PUSH PULL Motor ? If you set up twin motors in a push-pull configuration, what would be the right prop for the back motor?? When the plane is at standstill, the front motor sees air that is standing still and the back on sees a wind storm. As you go up to speed the front motor will unload and the back motor will be unloaded all the time and wont change that much. Seems like you would have trouble getting any efficiency out of the system. Maybe the thing to do is put a smaller motor in front to unload the back prop and make life easier for it. Or is it like going down hill in a car at 100 mph and give it the gas, you are not going to add much speed.  I must have the fever, I wake up in the morning with these dumb though in my head. Ain't life good??   The two full scale planes I have been studying with this configuration use the same prop and engine front and rear.  Fokker D-23 and Moskalyev SAM-13. Props and engines on the C337 (Skymaster - also known as 'Mixmaster') are identical except for an extra cooling fan on the rear engine. I flew a twin canard for a while that used a push-pull setup. It sounded very strange partly due to the rear engine having to chop up the turbulated air. On the first flight the front engine quit, and rear engine kept running.  Speed was reduced a little, but not as much as I had expected.  Possibly due to the increase in efficiency of the rear engine when the incoming air cleaned up. I think the front engine was a .45 and the rear was a .40. Both engines turned 10x6 APC props, with the rear engine using a pusher prop.  BTW, with both engines running, the torque cancelled out - an added bonus! The engines had a tough time synching up, but that was probably mostly due to the fact that one had it's fuel tank behind and the other was ahead.  So, in a climb, one engine would lean out a little and the other would richen a little.  In a dive, the reverse was true. It was a fun airplane - very fast!!! OHM's Law ? > E - voltage > I - current > R - resistance > >    E > ____ > >  I    R > > E = I x R > > I = E / R > > R = E / I Here's a very old, easy way to remember the relationship of the OHM's law components E - voltage = EAGLE I - current = INDIAN R - resistance = RABBIT     E = I x R     The Eagle sees the Indian & Rabbit equal I = E / R      The Indian  sees the Eagle OVER the Rabbit R = E / I      The Rabbit sees the Eagle OVER the Indian -- Why Down Thrust ? Lift is proportional to velocity square. For airplane with non-symetrical airfoil, say, the Clark Y, will going up too much with power up (even with zero angle-of-attack) if no down thrust, so you need some down thrust to compensate this. Not only Eagle2, many other trainers also need down thrust. Hope this helps. The reason: Since it is a flat bottom airfoil with a lot of positive incidence, the faster it goes, the more (LOT more) lift it generates.  The downthrust tries to compensate for this by pulling the nose back down as throttle (and speed) increase.  It would be a lot better to design trainers with a lot less positive incidence in the wings and make it fly more neutral. If the down thrust was lessened on the Eaglet, the plane could do loops just by application of throttle. Or rather, the difference in incidence angle between the wing and tail on this type of airplane is high. True incidence should be measured based on the zero lift datum line (i.e. the datum line that defines zero lift when it is parallel with the direction of flight). Flat bottom airfoils have to point significantly nose down to generate no lift, but are typically mounted with the flat bottom surface parallel to the tail's centerline.  Such airplanes have to be trimmed nose heavy, and are more pitch sensitive to changes in airspeed than would one with a symmetrical airfoil (with the wing mounted at zero incidence to the tail). Which makes me wonder why more people don't build trainers with big, fat symmetrical wings. They'd be easier to land, at least - less susceptible to gusts near the ground. Airfoil and center of gravity placement are independent. Most flat bottom airfoils are probably used because they produce lift at a slower airspeed, and they're easier to build (you don't need a wing jig). There's no reason you couln't move the center of gravity back and adjust the incidence to trim a plane with a flat bottom airfoil so it had neutral stability. Note that even with neutral pitch stability, it still wouldn't fly that well inverted (at slow speeds), because a typical flat bottom airfoil needs a large negative angle of attack (or a lot of speed) to produce "inverted lift". It's probably desirable for a trainer to have positive pitch stability (nose heavy) as well as slow speed flight, and be easy to build (unless it's an ARF). Gyros on Aircraft ? gyros are great to help stabilize a plane when "external factors" are interferring....On landings, the external factor is the pilot, I am not sure gyros would do that great..... <g> Unless we are talking about windy landings, where they might help. I saw a test on a small slope soaring glider, with 3 gyros ( one for each axe ), it was very surprising to see that small thing on rails, like a 4 or 5 meters...! In my experiance and opinion unless you're flying a helicopter gyro's are something you don't need.  Usually they are used where practicing the manuver (landing, torque rolling) whould be a better choice.  If you use a gyro you will probably become dependant on it and thats usually not a good thing. Glow engine to Gas ? I've heard that if you convert a glow engine to gas, you need to have roller bearings on the rod or run rich with the oil. Running too much oil kind of defeats the purpose, in my opinion, as the beauty of gas is the cleanliness. I would think that you'd want to use the spark with the glow so you can get more power if you are going to have that much oil on your plane...or is the gas oil that much cleaner? Anyway, that's not my question--somebody's sidetracking me, and I think it's the guy on the keyboard here. I have a friend who wanted to convert his Ryobi to glow fuel for extra power and low weight. (The flywheel and coil alone weight over 19 oz.) So, I guess I was wondering...if you go the other way, from gas to glow, and you already have roller bearings, can you run the glow fuel with very little oil, say 32:1 or even thinner, like a normal gas mix? What is this fuel crossover like? Can you keep the ignition and get even more power? Are you still going to have that nasty goo all over your plane when you are done, even with the roller bearings?  Many times you can't directly convert gas engines to glow because the carbs aren't compatible. They don't flow enough fuel (it takes nearly twice as much alcohol as gasoline) and some parts in the carb aren't compatible with glow fuels.  You will also find that gas engines are considerably heavier than equivalent glow engines.  I'm not saying don't experiment, just don't expect too much. Glow ignition is very imprecise in its timing, unlike spark ignition (generalization). Without having the ignition timing locked in, more oil is needed to remove more heat for those times when the effective ignition timing is too far advanced, not necessarily for more lubrication. It is easy to forget that our glow engines are air and liquid cooled, the liquid being the oil in our fuel, hence the extra mess. Notice the difference in cylinder fin area and crankcase bulk between gasoline/spark engines versus glow engines. It is not practical to utilize the same cooling methods with gasoline/spark engines, i.e., liquid cooling by expelling heated, spent oil, hence larger surface areas are required. The few high performance gasoline/spark engines that are available in the smaller sizes are very expensive, as I am sure you have noticed. The BME 2.7 being a fine engine, but not inexpensive, relatively speaking. Metal on Metal PROBLEMS ? ... on a trainer airplane (my first one with my brother)  everytime i was doing/practicing a loop, the plane goes crazy so i landed and, after crushing my mind seen that all was correct but on full down elevator the ailerons were crazy as hell, i finally realize that one tiny little end of the "Z" bended elevator pushrod was rubbing against the throttle metal cable i used, and at that point ...  i just cut 1/2 centimeter of the end at the elevator pushrod, reacomodate the servo throw and repeated checking .. NO MORE PROBLEMS !!!!! YES!!! metal on metal can generate tremendous EMF spikes.  I have had several planes where the metal clevis on a metal throttle arm had driven the receiver nuts at certain RPMs.  the only way to stop or prevent this is to use nylon clevises or ball joints on these high vibration areas. I even saw metal to metal EMF generated that was visible as arching at dusk! If you absolutely must have a loose metal to metal contact, one possible way to get around the RF interference is to "ground" one part to the other (ie- for a metal z bend on a metal throttle arm, solder a cable to the cable/z bend and ground the cable to the throttle, possibly by passing it thru one of the engine mounting bolts).  I am not sure if this is sound theory as I haven't tried it myself. You bet.  I am not sure about planes but on R/C helicopters it is a major concern.  On a helicopter there are many metal parts that are moving very fast.  If the parts are not moving properly they can definitely cause problems.  There are numerous stories where a high speed bearing goes bad  it stops running smoothly) and causes a PCM lockout and a subsequent crash. Loose screws and vibrating washers also need to be taken care of. The only counter measures that I can suggest would be to make sure that any metal to metal connections are snug.