I'm working on a Super Sportster twin and am wondering if any one here has built/flown one?? The modified wing span brings the wing size up from 55" in the kit to 60". Would it hurt the performance to go up to 65"?? 60" wing seems a bit small for a twin to me. [8D]

Fastguy, first I have not done a Super Sportster twin so this is only my speculation but I have done a lot of twin and more bashes. In some I have choosen to extend the tips and some have went without adding area. All were successful from just adaquate to superb and in every case the ones without the extended wings were the just adaquate variety.

What has worked well for me on the extensions is just to add a bay to the wingtips. Easy to do and pretty quick yet without strength issues.

Your project should be a good flyer either way but I think you would be happier yet with a few extra squares at each wingtip. Its a cool subject.

John[8D]

....as a reference, the Hobbico Twin Star is 56 inches. [sm=teeth_smile.gif]

Fastsky:

Yaw stability is effected by the length of the wing vs the length of the fuselage. If you extend the wing beyond the designed extension, (which is one bay on each side), you will need to extend the fuselage to compensate, or tracking and engine-out stability will suffer. You could increase the size of the tail, instead of extending the fuselage, but that is what the designer did in order to compensate for the designed extension and making it ever bigger might make it look a bit odd.

My first Super Sportster Twin flew just like the single engine Super Sportsters. Of course everything was built heavy in those days, so building it as light as possible can only help. I am building a Super Sportster Twin based on the SS 90/120 right now, and my wing extension is just slightly less than one bay per side. I am using light balsa for the blocks, tapering the hardwood wing spars and leaving out most of the plywood in the fuselage to lighten it.

Jim

Thankx for the replys. I will stick to the twin mods as per spec. then which is 1 bay added per side. I bought 2 new OS 32 SX engines for the twin based on previous experience with the engine on an LT25.

A SS40 twin is on my list as well... Maybe next winter. (I got the kit, I got the plans, just don't have the time. Other planes are ahead of it.)

Hope you post news/progress/pictures/flight impressions....

Good luck...

It looks like a crappy week for flying with steady rain predicted so that means its a great week for building!! Will get some pics when the build progresses to something worth while to take pictures of. I have a current plane with the wings of Metallic Green w/Neon Yellow bands and its great for maintaining visibility. I'll probably use that for the twin but am not sure what to use for the fuselage color. Have to think that over as the build progresses. [8D]

My Super Sportster Twin 260 is coming along. Here are some "in the bones" shots.

It is 80" wingspan, uses two OS 61 FX's and has tricycle mechanical retracts. Other airframe mods include extending the wings one bay on each side, increasing the size of the tail surfaces 25%, tapering the rudder and elevators to a sharp trailing edge and using dual throttle servos, dual aileron servos and dual elevator servos.

I started with a partial Super Sportster 90/120 kit and a set of Super Sportster Twin plans from RCM, but the differences from the original 40 size twin were too great and I had to re-engineer the bigger size.

As of now, it is ready for final sanding and covering.

Jim

jrf, Nice looking bird! How big are your fuel tanks? Any thoughts on flight times?

The tanks are 14 ounces each. Should be enough for 15 minutes plus, with plenty of reserve.

Jim

I just bashed a twin, and also mounted 14 oz tanks. My nancells are blocky looking. Kudo's on making yours look so streamline! It seems like all "production" twins really lack in the tank compasity area. I too was striving for a 15+ min flight time.

Looks great Jim. Have you considered sheeting the turtledeck. That is a smooth looking plane to have the stingers showing like that. I still regret not sheet my 4-stars turtledeck.
Kelly

Kelly, Are you talking just for looks, or for strength. Even with a exposed turtle deck, it's a good looking bird. I'm still pondering how he got 14 oz tanks in it without hollowing out the wing..........talking about strength!

Joe: The top sheeting is removed between the leading edge and the spar. The Dubro S-14 tanks sit on a light ply floor that ties the firewall, wing leading edge, and nacelle sides to the spars. And there is still 1/2" clearance on all 6 sides of the tank for foam padding. That is the way the original Super Sportster Twin was done and it is VERY strong.

Kelly: I agree, sheeting the turtle deck would be smoother, but I wanted to keep the Super Sportster look and that stringered turtle deck is a big part of it.

Jim

Joe, It would be for looks.

It so nice to have a twin SS....

A couple questions. The original RCM 40 size plans look like the tanks are built into the nacelles without a hatch, how did you do yours? I guess you could make a hatch on the top since the tank sits on a ply floor. Also I was considering using foam for the turtle deck, using the first and last formers for the shape. I have designed a short kit for the SS40 twin and would like to know what modelers preferences are. I include the extra 2 ribs and aileron servo boxes to place in the wing rather than use the center servo location and torque rods. What are some of your thoughts?

Sign Man:

I made a hatch as part of the nacelle top construction. Just tack glued the front top block on for the shaping and sanding. I haven't made a final decision on the method of attach ment yet, but I am leaning toward covering the hatch and nacelle separately and then using strips of covering to hold it the hatch in place. Ideally, a tank hatch would never be removed, but reality doen't always agree.

I used finishing resin to fuel proof the entire tank compartment, and drilled a drain hole through the firewall, in case of a leak. Then if I see raw fuel dripping from the bottom of the cowl, I can easily cut the hatch loose to make repairs.

Re: the short kit, I think the number of people who would be interested would be very small, but other than that, no reason not to.

Jim

I'm not for certain....but I believe jrf would be the one and only Jim Feldmann?? Hi, Jim!

Jim's RCM twin sportster was a great RCM plan design back when and his new 90/120 size looks to be a real "go-getter". You just may want to consider drawing up some design changes/ instructions, Jim, for those who want to build their Super Sportster as a sharp looking twin. Can't wait to see your model finished!

BTW: LOVE that Knockabout...flew the "u-know-what" out of 'er last summer and fall and that plane still looks like new. Lots of nice comments on both the looks and the flying ability of your design.

Joe

Hey guys love your build thread! - Thats a sweet machine!


Just a quick question on twin design concepts? Most people take a tail-dragger design and when it becomes a twin 99% of the time make it a trike. If your not planing on having retracks on the twin would a tail dragger twin be ok! Or is a tail dragger twin harder to take off / land?

I've got a fun sport design of my own call the Gold-Finch 40 and Iam sort of tweaking the idea of a mid to low wing version with twin .25's


PS: one thing I have found flying the GP-Profile P-38 is with the motors side mounted its a close fit to get the glow igniter on without the fuse getting in the way.

Thanks from a guy having fun doing his own stuff from a laptop

No real reason you cannot have a twin as a taildragger..think Sky Kings Songbird and military planes..other than the trike gear most likely saves a few props along the way....

Soft landings.

Jim who? Thanks Squeakalong, I particularly like the Knockabout also. I fly all kinds of airplanes, but I always take the Knockabout along for a bit of pure, no-stress fun at the end of the day.

The changes to the 90/120 Super Sportster to make it a twin turned out to be a bit more complex than the original 40 size. (Or maybe I'm more detail oriented now, 25 years later.) And RCM is no longer around to publish it. Anyway, this one is just for me.

Ken: If both engines accelerated at exactly the same rate during take off, then a tail-dragger twin would react just like a tail-dragger single. In full scale, the pilot can coordinate the engine speeds but model engines almost never accelerate together. The asymmetrical thrust combined with the natural instability of a tail-dragger on the ground makes every model twin tail-dragger takeoff a gamble. Tricycle gear helps to dampen the asymmetrical thrust.

If you build your twin as a tail-dragger, a good gyro is highly recommended

Jim

Thanks good advice on tail/dragger twins! - Sorry to be a bother but I would suspect you also have each engine canted outward 1 - 2degrees ? I've heard this standard on twin designs

There is no standard and some have recommended up to 7 degrees out-thrust in both engines. I have the left engine at 0 degrees and the right engine at 2 degrees right thrust. This is just to offset torque, the asymmetrical thrust of an engine out is handled by the enlarged vertical tail surfaces and the narrow spread of the nacelles.

Jim

OOOOOOKAAAAY....Jim.....well, nice twin there anyway.....