colmo-RCU

Hey guys, This is my first twin proyect, and I bought plans for a conversion of the sportster 40 (great Planes) from RCM. I plan to use gms 32s, which are brand new but i've bench-run very successfully.

I have questions regarding the ideal position of the engines, as I have heard they can interfere with each other. The plan calls for 0 incidences, and 0 thrusts, but I'm not quite sure.

Any tips are greatly appreciated

Colmo

William Robison

My Feedback: (3)

C:

The Super Sportster is a pretty good aerobatic sport plane when built stock. With the wing and stab at zero incidence it tends to fly the same upright and inverted.

To maintain the identity of upright and inverted you need to install the engines with no down or up thrust, though some out thrust is recommended by many of the "Twinsane" fliers.

The advantage of engine out thrust is lessening the immediate yaw when an engine quits. If you do a vector analysis of the delivered power you'll find there is a negligible effect on the forward thrust up to about 5 degrees out.

The advantage of having the engines dead away is that I think it looks a lot better. And when I lose an engine I throttle the other one back and land the plane.

Ed Moorman, a regular poster here, is a proponent of out thrust. Do a search on his name, you will find some of his comments.

Twinman (and I) set the engines dead away. I don't know exactly why Twinman does it, but as I said I choose the looks over the lessened yaw with one out.

A trainer twin, such as the Twinstar, has both out thrust and down thrust. Both to make it an easier flying plane. The down thrust decreases the trim change between power on and off, but it does upset the inverted flight.Since the plane does not have a symmetric airfoil we can't expect identity anyway, so the compromise in this case is a good one.

Hope I've given you enough to chew on, and decide what you want. As I said, the out thrust wont hurt anything but the looks, and might well save the plane for you. I wouldn't give it any down thrust though.

Bill.

jrf

My Feedback: (551)

I built one of those a few years back. Gorgeous airplane and a GREAT flier. The enlarged vertical tail surfaces give it a lot of safety margin in an engine out situation. I didn't use any out thrust and even though I had a lot of dead engine time, it was never a problem.

The dead engine time resulted from not padding the fuel tanks. Fuel frothing seems to be more of a problem with twins than with singles. Pad the tanks thoroughly with radio foam or wing saddle tape, and don't let them touch wood anywhere.

Jim

Cutlass 60

I flew my Super Sporster Twin for two years before I sold it in a weak moment. It is a good solid flyer. I ran OS 25 FX's in mine and the preformance was good. With the 32's in yours, the performance will be excellent. I would recommend that you run about two degrees of out thrust on both engines. It will not be all that noticeable but it will add a safety factor for the inevitable engine out that will occur if you fly it often enough. Good luck with your project.

colmo-RCU

I am a real plane pilot also, and we get a lot of engine failures on take-off at the simulator. Is it posible to control the yaw upon an engine failure with rudder as on the big ones?

also, I´ve heard that twin planes have the problem of an engine killing the other one due to the blast, or something like that. Is it true, and if so, how can I prevent it? Thanks a lot, .

Greetings, Colmo

jrf

My Feedback: (551)

If you have good airspeed when the engine quits, you can control the resulting yaw easily with rudder on this model. Maintain your airspeed until you are in position to make the runway, then throttle back and treat it like a dead stick on a single engine model.

If you have low airspeed and low throttle, throttle the running engine back immediately and treat it as a dead stick.

If you lose an engine at full throttle and very low airspeed (like on takeoff), no model twin is likely to survive.

The Super Sportster Twin is as forgiving as any of the other sport twins on the market today and a whole lot more forgiving than any warbird twin. (I know, it forgave me a lot!)

Jim (15 yrs model twin experience, zero full-scale)

And I've never heard of one engine killing the other. Maybe that refers to a push-me, pull-me twin, but even there, I doubt it.

William Robison

My Feedback: (3)

Colmo:

As jrf has implied, our toy twins have a Vmc just as the larger ones do. Vr is usually well below Vmc, but you can usually stay on the ground way past Vr to assure safe take off if one does fail.

In flying, if you always maintain your air speed in keeping with your throttle setting, an engine can quit with hardly a bobble; properly managed speed and power will always have enough rudder authority to keep you out of trouble. You should already have learned this in the simulator.

The biggest problem is your point of view. When you're in the plane correction is almost automatic, with an RC twin it has to be learned. Sad to say the lessons are sometimes painful. And expensive.

One engine blowing the other out? Hogwash.

Bill.

Gremlin Castle

My Feedback: (14)

As long as you stay above Vmc the rudder on a model will do the same for you as on full scale. The problems that arise however stem from the fact that the pilot is stationary and the perspective of the model is constantly changing. Since there is no mechanical feedback to the pilot such things as yaw or one rudder pedal going soft are not available as the first leading indicators of power loss.
Most models are overpowered enough to fly single engine but most model pilots do not have either the skill sets or the actual practice to to reliably carry off engine out problems. Some can but most never get that chance to practice engine out procedures on a model.
As always. lighter wing loadings coupled with excess power stand the best chance of coming through the loss of an engine.

colmo-RCU

Thanks for all the imput, I wanted to add that i´m thinking of programming the throttle servos on 2 channels to be able to idle one for engine trouble practice at high altitude. Is this simply idiotic?

By the way, the plans for the conversion seem designed by pica. It´s a carve and cover design that looks like it weighs 2 tons. I´m doing my best to make it lighter, seeing that I have the handicap of flying at 8500 ft above MSL. Anybody had any trouble with weight on the conversion?

colmo

William Robison

My Feedback: (3)

Colmo:

Talk to Twinman about independent throttle controls, that's his trick and he has done very well with it.

Pica design? Not so sir. That's just old school model building. Hollowing blocks was a common thing in "The Old Days."

Bill.

Robby

My Feedback: (18)

uhhmm,, ok...

I have a question...

Yet in your location it has From: Miami, FL, USA

Last time I was in Miami it wasn't that high... Did something happen in last few months there..?

jrf

My Feedback: (551)

I'd have to look it up to be certain, but having owned and flown both, I'm pretty sure the wing loading on the Super Sportster is less than the Twinstar. It is certainly less than the Dualist.

But lighter is always better.

Jim

scott282

My Feedback: (7)

Are the conversion plans an add to the kit. In other words, did you buy the kit and buy the plans seperately in order to bash the Super Sportster into a twin? If so, tell me more about this. I've been delaying in bashing anything into a twin without some sort of plan/direction.

Thanks,

Scott.

colmo-RCU

ok first of all, to Robby.

At the present rate in which Miami is producing garbage, the mountain (today is a hill almost 300 ft high, the highest place in Florida is made of JUNK!!!!!) will soon be 8500 ft high. However, I fly with a cargo company and spend almost 10 days a week in miami. As it´s easyer to get mail there than at home, I use the hotel´s address. But I live in Bogotá, Colombia, located on the Andes range at 8360 ft (bogota´s airport ARP, anyway) I build and fly there, so the plane is going to be able to overcome that. It´s funny, all the aerobatic contests here take place in other cities that are near the sea level because guys from those places complain they can´t get there planes to fly so high. But the fact is we do fly there and we have learned to build light, and always use max recommended powerplant or even a bit larger.
so no, miami hast changed since you last checked.

To scott, the plan is from RCM, just look for it on their website, and the idea is to use a complete super sportster 40 kit (the original, not the new cad design). minor mods are required since I got the new kit. Basically you enlarge the rudder and fin, add 1 rib length to the wing to lift the extra weight, and build the nacelles. Also you modify the nose, just carve a new one. They ask for tricicle gear but I´m taking the risk and building a tail dragger. The plan is very easy to understand and the instructions (the plan comes with the article transcript from the magazine issue) help a lot.

see ya all

colmo