Bill McCreadie

Posted by Ben B on 04/07/2011 13:08:52: Posted by Keith Simmons on 04/07/2011 12:39:45: Am I correct that you add an inch for the dia, but 'lose a inch for the pitch?   ie 10x8 3 blader for 11x7 2 blades? Is it the same for larger dia props, for example 20x8 3 blader for 21x7 2 blades or would it be 22x7 2 blades? Wouldn't have thought so, that's what you do when you want to pitch up/down but want to keep the load constant with the same number of blades. When going to 3 blades you'ld need to reduce the load (ie perhaps even less pitch AND diameter).     In my travels through the 'which prop size for which engine' sites and forums I came across quite a few sites which were of the opinion that moving from a 2 blade to a 3 blade was not really so much of a problem i.e. reduce diameter a little but leave the pitch alone. Anyone else come across this??   Bill

Posted by Steve Hargreaves on 04/07/2011 12:29:18: Do I guess Bill that you are converting an EP model to IC? If so then this prop issue is a typical problem. An electric motor can be "tuned" (or wound) to produce power at various rpm where as with an IC motor you have to take what you are given & lump it...   This means you could have a nice scale model fitted with a motor that is "tuned" to turn a large prop. Putting a suitable IC motor in it will mean you are stuck with the prop it will manage...   In IC the motor defines the prop...in EP the prop defines the motor....sort of..   If I am right & you are attempting a conversion then might I also suggest you take a look at reinforcing the firewall. EP models are often built very light & won't take the vibration of an ic motor.....   Hope this helps....   By the way I agree with the other posters regarding the actual prop size....a 20 would take an 8x6...possible a 9x4 two blade. Anything more than this & you'd be overloading it...       You are absolutely right! I had thought of taking up electric flight and to that end -- without much research -- I got an ART P-51D Mustang kit (balsa and ply not a foamie.) That was the easy bit!!! I then realised just how much extra was going to be required and the problems and caveats associated with e.f. not to mention the expense of complex battery charging and maintenance, horror stories of combusting aircraft and batteries, short flight times etc. etc.   All the while I have a selection of ic engines languishing on the shelf so I thought why not -- with appropriate reinforcing of firewalls and front end, I could have my very pretty model up and running with a system that I already understand and have used for years.   The challenge of getting a ic motor to fit into a rather slim front end would be interesting even if I had to fit it inverted to get it in.   I would be interested to hear from others out there who have tried and suceeded (or failed!!) to attempt what I'm doing and any hints and tips would be greatly appreciated.   Bill.

Posted by leccyflyer on 02/07/2011 21:13:02: The largest prop I use on miy OS .25FPs were 9x6" props, but I did get one second hand with a Graupner 9x6" three blader. Took it off for a 2-blader without using it.   The rule of thumb that I was given that going up to a multiblade prop is like adding an inch in diameter, per blade. So a 3 blade 9x6 would be similar to a 2 blade 10x6 and a 4 blade 10x6 would be like an 12x6 2 blader. Probably too much for a .40FP and defininetly for a .25FP. OK, I give up, unless anyone knows where to get smaller diameter 3 and 4 blade props.

Posted by leccyflyer on 02/07/2011 20:02:13: As Ken said, an OS ,20 would struggle to turn a 10x6 2 blader and would definitely struggle with a 4 blader.   The better news, if you can live with it, is that with a suitable prop - say an 8x6 or 9x5 - the motor will fly a 44" span, 2lb model quite nicely. Going to a decent .25 would give excellent performance - that's the motor of choice of the Cambrian funfighters, of that size and a little more weight.   That's also a lot more than 75watts/lb. You'd probably be disappointed with only 150w in a 32oz model, if expecting sprightly performance.   Would an OS 25 turn a 4blade 10x6?? or how about an OS 40

So I have an elderly but perfect OS 20 (I don't think they make them any more!) and it should do the job nicely. In order to retain the 'real' look it needs a 4 bladed prop. I got on to APC head office and they recommend their 10 x 6 - 4 blader -- I assume they know whereof they speak but does anyone have any comments?

Hypothetically, if a 150 watt motor is required to 'briskly' fly a 44 inch wingspan 2 lbs weight model what would the equivalent ic motor be??

Read you suggested thread with interest but still a little confused as everyone has a pet Tx position they swear by! Very little mention of Rx antenna position except for the dual antenna type being at right angles to each other. What about the Rx's which have only one short antenna with a shrink wrapped thingy on the end. How should these be positioned? Bill.

I have read these post with interest and am as confused as ever! I have also noted that there is not a lot of mention of Rx antenna orientation except for the dual antenna type being at right angles to each other. There are Rx's which only have one short antenna with a doofer at the end of the short cable, how should this antenna be oriented in the model? Bill.

I have come across various posts which refer to being careful with antenna positions but don't go into much detail. I have also seen that some Rx's have 2 antennas and some only have one. Are there rules as to how these should be positioned within the model and also on the TX? Bill.

My birthday is the day after the draw so it's got to be for me. I can fly the Mustang with my other hand!!

As a matter of interest, do lipo's gradually lose their charge (as NiMh batteries do) or is it a slower loss. Bill.

Gentlemen. Thank you for enlightening my darkness. I think I've got it now. My new battery arrived this morning. Now I have to start soldering Deans plugs to everything!! Wish me luck. Bill.

Hi Pete, the motor shown in the manual is nothing like the one supplied its very like the motor in your post except that the can is deeper. The shaft length seems to be necessary as the motor is mounted quite far back from the nose. I've looked at the spinner you suggest and it would seem to be about right. There is no indication as to diameter though. To look right it should be about 1.825 inches. I'd love to post pictures but I don't know how, could you let me in on the secret?? Bill

Hi Birdy, by balance charge do you mean plug the battery into the charger using the small white plug? Bill

Hi Chris, the prop shown is exactly the one supplied with my Vmar Mustang kit (not very macho!!) Its a very loose fit on the shaft. There is a recessed hex on each side of the hub which will take a nut. I'll try your suggested contacts and see what happens.

Does anyone know how to mount a prop and spinner on this motor. The shaft is 2.7mm in dia. and is threaded for 22.3mm of its length after which it reverts to 3.0mm. I am more familiar with diesel and glowplug engines where mounting the prop and spinner is much more obvious. BillEdited By Bill McCreadie on 14/04/2011 22:23:09

Thanks Pete B very useful info. Just one more thing (!!!) My nice new battery arrives I unpack it and admire its sleek good looks then what do I do? Is it charged? Is there a bit of paper with hints and tips on how to look after it? Not likely!! So how do you recommend I treat my new arrival?? Bill.

Thank you Pete. An island of clarity in my fogbound brain. Bill

I think its starting to dawn at last except for one thing(and again!!) Lipo batteries are listed as e.g. '3s 1800mAh 11.1V 20C' or some other C number. Does this not matter when attached to an 18amp ESC. BillEdited By Bill McCreadie on 14/04/2011 21:17:52

OK then given all the info in my original post concerning motor power (150watts) the ESC 18A max and a suggested 3s 11.1V Lipo can you suggest which battery power I need to handle the motor current and not overpower the ESC. or am I just proving that I still don't really get it? Bill

Aren't there caveats concerning battery power in Amps not being too much for the ESC? Mine says 18A max so what should the battery be?   There is no flight battery as the ESC has a BEC connection so that means that the Rx is on all the time unless the Lipo is removed for charging, or the wing removed and the BEC unplugged. (Unless it goes through a switch harness.) I'm sorry to appear to go on and on but please bear with me -- I'll get it eventually! Bill.

And another thing (once more!!) As soon as the BEC is plugged into the Rx, which has to happen before the wing goes on, means that the Rx is always on before the Tx -- doesn't it?? Mind you I can always switch on the Tx and throttle down before upending the model, plugging in the Rx and fitting the wing. I'll need to go back to my darkend room!! Bill.

Thank you for your patience. There is just one more thing(see- I told you!) The battery pack quoted is a 3S 1800mAh isn't there another number and letter needed ie 20C or 40C or some such?? Bill.

Sorry I should have said, the model is the Vmar P51 Mustang. After a lot of hunting on the net I have found that the motor is 150 Watt.   Can I make sure I'm clear on switching the system on, all is plugged in and the receiver is live, will the motor start?or will nothing happen until I power up the Tx and it sends a signal to the throttle control?   The Rx is only accessible with the wing removed so I would have thought that a switch isolating the BEC would have been a good idea.   As I have said before I'm very new to electric flight and have never even seen a watt meter, besides until I know what power of battery to safely fit I couldn't run it up to measure the wattage.   One more thing (I bet everyone says that!) the prop supplied is a 10x4.7 peach coloured slow fly model and looks a bit wimpy for a Mustang. Is there an equivalent 3 or 4 blade prop and spinner which would make it look just a little more like the real thing?? Bill

I've just opened the kit and out comes the electric motor & the ESC. Nowhere in the limited paperwork that appears next is there any indication of the motor size or power all it says (on the motor) is VMAX Brushless. Va 2410-12.   The esc is as follows :- VMX 18. Current 18A Max. and a vague recommendation for a 3s Lipo 11.1V. Given the above info what size of battery do I need??   Another question that bothers me a bit (I'm new to electric flight though have flown powered models for years) if I just plug the Lipo battery in to the ESC will the motor just start running? or will it just sit there until the Rx is turned on with the BEC plugged into the throttle slot. The more I write the more springs to mind !! Should the BEC be routed through a switch harness to power the Rx on and off.   I must stop now and go and lie down in a darkened room!! Bill