25% Great Planes Yak 54

[Stan Carter]

I installed an Axi 5320/28 with a Jeti Advance PLUS 90 amp Opto ESC in the plane and running 10S. I used a 18/10 prop and the plane had basically no power what so ever. Going vertical, it would almost stall. Would a 20/10 or 20/12 prop work better or is the motor to small for this plane? I haven't weighed it, but would venture to say it weighs about 13 to 14 lbs. All the Axi literature says for 3D on 8S the plane should weigh around 9 lbs. and for sport flying around 11 to 12 lbs. I'm thinking I need a larger motor.
Please let me know what you guys think.

Thanks,
Stan

[Fig Jam]

Stan,

Weigh the plane, once we know a few details a recommendation can be made.What is the AUW (about isn't good enough :) ) Do you want to stay with AXI or are you willing to consider other Brands? I'm presuming that you want to stay with a 10s setup, what size are the packs and what C rating are they?

Mike

[Stan Carter]

OK the AUW is 16lbs 3oz. and I still need a little more nose weight. I wouldn't want to go any less than 10S, but could go 12S. I would have to change the speed controller if I went 12S. I have four 5S 3300 25C FP packs that I was planning on using in the plane.

Stan

[BoneDoc]

Stan,

IMHO, 16 lbs is way too heavy for a GP Yak. That thing only has around 78" (if my memory serves me right) of wingspan. You need a plane in the 85-87 WS at that weight.

Also at that weight, you're really looking into 12S 5000 for great power. 10S 5000 on 14 lbs is acceptable also.

[Fig Jam]

Stan,

You can push your setup a bit more than you are currently :D , but the most you can ask from it on a 10s 3300 pack is a 20x8, that will give you around 21.5 lbs static thrust. Amps would be around 66 with PIN at 2225 Watts.

A great 3D pilot would be able to manage on that power setup, for the rest of us mere mortals we would want another 750~1000 Watts.

As Josh stated the plane is a little porky at 16.5 lbs, I've flown a DA50 powered one that weighs in at 15 lbs and it felt too heavy on the wing for good 3D (didn't stop me trying though) and it tended to snap out of high Alpha flight a lot.

Hope this helps, Mike

[Stan Carter]

Thanks Josh and Mike.
I agree its too heavy, but don't know why because there is nothing added except the servos, an AR7000 RX, RX pack (2S 2100 EVO Lite), Koolflight UBEC, ESC, motor and 2 x 5S 3300 packs and a pilot. Maybe the pilot is too heavy. :rolleyes:
I did have to add some weight in the front because I put the rudder servos in the rear, instead of in the front. So that needs to change, then the CG will probably work out better without the extra weighs.
Mike, it did exactly what you said about snapping when I would make a turn from going into the wind.

I'll try and put it on a diet and get it down a couple of pounds and see what happens.

[Stan Carter]

I moved the rudder servos from the tail to the front of the plane and put a set of 5S 5350 F3A packs in place, then I checked the CG. The CG is where it is suppose to be now, but the plane still weighs 16lbs 6ozs. With the plane put together ready to fly, I took a digital fish scale and tied it to a post and to the tail of the plane. With a 20x8 APC, I used my Astro Flight watt meter to see what kind of amps and watts I was drawing. The digital fish scale said 12lbs and the motor was drawing 1890 watts. Changed the prop to a 18x10 and then I had 12lbs and 1400 watts, put on a 20x12 and then I had 14.5lbs and 2100 watts. Then the motor quit and never would run after that, I haven't looked at yet to see whether it is the ESC or the motor. From what you guys have said, it looks like there is something wrong with the Axi 5320/28.
I removed the 1.6 lbs of weight from the front, that would make it 14 lbs and in the ball park for the correct weight, but then the CG would not be where it is suppose to be. Could I extend the motor out further to accomplish two things. One to get the prop out past the big cowl farther and two might help the CG.
What motor would I need to get to fly a 16 lb. plane and I won't to go to 12S, so a motor that would be good for 12S is what I would be looking for. Hacker A60 16 or 18M?

Thanks for any help,
Stan

[Fig Jam]

First of all you you need to decide if you want to continue with this project, I say this because even when you get the power system optimized you're still going to have a heavy plane :( .

Now let's say you wish to proceed, first thing you must decide is if you want to have the simplicity of an Outrunner with it's associated inefficiency (more Watts wasted in heat) or a much more efficient Inrunner (but a lot more expensive).

Let's look at the Outrunner option as that's what most people would choose and let's also take a look at what Prop size the plane will handle. If memory serves me correctly the U/C is a bit flexible on the GP YAK so 22" diameter is really your limit and a half square pitch of 10"~12 ". AUW is still going to be around 16lbs so we need a motor that will turn a 22x12 at 2500~3000 Watts PIN on either 10s or 12s (if I read your last post correctly). If you wanted to go with Hacker I would recommend the A60 14L, you could start out on 10s and see how you liked the power and if you felt you needed more the you could run it on 12s.

Mike

[Stan Carter]

Mike
Could I extend the motor out further to help the CG? Then I could remove the weights I had to add in the front.

I take it your not a fan of Outrunners. What Inrunner would be a good choice, a Neu with a gear drive?

Maybe I should put a DA50 in it and the weight and CG problem would be solved. :eek: :D

http://www.rcgroups.com/forums/showthread.php?t=553071