Any experience of IC to Electric ?

[Andrew Moore 7]

I'm looking to swap a reasonably aerobatic model with an OS46 in to electric.

I have a spare motor & ESC knocking around that I hope will be big enough. I'm more concerned about things like thrust angles, downthrust, C of G etc.

Could you give me some pointers ?

Spare engine I have have is an E-Flite 1200 ? with 70amp ESC

[Denis Watkins]

Having done both IC to electric, and electric to IC Andrew, at least 8 models

The C of G always remains in exactly the same designed position

And have never altered the thrust from zero on any of these models

But some models may need slight downthrust

[Nigel R]

Keep the target prop and rpm the same, and none of those factors change.

"Hope will be big enough"

Just my guess, but, a 46 probably needs 750-800W powertrain to do a "straight swap".

edit: I don't know the EFlite motor you spec, google doesn't seem to know it either?

Edited By Nigel R on 09/07/2018 10:53:35

[The Wright Stuff]

Posted by Denis Watkins on 09/07/2018 10:46:21:

But some models may need slight downthrust

I'm scratching my head to fathom out why there should be any difference between IC and electric in terms of downthrust. After all, how do the aerodynamic forces 'know' that the power source has changed?

Is it down to different prop wash from electric type props? A reaction force from the exhaust direction on I.C.? Any other factors?

[Nigel R]

WS, they don't of course.

Prop dia, pitch and rpm have a bearing on right thrust. Downthrust less so IIRC. The pattern crowd have some well trodden trimming methods to get right thrust set to minimise prop impact on airframe behaviour in various attitudes.

Or, I seem to remember the consensus a while back, was you could mix in a bit of right rudder for varying throttle positions, for a comparable effect.

[Peter Miller]

My Moodelsnever use side ordown thrust.

They will swing left on take off but that is what the rudder is for, a dab of right rudder on the take off roll and that is it.

My "The Ohmen" electric powered model does have a very hard swing to the left on take off. Again, a bit of right rudder and let it off once the model leaves the ground and no more attempts to turn.

[Biggles' Elder Brother - Moderator]

OS claim that a 46 will knock out 1.2kW (seems optimistic to me!) but let's assume that's so. That sort of power level is certainly achievable with electric power - I have 3-4 models that dish that sor of power out.

And 70A for your ESC is kind of OK too - with 6s battery at say 65 A you'll output around 1.4kW

The problem is this motor - an E-Flite 1200? I never heard of it! Nor can I find it to look at its spec. Can you tell us a bit more - maybe give us a photo? Anything really to help id it.

Once we have that we can give you more advice.

BEB

[Nigel R]

"OS claim that a 46 will knock out 1.2kW (seems optimistic to me!) but let's assume that's so."

Not a chance, BEB - 1.2kW is grade A manufacturer's hyperbole*. Produced under the most perfect of conditions at massive RPM.

Back to reality. A standard silencer on 5 or 10%, at 11k? 2/3 of that, at best.

I'd suggest 4S at around 50A would more than suffice. Or a 5S at 40A.

* Hyperbole isn't the phrase I'd like to use, but I'd have that phrase deleted by one of the mod team...

[Andrew Moore 7]

Thanks for the help so far guys, would anyone like to suggest a suitable motor and ESC combination to replace the OS46 above so I have enough power but not too much ?

When switching from IC to electric, presumably my 4S or 5S battery would sit around where the fuel tank currently is ? Also, as IC engines are heavier, will I not end up putting loads of nose weight in if I dont have alot of space to move the battery back & front ?

Very grateful for the answers so far on this thread - really helping

[The Wright Stuff]

Andrew, might be worth telling us exactly what the model is: you may find someone has already done a conversion...

Yes, getting the battery far enough forward to balance without adding too much weight is usually the biggest challenge with converting to electric. Be creative about how the battery might fit in to get it as far forward as possible. Can it stand on end? At an angle? You may consider using a multiple packs in series or parallel if the smaller size allows you to get them further forward.

Best wishes, this is one of BEB's (many) specialist subjects, so I expect he can elaborate!

 

Edited By The Wright Stuff on 09/07/2018 13:45:28

[Geoff S]

I've done a number of conversions to electric of what were designed to be glow powered models and quite often the main problem is getting CoG right. A modern brushless electric motor is lighter than a glow engine plus its silencer so it's essential to get the battery as far forward as possible to avoid as much as possible the need to add ballast. Whilst the former fuel tank bay is a tempting space it's often too far back so make arrangements to push at least some of the battery through the firewall.

My two latest conversions have avoided the need for ballast. My quarter scale Mew Gull has its 6S 5Ah LiPo mostly in the tank bay but the front is pushed through the firewall. It does have the advantage of a long nose. My DB 58"ws Gypsy/Cirrus Moth has the battery (4S 4Ah) under the motor and the former tank space just has the esc.

Down/right thrust, CoG and even weight (assuming no extra ballast) are the same for both glow and electric power.

Geoff

[Trevor Crook]

My electrified PM Ballerina balances perfectly with the battery in the tank bay. Power system is a bit different to those quoted above - 900kV motor turning a 12x8 prop on 4000 3s, 40A esc. Flies well on just under 500W, but it's got a big wing, which helps. I'd guess the performance is similar to a "cooking" 40 or 46, such as an OS LA. As said above, if we know the proposed model we can give more relevant help.

[Andrew Moore 7]

Model is an Extra 330 about 10 years old

Fuel tank is right behind the Firewall so I guess I maybe able to sort the C of G, may even be able to put my battery or 2 x smaller batteries across fuselage rather than length ways

[Nigel R]

"suitable motor and ESC combination to replace the OS46 above so I have enough power but not too much "

Andrew

I'm currently flying a 40 sized airframe (a 57" span aerobatic model) using a 3548 size motor (900kv), a 60A ESC, 11x8 prop and a 4S 5000mAh lipo.

AUW is just shy of 5lbs, it accelerates vertically (at the end of the flight) and will stay up for 11 or 12 minutes.

Motor is a Tornado Thumper 3548/900kv (web page here). Other brands are available.

The ESC is a Hobbywing 60A, more commonly sold by Hobbyking as the Plush 60A.

The lipo has to be shoved back, roughly one third of it is over the wing, the rest sits in the tank bay.

Previously, it had flown many times with a 3900mAh lipo, this went entirely in the tank bay and provided 8 minute flights.

Hope that helps.

[Biggles' Elder Brother - Moderator]

Hehe my comment "seems optimistic" was my polite way of saying what you said Nigel!

OK let's be a bit more serious - let's say 800W - 900 to be generous.

Off a 4s we'd draw about 55A to do that. So we need an ESC like this:

That will cover us up to 80A - a bit of headroom which is always good.

For batteries I'd look at a 4s 5000mAh

We want the prop to nominally hit about 10krpm at full throttle (it won't, but its a design figure). To do that off a 4s battery outputting 14.8V the motor would need a kV of around 600-650 ish. It must also be able to handle 60A.

Something like this maybe - though the kV is a little low. This one might be better.

BEB