i am drawing up plans for standoff scale twin and am trying to get good single engine stability to make it flyable on one engine.i have built and flown many multis from kits and plans but this is my first attempt at my own scale aircraft.aerobatics are not really a consideration.i am using the airfoil from notheast aerodynamics sport air 40 .wing and stab are set at zero degrees.engine thrust line is about 1 1/2 inches above wing centerline and 5 degrees dihedral per wing panel and i am seriously thinking of setting the trust line at minus 5 degrees to help prevent the death roll when one engine quits unexpectedly causing the running engine to rise and yaw.no side thrust will be used.my concern is that it may be too much and cause the aircraft to taxi for ever.twin stick used 5 degrees down and side thrust[different amounts]on both engines.duellist is plus 2 on wing and stab but minus 7 on engines my twin air is 0 degrees all around.will be using a gyro on rudder for first flight and single engine testing.span is 74 inches cord 11.25 inches and 2 k&b 45's for power.weight 10 pounds.flaps and retracts used.almost tempted to compromise and go to 3 degrees downthrust.comments,suggestion?

CaptJack......there are several things that immediately come to mind........ Making sure that you have adequate powerplants for single engine performance.....probably the biggest "Killer" of attempting flying on "One" is wing-loading........high wing-loaded airplanes want to go upside down "Immediately" or sooner.......downthrust helps slightly for one engine ops ...but isnt a remedy.....too much downthrust interferes with established wing/tail incidences making a plane climb/descend while adding or retarding the throttles.......I would concentrate on engine "Reliability" thats whats gonna make flying more enjoyable.......fuel systems and tuning will give best chances of not flying on one........My "Duelist" flew fine on one engine....My "Z" B-25 not so....goes upside down in a "Flash".......Again make what you have "Reliable"....You'll hear that from "TwinMan"many times over........best way to stay in the air...... Good Luck.....Bill......

after 30 plus yearsof flying twins you are right about reliability and i have proiven that on all the twins i fly but murphy.s law comes into play also and since this is a new plane from cratch,my plans i am trying to make compensations for the inevitable one engine thay will happen,i have also found that overpowering a twin causes the deathroll much quicker than one that is powered right.back in 72 i built a 48 inch twin wing derringer from scratch.powered by 2 s.t g-15,s.this flew as your described b-25 when an engine was lost.however replaced the st 15 ,s with os 10's and when an engine quit on climbout right sfter takeoff and thge deathroll started,cutting power stopped it immediately.plane leveled off on its ownmade one turn into good engine and landed.there is an area where too much power causes problems also.as a desinger it is my job to try and eliminate problem areas.hence this post.

On another thread I describe using engines with counter rotation and outhrust. Any comments on that strategy for solving the one engine out syndrome?

have you flown a twin? counter rotating engines help with p-effect on the rudder and would help eliminate yaw but the deathroll would still occur.deathroll is when the wing panel with the running engise risesand the wing panel with dead engine drops at full power the plane will do an axial roll of close to one per second compared to the one in 5 seconds using airlerons.downthrust should slow the roll rate so you can recover and landgyro coupeled to the rudder will also help correct.you do not want to use airlerons .

one other thing is counter rotating engines and left hand props are hard to find and are more money.even jack stafford said counter rotating engines were not worth the extra cost when he did his twin commanche.besides his b-24 is a dream to fly on 3-4 engines never did 2 out on the same side though and that weighs 14 pounds

Actually, I haven't,,, yet. But, now you guys are making me scared.

I kind of thought that severe yaw would be the problem with one engine out. Is the deathroll due to torque reaction? If so, wouldn't it be severe for the one engine and not so bad for the other? My set up has the left engine going ccw (normal) and the right engine going cw (reverse). The torque reaction of the live engine would be countering the drag of the dead engine/wing. Along with outhrust, I kind of thought that this would virtually eliminate one engine out problems.

Regarding P-factor. Not a uh,,, factor here as the rudder is single and out of the slipstream of the two engines. Hmmm,, now I'm getting the feeling that my rudder/fin is going to be too small.

In 1/2A sizes, reverse props are common, available and cheap but you're right about the reverse engines. The only reverse cranks that I know of are the Cox and the old K&B/Veco .19

Far as death roll,,, is there a chance that there's some kind of P-factor at play here that's operating off of the wing instead of the rudder?

Andy....Theres a few flt characteristics and engine factors that contribute to Single engine "Spins" or" Death Spiral"......during T/O or climb at slower speeds with high wing-loadings or inadequate powerplants when an engine fails theres the "P" factor to deal with....adverse yaw from assymetric thrust....and lost lift on the wing that the engine failed.......depending on type of plane an immediate inversion occurs which is a problem if throttles aren't retarded....an outright spin could occur...or if your"extremely" fortunate and the plane your flying is slow to react to the engine out you "might" be able to correct in time.........the best to hope for is an engine failure @ cruise with plenty of altitude....even with an engine failure and and a roll to inverted ...one still can retard the throttles ,roll the airplane back over and make a landing with throttles retarded and good descent rate to touchdown......Have accomplished this with my "Z" B-25...... some planes fly fine on one engine....lightly wing-loaded with good powerplants......"Twinstar" or "Duelist" are good examples......but usually things happen so fast its pure reaction to the problem that gets your plane back.......unless you have a "proven" plane flown on one engine....its most prudent to land immediadtely after an engine failure....Bill......

I have great admiration and respect for the guys flying LARGE multi engine, scale planes. Courage comes to mind. I can see I'm going to learn a lot from this experiment. Mostly, that for multis, and one engine out,,, the operative word is, "don't let it happen"
Or at least make it happen at altitude. Altitude is your friend I guess.

what is a "standoff" scale twin????

look in old ama rile book from a distance of 10 feet or so plane looks like real plane.top gun scale has all the details.top flite gold kits are stand off scale.

looks like set the engines at zero and try to do yrial and error using ernst thrust plates behind the mount.thet go 1,2,3 degrees per set and can add 2 and 3 for 5

What do your nacelles look like? If the engines are mounted up above the chord center line, then you have effectively added some down thrust. If the engines are well below the wing, ex. B25 style, then you have effectively added up thrust. The thrust of the engines will cause a moment about the center of lift.
(change of subject) Imagine the plane is coming directly at you. One engine is out. The plane is yawed slightly toward the dead engine. You will see more of the bottom of the wing on the "good engine" side. (in this example, the plane must have dihedral). Just as a plane is turned using rudder only, as in a three channel model, the "leading" wing has a higher angle of attack and now generates more lift than the "lagging" wing. I am not suggesting that asymmetrical thrust isn't the cause of the rolling tendency, I am merely making a point that it isn't the only thing that is causing the roll.
According to Flight Safety magazine, the effective way to counter this dissimilar angle of attack of the two wings, is to "carry the dead engine high". This will effectively give both wings the same angle of attack even though the plane is in a yaw. I have tried this. You can actually attain equilibrium and fly "hands off".
Well, there you go, one more variable to ponder!
By reducing the amount of control surface deflection, ie. not haveing the rudder and ailerons hard over, you will induce less drag and this will help to conserve airspeed.
One other thing that I have found: swept rudders might look cool, but when fully deflected cause a slight pitch-up moment that must be countered with down elevator. More drag when you don't need it. Speed is control.

thrust line is about 2 inches above chord line how does that correlate into degress of downthrust?just like 1 degree of wing sweep is egual to 1 degree of dihedral.the idea here was the down thrust would help to carry the dead engine high,by trying to pull the good engine down and would help slow or stop the rollthis is a scale private type plane so aerobatics are not a major concern. easy safe scale flight is.

Not exactly. Think of it this way: Loose an engine, loose half of your down thrust. The plane that was trimmed to fly with both engines running will now start to climb. If you try to counter it by adding more down thrust, then you you will still loose half of your down thrust when you loose an engine.

CaptJack..........Downthrust is only part of the equation.......other criteria such as wingloading........inherent/parasitic drag.........type of airfoil(s)......engine thrust.........type of aircraft........etc...all add in......to how a twin will behave with an engine failure..........I dont think building an airplane solely for the purpose of worrying about loosing an engine is a good reason to build it....... first priority is making reliable powerplants.......thats the best way to avoid single engine flying......as a general rule even when a failure occurs theres not time to articulate a plan....its just response to the problem.......the easiest way I know is build a plane that has a "known" single engine capability and practice flying on one engine(such as a duelist) ...thats what I did and flew many flts around on one engine....pushing the plane to find its limits.......its actually quite docile on one........it performed best with a combo of aileron/rudder trim .....but as much as one can be prepared for an engine failure.....haven't seen too many up high with cruise power...best time to have one......usually at some critical phase of flt.....T/O...landing or in transition.......build it, fly it...If an engine fails....so-be-it........Bill.......

Let's get an understanding of P-factor out there. P-factor is a yaw induced by the propeller when the airplane has a non-zero angle of attack. At positive angle of attack (airplane), the downward moving propeller blade sees a higher angle of attack than the upward moving blade, and thus creates more lift, which is where the yaw comes in. This is why there is a critical engine on a twin. For tractor propellers that rotate CCW when viewed from the front, the critical engine is the port (left-hand) engine (this is the one you don't want to lose).