538 forum posts
To throw in another odd-ball,. What IC engine would be needed to turn a 17" x 8" prop ?
I fly a scratch built Douglas SBD Dauntless using a 17" x 8" prop, on 3s at 340 watts. It's 67.5" span and flying weight is 4 Lbs - 12.5 oz, and that includes retracts.
It flies quite scale like, obviously not a pylon racer.
For scale model, an electric motor can swing a much bigger prop for its weight, plus if you want to you can build quite light for electric.
I built the TN 70" Spitfire, (free plan in RCME Autom Special 2010, mine actually ended up at 72" span). But I used Depron and a small amount of balsa. Still used the TN molded exhaust stacks, lower cowl and cockpit. The plans quote a expected flying weight of 15 Lbs for the original build and IC engine power. Mine is 7 Lb 2 oz flying, on 6s, turning a 15" x 8", (originally a 16" x 10" but still flies as well on less amps).
I'm not arguing whether IC or electric is cheaper or better, but that it's just different, if you want it to be.
|The Wright Stuff||06/12/2018 15:09:02|
1383 forum posts
Peter makes a good point, which refers to a question I asked earlier in the thread. Whether to calculate cost per flight, cost per minute of flight, or cost per flying session?
Personally, I find that although my I.C. flights tend to last maybe 2 to 3 times longer than my electric flights, I don't fly 2 to 3 times more flights in the session. Therefore for me, cost per flight is the best metric. Others might differ.
|Nigel R||06/12/2018 15:12:38|
2325 forum posts
Pete, I don't think you're a million miles out. But some numbers need adjusting.
In my experience, I'd expect a Irv53 to spin that 11x8 APC at 11k just like you did, and run an 8oz tank for about 15 minutes until dry. In fact my dad flew a Chilli Wind with this exact setup for a while, until a runway inconveniently ended the fun for that particular engine.
With a replacement fuselage, I'm flying the model, sporting electric doohickeys, which spin (wait for it) an APC 11x8 at (wait for it) 11k. No, it's not the exact same prop, the first one left bits of itself in the runway. The lipo being used is a 4S 5000mAh. Now, a normal flight time, 12 minutes, with careful throttle, BUT the kicker of course is that at full bore that is drained in 6 minutes.
Let's say I've bough 4 gallons of Weston Prosynth @ £15/gallon. At around 20 goes per gallon, 20 x 4 x 15 = 1200 minutes for £60.
The lipos cost £30 each (Turnigy jobs). 6 minutes x 100 charges (before expecting end of life), or 600 minutes for £30. Rather astonishingly - after adjusting to match the IC runtime - that's £60 for 1200 minutes.
I didn't massage anything. I might have a couple of details a bit hazy. Irvine 53 consumption needs to be checked! The lipo setup is a definite.
Edit: If you shop at Overlander or 4-max or one of the fast vanishing Ye Olde Local Model Shoppe, electric starts looking less cheap.
Edited By Nigel R on 06/12/2018 15:39:21
|Dave Hess||06/12/2018 15:13:21|
|300 forum posts|
Can you tell us how much the motors, ESCs, motor mounts and batteries in those two planes cost so that we can compare?
|Geoff Sleath||06/12/2018 15:16:24|
3145 forum posts
I've just done the same Andy except my Wot4 is running on 4S 4AH LiPos mainly because I have a lot of them I use in other models. I'm using a fairly expensive motor I happened to have fitted to a model I very rarely fly (a Foxy). It's being very understressed with a 12x6 prop which delivers 700 watts at 10k rpm. As the model only weighs about 5lbs ready to go it has adequate performance and I get an easy 10 minutes without taking the battery anywhere near a critical discharge state.
It suits me perfectly, especially for winter flying when what's needed is a reliable model and no faffing in the cold. I don't think it really matters what you fly or how you choose to power it as long as you enjoy it and it doesn't frighten the horses
538 forum posts
Not easily as the Dauntless was built 10 years ago, the Spitfire 6 years ago, (and both are still flying).
Dauntless - Emax 4020 - 520kv motor, Zippy 4000mAh 40C 3s battery x1 (current battery, have used others)
Spitfire - Emax 4030 - 385kv motor, Zippy, as above, 3s x2 (6s power).
Most electric motor come complete with a mount, ('X' mount), and prop driver.
The Zippy batteries, I have 6 3s packs, (plus some older ones still usable).
I would add that cost is probably not that easily compared, I have no clue how much the electricity cost charging them.
Edited By eflightray on 06/12/2018 15:37:46
|1344 forum posts|
To give you a guide as to what my Wot 4 setup cost:
ESC Emax BLHeli series 80a UBEC £26.00 (Found these heli ESCs work just as well)
Turnigy SK3 4250 500kv 1350watts motor £30.61.
Motor Mount, included with motor
Battery 5S 4000 40C battery £31 (heavier battery balances the Wot 4 without extra weight.)
Charging cost per battery (2 flights at least) less than 1p.
|Percy Verance||06/12/2018 18:54:20|
7385 forum posts
Ok, we've all done the sums and worked out what costs more. But there can sometimes be much more at stake than the material cost of fuel, engines, lipos or esc's etc.
I - and other flyers in my club - use what would be an extremely noise sensitive site. Anyone using an i.c. engine would, I'm certain, be moved on in fairly short order. The cost would ultimately be the loss of our site. Too big a price to pay I reckon........
Edited By Percy Verance on 06/12/2018 18:57:50
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