Wow - I didn't realise how powerful these brushless motors can be

so nearly 1KW per pound. How many oz of fuel for say a ten minute flight then?
How much does the engine mount weigh?
How much does the throttle servo weigh?
How much does the prop weigh.
All these are lighter, on electrics
Reply to
The Natural Philosopher
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I was using figures provided ;p
10% runs $23 - $35 a galon around here.
Ken-Ohk
-- Ken-Ohk
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Reply to
Ken-Ohki
From Tower Hobbies:
[[[ INCLUDES: One Assembled .32 SX Engine One Set of Instructions, Poster, and Decals One Muffler (OSMG2873)
SPECS: Displacement: 5.23cc (0.319 cu in) Bore: 19.5mm (.77") Stroke: 17.5mm (.69") Output: 1.2 BHP at 18,000 RPM Weight: 270g (9.5 oz) 12.32 oz w/muffler Practical RPM Range: 2,000 - 22,000 RPM Crankshaft Thread Size: 1/4-28 Recommended Props: 10x6, 10.5x6, 11x6
]]]
Average fuel weight is half of, say, 6 oz tank. Total for fuel, engine, tank, mount, and servo is right around a pound. $150 will put it into the air for 10 minutes WOT.
Regarding power at realistic revs, I'm also working with nominal battery capacity, not motor and gearbox efficiency. I think, without much analysis, that they're close enough for talking purposes for now.
Work with me on this. I'm willing to be convinced about big electrics. How big is a brushless that can sink 1 kW? I'll confess to not have tried to size one that large. My guess is it's at least as heavy as the nitro engine with fuel.
Reply to
Boat
If you are going to sell it at a decent price let me know........its ok I will take the blood with it. :-)
Mike
Reply to
Mike R
Does all this talk about electric vs. glow matter much???? Remember $economics$ does not fly the plane. YOU fly it and it is YOUR choice of power plants that fly it.
Mike
Reply to
Mike R
Right, and the responsibility of choice demands that you educate yourself about the issues.
Speaking of choice, and to drift completely off topic, it's likely that I've invested more time, effort, and money researching electrics than I have on the larger issues coming up next week Tuesday. Are you, Mike, ready to make an informed choice that day?
Reply to
Boat
Who cares if they are lighter on electrics? The battery weight alone to get that kind of power would not only be heavier, but be VASTLY more expensive as well.
Average fuel weight would be 1/2 the tank capacity since the engine would run just as well with one ounce in the tank as when full. The battery weighs the same charged or discharged and power drops ad the battery is discharged.
-- Paul McIntosh
Reply to
Paul McIntosh
Economics certainly DOES fly the plane when it comes time for me to decide how to spend my hobby dollars.
"gee, I can buy two 40 size glow planes or one equivalent electric..."
-- Paul McIntosh
Reply to
Paul McIntosh
Motor that can do a kilowatt? Hacker B50..XL at 11oz will easily do that.
Cells? at probably a pound and a half. maybe an ounce or two for ESC.
Lets say the whole thing with prop gearbox and so on 3lb.
Now look at that .32.
12.32 with muffler, 3 oz of fuel, plus 2 oz of tank. about 2oz of servo. About 3 oz of engine mount. About 2 oz of strengthening around teh nose to make sure it doesn't vibrate out.
Total excess weight about 24oz?
BUT unless you are flying a plane where prop RPM of 22,000 suits - e.g. FAST - it is not in reality delivering anything LIKE 1.2bhp.
Swinging a 10x6 its probably doing what? 9K RPM? 1K RPM? that is doable with less than 500W.
What I am driving at here is that unless that fabled IC engine is screaming at ear numbing RPM, its not actually generating the power it can do. Nothing like.
Believe me, Ive done the calcs. Someone wanted to turn a 8x8 at 17,000 RPM or something to replace a tuned .36. Simply its not on. Not with current electric, BUT if you look at the prop size and RPM of a typical 4 cycle 60, it is easy to get the same prop RPM at similar weight.
Or to put it another way, IC engines don't match props very well, but geared electrics do, and allow very efficient props to be swung at best RPM - usually well below 10K.
The slower the plane, the more suitable it is for electric power. Only the red hot 120mph plus birds really uitlise IC power efficiently. They need IC to be competitive. Anything slower - there is very little to choose.
I am not saying that on a test bench, pound for pound, you can match an IC engine on power, but in the air, in typical configurations, mostly you can.
The main downside is of course cost. To me that's the only downside.
I estimate that at best its 3.5 watts per dollar for a flight pack so 200 dollars for a brake horse power is about ball park, plus around $200 for the motor ESC minimum.
So 400 dollars for a typical cooking .40 replacement.
Its a lot of dollars. OK the flight pack can be used in several models, so thats not too bad, but with about 200 flights on the pack before its fairly wrecked, its a dollar per flight running costs.
Actually I don't regard that as a particularly high price to pay, since most of my airframes get wrecked completely in about 50 flights. And most cost at least 50 dollars to make.
But it is fairly significant.
Having made the investment in motors ESC's servos receivers etc, and packs and a charger, I now have many models to build and fly, and not much further expense apart from airframes and packs to go. No fuel to buy. I am moving up towrads .40 sized stuff, but that invloves me in a much bigger expense - travelling to a suitable flying field. THAT costs me about 10 dollars per expedition. MINIUMUM. Whereas I can fly smaller electrics off the fields and parks.
Reply to
The Natural Philosopher
Guilty. Imagine my puzzlement over your puzzlement. (Why run less??)
...
Still looking for that link. It was specific to a particular battery, and presumably representative of current top tier consumer lipos. The information and discussion you're looking for is "cycle characteristics" or cycle life. In general, the cut off is not sharp. Useful life is loosely defined as where the pack capacity falls below 80% of nominal. Just the same, 300'ish is very far removed from 500+ cycles.
Here are a few other links, with less detail than the document I have in mind. There's no particular significance to the links below, except they discuss lipos at a depth beyond typical r/c hobby store product pages. They were in my history list for the past two weeks, the likely time frame I saw the document I referenced.
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?ExhibitID=17157 I give up. If you find reasonably complete documentation, I'd like to hear of it.
Reply to
Boat
I think it does to people who are considering electric, or glow, and want to work out what to expect, yes.
They are not the same thing, similar, but not the same.
One overriding issue for me is the distance/time and cost of travelling to a suitable place to fly medium large glo planes.
Reply to
The Natural Philosopher
I'm talking about those that carry the running glow plane to the runway. We don't allow taxiing in the pits at two of our fields, and the startup benches are right at the flight line at our third field.
Yep. Got thrashed once myself before a plane's maiden flight. A bug in the ESC that bypassed the arming sequence if the throttle was set to full, and the wrong servo-reverse setting on the throttle channel... Ever since, I work from behind the plane...
Yep. Properly handled, you never have to go near the spinning prop, or even an armed prop.
Agreed.
Reply to
Mathew Kirsch
Or you could build two 40 size glow from plans,spare monokote, spare servos, receiver and balsa sitting in the shop, and the money you save can be used to by electric motors/ gearboxes, batteries..................but its your hobby dollars and I and no one else has the right to tell you how to spend them.
Mike
Reply to
Mike R
You missed the point completely. The extreme cost of .40 and up equivalent electrics have kept me out of it because I can buy (build, acquire, etc) more planes and engines for my modeling dollar by staying with glow.
-- Paul McIntosh
Reply to
Paul McIntosh
Motocalc 7.09. STP, 12C max. (5 minutes WOT)
Hacker B50 11XL + 3.7:1 PG, 16x12, 6200 RPM. 2100 mAh 5s3p. Static thrust and duration WOT is 154 oz for almost 6 minutes, or closer to 10C discharge rate. 8 to 9 minutes duration with the prop unloaded. On something like a G.P. BigStik 40, it's very well rounded with top speed of 70 mph and unlimited vertical. Throttled back to 75%, it should stay up 15 to 20 minutes. Wing loading is quite high at 22 oz/ft^2; low speed and longer durations probably won't be interesting or fun.
I can't find high discharge single cells, 10C 2100 mAh sustained. I found a Kokam 5s1p 2000 mAh 15C pack at hobby-lobby. $169, 10 oz * 3 = $507, 30 oz. (8 oz more than used in the performance estimate. Wing loading is closer to 24 oz./ft^2.) You could drop one of the parallel packs and take advantage of the 15C rate, but even nominal duration is only 4 minutes then.
BEC isn't possible with 5 series cells; you'll need a separate radio pack, 5 oz for 4x1200 mAh; $20.
Hacker 70 Opto or CC Phoenix 60. $145.
Hacker B50 11XL + PG $320. 11 oz + gearbox (no specs for gearbox weight). Alternatively, a Torcman 430-20 12T 10 pol, similar performance, 240 Euros, 13 oz, no gearbox.
Astro Flight 3.5mm connectors, $10, 10 g.
Deans Ultra plug, 1 pair. $3.
Parallel harness or board: $10.
Not all chargers can handle 5 series cells. The Astro Flight 109 charges up to 9; the Triton only 4 in series. $130 for the Astro Flight, 8A capacity.
It's a touch over $1000 onboard, and somewhat more than 4 lbs for the powertrain. It'll fly like dickens, alright, but that entry fee is quite steep.
As to flying that in the local park, I wouldn't do it. It has 2500+ lb-ft of kinetic energy when it gets going. Contrast that to 100W, real backyard flying. Different ballgame, cost-wise and every other way you measure it.
Reply to
Boat
Do you really have to build one that heavy and spend that much to go 70mph???? Check out Dave Fritzke's R/C Plan Page
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and check out The Pacer plans. Direct drive 480 might do it. Let me know what you think.
You would really attract allot of attention if you did.....and possibly local law enforcement. :-)
Mike
Reply to
Mike R
Engine/motor cost aside, fuel/batteries for a 5 minute
That is a brain-dead comparison. If you count a conservative 1000 re-charges and negligible recharging costs then the nimh should be $0.01 and the lipo should be $0.06. If your time is worth anything then it slants even more drastically towards the electrics. I usually arrive at the field with gassers prepping their plane, get in 20 minutes of flying, and am driving back to work before they even take off. The gasser still has to fly and unprep and make some snyde comments to me ;)
Steve.
Reply to
Steve Banks
And it isn't much of a stretch for a do it yourselfer airplane builder to extend into a do it youselfer electronics builder. Electric motors can be cheap and electronic components ARE cheap and lipo batteries can be had for $20/amp hour. NIMH are much cheaper but heavier. At the speed 400 size it is extremely affordable, like $30 for a 1500 mah off the shelf nimh pack + esc + motor and some push on props plus a wall wart to charge it. It's just about perfect for pushing styrofoam and tape through the air (and maybe some corplas). I personally would not attempt to convert a 0.40 (or even a 0.20) size plane to electric though, not until a better electric power source comes around, if then. That seems like good gasser territory. I can't argue with someone who wants a good power to weight ratio, I understand completely. But electrics have much more room for your average do it yourselfer. You can't do much yourself with a gas engine and fuel tank to save money without investing 10k in machining equipment, but you can build circuits and battery packs with a $5 soldering iron and build ESCs and such for just a few dollars in parts (lots of stuff on the web). You can even time and custom wind your own motors with magnet wire if your bored.
Steve.
electric..."
batteries..................but
Reply to
Steve Banks
LOL. Well, that's part of the point. The exercise here was to get .30 or .40 power out of a battery and through a prop. If the exercise was to push kleenex and toothpicks to 70 mph, there are other solutions. It's funny how history repeats itself. The Pacer would be fun as a foamie and a low turn CD motor.
Reply to
Boat

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