A bit disillusioned with my first prop driven electric flights yesterday

[Myron Beaumont]

Yesterday I flew my Trixie that I had converted to lekky power from my trusty 15 IC engine .Now the only other lekky A/C i have flown before was my scaled up EDF Ezefan No problems but a bit fast . Admittedly it was a bit gusty and the Trixie is a typical summer evening machine.It's a typical cabin type high winger like an Auster or similar (loads of washout on the wings /dihedral etc.) If you remember a couple of weeks ago Phil visited me to convert me to lekky It was a bit bit blustry too and crashed both A/C. .That's what spurred me on to "Have a go on the same bit of land"

To cut a log story short I managed a couple of flights but on the second one I hit a tuft of grass on my arrival .The prop lost a blade & the motor shaft bent.Fortunately I had the prescence of mind to buy 5 props from BRC a while back.I have managed to straighten the drive shaft ,more by luck than judgement ,and getting the rpm as slow as poss to see which way it was bent I thought I could smell something burning .No ,thank God ,it was Chrissy stood behind me with a hot sandwich . I was just about to get my lipo out very quickly having heard all the horror stories .

Basically ,I'm saying that I'm not impressed & shall convert back to my IC engine .

Unless someone tells me otherwise based on just my first bad experience

Myron

 

[Tim Hooper]

Myron

 

Can you tell us what powertrain you're using? To replace a .15 glo motor, you're probably goign to need at least 200 watts.

 

tim

[Tom Wright 2]

As often said the prop doesn't mind what turns it ,a decent 200W- 250 W as Tim sugests ,can equal the power of a .15 but for instance if a 180W bell motor was used without the shaft trimmed down a bent shaft is guaranteed ,For test flying models with small EP motors the cheap slow fly props put less bending load on the shaft and cost little to replace.

Don't be disheartened Myron electricery can be an interesting and practical extension to the oily activities. .Tell us more.

Tom.

Edited By tom wright 2 on 24/05/2011 13:50:45

Edited By tom wright 2 on 24/05/2011 13:53:17

[Myron Beaumont]

Tim & Tom

Thanks for your replies.The spec is as follows

Trixie 1lb 9oz weight all in -42" span Towerpro 240-21T motor (BRC)Hi-model 20 AmpESC Prop-GWS EP 7035 -Lipo 3s 1800 mAh.

I don't think power is the problem,it handlaunches easily with a few mph headwind (Beaufort 2).By the way the original power source was stipulated as being 10 to 15 IC so I was on the side of having more than enough power -which I found to be true & it flew on about 1/3 to 1/2 throttle

Cheers Myron

[Tom Wright 2]

Well then it seems the issue is the bent shaft ,which i m sure provokes the thought "that would have not happened with ic".

Well probably not , but did you reduce the shaft length ,and fit a slow fly prop?it makes quite a difference .

Although the tower pro is a good and very inexpensive motor the shafts are very soft and can bend inside the motor as well,i cut the shaft down and use a prop adapter ,or a prop saver can also help reduce the stress on the shaft.

To be fair to the little motor look at the comparison between that and the cost of a .15 ic .

A motor costing a little more is IMO less trouble generally ,we have run those 200W BRC motors for a very long time without problems,the tower ones do also suffer from grub screws coming loose and poor threads,but if you have spares on stock its easy to keep them going.

 

Tom.

[James40]

I dont see how hitting a mound and snapping a prop can put you off lecky flying? That will happen to an ic prop too surely?

I find lecky so much easier, cleaner and quicker to get up and running that I won't go back to fuel.
I'm in the process of fitting a 110 electric motor to a Hangar9 P-51 at the moment, so much less hastle than exactly the same plane with a petrol FG-20 I have permanently hanging on my workshop wall!

[Myron Beaumont]

Hi James

It hasn't exactly put me off completely .As I said ,I was disappointed that the spindly little shaft bent as it did (never looked right to me from day one ).It wasn't a power dive =just caught a softish tuft of grass about a foot high.Anyway ,I can see the reasoning behind the shortening of said shaft & the use of a better collet arrangement .That means remounting the motor further forward etc etc so I'll probably put back my 15 & use my lipo / motor/ESC etc on a powered glider I mentioned in the thread by Timbo an hour or so ago .

[Tony Smith 7]

I don't know that motor, but replacement shafts are usually less than £1. Better to have a couple of spare than struggle trying to straighten it out.

[Pete B]

Myron,

 

If your motor is a 2409-21T, you can see how I shortened the prop shaft on my little Cub about halfway down this page.

 

I haven't had any problem with bent shafts -yet!

Pete

 

[Tom Wright 2]

Myron.

This little motor from BRC fitted with a folding prop solves all the problems.

 

[Nick Farrow]

Hi,

 

I would also second the use of a folding prop.

 

My local patch is very bumpy (tufts, rabbit, mole hills etc). When I first started every other flight seemed to have bent a shaft (on different motors, but both less than 4mm). For the last year I have flown with folding props and never had one since. I have never flown IC and personally cant see that is has any advantages - I guess its what ever works for you

[NigelH]

"1lb 9oz weight all in -42" span Towerpro 240-21T motor (BRC)Hi-model 20 AmpESC Prop-GWS EP 7035 -Lipo 3s 1800 mAh."

 

I reckon that you meant to say that it's a 2408-21T motor. BRC must have sold millions of those.

 

If that the case, it also goes very well with a GWS 8x4 HD prop which is more efficient than the slowfly props. Got a pic of your installation ? Rather than using the full length shaft, you can use the stick mount that comes with that motor plus a stick to slot it onto. Or do what Pete demonstrated.

 

[Terence Lynock]

Bent shafts are a trademark of Chinese motors and even the more expensive motors can have the problem.

If it is a metric shaft then no problem, I go down the engineering cum hardware place and buy a length of silver steel the same diameter, cut it to length then heat it to a cherry red and dump it in transformer oil to harden it, next step is into the oven for ten to fifteen minutes at 350f to temper it and let it cool naturally.

I used to make my own plane blades from ground flat stock and its the same process, if the shaft has grooves for circlips you can cut them with a 1'' diamond disk but it takes a lot of care,