Engine size and pulling power

**Cribbs74** Thu Feb 28, 2013 12:54 pm

I can never remember how much weight each cox engine can safely pull. I am specifically looking to find how much weight a Pee Wee will pull.

I was thinking it would be nice to have a sticky thread that has a table that we can use to follow when building.

Can anyone direct me to that info?

Thanks,

Ron

SuperDave Thu Feb 28, 2013 1:12 pm

Ron:

It would depend up the type of airplane selected and how well you want it to perform.

My PeeWee .020 flys very well considering it is a slab-wing on a 16" bipe. I found a BW .049 made "Lil' Toot" far too nose heavy with the glide angle of a brick. Laughing

SD

**Cribbs74** Thu Feb 28, 2013 1:20 pm

SuperDave wrote:Ron:

It would depend up the type of airplane selected and how well you want it to perform.

My PeeWee .020 flys very well considering it is a slab-wing on a 16" bipe. I found a BW .049 made "Lil' Toot" far too nose heavy with the glide angle of a brick.

SD

That's the problem. It may be all well and good for a kit plane. The kits give you a range ie: .020-.049 for the Li'l Toot, so you know from the get go if you pick an engine in that range it will pull the plane. However, if you are designing/scratchbuilding something then a rough guide would be helpful.

John Goddard Thu Feb 28, 2013 1:32 pm

I think this should be sticky'ed but that's just me
Very Happy

http://personal.osi.hu/fuzesisz/strc_eng/index.htm

**Cribbs74** Thu Feb 28, 2013 1:41 pm

John Goddard wrote:I think this should be sticky'ed but that's just me

http://personal.osi.hu/fuzesisz/strc_eng/index.htm

That is a good bit of info JB however, it doesn't factor in the plane. I agree it should be stickied though.

What I am looking for is:

Cox .020- max plane weight 6oz etc.

I just threw 6oz out there as I have no idea what it will pull around.

John Goddard Thu Feb 28, 2013 3:03 pm

The Bacaruda weighs 5.5 oz Ron and now it's
Running right it takes off straight upwards.
However before I got it running well it kinda
Limped around the sky like a asthmatic ant with
Some heavy shopping. Very Happy

Don't forget wing area is important, my Old timer
(55 in span and 26oz) and Kim's Bird of Time both
Fly well with tiny 049's.
My FMK aerobic was supposed to have a td 020 in it
At 22in w/s and 8oz it supposed to be aerobatic as well.
Very Happy

Surfer_kris Thu Feb 28, 2013 4:13 pm

The pulling power (at different air speeds) can be obtained from the MVVS sheet; prop-power-calcualtor

Then it depends on what model and type of flying one is after. Minimum thrust for level flight is about 1/3 of the plane weight and a power to weight ratio of more than 1:1 is easily feasible nowadays with modern radios too.

pkrankow Thu Feb 28, 2013 4:20 pm

There is a relationship between thrust and what you want to do.

If you want to go vertical, such as stunt flying, then you want the thrust to be greater than the weight of the plane. So for an .049 engine 6 ounces is a good weight for a control line stunt plane, 7 oz a maximum with the .049 putting out a typical 6 oz of thrust.

On the other hand that same 6 oz of thrust will take a 2 meter glider aloft just fine even though the glider weighs in around 48 oz.

Phil

**Cribbs74** Thu Feb 28, 2013 6:36 pm

All good info.

I think I am over complicating the question though. Let's try this......

I am planning on building a .020 sized Combat CL plane, how heavy can this plane be (roughly) before it drops out of the sky?

**Cribbs74** Thu Feb 28, 2013 6:47 pm

Wait, I think I get it now.

A 4.5x2.5 turning 16K puts out 4.2oz of thrust so therfore my model should weigh roughly 4oz or less to be a capable stunter?

Is that correct?

pkrankow Thu Feb 28, 2013 7:19 pm

cribbs74 wrote:Wait, I think I get it now.

A 4.5x2.5 turning 16K puts out 4.2oz of thrust so therfore my model should weigh roughly 4oz or less to be a capable stunter?

Is that correct?

If you require unlimited vertical, yes. If you do not require unlimited vertical then it can be slightly heavier than the thrust (say 10%-15%) and still have enough power for acrobatics.

All else being equal lighter performs better.

On the other hand I have looped by sailplane without power...

Phil

**RknRusty** Thu Feb 28, 2013 10:00 pm

For CL, I pull my 6oz to 9oz planes pretty fast with Tee Dees, .049 and .051.
I'd hate to see my 6oz Satan(I know it's overweight) try to lumber around with an .020. Forget it on the BFS at 7.2oz.

John Goddard Fri Mar 01, 2013 9:22 am

cribbs74 wrote:Wait, I think I get it now.

A 4.5x2.5 turning 16K puts out 4.2oz of thrust so therefore my model should weigh roughly 4oz or less to be a capable stunter?

Is that correct?

Is that prop size correct Ron or should it be 4.5x2 ie 020 Cox?

If so I think you may be underestimating your Peewee.
Very Happy

**Cribbs74** Fri Mar 01, 2013 9:36 am

John Goddard wrote:
cribbs74 wrote:Wait, I think I get it now.

A 4.5x2.5 turning 16K puts out 4.2oz of thrust so therefore my model should weigh roughly 4oz or less to be a capable stunter?

Is that correct?

Is that prop size correct Ron or should it be 4.5x2 ie 020 Cox?

If so I think you may be underestimating your Peewee.

Yes 2 pitch, my mistake. Static thrust still comes out to 4.23oz though.

I figured 16K is conservative however, better to expect less and get more. I will also more than likely cut down the 4.5 as I feel it is too much load for the Pee Wee. I went from 4.5 to the 3 bladed 3.125 on my Li'l Gem and it made a remarkable difference in the air. Sounded a heck of a lot happier too.

Ron

shell shock Fri Mar 01, 2013 9:42 am

i believe The Max for a .02 is 10oz. Now mind you, that depends on alot of factors as well. I know that a surestart can fly approximately 360g (cox internationals banana plane comes to that I believe) the problem with this question is every engine is different.

crankbndr Fri Mar 01, 2013 9:55 am

Not sure of the weight yet but the Mini Ringmaster has a 19" span and 77sq" area, it was made for a Pee Wee.

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