I know this is an older post but I have laser cut the twin modification from RCM plans. It says extend the wing one bay and shows how to enlarge the tail. I can send you a short kit if you haven't started yet.

This is my Super Sportster twin made from a 60 kit. The wing span is 72". I added 11" to the center of the wing. I also added 1.5" to the front of the rudder. Running a two OS55 AX engines. Hope to test fly it soon. The picture is a little dark.

Nice plane Robtck. Let us know how she flies. I just picked up the 40 twin plans. I also have the 60 and 90 kits - I might try bashing one of those into a twin - probably not until I retire! "The sign man" (post #26) can laser cut the parts for these.

Steve

I used the RCM SS twin plans as a guild to build mine.

It came out very nose heavy. So halfway between the wing and tail I added a compartment for a 5cell 2400 mah battery. Now the cg is right on - no lead added.

Did the test flight on the Super Sportster 60 twin today. I had two problems with the right engine. The idle mixture was set way to rich. It took about 30 minutes to have both engine in sync. The first problem was the ground handling is not very good with the set rudder throw. To fix this, I will have to trim the elevators to allow more rudder throw. Take off was fairly short, maybe 40 ft. With a fast climb out. This plane is fast - somewhere around 90 - 100 mph. Well two minutes into the flight the right muffle end came off. Shortly thereafter the right engine died. This is a bad thing two minutes into the first flight. This gave me a chance to see how it would fly on one engine. At half throttle it will fly it will almost fly hands off with very little rudder input. On landing Mother Nature decided to throw some gusty wind my way, just to make the landing a little harder. At about fifteen feet above the runway, I hit a gust of that ballooned the plane up 8 feet. I add power and down elevator to stop a stall, but I was behind the power curve. The result was a broken right wing and broken left prop. No other damage.

Specs
Wing span 72�
Wing area 864sqin
Fuse per plans
Engines OS 55AX with Master Airscrew 12x6 prop
Rudder has one inch added to leading edge
Wt is 9lbs 1oz

Now do I fix this wing or build a new wing? This plane will be a lot of fun once repaired.

Ouch! Sorry to hear about your mishap. But glad to hear that you will repair it.

I use red (high temp) silicon sealer on all of the muffler joints including the muffler to engine joint, the mid-muffler joint(s) and both ends of the long bolt. Haven't had a muffler loosen up or leak in the ten years I've been using it.

Jim

Robtck...

Bummer about the damage.. Glad to hear it's repairable, and you will fly again..

How well did it balance out? Was it hard to balance? Or did it turn out pretty close...?

On past models, I've used thread locker. But for some reason I forgot to use it on this plane.

This plane did come out nose heavy. I made a battery compartment half way between the wing and tail. Then I installed a 5cell 2400mah battery. This gave me a bigger battery with no dead weight added. This weekend I will try to get some pictures of it.

Here are some pictures of my battery compartment.

http://www.rcgroups.com/forums/showthread.php?t=400852 is this the model you are talking about?

tail looks different?

http://www.greatplanes.com/airplanes/gpma1044.html I wonder.......... good conversion? with two 90s? or two 60s?

The engineered conversion uses an extended wingspan, extended wing sheeting, enlarged tail surfaces and a modified nose structure. And tail dragger twins are very unpredictable on the ground. You really should convert it to trike gear. It would be a lot of work to make the twin from an ARF, but certainly possible.

The Giant Super Sportster Twin would probably weigh 16 - 18 pounds. I would use 1.20 four strokes on it, but 91 two strokes would also work.

Jim

jrf, do you have any sketches or drawings for the 90/120 twin nacelles? I just acquired one this morning and the wing is already built. I would like to make it a twin and have a couple of questions.
Did you extend the center section sheeting out one wing rib?
The wing is built for taildragger landing gear. I think it will be a simple task to cut open the sheeting and install another set of landing gear blocks for trike. Would it be best to try to cut off the wing tips or just cut the last rib and extend everyting with a new rib from this location?
I also like the idea of 2 elevator servos. Did you mount the rudder servo in the tail, also or in the fuselage under the wing? Do you think it would be too much weight to locate 3 servos in the tail?
I would gladly pay you for any drawings you have.
Thanks in advance for any help.
Rick

Got in late last night and I'm going flying this morning. Will be happy to answer your questions when I get back this afternoon.

Jim

Jim

jrf, thanks for your response to my questions. Yes, some photos would be great to give me a reference.
I was thinking of the same method you explained to extend the wing.
Thanks,
Rick

Here are some shots of the nacelles and the fuse nose. I went with sideways engines and pitts mufflers. That explains the large cutouts in the right side of the nacelle. My hatch covers are tacked on for now, but removing them reveals the 14 oz tanks and the throttle servos behind the tanks.

Jim

The Giant Twin Sportster is alive and well on the way.
Set up for a pair of OS 91 Fourstrokes, but I am not sure what the single engine performance will be like, so I designed it to be upgraded to 120 FS if needed (will accept up to 16" prop).
Nacelles are detachable (fits like a fuse with dowels and wing bolts) and can take a 16 oz tank.
Gear is fixed and tricycle.
Should be flying in 2-3 weeks.

Good job! Let us know how it flies.

Jim

I finally got the time to start fixing my sportster twin 60. The new wing panel is build and installed. Next week I can start covering.

Im setting here reading this thread and thinking hey I have a SS 40 setting here needing some reworking done I could modifiy it into a twin ! see what happens when ur bored your gears start turning and you come up with a new project! Well kepp up the good work guys Ill be dropping in and out checking on your progress Im cleaning off the bench to start a new project see ya!!

Well I finally flew the Giant Twin Sportster yesterday after a couple of mods.
When I first tried it, I found the nose wheel assy was just not strong enough for the model. New assy fitted, engines run in and off to the field.
She flew straight off the drawing board,only a couple of minor mod's (more down thrust, less control throw).
It is not overpowered with the .91's, will climb about 30 deg. angle. It was flown hot until I start doing some engine out training and see what its VMCA is like.
Setting up the radio so that I can have independant engine control and train single engine (get the fingers working).
Now think about the big DC3......!

HI DKM,
Did you get any pictures? I'd love to see that big bird in the air.
I just got the plans from RCM the other day. The plans and instructions were very good but I was a little disappointed there was no provision for retracts. I don't like their single throttle servo setup either. The plans were drawn 25 years ago. I guess things have changed. I'm going to stick to the 40 sized plane and add retracts if they'll fit. Please keep the posts and pictures coming.
Jim

I finnally flew my sportster twin. It took about 4 1/2 months to build using the RCM plans and a sportster kit. I built the 40 size plane with dual OS 55AXs. I built it according to the plans except it has dual aileron and throttle servos. I considered retracts but I did not have much room and I wanted to keep it simple. It flys great. It's a screamer. The first flight was really hairy getting it trimmed up. Now it flys great. I have about 10 flights on it.