My latest build - worried about the motors

[npowell28]

Attached is a photo of my latest build 54 inch cargo type plane very loosely based on a c130. (it's not finished yet). Total weight when finished will be about 50oz, wing area of 430 sq inches giving a wing loading of 16-17 oz per sq foot.

I'm planning to use 2 x Keda TR 2837/18 motors(see flybrushless for details)

http://www.flybrushless.com/motor/view/494

I might have cocked up a bit. I was planning to use 10 inch props but that doesn't give me a great deal of ground clearance. I fly off a cricket pitch so i can see there being a few broken props. I'm thinking of dropping down to an 8 or 9 inch prop. Flybrushless results show that using a 3s battery the thrust with a 9x5 prop will give over 20oz's of thrust. Obviously that will give me about 40 oz's of thrust.

Just spotted my deliberate mistake. I read somewhere that thrust:model weight ratio should be 1:3 not 3:1 as i originally posted.

Cheers everyone

[rcers]

Originally Posted by npowell28

sI read somewhere that thrust to model weight ratio should be 3:1. Is this right??

Cheers everyone

Heavens no. That is super stunning power - well past what is needed. Forget about thrust. There are much better ways to assess motors - most use watts per pound for a better idea.

Mike

[pmullen503]

You'll have plenty of power for a cargo type plane. Looks like you can "prop up" to a 9x6 or 9x7 if you feel the need without stressing your motors.

Your wing loading is very reasonable, you'll probably find you can fly around nicely at 1/2 to 3/4 throttle.

[mclarkson]

Planes fly just fine with less that 1:1 thrust-to-weight. I believe a 747 has a thrust-to-weight ratio in the neighborhood of 1:3 or 1:4, for example.

3:1, as was stated before, is crazy, crazy power. That's for 3D planes and speed record attempts.

[npowell28]

Originally Posted by rcers

Heavens no. That is super stunning power - well past what is needed. Forget about thrust. There are much better ways to assess motors - most use watts per pound for a better idea.

Mike

Thanks all. AUW will be about 52 oz's.

[npowell28]

Originally Posted by npowell28

Attached is a photo of my latest build 54 inch cargo type plane very loosely based on a c130. (it's not finished yet). Total weight when finished will be about 50oz, wing area of 430 sq inches giving a wing loading of 16-17 oz per sq foot.

I'm planning to use 2 x Keda TR 2837/18 motors(see flybrushless for details)

http://www.flybrushless.com/motor/view/494

I might have cocked up a bit. I was planning to use 10 inch props but that doesn't give me a great deal of ground clearance. I fly off a cricket pitch so i can see there being a few broken props. I'm thinking of dropping down to an 8 or 9 inch prop. Flybrushless results show that using a 3s battery the thrust with a 9x5 prop will give over 20oz's of thrust. Obviously that will give me about 40 oz's of thrust.

Just spotted my deliberate mistake. I read somewhere that thrust:model weight ratio should be 1:3 not 3:1 as i originally posted.

Cheers everyone

Sorry spotted my deliberate mistake so edited my earlier comment for continuity.

[npowell28]

Update, I haven't flown it yet but i've put the watt meter on it. 135 watts per motor on 10 x 6 props and 150watts on 3 bladed 10 x 7 props. This is on freshly charged batteries so it should take off ok. According to my very unscientific test, digital scales against the wall, its giving nearly 3lbs of thrust. It certainly got all the dust out from behind the radiators.

I'll update as soon as i've tested it.

[dahawk]

Very nice plane. With that kind of power, you have a STOL
like the full scale C-130

Let us know how she flies !

- hawk

[npowell28]

Originally Posted by dahawk

Very nice plane. With that kind of power, you have a STOL
like the full scale C-130

Let us know how she flies !

- hawk

Will do. Haven't got much work left to do now. Trying to figure out the best way to paint it. It's either that or i'm just putting off that maiden. Suppose you've gotta give it a go at some point. LOL

[npowell28]

Tokk it out for its test flight today. It flew but just seemed to lack power. I made sure that the COG was fine. If anything it was more weighted towards the front. Just seemed to fly a bit tail down. It was just a tiny bit but seem to lack authority. The motors only give 110w each and the plane weighs 3lb on the dot so i'm guessing that they just need a little bit more power. I've tried a new motor that gives 150w on an 8 x 4 prop so i'll give them a go i think.

Apart from that looks cool in the air.

[npowell28]

Just an after thought, i expect that the this could be the nose pitching up due to not enough/no downward thrust on the motors. I'll add some and give it another try.,

[subzJC]

How did your motor swap work out for you?
I hope you still have your airplane, atleast in one or two pieces.
Please share your story.
Thanks!

[npowell28]

Originally Posted by subzJC

How did your motor swap work out for you?
I hope you still have your airplane, atleast in one or two pieces.
Please share your story.
Thanks!

Hi thanks for the interest. After my initial test flight, my make shift runway(cricket wicket) became really wet and bumpy. This planes belly is really low to the floor and needs a good surface to fly off. So unfortunately it's in the hanger, well on top of my wardrobe, until the better weather comes back.

Having thought about it though, it should really have enough power on the motors it has. I am going to lessen the angle of attack somewhat by raising the trailing edge by a couple of mm and go from there. If that doesn't have the result i'm looking for then i'll change the motors. I do think though that having more power will just make the balooning worse.

I'll have to wait until spring arrives unfortunately before i find out.

It did give me time to paint it though. I'll post some pictures next time i get it off the wardrobe.

[subzJC]

npowell,

thanks for the reply!
Most times it is best to take extra time to think about a problem.
Any chance of doing turf maintenance on the cricket wicket?
I would really like to see the paint job you put on the airplane.

Have a good one!

[npowell28]

Originally Posted by subzJC

npowell,

thanks for the reply!
Most times it is best to take extra time to think about a problem.
Any chance of doing turf maintenance on the cricket wicket?
I would really like to see the paint job you put on the airplane.

Have a good one!

No i'll have to wait for the better weather. Don't want to mess up the work that the groundsmen do.

[npowell28]

Ok this is the paint scheme so far. The blue painted window will be replaced shortly with a cockpit and proper windows. Motors will also get covers when i get the chance.