Pumatraca

Today we have tried to prove the Ed Moorman theory about : 8 degrees out thrust lines of the engines on my twin. When decrease, rpms, on one engine, emerge the adverse yaw, and have to correct with some rudder, but not too much. The power of the engines, not affected.

[youtube]http://www.youtube.com/watch?v=f1IlMRSVRlE&feature=related[/youtube]

Ed_Moorman

My Feedback: (1)

I'm glad to see you tried engine out thrust on your twin. My idea was to help people with a twin who don't have the pilot skill or presence of mind to use rudder when one engine fails. I think with 8 degrees out thrust, the plane won't roll or yaw so badly that it will crash.

I never did see one engine of your engines completely off, so I assume you brought one back to idle and kept the other full rpm.

I would think that having one at idle might cause more yaw than having it completely off. With the prop still turning, you create a disk which could cause more drag than with a dead engine.

Please send me some photos of your plane and some with your and your plane.

2 OS .46AX engines, correct?

What airplane/kit is it?

The owner's name and the pilot?

My email is [email protected]

Pumatraca

Hi Ed it's true, in the video the emergency tests are not seen, because my cameraman was helping me during the fly as a co-pilot, but you are right, I never stopped the engines during the tests, because I was afraid, but during the tests I 'd verify that with very little rudder the plane could be recovered. The pilot was me. The model was designed and constructed by a friend J.R. Yunes., and originally it was flying with two MVVS 40, wich were replaced by two OS Ax 46. Here some images! Thanks Ed!

Pumatraca

Some more photos.

Pumatraca

Model plan-

Prairie Mike

Ed,
Why is it that no one mentions critical single engine airspeed? I've made a takeoff, single engine, on my Twinstar and made single engine go arounds with my Dual ace, but had plenty of airspeed during both problems. If you get slow enough I don't care how much power or thrust you've got a twin will want to roll over and kill itself. Critical single airspeed is important and yet not many in RC understand that concept.
Your comments??

Ed_Moorman

My Feedback: (1)

Hey, Mike,

You sound like a full scale pilot. I'm retired USAF & my twins are T-37(both student and instructor), F-4C/D/E & F-111. The Air Force doesn't even count them as multi-engine. They call them "center line thrust" and count them the same as a single engine.

In a full scale plane, you have the indicated airspeed right in front of you, plus, you can see the nose swing from the yaw. You know how much speed you have before getting down to critical airspeed and you know how much rudder to use. The only way we have of knowing airspeed on an RC plane is an experienced guess. There is no way of knowing how many knots you have to spare. Knowledge of the plane means a lot, too. Given a sport plane with a good amount of power and a reasonably light wing loading, you know you have a lot to play with. When I did my out thrust test on a Twin Tiger 2 with 2 OS .46AXs, I knew I had plenty of power for 1 engine flight. I also knew the wing loading, even though heavier than a stock, single engine Tiger 2, was still reasonable. That and the fairly thick airfoil meant the plane wasn't going to go crazy when an engine quit. That's the reason I had no qualms about filling one tank only 1/3rd full and flying until it quit unexpectedly. With a heavy scale plane, I would never try this. I test flew 2 giant B-25s, a Great Planes and a Nitro Models one. Neither one lost an engine, but had they, I would have throttled back the other one and headed for the tarmac. I try to stay close in on test flights, just in case.

The out thrust idea, and I originally read it in a magazine some 20-30 years ago, is for first time twin fliers and guys who are not adept using the rudder and power control, the left hand. It doesn't look very good, but it does work very well and the loss of forward speed is negligible.

You mentioned a Twin Mustang. From my twin experience, I feel the twin fuselage configuration is the best twin configuration for RC. I think the air flow gets channeled between the fuselages and helps keep the yaw down. At least my best flying twin was a twin fuselage Sky Raider Mach II.

Lifer

My Feedback: (1)

Mr. Moorman,

What engines do you have in the Twin Skyraider?

Ed_Moorman

My Feedback: (1)

Lifer,

I started with GMS .47s, but I didn't like the reliability. The OS .46AXs in my Twin Tiger 2 ran so well, I bought 2 more of those.

I had nothing buy good luck with the GMSs, both .47 & .32 in single engine planes. In a twin, I shoot for as close as perfect reliability as I can. I have tried Magnum .52XLS 2-strokes, Thunder Tiger .46Pros, although both were older engines, Magnum .28s, GMS .32s, and ditched all of them. OS .46AX is my first choice for twins. For larger planes, I think the OS .65LA is a great choice. They are very reliable and as powerful as the .61FX. For the smaller planes, I like the OS .25FX. If you want to use a slightly larger prop on a .25/.32 size plane, try the OS .40LA or .46LA or the TT .42GP. These engines make the best power for a .25/.32 sized plane and you don't have to max out the needle either.

For 4-strokes in a smaller scale plane, we have had great luck with the Magnum .52 4-stroke.

If you search back in the Twin Forum, you'll find a page of my hints, most of which were learned the hard way as Flaps and I built 25 twins.

Mainly, we learned you can't tweak an engine on a twin as lean as on a single. Tune each one individually with the other engine off, then top off the tanks, crank both and fly. Hold the nose up at full power to insure they aren't going to lean out and sag or quit. You should be leaving a slight smoke trail at the first of the flight. I have a couple of tachs and never use them. I tune each engine like I do for a single engine plane, slightly rich. DO NOT let your buddy tune your engines. They will always set them too lean. I speak from experience. here.

I use a part castor fuel, Omega 10%. It seems to handle the heat better than the all synthetic oils.

Pumatraca

Hi ED: finally I've dared, and shut the engines!. First shut down the left, then the right. At 50% throttle, the yaw was minimal, but over that level, was significant!!. Enjoy the video! Greetings.-

[youtube]http://www.youtube.com/watch?v=YWQuerxiKus[/youtube]

Pumatraca

https://www.youtube.com/watch?v=YWQuerxiKus