I am planning to build a stunt trainer for a Cox sure start Motor. The plane should be 20" wing span with 120 square inches. The engine will produce about 14,000 rpm with a 6X3 prop.
It will have about 12 oz of static thrust and should fly the plane between 35 = 40 mph. what should the maximum weight be for good stunt trainer flights. I am expecting it to weigh between 8 and 11 oz. all up weight.

Hi Propjobbill

I'd be aiming for 8oz maximum, and ideally more like 7 - shouldn't be too hard to achieve with 20"/120 sq.in.

I've just finished a profile fuselage/built-up wing model for a Norvel 061 - about 27.5"span and 150 sq.in. Despite having a fairly hefty wing-mounted landing gear, it still comes in at just under 9 oz. - and I'm no master builder.

Hope this helps

Steve

The plane is going to be heavier than usual because it will have a coroplast 2MM wing with airfoil, and some 2MM coroplast in the fuselage. I know the coroplast will add about 3 oz. but it will make the plane almost unbreakable. I am building it to teach my grandson to fly.

Propjobbill

Forget the coroplast, it is way too heavy. Your projected weight is way too heavy for the surestart if stunting is your goal.

Instead visit the aeromaniacs.com website and build an aerobatic platter out of foam board. You should be able to build a stunt ship that weighs under 6 oz with this building material. These planes are nearly indestructable and stunt well at light weight.

Scroll on down to the bottom of their home page to see some serious stunting with the platter.

I have taught many kids to fly with this plane and it tolerates crash after crash. Sometimes a little CA and it's back in the air in minutes.

If you place the weight toward the front as depicted on the plans it makes a great trainer. Move the weight towards the back and it stunts well. I've flown the platter in 15 mph winds and it stays out on the lines, no problem. You can build a platter for less than $5.00 and if you find the foam board on sale you can build one for less than $3.00

I can't imagine a better plane to learn on than the platter.

Hi 2Fast,

I just printed our the plans for the plater, The only thing I may have trouble with is putting a set of wheels on it. I have a lot of foam core. I've considered this plane many times, but your comments about it has helped me make up my mind. I have bought several sheet of foam core at Dollar tree for guess what $1.00. The sheets are 20" X 30" and I can make 3 planes from each sheet. Thanks for the advice

For a trainer Durability is significant and coroplast can be your friend and weight is not so much an issue. Throw the word "stunt" in there and that changes everything. Weight becomes much more important. Extra weight becomes a huge liability when stunting. Ask any serious C/L stunt flyer. A stunt plane should be built for flyability not durability. If you still think you need durability then maybe not quite ready for more than simple loops and wing overs.

As for the Sure Start you should be getting more than 14000 RPM. What prop are you using? Cox engines thive and oerform best at higher RPMs. Even the Sure Start. Your best bet is to use a 5.25X4 or a 5X3 prop. Line length and diameter become more important to get the kind of performance needed to do stunts.

Robert

Thanks for the comments, I am putting a plane together for training out of coroplast it should weight in at about 8.oz. . But I like the platter idea also. I just cut out 3 platters.


What kind of paint do I use for the foamcore. To keep it light and also fuel proof. Any comments for building with foamcore would be appreciated

Thanks Bill

i built one for my son with a coroplast wing and balsa fuse and it's got a cox .049 babe bee. it's way too heavy compared to others i've built out of all balsa. we have pounded the balsa "skyrays" into ground and they will take a lot of abuse. i paint all of mine with cheap spray paint and don't have any problems with fuel. just my 2 cents!

Which brand spray paint do you use?

I have used anything from KRYLON.Rustloem, to cheap Wal MART paint .I have good luck with them all.

I have found KRYLON not to be glow fuel proof. The "Stopsrust" Rustolium is but it's heavy.

I've used the Wal-Mart paint, current price $1.12 per can. I have not had a problem with fuel proof, but that was with 15% or less nitro. However it will eat foam. On the platters that I'm building I will try latex with a coat of Min Wax Gloss urethane on the top.

on the "osburn platters" i built .i sealed edges of foam with white glue and sprayed with krylon and had no problems.

Some guys have reported bad results with metalics and clear Rustoleum. I THINK the colors are OK. Note that this is just from reading threads, I have not used those spray cans yet.

One of the key notes seems to be to let it dry for about a week before it becomes really fuel proof. Again, hear-say.

George

I had not considered sealing the foam with glue, I can see where that would work. As a result almost all paints that were fuel proof would work. I will give it a try on my next foam core project.
The reason for latex is because it won't hurt the foam and the polyurethane seals the latex, However I have found that most latex paints are fuel proof if allowed to completely dry.
Thanks