vmsguy

I'm working on electrifying an Ultra Sport 60. And I want to make sure I get the power system correct.

I looked at the plans last night and they specified 3 glow engine/prop combinations.

1. (4-stroke) OS MAX FS-91 with 11x11 prop
2. (4-stroke) OS MAX FS-70 with 11x9 prop
3. (2-stroke) OS MAX .61 SF with 11x8 prop


I *think* I've come up with some combinations that will work.

I guess my first question is....

What RPM can I expect these motors to spin these props? At half throttle? At wide open?

The reason I ask this comes from one overruling requirement. I am using stock landing gear, so I have the same prop clearance as I would if I were flying glow.

So, to my reasoning... If I have to spin the same diameter props, I must spin them at the same speeds to get the same performance.

My goal is to have an electric plane the flies the same as a stock built/powered glow version.

I'm not interesting in uber performance setups (tuned pipes, larger motors, etc.)

I hope that makes sense...

I hope someone out there has these motor/props and has some measurements with a tach....

Thanks in advance...

Warnberg

My Feedback: (1)

For tach readings check out this thread... http://www.rcuniverse.com/forum/forumid_173/tt.htm

Gray Beard

My Feedback: (-1)

Not A clue about anything electric but those props are nothing I have ever tried on those engines except the .61 I never tried those combos so I can't say good or bad but they just struck me as odd??

vmsguy

I pulled them off the plans last night... I could have written them down incorrectly... I'm at work (gotta pay for the airplanes somehow) If someone has a set of plans available.. could they verify???

One of my motor configs has a 11x8 prop, spinning at a max of about 12K.... I'm hoping that will come close to the .61 2-stroke config..

In the meantime.. research continues...

beau0090_99

Yeah that sounds strange as well. Usually a .60 sized engine would be swinging something in the 12-13 inch range. Also, if they are suggesting a 4 stroke, that will usually turn something larger too. I believe the 4s' make power lower int he RPM range, much like BL motors would. Do you have the plane built yet? What kind of ground clearance do you see from it, when it is sitting level on the bench?
Good luck,
Curtis

carrellh

The SF is a plain bushing engine so 12k is probably a decent number to shoot for with the 8 pitch prop.

The 91 four strokes usually seem pretty happy turning around 10k. The 11x11 is a pretty light load for the engine but it is on the recommended list in the manual. APC makes a 11x12 which is also on the recommended list.

<< EDIT >> I use a 12x6 on a 61 two stroke. The "load" is similar to a 11x8. My engine is an ASP, ball bearing model, and it turns the 12x6 around 13k but I do not remember the exact number

hogflyer

For the .61's I fly in pattern type planes I use either an 11 X 7 or 12 X 6. For the US 60, with a .61 2c, I'd lean more towards the 11 X 7 since it'll give performance closer to the older pattern planes (the US 60 is an outgrowth of the Bridi Kaos 60). Not sure on an electric conversion - you may want to ask they guys in the lekky forum since you are getting into more specialized, rather large and very expensive motors/esc's/voltage regulators/batteries.

Hogflyer

Campy

My Feedback: (1)

Have you run the specs of the plane through MotoCalc ? Motocalc will put you IN THE GENERAL BALLPARK as far as motor type/size (and/or gearbox_, prop, and battery. If you go to the opinion section, I have found it to be pretty accurate as far as performance is concerned. FWIW - Motocalc has a free D/L with a 30 day full function trial period.

The other way you can do a setup for electric is to take a READY TO FLY WEIGHT for a glow setup, then use the following to determine the size motor you will need:

60 - 90 watts per lb = barely flyable to trainer type flying
100 - 150 watts per lb = general sport flying and mild aerobatics
150 - 250 watts per lb = aerobatics and MANY SCALE warbirds
250 - 300+ watts per lb = 3D
450+watts per lb = wings are optional {:-)

These figures are approximations and will vary by wing area/type of plane. For instance, a SCALE 5lb Piper Cub will fly reasonably well on a 300 - 350 watt motor, but a SCALE 5lb P-40 warbird is going to need about a 700+++ watt motor to fly.

This is MUCH LESS ACCURATE, but it will still put you in the ballpark as far as the motor is concerned - you just have to do more work selecting the specific motor, battery, prop, etc.