200 watts /lb KWIK-E! - RC Groups
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Jun 01, 2002, 06:56 PM
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Gerald's Avatar

200 watts /lb KWIK-E!

I was blown away by how fast my Kwik-e flew today. I mean it looked like 100+ mph! The motor was making some high speed vibration noise too and the model was making a shrieking sound as it streaked past then to pull up into a steep high speed vertical climb becoming just a spec in only a few seconds.
And then the motor cut off after only about 3 minutes. I knew something was odd.

Something looked strange when I went to remove the battery after the flight. It looked slightly too short!!?

DOH! This is what you get when you accidently fly with an 8 cell CP1300 pack instead of the correct 6 cell 2400 pack!

According to motocalc it would have been pulling about 55 amps and spinning that little 6x6 prop at about 21K RPM! About 380 watts and less than 30oz all-up. Battery was a steaming hot potato when I removed it but I think it will be OK. It didn't appear to have vented. Don't try this at home folks.
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Jun 01, 2002, 07:02 PM
Resident Maniac
Toaster's Avatar
good thing you pack is safe. But that was a great three minutes, eh?
Jun 01, 2002, 10:24 PM
Product Manager at Hobbico
GWRIGHT's Avatar
i did some flying on 7 cells during "testing" and recorded over 50 amps static,.. probably high 30's in the air. Motor was fine,.. 50 amp ESC was fine,.. but pushing the prop over 16K kinda scared me, as that's the "redline" number from graupner. Motocalc is far from accurate with this setup,.. you'll not see near the rpms that it predicts,..nevertheless, it does "GO" real well anyway. 8 cells would have probably got you near 17K on the prop,..which would be over 100mph pitch speed,.. so it musta been smokin!
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Jun 02, 2002, 10:11 AM
Registered User
Peter W's Avatar
surely a few extra rpm won't make the prop fall apart? and it's okay if it does that in the AIR! endo is fine too but is the speed gain of using seven cells over 6 only 5mph or so? i just need to know if i should keep my seven cell packs or not i guess.....getting an e3d soon but will sell the twinstar with a bunch of other stuff......

Jun 02, 2002, 11:48 AM
Registered User
Originally posted by Peter W
surely a few extra rpm won't make the prop fall apart? and it's okay if it does that in the AIR!
Yes, it could, and yes it would matter if it did it in the air, as it would vibrate the plane to death with only 1 blade spinning.
Jun 02, 2002, 12:21 PM
Motors beat engines!
Did the motor hold up to this?

The reason I ask for is that if it was undamaged, perhaps that means the endo can handle far more than the accepted 40 amps at least for short motor runs.

Lots of potenetial applications, like for instance having a
REALLY fast 2 minute kwik-e race!

Hows the comm and brushes look?

Dean in Milwaukee
Jun 02, 2002, 01:00 PM
AMA 697691 / FAA 13675
That's pretty funny, Gerald!

You have to watch those CP cells closely. The same thing can happen between an 8-cell CP2400 pack and a 10-cell CP1700 pack since they are the same size.
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Jun 02, 2002, 03:13 PM
Product Manager at Hobbico
GWRIGHT's Avatar
yes, the endo will handle a lot more than the 40 amps i recommend on 10 cells, i've ran them in the mid 50's without a problem, but brush life goes way down,.. a dozen plus flights per set.
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Jun 02, 2002, 04:12 PM
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Gerald's Avatar
Well, I know that Motocalc is only a tool and is not always accurate, but I bet the RPM did keep rising as the plane speed increased. I was using the prop constants for the Aeronaut folder. It seems that this Graupner folder is not that well balanced or perhaps not well centered anyway. It vibrates even in the normal RPM range and I could hear loud vibration in the air as it reached very high speeds. Even if the prop doesn't come apart it's sure to be hard on the airframe and the motor mount so I would advise against over-reving it. For these very high RPMs it would be best to go with a fixed well-balanced prop.

I haven't checked the motor yet but I may need to clean up the commutator as a result of the high current. It's sad though because after getting a taste of this kind of performance it will be hard to go back.
Ok I just checked and discovered that my motor mount screws were loosened. I removed the motor and the comm looks fine. It is perfectly shiny with only a tiny bit of dull surface about 1mm wide at the edge of each comm segment. There is no brush dust even. I found part of the cause of the prop vibration. The spinner retainer screw is too long and bottoms out before the spinner is fully seated. I cut it down by about 3mm and it's much better now. I put a little Loctite on the motor mount screws this time too.
Last edited by Gerald; Jun 02, 2002 at 04:36 PM.
Jun 03, 2002, 01:44 AM
Blew out my flip flop
David Hogue's Avatar

Dont worry about the motor or pack, just be careful you dont rip your wing off....

Jun 03, 2002, 06:23 AM
Registered User
Peter W's Avatar
awww i feel sorry for you....you must have had unlimited vertical with that 'setup'! and the limiting factor being the prop!
are you gonna do it again?