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Old 10-07-2015, 04:42 PM
Low_Cal is offline
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Quote:
Originally Posted by chymas View Post
As soon as they are big enough to put a gas motor in.
Haha, love that answer!
I would modify it a little to "As soon as they are big enough for a GOOD gas motor".


Which for me, is 30cc size. I used to fly some 30cc planes on electric, but once the DA35 came out, I found that I preferred that - much cheaper and easier to "refuel".


So, I think the original question should be "What is the smallest plane a gas motor works well in?" Ans., 30cc size.


Everything smaller than that is just awesome on electric . . .
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Old 10-07-2015, 07:15 PM
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Quote:
Originally Posted by Low_Cal View Post
Haha, love that answer!
I would modify it a little to "As soon as they are big enough for a GOOD gas motor".


Which for me, is 30cc size. I used to fly some 30cc planes on electric, but once the DA35 came out, I found that I preferred that - much cheaper and easier to "refuel".


So, I think the original question should be "What is the smallest plane a gas motor works well in?" Ans., 30cc size.


Everything smaller than that is just awesome on electric . . .
I'm absolutely loving my HyperActive48 with a 10cc gasser. Small gas can be a lot of fun too!

"Refueling" the big electrics isn't a huge deal if you've already got the hair-dryer or microwave oven going!

- Case
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Old 10-09-2015, 05:32 PM
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When they get bigger than full scale, or when you need more flight time than it takes to fly the English Channel.

Airbus E-Fan 'electric plane' completes cross-Channel flight - BBC News (2 min 10 sec)
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Old 10-10-2015, 05:25 PM
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I have a 30cc electric. don't think id do it again. 2 batterys each flight and about the same power as gas. my favorite electric size is 60". it flys like a 30cc but insane power and not terrible on batterys
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Old 10-10-2015, 10:50 PM
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When you cannot get MORE than 7 minutes of an exciting flight.
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Old 10-19-2015, 04:14 PM
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Okay, all kidding aside, for those who are interested in the real qualifier, consider this:

First, unlike a gas engine, the RPMs of an electric motor are governed by volts and motor Kv. Although most motors can freewheel on the down line, reverse EMF (electro motive force which is caused by the motor generating voltage back to the controller) will normally help to limit RPMs and enhance the braking affect.

Second, a propeller's tip speed is directly proportional to the compressibility factor, just like every airfoil approaching the speed of sound. It has already been calculated that any speed over Mach 0.7 will begin to greatly reduce the propeller's efficiency.

Third, motors are affected structurally by precession, and the forces generated when angular momentum chases Torque in the same direction 90 degrees to the left of the thrust line. After a lot of testing through the years, I can begin to suggest that motor structure needed to manage precession is directly relative to the motor weight -- by a value of 2.5x. So a 24x10 Falcon CF propeller spinning 7250 RPMs will produce a precessive force of 3.88 kgm2/s, so a motor of a minimum of 970g will be required to manage the props precession at 7250 RPMs.

Forth, the power needed at the shaft to power a 24x10 Falcon CF propeller to 7250 RPMs at sea level and 72*F is 7.2 HP, or 5369 Watts-out. This typically translates to 6356 Watts consumed at the typical 84.4% efficiency at this power level. This means about 123A using 14S and 143A using 12S LiPO packs.

Fifth, at 123A using 14S and 143A using 12S LiPO packs, we will need a capacity of 5681mAh at 123A and 51.8v and 6627mAh at 143A and 44.4v in order to obtain a 6 minute flight time at a 35% power average (27C discharge rate to a safe 20% of capacity).

Sixth, when we get into the higher current levels, we can begin to approach the point where we are consuming almost 1000mAh every minute at a 35% power average. Each 1000mAh in a 14S pack weighs between 330 and 370 grams. This is 13 oz... and 11.2 oz for a 1000mAh of a 12S pack.

Seventh, we always determine power requirements by calculating the power loading we require to obtain the flight characteristics we are looking for. For example, if we are trying to obtain the same power level in a 27 pound plane as a DA-120 can provide, we know that we need about 8100 Watts-in. On a 14S system, that will mean about 156A. This is what will be require to spin a 29x10 prop to 6000 RPMs, but the precession is a high 7.8 kgm2/s, which means I'll need a 1950g motor and a 14S 8000mAh battery pack for a 6 minute flight. The motor and the battery pack will weigh 10 pounds. I now have to compare the gas engine and fuel weight to this and decide if the power to weight is feasible. It's really not.

When I analyze the planes I buy, I look at the available electric power systems, and the feasibility of powering them with electric systems. From a 2-to-1 thrust to weight ratio requirement of 3D and XA style of flying, I can personally drawn the line at a 26x10 spinning 6700 RPMs on a motor weight no less than 1100g mounted on a plane no more than 24 pounds all-up with a wingspan no more than 100" using 14S 6000-6200 mAh batteries. This is a 285 W/lb power loading with a prop that is 26% of the wingspan for 6 minutes.

BTW -- I would of course also expect this 24 pound 100" plane to have a wing area no less than 1800 sq in so that I can also have the 8.7 oz/cu ft cube loading and 31 oz/sq ft wing loading that I prefer. 1850 would be better -- under 8.5 CL and under 30 WL.

Unfortunately, there are not many planes out there with a 100" wing span that will weight 24 pound all-up with an electric set up and still come in with an 8.5 oz/cu ft cube loading. But there are a few where all the numbers do work out if you are willing to work at it, and pay attention to the math and manage the component weight. Ah, you know... like we do in full scale.
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Old 10-20-2015, 05:39 PM
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Hi All


Well been flying 2 Ef Edges 50cc ones
one with a Hacker Q80 and one with a DLE 55 in it
had the last 6 months flying them back to back and its been very interesting got to say
The planes are set up and the C of G are the same (half a tank of fuel ) in the petrol one
everything is the same other than the motors and got to say that the Electric one is so so very much smoother and on average it uses 130 milliamps less per flight if not more and has way way more power than the DLE
the 100cc Sukhoi I have is nice but to big and you need to much gear for a days flying,i am luck in that I have enough packs for 8 flights which for me is a days flying so I don't need to talk all my chargers and generator,the petrol one is even less as in just a fuel can and that's it
love both and I don't find a 50cc electric to be to big or a hassle at all but the 100cc is to big in my view
just strange that there so very different to fly
I am going to build a 3W Yak (air runner ) over winter electric so wish me luck on that one LOL
as its big and beautiful and been my dream plane since it came out and now I have one
so if this is still going next year I will report on how its going and if a 40% is even worse that a 100cc electric
happy flying all
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Old 01-02-2016, 10:03 AM
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Never to big . Hacker 200 4 7cell lipos 40% Hanger 9 SU26 .Nothing but fun
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Old 04-28-2016, 09:12 PM
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H-9 46% Ultimate E-Powered

So how about this bad boy.........normally powered with a 150 to 210 cc gasser this one flies on ,alien power 120x90mm brushless motor 275cc equv,.jeti 300a esc ,cap pack, 4x8000mah 6s packs combined to 12s, 12 min flight imac , 8 min 3D....flying on a JC 34 x 16 prop, Xoar 34 x 12

Built extremely light....38 lbs all up including batteries, ESC, etc.
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Old 04-28-2016, 09:27 PM
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That is great flight times. 12 minutes! ! Is there any video?

Keith
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Old 04-28-2016, 09:29 PM
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Guess this proves that in our hobby, there is no limit.
http://www.flyingmag.com/extra-unveils-electric-330le
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Old 04-28-2016, 10:01 PM
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I don't want to know how much those batteries cost!
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Old 04-29-2016, 12:59 PM
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uomo ludens modellesticus
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Beauty!
www.flyingmag.com/magnus-efusion-rolls-out-at-aero-friedrichshafen

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Old 04-29-2016, 01:31 PM
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Just let me as an asside ask: When do you switch from gas to electric?

My answer was when I am fed up with cleaning the underbelly/canopy of my gasser.

That works out real well for helicopters. The jury is still out for me on my EF 91 Extra just for the fact that my flying time are too short to my liking, around 6 minutes. But it flies great during that time.

I have to find a better combo or make it lighter to handle bigger batteries. The 12 minute flying time for the Ultimate mentioned above makes me jealous.
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Old 04-29-2016, 01:41 PM
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Quote:
Originally Posted by Aeroplayin View Post
Okay, all kidding aside, for those who are interested in the real qualifier, consider this:

First, unlike a gas engine, the RPMs of an electric motor are governed by volts and motor Kv. Although most motors can freewheel on the down line, reverse EMF (electro motive force which is caused by the motor generating voltage back to the controller) will normally help to limit RPMs and enhance the braking affect.

Second, a propeller's tip speed is directly proportional to the compressibility factor, just like every airfoil approaching the speed of sound. It has already been calculated that any speed over Mach 0.7 will begin to greatly reduce the propeller's efficiency.

Third, motors are affected structurally by precession, and the forces generated when angular momentum chases Torque in the same direction 90 degrees to the left of the thrust line. After a lot of testing through the years, I can begin to suggest that motor structure needed to manage precession is directly relative to the motor weight -- by a value of 2.5x. So a 24x10 Falcon CF propeller spinning 7250 RPMs will produce a precessive force of 3.88 kgm2/s, so a motor of a minimum of 970g will be required to manage the props precession at 7250 RPMs.

Forth, the power needed at the shaft to power a 24x10 Falcon CF propeller to 7250 RPMs at sea level and 72*F is 7.2 HP, or 5369 Watts-out. This typically translates to 6356 Watts consumed at the typical 84.4% efficiency at this power level. This means about 123A using 14S and 143A using 12S LiPO packs.

Fifth, at 123A using 14S and 143A using 12S LiPO packs, we will need a capacity of 5681mAh at 123A and 51.8v and 6627mAh at 143A and 44.4v in order to obtain a 6 minute flight time at a 35% power average (27C discharge rate to a safe 20% of capacity).

Sixth, when we get into the higher current levels, we can begin to approach the point where we are consuming almost 1000mAh every minute at a 35% power average. Each 1000mAh in a 14S pack weighs between 330 and 370 grams. This is 13 oz... and 11.2 oz for a 1000mAh of a 12S pack.

Seventh, we always determine power requirements by calculating the power loading we require to obtain the flight characteristics we are looking for. For example, if we are trying to obtain the same power level in a 27 pound plane as a DA-120 can provide, we know that we need about 8100 Watts-in. On a 14S system, that will mean about 156A. This is what will be require to spin a 29x10 prop to 6000 RPMs, but the precession is a high 7.8 kgm2/s, which means I'll need a 1950g motor and a 14S 8000mAh battery pack for a 6 minute flight. The motor and the battery pack will weigh 10 pounds. I now have to compare the gas engine and fuel weight to this and decide if the power to weight is feasible. It's really not.

When I analyze the planes I buy, I look at the available electric power systems, and the feasibility of powering them with electric systems. From a 2-to-1 thrust to weight ratio requirement of 3D and XA style of flying, I can personally drawn the line at a 26x10 spinning 6700 RPMs on a motor weight no less than 1100g mounted on a plane no more than 24 pounds all-up with a wingspan no more than 100" using 14S 6000-6200 mAh batteries. This is a 285 W/lb power loading with a prop that is 26% of the wingspan for 6 minutes.

BTW -- I would of course also expect this 24 pound 100" plane to have a wing area no less than 1800 sq in so that I can also have the 8.7 oz/cu ft cube loading and 31 oz/sq ft wing loading that I prefer. 1850 would be better -- under 8.5 CL and under 30 WL.

Unfortunately, there are not many planes out there with a 100" wing span that will weight 24 pound all-up with an electric set up and still come in with an 8.5 oz/cu ft cube loading. But there are a few where all the numbers do work out if you are willing to work at it, and pay attention to the math and manage the component weight. Ah, you know... like we do in full scale.
Lol, talk about over thinking things, I subscribe to the "if it goes beep I fly it" brigade.

For me anything over 60" is gas for me, flying for 5minutes and puffy expensive batteries just do not cut it, I do have several 60" models though, they are my lazy day planes.
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