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Will it be strong enough.

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Erfolg11/12/2012 18:00:13
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11373 forum posts
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I am doing a conversion job at present on an old trainer to electric.

mm1.jpg

I have just about finished and will do some ground tests when feeling a little better. There is one potential fly in the ointment, and that is the propeller.

I am using a Turnigy 3542 and hope to be pulling about 250w.

However the only propeller I have in stock is a APC 10 *6. I normally use a JXF polycarbon prop.

I am anticipating the revs to be about 10,000.

I am concerned that the APC will not be strong enough and shed a blade. Will it be prudent to wait until I receive the JXF prop.

Have others used APC for a similar duty

Tim A11/12/2012 18:16:29
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11 photos

Hi Erflog, I use a Turnigy 3542/1000kv on my Tyro 150 3s batt. using a 10x8 APC pulls about 330w in flight at approx 9600rpm no problems flight times of about 12 mins easily. Plane weighs 1400 gms.

Tim Mackey11/12/2012 18:21:59
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Why would you suspect the APC would shed a blade Carl?

VERY unlikely IMO, assuming of course its not damaged in any way

Edited By Tim Mackey on 11/12/2012 18:22:21

Erfolg11/12/2012 18:25:37
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Tim

I have had some blades shed on my electric models, mostly folders.

I have seen other peoples models shed blades.

It does happen and APC does not seem as strong as the polycarbon types.

Anyway, not heard much from you recently, hope you are keeping well.

Malcolm - coolwind.co.uk11/12/2012 18:35:25
177 forum posts
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The APC website gives the max rpm limits for its props. I've never had a problem with APC on IC or Electric - they are one of the quality manufacturers. An APC electric 10x6 should be good for 14,500 rpm

APC Suggested RPM Limits
Glow Engine and Speed 400 Electric Props
Maximum RPM=190,000/prop diameter (inches)
(For example, a 10x6 glow engine prop should be limited to 19,000 RPM)
Thin Electrics and Folding Electric Props
Maximum RPM=145,000/prop diameter (inches)
Slow Flyer props
Maximum RPM=65,000/prop diameter (inches)
Malcolm
PatMc11/12/2012 19:31:13
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I've been using an APC 10x7 in my Druine Akrobat for about 18 months. On 4s it pulls 460W at 10,800rpm. Never had any problems. I think a 10x6 at 10,000 will be taking substantialy more than 250W.

PS. I think you'll have to change the thrust line of the motor. wink 2

Erfolg11/12/2012 19:35:25
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Seems my fears are ill founded. Better ask than be sorry though!

Erfolg11/12/2012 20:25:24
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The upthrust helps with an early rotation!

It should do about 10,000 revs , what information that is available with the motor indicates somewhere between 220 -289 w that is the difference between a 10*5 & a 10"*7. As with most of these things, I will have to measure and see what actually happens.

It is good to know that the prop should be fine.

Biggles' Elder Brother - Moderator11/12/2012 22:37:39
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Erfolg,

how are you - on the mend I hope?

Re APC props - I've got an APC 14x7 on my Piper Cub and that's drawing over 1kW, not had any problems at all!

BEB

Richard Wood12/12/2012 10:33:47
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1088 forum posts
164 photos

Hello Erfolg,
No problems with APC E props here either.
These are the best props I've used - I replaced a 9x6 Master prop
with an APC in one particular model & the improvement was noticeable.


Erfolg12/12/2012 11:25:12
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As the saying goes "you should not judge a book by its cover".

I am somewahat reassured. I have been influence by the rather soapy, soft feel to the plastic. Reaming to size, being easy as the material cut freely. Where as the props I have come to trust have a gritty and fibrous structure.

Again it shows how you are influenced by your background. Feeling comfortable with the notion that energy is dissipated by the growth of cracks around the interface of the fibrous material in Matrix structures. Thereby dissipating energy, without immediate catastrophic failure. Taking many cycles to failure.

I also have been concerned that loading rate and temperature being more important with polymeric materials than metallics, and composites.

As to my health, it improves, slowly. It is now over 4 weeks since my problems started. I then thought, not to worry, only a cold, I will be better in 7 days. I am hoping to go out for the first time tomorrow, for a short period. I will have then finished my second lot of penicillin.

Erfolg15/01/2013 13:48:00
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I have just finished the conversion, on receiving the Rx, set the Tx up and run the motor.

I have just weighed the model an it is an alarming, for a electric flyer at 1.8kg.

I may not have enough watts. Until I do a watt meter check I will not know.

mm4.jpg

mm6.jpg

It seems that IC models were built a lot heavier in the past, or maybe by me.

The span is 54".

Steve Hargreaves - Moderator16/01/2013 15:49:54
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I'm sure it will be fine Erf.....as a trainer you don't need ballistic performance after all......if you need more power fit a bigger prop...I have the same motor with an 1100kv fitted with an 11x7 APC.....gives me nearly 400watts from memory....

crispin church16/01/2013 16:35:21
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442 forum posts
102 photos

should be more worried about your motor pulling off that ply dont look as it fixed in by much ?

Erfolg16/01/2013 16:55:30
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11373 forum posts
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How about 4 off by 2 BA and 4 off 4BA bolts and nuts?

The 4 Ba are in the motor mounting, to fit the holes provided.

Biggles' Elder Brother - Moderator16/01/2013 21:17:08
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You'll be able to pull a tractor with that Erf wink 2

BEB

PatMc16/01/2013 23:22:10
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Erflog, this is my Veron Robot, 45" span, 1.5kg using a Graupner 9x5 slim prop pulling 230W at 10800rpm. Converted to EP from Enya 09 power but has flown using a Fox 15, Silver Swallow 2.5 & PAW 19.

A good rate of climb & all the usual aeros with EP which is probably delivers more power than any of the ic engines used.

Erfolg17/01/2013 12:34:55
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11373 forum posts
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Hi PatMac

Your "Robot" really looks good and it is encouraging that it flies so well. It certainly looks to have a good climb.

Although my model has flown on a OS 25, it was underpowered, in that short grass and a long take off run was required to get it off the ground.

It was re-engined with a Merco 35 with after market P&R muffler, which probably knocked the power back. I am assuming that the quoted max power of 0.55bhp on 15% nitro, is well above what i was getting. Using a bigger prop, no nitro, bigger higher restriction muffler, I guess anywhere from 0.3-0.35 bhp.

So I am hoping that if I can get +250w it should be ok. The weak point of electric, this can drop off quite quickly.

Time will tell.

The trouble with IC models (at least built by me) they tend to be very robustly built. The motor mounting is beech beams, a aluminium plate, which can be seen in one of the photos. The front end is also glassed over ply and balsa. The tailplane is of a foam balsa solid construction. The undercarriage is also built for aircraft carrier deck landings, being torsion bars, set in a beech block, channelled out, mounted on a ply base, with ply spreader plates. All over constructed for electric needs.

It was the 5th  RC model i had built!

Edited By Erfolg on 17/01/2013 12:35:22

Edited By Erfolg on 17/01/2013 12:36:47

PatMc17/01/2013 19:59:41
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4200 forum posts
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Have you considered removing the nose leg & shifting the main gear forward to convert it to a taildragger ?

IMO if you fly from grass it's a better option for a model of this size - less ground drag & the wing is held at a good AofA from the start of the take off run.

Erfolg17/01/2013 20:28:01
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Good God Nooooo!

I want it to pass the "A" test. So I want to give myself the best chance I can get, with what I have.

Trikes take of easier and land easier. Far more practical really.

I guess you are thiking of saving weight and drag?

To save any real weight I would have to tear out all the gubings for the torgue rod bit. Otherwise the weight will probably go up, rather than down.

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