electric conversion

[Patrick Shepherd]

I have been considering convertine a Precedent T240 (14lb 8' span trainer type model) to electric power but am unfamiliar with electric power trains for models of this weight. I have flown this type of plane adequately on a Laser 75 fs, but could probably use a little more power. Suggestions for suitable motor/esc/lipo/prop combos would be most welcome.

[Eamonn Fahey]

Where's Timbo when you need him?

Sorry I can't help Patrick but someone on here will know.

[Steve W-O]

What is the weight without the motor and fuel tank

How long do you want it to fly on a battery?

What is the wing area

What is the wing section?

How do you want it to fly?

Is your runway long grass?

Is there any restriction on prop diameter?

Is there any restriction on battery size?

May be easier to look for one or a similar plane that someone else has done already, there is a list on the forum

[Tom Wright 2]

Patrick

The starting point is to look a motors that will comfortably give power that equals the model weight multiplied by 100 the answer is in Watts .If the model requires more than 400-500 Watts then a 4 cell lipo would be advisable ,or if the power requirement is more than 800-1000 Watts then a six cell may be required.

If you model is a 5ft span 5-6 lbs trainer with a plank wing then 450-700 watts should do the job the use of higher power depends on the pilots experience and airframe structural integrity

Tom.

.

[PatMc]

A full size Piper Super Cub has about 40W/lb at full power. The T240 should fly fine on the same but 1000W would give a generous 70W/lb for a 14 lb model of this type.

First thing to consider is the battery. 6 mins at full throttle (WOT) should give about double that flying time per charge with normal throttle management. This means the battery should be capable of 100WHours. A 22.2v (6s) lipo of 4.5AH capacity would deliver this at a 45A.

A motor capable of taking continuous 50A should be able to deliver the power with a prop sized to suit it's KV & a 60A ESC.

[Peter Beeney]

Patrick, I’m afraid I’m not into electric flying very much at all, but from reading your OP I’d say you are considering replacing the Laser 75 with an electric motor, gaining a bit more pokey on the way. So maybe a little attempt at a approximate comparison may give you some idea. (And me!). At a complete guess the Laser has about a 1hp, or 746 watts output, and it turns a 14 - 15 by 6 - 8 prop. I’ve no idea of the revs, 8 to 10 thousand perhaps, although that maybe be a bit optimistic.

So more or less considering the first motor I came across, a NTN Prop Drive Series 42 -58 500 kV/ 1300W, lookee here it’s possible that something like this might be suitable. It will turn a 15 by 8 prop on a 5S, 18.5V pack, consuming 760 watts at 41.1A, or a 15 by 8 on a 6S, 22,2V, that equates to 1256W at 56.6A. You can also use a 7S battery, or alternatively a 16 by 10 prop, on all three battery sizes, but that does increase the current flow proportionally.
The kV, or unloaded revs per volt applied, would be a maximum of 10,500 on a fully charged battery, 4.2V/cell, but with a prop on it will be less than that, say 9,500 at a complete random guess. That give you a theoretical max speed of 71 mph flat out. It would be somewhat less than that, though, for a start the average battery voltage is 18.5V, perhaps a bit less on load, that could reduce the prop speed to say 8000 rpm, again, a guess, the speed is now down to 64 mph.

Choosing a mid point between 760 watts and 1256 watts, 1000 watts, 45 amps and to get to this you might need a 6S on say a 15 by 7, so if you wanted a duration of ten minutes then 10 by 45 divided by 60 = a 7.5 Ah pack. This gives you 10 minutes flat out, probably 20 with normal flying. This ties up very nicely with PatMc’s post, so we agree on something. All these figures can be adjusted to suit. A 15 by 7 will fly the model slightly slower yet again, but with slightly better acceleration. Although the ad doesn’t list a 14 inch prop this also may be a consideration.

The motor plus a 7.5 ampere hour battery and 60 amp speed controller will weigh around 3.5 - 4 lb. (Rough guess). Perhaps a bit more than the Laser and fuel, but I’ve no idea of the a Laser’s weight, so maybe not.

As you can see, this is all very much making it as I went along, but hopefully there are some clues in there somewhere, or maybe they are only hints……

Good Luck!

PB

[DAVE MATTHEWS 2]

Hi Pat, excuse me "butting in" on an old post but I run a T240 on electric for towing . I run a turnigy 5065 - 380kv on 10s producing just over 2kw and I tow 4m gliders up and it will loop quite happily from level flight. I think 2kw is what you should be aiming for.

Cheers ,Dave

[Dyl]

This is quite helpful.

**LINK**

Ta Dyl