Pitts Special Challenger 40 Engine choice  
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All Forums >> RC Airplanes >> ARF or RTF >> NitroModels Support >> Pitts Special Challenger 40 Engine choice
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Pitts Special Challenger 40 Engine choice - 3/7/2007 2:27:29 PM   
crebulus


 

Posts: 61
Joined: 1/11/2006
From: Montgomery, TX, USA
Status: offline 		Should receive my pitts this friday, excited to get started on it. Only thing that is bothering me is the engine choice. I've narrowed it down to three. I'm sure yall have plenty of input to give on this. What I want is to be able to fly without much limitation. My three choices are:

1: OS 55ax
2: OS 46ax
3: Magnum XL70

There are a couple of things holding me back from the magnum. Mounting inverted, and having to use a different fuel. All my planes now use 15% cool power all synthetic. The magnum says you cant use all synthetic. I don't know if that's just a recommendation though, because I've been using it in a saito 82 for a long time now.


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RE: Pitts Special Challenger 40 Engine choice - 3/7/2007 6:17:58 PM   
opjose



Posts: 5832
Joined: 11/26/2005
From: Poolesville, MD, USA
Status: offline 		The Pitts is really a .30 sized plane.

The .40-.50 recommendation for it, is for 4 strokes, not 2 strokes. Check the last page in the manual where this is spelled out.

That said I'm putting a TH .46 in mine which I KNOW will vastly overpower it.

I would not go as far as the 55ax though on the Pitts... even the .46 will give it unlimited vertical.

The XL70 is less powerful than the 46ax in terms of bHP, so it may do, though on a plane this size it may be a bit more problematic in terms of mounting.

Inverted is typically nothing more than a tuning issue. If your engine doesn't run well inverted, then it is not properly tuned or it has some other problem that would need to be corrected anyway... after all you WILL be flying the plane inverted at some time right?

As far as the Synth fuel, I run 10% Cool power on a Magnum XL 1.80 RFS all the time w/o problems.

I did break the engine in with a mix of 10% Cool power and 10% Omega in a 50/50 ratio, but once it settled down I switched back to only using synth.



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RE: Pitts Special Challenger 40 Engine choice - 3/7/2007 7:18:33 PM   
crebulus


 

Posts: 61
Joined: 1/11/2006
From: Montgomery, TX, USA
Status: offline 		I love the idea of just using the 46, that saves me some cash. If a 46 will give it almost unlimited vertical, then that's all I need. I even have an old italian ST .40 laying around. Wonder what that would do for it?

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RE: Pitts Special Challenger 40 Engine choice - 3/7/2007 7:24:49 PM   
opjose



Posts: 5832
Joined: 11/26/2005
From: Poolesville, MD, USA
Status: offline 		The ST .40 should also do fine assuming you could get at the needle valve with the in cowl install.


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RE: Pitts Special Challenger 40 Engine choice - 3/7/2007 7:52:48 PM   
crebulus


 

Posts: 61
Joined: 1/11/2006
From: Montgomery, TX, USA
Status: offline 		Yes, that needle would get in the way and be pain. Think I'll go with the 46ax.

Thanks for the info opjose. It's much appreciated.

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RE: Pitts Special Challenger 40 Engine choice - 3/28/2007 6:09:17 AM   
Tailspincharlie



Posts: 57
Joined: 1/11/2003
From: Bakersfield, CA, USA
Status: offline 		I have a Super tiger 40 in mine and it performs great. No problem cutting out the cowl around the engine. Needle was no problem either. It worked for me.
Happy flying, Tailspincharlie

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RE: Pitts Special Challenger 40 Engine choice - 3/28/2007 4:01:49 PM   
opjose



Posts: 5832
Joined: 11/26/2005
From: Poolesville, MD, USA
Status: offline 		There's TONS of room in the cowl, so the Supertiger fits just fine.

The minor problem is with the way the Supertiger carb works.

The pin that juts out of the needle valve is the actual needle itself.

If you side mount the ST the needle may stick out the top of the cowl, and depending upon your configuration this may make getting the cowl on and off difficult or may require a larger or unusual cutout.

Inverted mounting works but then you'll need to rig up something for adjusting the needle, or need to cut a groove in the needle to be able to turn if via a cowl hole.



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RE: Pitts Special Challenger 40 Engine choice - 3/28/2007 4:05:46 PM   
crebulus


 

Posts: 61
Joined: 1/11/2006
From: Montgomery, TX, USA
Status: offline 		I've already built it with the 46ax. The thing almost has too much power. I love it so far. Haven't gotten everything dialed in just right on the control throws(little squirrly in the air), but I'll get there this weekend. Great little plane

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RE: Pitts Special Challenger 40 Engine choice - 3/28/2007 5:21:23 PM   
opjose



Posts: 5832
Joined: 11/26/2005
From: Poolesville, MD, USA
Status: offline 		Yeah I find you need a fair amount of Expo on everything except the rudder.

I keep the rudder Expo low so that I don't oversteer during takeoffs and landings.

To keep it from being too much of a handful my low rates are around 40% of max.

At high rates I'm afraid of breaking a wing strut as this thing will snap roll violently due to the short tail.


I'm tempted to try a 13x4 prop on it to slow it down a bit...

On the other hand, chop the throttle and it slows down quickly...



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RE: Pitts Special Challenger 40 Engine choice - 3/28/2007 8:34:29 PM   
crebulus


 

Posts: 61
Joined: 1/11/2006
From: Montgomery, TX, USA
Status: offline 		I am going to do the same thing with my low rates. Good to hear it's worked for you. I was thinking of using a 12.25 x 3.75 to slow it down. I used this successfully on other planes.

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