still4given

I'm planning to build an extreme cub for our warbird racing. Normally guys stick a Nelson 40 in it. I want to use my SJ50. The original used a foam core wing with a ReVlution airfoil reduced to an 8" cord and 48" span. I will need 475 inches to be legal with the SJ50. Is there a faster airfoil that can get me to 140 MPH?

bob27s

My Feedback: (19)

The last version wing on the Revolution was pretty darn good. Mike DelPonte always kept on top of things. I am not sure you would want to change from that.

But consider this .... how/why are you shortening the chord?

If you just take the airfoil design (stock set of Q-500 cores), and trim the TE or LE to change the chord..... that messes up the entire flow pattern.

If its the same airfoil, just scaled to 8" ..... no problem.

On that plane, the airfoil change beyond that is not going to gain you much speed.

Bob

still4given

Hi Bob,

Sorry, I should have been more clear. Yes the airfoil was scaled down to 8" because with a 40 two stroke you only need 400 square inches to be legal in our warbird racing. An 8" cord and 48" span + tips gives just over 400. I need 475 sq inches so I thought to scale it up to a 9" cord. I was just curious if there was a better airfoil now. Do you think I can get 140 MPH with this cub and my SJ50 with the gold pipe?

Thanks, Terry

bob27s

My Feedback: (19)

There are a few airfoils out there folks have been playing with. Some work better for level flight speed, some work better for turning and exit speed. A few are very hard to build using foam/wood construction. The one you have now is probably the best you can do for this application.

From the look if the airplane, should be possible to get it up near 140. You would probably want to run the SS muffler, 8.75x8W prop would be a good place to start.

still4given

Hi Bob,

I don't actually have the airfoil yet. A guy who has one, sent me the plans and instructions for building it. It didn't include the airfoil. The instructions say,

"The original models used an airfoil from a Revlution Q500 but an airfoil could be made using a a more modern airfoil section such as that used on the Viper (Selig S8064), Vortex (NACA 66X012) of perhaps one of the MH series for Q500's (MH 18, MH 18A, etc) that can be built using traditional foam cores with basa sheeting methods."

This is why I'm asking. I will have to have a core made so I might as well get the best I can while I'm at it.
I new you were pretty knowledgeable about racing so I hoped you might know the best airfoils in use today.


Presently, I have the red muffler and the gold muffler. Is the SS the black muffler? If I have to buy anothere muffler, I might be better off watching ebay for quickie motor and just go that route. I liked the idea of having a more user friendly engine but to be competitive in the gold class I will need to be up around 140MPH. I guess one of the advantages of using the quickie engines is I could stay with 400 square inches.

Thanks again, Terry

still4given

Hi Bob,

I built the cub with the smaller wing and am flying it with a Nelson Q500 engine. Goes like stink! I still want to build one for my SJ50. I have the red pipe, gold pipe and black pipe. Which would you suggest for this application and what prop?

Thanks, Terry

bob27s

My Feedback: (19)

Hi Terry...

sorry for the delay responding.....

I would probably go with a standard 9x7 prop and the gold muffler. Proven combination, and if the plane is quick, it will unload quite well.

Bob

still4given

Thanks for getting back to me. I'll give that a try. I lost the Nelson powered cub last Saturday due to a collapsed elevator pushrod. I'm going to try to build the JS0 cub this week. Is the SJ50 most comfortable RPM wise with the Gold muffler? What Ground RPM should I bee looking for?

Thanks again, Terry

bob27s

My Feedback: (19)

Runs fine .... the gold muffler (aka SS muffler) runs "over" 17,500 peak. 18K is ideal target.

On the SS40 sport racing engines, with an 8.5x7.25 prop we set that engine at 20,000 The SJ50 sleeve is timed about the same.

still4given

So can the SJ50 run 20,000 with the black muffler? The cub flew very well with the Nelson and an 8.8x8.75 at about 19,000 on the ground. Going to need something similar to get to breakout.

Thanks, Terry

bob27s

My Feedback: (19)

Yes, it can, but you will have to back off on the prop size (like that 8.5x7 size). But you may find it works better with the gold muffler. Gets on the pipe and just stays there - does not need to deep stage in flight like the black one does. Give both a try... just keep the prop light.

Chances are your little cub will respond well. Be smooth

still4given

Thanks Bob,

I'll leave the Gold pipe on it. I've got a few different props so I'll just try a few and see where it gets me. This cub will be slightly larger since I need the extra wing area to run a 50. These fly really well and it's easy to be smooth with them. They have no bad habits once you get them off the ground.

I'll come back and post wnce I've flown it. Might even send a pic to Dub in case he wants to put it in the gallery.

Blessings, Terry