Thread: Discussion Dynam Skybus DC-3
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Old Oct 08, 2012, 05:30 PM
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Belgium, Vlaams Gewest, Hasselt
Joined Aug 2012
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I fly the Belgian colored one with the Mrrcsound system (article and pictures somewhere on previous pages). Having read the thread before building, I installed tail wheel steering because I only fly on a tarmac surface, and more for the sake of good looks changed into dubro wheels all around. Tailwheel was no problem to replace, but I had to drill out the mainwheel axis. I initially replaced those with plastic ones but after a few landings they cracked, leading to a prop hitting the surface and bending the (much too long) prop shaft. I then used 4mm carbon rod axis and have not had problems since.

As from the first taxi out I noticed the airplane's tail had a mind of its own. With idle power the steerable rubber wheel worked well if not exposed to too much crosswind, but with any (taxi)power application, steering was ineffective and the tail waggled wherever it wanted. Keeping the elevator full up and using only moderate power during taxi largely eliminated that problem.

Opening the engines up for takeoff was another story, either crosswind or unequal thrust made it extremely difficult to maintain runway heading. Propwash from the engines didn't blow over the rudder, and with the tail low that rudder also didn't get any clear airflow over it untill the the aircraft reached two point (instead of 3 point attitude). It thus invariably weathervaned into the wind and if after takeoff you applied ailerons too quickly to regain runway heading, it had the tendency to tipstall and drop a wing into vertical.

After a few whisky's and long sleepless hours in bed I came to the conclusion the problem probably was caused by the 14 downthrust of the engines. During taxi and initial part of the take-off roll any power application results in much more air being blown over the horizontal stabilizer as under, creating negative pressure and thus almost cancelling any (gravity) friction of the tailwheel to steer or counteract other forces.

I thus developed a different takeoff technique, also because of the overpowered nature of this model and the desire for more scale like operation. I always taxi with stick full back and after lining up the aircraft make a dry takeoff run in my brain, forcing myself into an "unnatural" approach if things get out of hand. I mentally say 3 times RUDDER, RUDDER, RUDDER so I am well prepared to correct any deviation without aileron application because the result of the latter is often disastrous.

Now the actual takeoff. No question of opening the throttle as on many other of my planes, but VEEEERY slowly open the throttle with full back elevator allowing the airplane to accelerate down the runway with the tailwheel firmly on the ground allowing directional control. Now comes the delicate part: keeping the tail too long on the runway and the Dakota gets airborne with too low a speed for adequate lateral control. Lifting the tail too early or too abruptly and the the p-factor (gyroscopic force created by the 2 props being tilted down) and/or unequal engine power or crosswind gust, will cause your aircraft to head off one side or the other. Either you abort and try again from standstill, or open up the throttle fully to get it airborne before you get to the side of the tarmac. For the last option, keep the climb angle shallow and initially allow the airplane to choose it's direction by itself. Do not attempt to correct with ailerons until sufficient speed has built-up but use moderate rudder to just keep the wings level.

If everything runs as planned, when reaching sufficient forward speed and the plane is still accelerating down the runway, slowly release the back pressure on the stick allowing the tail to rise while applying small rudder corrections to maintain runway heading. Forget large rudder inputs because the plastic landing gear struts don't like lateral forces being applied to them. During assembly, refrain from using "hard" glues to fasten them to the wing because they will quickly show cracks and are difficult to repair. Use the "bad soft" glues you collected in other ARF's kits but didn't dare to use because you were afraid the parts would come apart (ie white FMS tubes). On the Skybus gear they are just what you need to absorb excessive forces, just check your gear after every flight, it's easy by removing the magnetic block covering your ESC's.

After the tail is in the air the airplane will accelerate even better because induced drag has been drastically reduced. At that moment, leave the throttle where it is (often barely around half throttle) and concentrate on tracking straight. If everything goes normal, the airplane will lift off by itself and climb out with a shallow angle (as the real DC3). If due to the increased and long ground roll you have trouble maintaining runway heading, at that point a slight up elevator input to clear the runway helps, but please release back to neutral immediately to allow the speed to build up.

In the air it flies nicely on ailerons, but again once on final approach, leave those ailerons neutral and pick up any wingdrop, how slight it is, with rudder. Just as before takeoff, mentally say RUDDER, RUDDER, RUDDER when you are in final approach.

This model airplane handles completely different from the real DC3 (I had a rating during the 90's) for take-off and landing, it is beautiful and rewarding but just as it's big brother requires a fine technique to operate safely.

Happy take-off and landings....
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