I can't wait to fly my new 480BB motor!!

[atckirk]

I am new to electrics and am converting an old Quickie 200 pylon racer. The thing would just barely stay above stall speed with the rocket 400 so I got a 480BB from the LHS and played around with motocalc to figure out what prop to put on it. I can't wait to fly this thing, it has twice the static thrust than the 400. I'm thinking of cutting down a 6x3 folding graupner to 5x3, is the balancing that critical? What's the best way to trim it down? Thanks, Kirk.

[John E]

By moving down from 6x3 to 5x3 the 480BB Race drops a couple of amps, but there is a major drop in thrust. Because of the increased need for full throttle with a 5x3, both flight times and performance are greaster using a 6x3.

You are looking at well over 16 000 revs from that motor and I would be very reluctant to use it direct with a folder - I would make sure that everyone is well clear before running the motor up.

I'm also a relatively new glow convert (this time round!), and I'm not convinced that converting successful glow models is the way to go - the design requirements are so different. I am rapidly coming to the conclusion that the real answer to properly performing electric models is to work with dedicated electric designs.

Good luck, John

[Mark Wood]

Originally posted by John E:
I am rapidly coming to the conclusion that the real answer to properly performing electric models is to work with dedicated electric designs.

It's all in the weight before adding the powertrain. Flight designs are all essentially the same, are they not?

mw

[John E]

[quote]Originally posted by groundloop:
It's all in the weight before adding the powertrain. Flight designs are all essentially the same, are they not?
1) Exactly
2) Yes, there is no need for aerodynamic changes simply because of a change of power plant or even if a power plant is not to be used, but the structural requirements are wildly different when using IC engines with their vibration and inevitable oil ingress eventually causing some weakening of the structure. Clearly the best way to keep the initial weight down is to design for the electric power system and avoid the structural excesses of IC design. Examples of this are that the battery needs a strong mounting, but to simply add this to a glow design is to double up on structure when the battery tray can form a major part of the fus around it, and motor mounts, I read a lot about people using the original 1/4" birch ply glow motor mount for electric conversions when it appears, to me, far more sensible to design a new motor mount that can not only hold the motor, but form the major part of the nose structure.

Just my humble opinion based on quite some time spent IC flying, building some dedicated electric designs, and currently considering these very issues in a 4*40 conversion.

Regards, John

[stefanv]

Originally posted by John E:
By moving down from 6x3 to 5x3 the 480BB Race drops a couple of amps, but there is a major drop in thrust. Because of the increased need for full throttle with a 5x3, both flight times and performance are greaster using a 6x3.

For a pylon racer, static thrust isn't everything. The 5x3 will definitely give less thrust when the plane is not moving, but it will most likely give more thrust at flight speed. And, because of the higher RPM you're going to get, it isn't going to run out of pitch speed as soon. However, a better choice would be a 5x4 fixed prop.

You are looking at well over 16 000 revs from that motor and I would be very reluctant to use it direct with a folder - I would make sure that everyone is well clear before running the motor up.

Agreed. The Graupner 6x3 folder should not
be used much above 11,000 RPM or so.

Stefan

[Andy W]

In my opinion, you need a Graupnber 5x5 CAM fixed prop.
..a

[John E]

My experiences of the 480BB Race using fixed 6x3 and 5x3 props are with a Pico Jet and a 26" span "Quickie" type model - in the air (and we have tried some trendy pylon props on both), however, I'm more interested in up and down flight rather than going as fast as possible in a straight line. To the point - the load of the 6x3 is more appropriate for this motor than the load of the 5x3 IMHO, and I guess that Stefan's 5x4 and Andy's 5x5 are around the same ball park.

Good luck, John