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Old Oct 07, 2010, 01:07 PM
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Motor selection for IMAC.

I'm thinking of electric powering my new Comp-Arf Extra 330L 2.3 to fly IMAC in the Basic and Intermediate classes in the future and I was wondering if anyone out there has experience with this plane and electric power. I have three power setups I could use a Hacker A80-8, Hacker A80-10, Hacker A100-10 all with the appropriate ESC's and batteries. Any comments would be appreciated
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Old Oct 08, 2010, 03:21 AM
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Moss, Norway
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Well, for comparison I am powering a SD Yak 54, 33%, 2.4 meter wingspan with a Neu 1527, 5700-6000W. I guess the Comp ARF Extra 2.3 is about the same size and weight. The Neu motor with gearbox and prop driver weighs about 900 grams. The A80's weigh 1450 grams, and the A100 weighs 1900 grams.

With current battery technology we are still at a stage where battery weight and capacity is a major factor when flying IMAC. You don't need massively overpowered models for maximum WOW factor during one or two "pulling out of hover" maneuvres, but you need a reasonably large battery pack to enable you to complete two sequences. In IMAC you are "on the power" for a good bit of the time. In the Yak I have a 10s10Ah set-up, total battery weight about 2600 grams. (4x Turnigy 5s5Ah packs. There are some lighter options available). Although you may want to use a different configuration, that is an indication of the amount of energy required. I flew this model in Sportsman by the way. I think for best performance in IMAC you would be better off with a lighter motor. (But the A80's would certainly be enough for that plane if you decide to use what you already have.)

Regards,
Magne.
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Old Oct 08, 2010, 07:33 AM
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Thanks for the response Magne. The Comp-Arf is a tail heavy plane, with the current gas power (MVVS 58) and A123 receiver batteries in front of the wing tube it balances at the recommended CG and weighs 20lbs dry. So I'm hoping it will be ok with the A80's extra weight over the Neu that way I can use what I have. I also have a NIB Pilot-RC 33% Yak still in the box which will be electric powered when I get around to building it.
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Old Oct 09, 2010, 12:24 PM
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I flew the last IMAC season (Sportsman) with a Hangar 9 35% Extra powered by a Hacker A100 motor, Spin 200 ESC, and 4 x Hobby King Flightmax 6S 5800 mAh batteries. Worked very well. Check out the thread.

http://www.rcgroups.com/forums/showthread.php?t=1157267
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Old Oct 09, 2010, 12:32 PM
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Originally Posted by Geoff Dryer View Post
I flew the last IMAC season (Sportsman) with a Hangar 9 35% Extra powered by a Hacker A100 motor, Spin 200 ESC, and 4 x Hobby King Flightmax 6S 5800 mAh batteries. Worked very well. Check out the thread.

http://www.rcgroups.com/forums/showthread.php?t=1157267
Hi Geoff, I've been following all your builds and threads(awesome stuff)closely as there is a lot of great info on all of them. I was thinking of using my A100-10 in my 33% Yak and the A80-10 in my Comp-Arf Extra 330L 2.3 for IMAC flying.
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Old Oct 10, 2010, 01:06 AM
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Quote:
Originally Posted by fu-corsair View Post
Hi Geoff, I've been following all your builds and threads(awesome stuff)closely as there is a lot of great info on all of them. I was thinking of using my A100-10 in my 33% Yak and the A80-10 in my Comp-Arf Extra 330L 2.3 for IMAC flying.
I would think that the A80 would power the 33% Yak assuming that it was reasonably light. Remember that I powered the 33% Hangar 9 Sukhoi with the Turnigy 80-100 running at about 5000 input watts.
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Old Oct 10, 2010, 08:22 AM
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I've read on other threads that the Pilot-RC 33% Yak is supposed to be the lightest built Yak so far. I have both A80's should I put the A80-8 on the Yak and the A80-10 on the Comp-Arf Extra? or the other way around?
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Old Oct 10, 2010, 01:21 PM
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Quote:
Originally Posted by fu-corsair View Post
I've read on other threads that the Pilot-RC 33% Yak is supposed to be the lightest built Yak so far. I have both A80's should I put the A80-8 on the Yak and the A80-10 on the Comp-Arf Extra? or the other way around?
Theoretically the lower KV motor (A80-10) would be able to swing a larger propeller and would be more efficient. This may not always be true as I ended up preferring to use the A100-8 with a 24x12 rather than a A100-10 with a 27x10.

One of the European pilots (I think it was Magne) pointed out that the greatest efficiency (for aerobatic flying) is obtained by using the highest pitch propeller which might explain my favorable resules using the 24x12.
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Old Oct 12, 2010, 12:12 PM
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Quote:
Originally Posted by Geoff Dryer View Post
Theoretically the lower KV motor (A80-10) would be able to swing a larger propeller and would be more efficient. This may not always be true as I ended up preferring to use the A100-8 with a 24x12 rather than a A100-10 with a 27x10.

One of the European pilots (I think it was Magne) pointed out that the greatest efficiency (for aerobatic flying) is obtained by using the highest pitch propeller which might explain my favorable resules using the 24x12.
I remember reading that on your post, well I guess I'll try the A80-8 on the Comp-Arf Extra 2.3 and the A80-10 on the 33% Yak in the spring and see how it works out.
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Old Oct 18, 2010, 05:53 PM
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Originally Posted by Magne View Post
Well, for comparison I am powering a SD Yak 54, 33%, 2.4 meter wingspan with a Neu 1527, 5700-6000W. I guess the Comp ARF Extra 2.3 is about the same size and weight. The Neu motor with gearbox and prop driver weighs about 900 grams. The A80's weigh 1450 grams, and the A100 weighs 1900 grams.

With current battery technology we are still at a stage where battery weight and capacity is a major factor when flying IMAC. You don't need massively overpowered models for maximum WOW factor during one or two "pulling out of hover" maneuvres, but you need a reasonably large battery pack to enable you to complete two sequences. In IMAC you are "on the power" for a good bit of the time. In the Yak I have a 10s10Ah set-up, total battery weight about 2600 grams. (4x Turnigy 5s5Ah packs. There are some lighter options available). Although you may want to use a different configuration, that is an indication of the amount of energy required. I flew this model in Sportsman by the way. I think for best performance in IMAC you would be better off with a lighter motor. (But the A80's would certainly be enough for that plane if you decide to use what you already have.)

Regards,
Magne.
Hi Magne, Ok I'll have to admit I'm not very knowledgeable in the area of engineering but if I could substitute my 13.2 oz motor dome with a motor mount that weighs less and fits my A80 it would save a lot of weight. Have you ever heard of anyone that makes them? Here is a link that shows one for the Neu motor on Comp-Arf's website.

http://www.carf-models.com/public_ca...%20300L%202.3m

If anyone out there knows of someone that is making this type of substitute mount for the Comp-Arf Extra 2.3 to eliminate the heavy motor dome let me know please and thanks.
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Old Oct 19, 2010, 02:55 AM
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Moss, Norway
Joined Jul 2003
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Hello.
I am pretty certain that the pictured motor mount on the Comp-ARF is a "home made" type, and not a commercial item. But it does the job perfectly, is light and probably stiff.
If you used a rear mounted Hacker motor, your mount would be significantly simpler and shorter.
All it would take is one plywood mounting plate, four carbon tubes in the corners, and four diagonal carbon tubes. (Or long "stand-offs, although I personally dont like that solution if they are too long.) If you search through this "Giant electric planes" forum, you will see a large number of different approaches on how to mount electric motors. Most of them work fine, but some a heavier than necessary.
My 2,7 meter Votec has a composite fuselage not too dissimilar to yours, i.e. it originally had a separatee composite engine dome that was bolted to the front of the fuselage. I removed this and replaced it with a home made plywood frame that works as both a motor mount and a battery mount. (In that way, when I converted the model from gas to electric I did not do any irreversible modifications. The model could actually be converted back to gas in an evening. But of course, that would be a waste of an evening, not going to happen!)
I mount the batteries (15s2p) with velcro straps to a separate mounting plate outside the model, and then I insert this plate into the motor/battery mount. The front of the battery plate has two "tongues" that fit into two holes in the mount, and the plate is fixed with a single nylon bolt/nut at the rear. This is because the batteries fit inside the fuselage under the front deck, and access to making up the velcro straps etc. inside there is very limited. You would probably benefit from doing something similar in your model.
I may have some pictures at home that shows this, which I could post in a couple of days if you are interested.
Magne
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Old Oct 19, 2010, 07:22 AM
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Thanks for all your help Magne, lots of great info, I'm going to try and do something different in the motor dome department as it will save me quite a bit of nose weight then I can put my batteries in the forward position like your describing in your 2.7 build. Pictures would be greatly appreciated. I found one thread where a fellow made up an inside cowl ring, mounted it to the back of the cowl then modified the cowl by fiber glassing in a carbon fiber motor mount plate at the nose for a Plettenberg 25-8. It looked ok but I'm kind of wondering if the cowl is capable of taking all that twisting torque? Here is the link to the cowl mod,

http://www.rcgroups.com/forums/showthread.php?t=1107601
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Old Oct 21, 2010, 05:20 AM
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Moss, Norway
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I am sure there are many ways to skin the cat, this was my way.
This installation makes it possible to go back to Gas power, if I want to. The whole motor/battery mount bolts to the front of the fuselage, and a couple of bolts at the rear down on the landing gear mounting plate.

Magne
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Old Oct 21, 2010, 08:21 AM
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Wow that looks awesome and I bet it's nice and light too. That would be the perfect way to go in my plane.
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Old Nov 08, 2010, 09:20 PM
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Hi Magne, what size Neu and gear box is that in the pictures?
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