Thrust needs
 

What is the formula for finding the thrust needs for a 21 lb. 1/4 scale super cub.

Leroy

A 120 to180 4 stroke will fly it great,, that's all the formula ya need ;)








3 days with no replies,, dang this site is all but buried,, sad

Hi!
20cc four-stroke and a 16x6 prop! All you need to know!

How long is the runway? Are there any trees to clear?

Have you every seen an airport? They try to place them so that these are not issues.

The formula would alter with needs. So you have a great field, you get away with a little less. You are at 4000 ft, you need a little more.

Are we talking 1/3 scale here?
What are your flying sites requirements?

Do you really want the formula? Drag vs power = thrust / minimum flying speed.

Whenever I get a question like this, I point out that a 1 million pound 747 flies mach 0.85 with 1/4 million pounds of thrust. In your case 21/4 = 5.25 pounds of thrust to fly mach 0.85 at 35,000 feet (yea right).

So what is your real question? What motor to choose?

My Sig 1/4 scale Cub, comes in at 17 lbs. I fly it hard sometimes, but, throttle back and fly scale too. I have a ST 3250 in the nose swinging a 18 x 6 beechwood prop at almost 10000 rpm. It will not sustain a hover, but, comes close.

I always recommend plenty of power, just be careful of when and how you use it. I would go with a 35cc or larger.

Just my HO.

Leroy,

I am going to add another dimension to consider. What weight to you need in the nose to obtain a good cg? My 1/4 scale L4 (Nosen) was a beast at 22#, but a very fun friendly flyer. I had a Quadra 42 in the nose that gave a surplus of power, but also provided needed weight up front. In full scale the Super Cub carries a lot more power than the J3, so something that will swing an 18x10 prop smartly would be a good choice (though I will bet you will need lead in the nose for balance). In my book at least.

Have fun with it!

Bedford