Adequate static thrust for model?
 

I'm building a rudder-only 25" WS Fairchild. I've set-up a Cox Pee Wee 020 (extra shims, low nitro% fuel) so that it's turning a Zinger 7X3 at around 4400 RPM's. I estimate that wet weight will be about 5.5 oz.

Will the Zinger provide enough thrust for scale-like flight?

RE: Adequate static thrust for model?
 

Scale-like flight is iffy with a small plane.
Sometimes they're twitchy.
Try it and see.

RE: Adequate static thrust for model?
 

I'm curious what thrust/wt ratio would be appropriate in this case. Any suggestions?

George

RE: Adequate static thrust for model?
 

I have a 1/2A Texaco model that weighs 19 oz. In trying to understand power to weight ratios better for electric models I ran the engine with a fish scale attached to the fuselage. The 049 running with an 8x4 made 9 oz of thrust. This 50% thrust to weight provides a nice scale like climb. A 56 oz 72 inch span electric old timer has a motor and prop that generates about 26 oz of thrust and climbs at a 20 to 25 degree sustained angle. Not far off classic cabin scale type performance. So from these two I would say that a 1:2 thrust to weight ratio translates to "nice" classic aviation type scale performance. From that you're looking for about 2 1/2 to 3 oz of static thrust.

Once you get the model built you can do the fish scale thing yourself. Or make up a little wheeled "car" out of some hard free rolling wheels attached to a plywood base and an engine pylon and use that with a scale for thrust measurements. From there you can get as fancy as you want in the design of a thrust test rig.

RE: Adequate static thrust for model?
 

Bruce,

Nice to hear from you over here in the aerodynamics forum. I looked around for electric APC props-- the only 7 inch ones were 7X5, I think. I have a reg APC 7X3, but it's way too heavy-- almost 1/2 oz. Which APC props were you talking about?

Watching the fat Zinger 7X3 being spun by the mighty Pee Wee is quite a sight. If I can get the RPM's up to 4800 and keep the total weight of the model to about 5 oz, I think things will be ok. It would be great to have a Pee Wee slow (and not-so-noisy) parkflyer.

Thanks a lot for your help.

George

RE: Adequate static thrust for model?
 

for the lil Cox engine - --I still have TeeDee 10/20/49-- and for small electrics -here is the thrust stand I designed -which I also use to prove real thrust and power consumption-not calculations-
The little wheeled carts etc-- are simply to much work -for me and this has ONE moving part.

The principle is obvious - a 90 degree arm with pivot at base.
the oz/grm digital scale reads accuratelyand they are available anywhere at office supply outlets.
stand material costs - buck or so

RE: Adequate static thrust for model?
 

Serce, in that case you can reshape the Zinger so something a bit more classic looking and not so clublike. I'll post a pic of what I did to mine later. I've also got a bit of a write up drawing if I can find it. What I'll be showing you is ONLY good for slow RPM stuff but it works and greatly reduces the weight of the Zinger.