could taper the wing, but make it longer than the 15" minimum wingspan.  It's a fact on full scale planes that a long, thin wing has less drag than a short, fat wing.  I thought about it for a long time trying to decide if that also held true for a small C/L plane, but in the end decided to go for a short, fat wing for structural strength.

The Short, Fat Mark

batjac wrote:If you're gonna try to make the wing shape scale, you're going to run into the same problem I had.  At 15" wingspan, I couldn't make a scale wing shape.  If your root chord is only 3.1", you're not going to be able to taper the wing.  It'd have to be 2.9" at the tip to maintain the 45 square inch rule for the wing area.  To make my wing scale, the root would have been just at 3 1/4", so my tip couldn't have been any less than 2 3/4" to meet the 45 sq.in. rule.  I went ahead and made my root 4" and then scaled the taper to make as scale-like a wing as I could and still maintain 45 sq.in.  Or, you could taper the wing, but make it longer than the 15" minimum wingspan.  It's a fact on full scale planes that a long, thin wing has less drag than a short, fat wing.  I thought about it for a long time trying to decide if that also held true for a small C/L plane, but in the end decided to go for a short, fat wing for structural strength.

The Short, Fat Mark

Ah, hell, you're right. I think I'm less than 30 squares as it is. Back to the drawing pad. Well it's gonna be a cold rainy weekend, so that'll be a good dining room table project. I'm headed back out to the shop to continue on the Yak now. I didn't get to work on it last night.

Thanks for alerting me to that oversight before I cut wood. Maybe it will look like a P-51 and a U2 mated.

Rusty

I am so glad I chose a simple wing shape...

Phil

Templates for speed plane #2:

Any guesses?

Jim

Why I can't get this prop in my country ?????????


I have to order some in the USA....

That's one badass little prop. That's about what I had in mind too.

navion34 wrote:Why I can't get this prop in my country ?????????


I have to order some in the USA....

Rémy,

Have you tried already Syracom, north of Rouen?

http://www.syracom-modelisme.com/

I think you better phone them because they have more in their shop than displayed on their website. I've been there already and they have gotsome tiny props on their shelves.

Lieven

Thanks Lieven, I will call them,

OVERLORD wrote:When I looked at the wing this evening, I noticed that it starts to take the shape of a giant propeller; and it's a pusher!

Lieven

I got fed up with my warped 2 ply wing. I tried several times to straigthen it using weight and water, clamping it, put pieces of wood under the parts to correct and using a hairdryer. All in vain. I will make a new one out of a solid plank and try to carve the holes for the inserts with a knife.








Lieven

OVERLORD wrote:

OVERLORD wrote:When I looked at the wing this evening, I noticed that it starts to take the shape of a giant propeller; and it's a pusher!

Lieven

I got fed up with my warped 2 ply wing. I tried several times to straigthen it using weight and water, clamping it, put pieces of wood under the parts to correct and using a hairdryer. All in vain. I will make a new one out of a solid plank and try to carve the holes for the inserts with a knife.








Lieven

Cut the holes for the inserts all the way through. Save the pieces you cut out to use as "plugs". Install inserts, glue plugs on top of inerts, sand the plugs flush with the top of the wing when the glue is dry.

Jim