sjhanc

My Feedback: (3)

TimD,
Kcollier was asking about running a SCALE sized prop which would have a diameter of 26+ inches. I have a ZDZ 80RV which easily turns 26-12 2 blade or 24-12 3 blade with incredible speed and vertical performance, but it can't do as well with a 4 blade prop. Your DA 85 will turn an UNDERSIZED 4 blade prop but he was asking about WHICH engine would turn a SCALE sized prop. Not the same thing. Electrics can turn a scale diameter ELECTRIC prop but these props can't be bolted onto a gas engine, they don't have the structural strength to withstand the gas engine's power pulse. My ZDZ engine's power pulse is so strong that it throws the blades of some of the gas WOOD props that are recommended for it. I have the scars on my fingers as a result of blade loss on starting.
To get SCALE performance on a SCALE sized 26 inch diameter prop the minimum displacement is 100cc+ and a 2 cylinder engine with the firing order arranged at 180 degrees (2 firing events per revolution 180 degrees apart) would work better and have a smoother power delivery than a big single. Even twins that have both cylinders firing simultaneously have a destructive power pulse.

The MOKI radials can turn 4 blade props with scale diameter but these engines don't fit the nose of a Mustang. DA makes a custom built 100cc+ inline twin that can do the job in a Mustang but a complex baffle system is needed to keep it cool. I have had to be satisfied with the smaller than scale Varioprop designed electric props to match the 65cc electric motors (6000+ watts, over 8 horsepower) and I have tested Zinger wooden 22-16 4 blade props (7400 watts, almost 10 horsepower). The Zinger flew the 30lb. plane well but speed was down to about 105 mph and constant current draw at all throttle settings was too high for the electric systems to be able to withstand for more than 3 minutes. A 100cc+ gas twin is capable of turning this size 4 blade (22-16) but this is still not a scale sized prop. Flight performance with the Zinger 22-16 (it needs 10 horsepower) is adequate but I too want a scale sized 4 blade on the front of my warbird.

I have a set of Zinger 24-16 blades (for gas engines) but the power requirement is too great for any power system I now have, and they are still smaller than scale size. I have looked long and hard at the Biela 4 blades but they aren't scale sized and are built for gas engines so would have excessive current draw on my electric motors.

The Canadian built 110cc Widowmaker 4 stroke, 4 cylinder is promising in a Ziroli 98 inch wingspan model but, for me, bolting on a $5,000+ power system is more than I want to risk losing in a crash. There are some European built Inline 4 stroke, 3 and 4 cylinder engines available that have demonstrated the ability to turn large props and both the SOLO and Varioprop gas props can and have been used on them because these props have ground-adjustable pitch (again, high cost). The need for much higher pitch is there because the large 4 blade scale sized props lug the motor rpm down so much that any pitch below 14 inches (Biela) won't even reach Scale speed, (75-90 mph) in the 1/5 to 1/4 scale warbird.

There is an American-made 2 and/or 3 cylinder gas 2 stroke in-line engine that the pylon racers use but this is a Ziroli warbird sized engine, and from what I have seen, its in-flight reliability stops me from trying it (most of the flights I have personally witnessed ended in a dead stick landing with gear and wing damage). To me, 100% power plant reliability is paramount in these high value airframes that don't glide when the motor stops before the landing. This is why I have stuck to using DA engines in my expensive warbirds. The flyaway total cost of my electric P-51B at $4,500 is almost too much to risk (for me). And I have had almost 100% reliability with my electric power systems to date, even when I had an in-flight failure of a 4 cell LiPo pack (1 of six), I was still able to have a powered approach to a successful landing.

I have sold my Zinger 4 blade prop to someone else who wants to try it on a large gas engine.