Power Loading

Dr. Larry J. Crabb (docc@aristotle.net)
Tue, 16 Jan 1996 18:20:14 -0600

Okay,Doug, if I must. Also, hello Guy! Long time no talk.

I too, appreciate the absolute scale equality of painted coverite over
momokote, or any other film. I also appreciate and understand (and accept)
my own flying skills. Having kept a sustained flight log of many, many
flights, I determined that those planes which I demolished, without
exception, flew at greater than 21oz/sq.ft. of wingloading. Those which were
difficult, but I managed, flew at greater than 18oz./sq.ft. Then, I began
to build as light as possible. I had not demolished any plane that had
wingloading less than 17oz./sq.ft. Then, I began building WW-I biplanes
and, low and behold, the weight-area ratio went way down and I was
ecstatic! I was becoming like Tony Fokker in that if two wings were good,
then three wings were better. So, using Monokote and ignoring perfect scale
appearance, I built seven biplanes and used .45 Supertiger engines in all
of them. They flew great and I couldn't have been happier, since they were
all scratch built to begin with. Then, Joe Jakoncyuk (a purist and WW-I
historian) came along and we became fast buddies. His five WW-I planes
were all so beautiful and all covered with painted Coverite and weighed
tons, Each had, at least, a .61 sized engine. However, they weighed a ton
compared to mine. Even so, I decided to experiment. I striped the
Monokote from my Nie. 27 and recovered with Coverite. I painted the
Coverite using 21st Century paint and took it to the field. Alas, it was
sluggish and required almost full throttle of the ST .45 to maintain
flight. I replace the ST with a .61 and now it's back to normal. Then, I
revamped my Spad XIII, which was covered in solid Olive colored Monokote,
only this time I didn't strip it. I had found a paint that would adhere to
Monokote and was utterly resistant to fuel. Hooray! 1st, I hand painted
the proper camouflage colors to the monokote then sprayed the entire plane with
clear. Now, it's difficult to distinguish it from painted Coverite. Since
the Spad already had a .61 engine, I kept it there. However, it requires
more throttle than usual to do the same flying and doesn't glide into
landings nearly as softly as before. End of Chapter I.

Chapter II: I wondered why all this extra power was needed. I knew that
the before and after "weights" of the planes varied from 8 to 12 ounces,
but their wingloadings hadn't changed that much, say 16.5 to 17.8. Then, I
asked my son, who was a senior at Henderson State Univ. majoring in
aviation at the time (now a 1st officer for Lone Star Airlines) what had
happened. I explained everything and he told me he'd get back to me after
he discussed it with his professors at Henderson. The answer came back in
the form of a treatise on "Drag." Not just "parasite drag" but all forms
of it. I learned a lot! As it comes, the texture of a plane's surface is
very important consideration and directly affects power loading. If you
ever stop to think about it, had the mfgers. of WW-I planes had used a
smoother (less draggy) covering material, they wouldn't have been searching
for more powerful engines all the time. Not only the covering materials
held them back, but struts, wires, landing gear and spreader boards...the
whole works were nothing but drag-inducing structures.

Chapter III: I made one last experiment. I took my Fokker D-VII, which
was all red Monokote, and sprayed it with semi-gloss clear "Perfect Brand"
polyurethane spray paint and extensively dulled its surface. Results? No
change in its power loading and, also, no change in its weight that my
highly accurate scales would measure.

Chapter IV: I'm not stipulating that the parasite drag of painted Coverite
is the entire cause of my needing additional power, but considering the
additional weight, the two combined to have the negative result of needing
more power. By the way, I made one more experiment in weight while I was
revamping the Nie. 27. I weighed it while covered in Monokote. I stripped
the monokote, covered it with Coverite and weighted it again. The weight
increased only 1 (one) ounce!! However, weighing the plane after spraying
it with silver 21st Century paint, its weight increased by 12 ounces. That
was enough to put the wingloading up to 18.2 instead of 16.4, or something
like that. I have the figures, but not before me.

Well, Doug. That's the extent of my knowledge on the subject, which, I
might say, has a lot to do with actually judging the flight characteristics
of the planes after the experiments were done. "The proof of the pudding
is in the eating of it," I always say.