John,

Just some quick observations:

1. 30-35 mph may be too slow for a plane this size (you will never get it to do "high flight" or loop.

2. 4 inches of pitch is four inches of pitch regardless of the diameter. If you want to use 4 inches of pitch you shoud look at running closer to 10,500 rpm. I do not think 8000 rpm will get you very far off the ground.

3. Even 12/6 @ 8000 rpm will not get this beast off the ground. I run props close to 12/6 @ around 9200 rpm for a 70 ounce model with half the area.

4. A 4S battery is simply too small to get the job done. if you are going to turn an 18" dia prop you will need a lot more than 4000 mA to get through your routine safely. Even if you want to use a 12" prop you will need to go to at least 5S so you don't melt your ESC.

5. IMHO I wold opt for a direct drive and do away with the extra weight and complexity of the reduction drive.

Please look up the posts at the very start of this forum from Mike Palko about selecting the correct size motor for your model. At 10 lbs I am thinking just as a WAG that you will want about 1300 watts to even think of doing a loop.



Kim.

Thanks for the comments.  The Jenny is a a slow flier but with a blunt nose and lots of wire drag. The level flight power will likely be about 600w, maybe more.

Line III predicts about 12-14 lbs of line pull at 30-38 mph, however, I suspect it may fly OK slower than that.  Looking at the CC program, and starting with my E-Flight 46, 18-6 prop at 2:1 reduction and a 5s pack, it shows power at ~570 watts and a static thrust of 98 oz. That's about 80% the weight of the airplane, so should be plenty. Motor turns 10700 and prop is at 5350.

Remember that the real Jenny was a miserable airplane by today's standards, rate of climb was about 5000 ft in 20 minutes, so I'm not after stunter performance here, but a realistic flight, as slow as it will go and fly in a stable fashion. I really don't know how fast (slow) that will be.    A loop may turn out to be out of the question, even with a diving entry, the Jenny may just slow down too fast. I would expect to take several laps to climb to the high flight position.

The flight time with a 4000 mAh battery is forcast to be 7.19 minutes which would be 40+ laps at 10sec laps. However, the CC program doesn't account for the drag of the plane, so it maybe substantially off-base as to the power required to actually fly it.

Another factor, the swept area of an 18 inch prop is over twice as big as a 12 inch prop and according to Martin Hepperle's propeller scaling math, the 18 inch diameter requires 7.6 times as much power as the 12 inch, pitch and rpm being the same. However the rpm is cut by a factor of two in this case, which still requires 3.8 times the power(may not be correct, as I think this is probably non-linear). If I run the 12-6 case in the CC program, it shows a power of 444 watts, which is 78% of the 18 inch, 2:1 case, not 26% as Hepperle's work predicts. So, I'm not confident that the CC program is correct, and they say it is just an "estimate".

Thanks to Kim's suggestion I also have been looking at an E-Flite 90. This motor is 325 Kv and would spin the 18 inch prop at 5700 rpm on a 5-cell pack, making somewhat more static thrust. That would be direct drive. The weights come out about the same as 46 + belt drive.

My general feeling right now is that I'd rather have the 90 in there, loafing along than the 46 running at its limits.

The 46 has the advantage of being here and about half the cost of the 90 for controllers, etc.

I did some hunting in the forum and couldn't find the posts you are referencing. How are you calculating the power requirement?

Thanks for the help, you guys.

John

No, they are all RC. They fly pretty well and very much like the original, ie carry some power all the way down, they slow down very quickly. There is one electric being flown and it has an Axi 4130/16 with 2 6s2p 3700 packs in parallel, swinging a 17-6. It weighs 12.5 lbs, so now I'm worried about staying under the weight limit. Oh well, it's always something. A calm day for sure, and for sure got to have throttle control, which means an RC receiver and battery pack.

Are you enjoying Switzerland? What are you doing at CERN, or can you say?

John Witt