60 or 90 LX?  
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All Forums >> Glow Engines, Gas Engines, Fuel & Mfg Support Forums >> Engine Manufacturers Direct Support Forum >> Jett Engineering Support >> 60 or 90 LX?
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60 or 90 LX? - 2/17/2007 2:04:43 AM   
fred685


 

Posts: 97
Joined: 1/25/2002
From: salem, VA, USA
Status: offline 		I'm starting a Direct Connection F-20. It's a 40 size, but if I shorten the nose, the 90LX will fit nicely. My question is, how much faster do you think the airplane will be with the 90 over the 60? I'm sure it will be faster, but will it be worth the extra weight? I'm sure you can't give me an exact speed comparison, but your best guess would be helpful.

Thanks,
Fred
       Post #: 1

RE: 60 or 90 LX? - 2/17/2007 9:58:03 PM   
bob27s



Posts: 4637
Joined: 4/9/2002
From: Cleveland, OH, USA
Status: offline
quote:

ORIGINAL: fred685

I'm starting a Direct Connection F-20. It's a 40 size, but if I shorten the nose, the 90LX will fit nicely. My question is, how much faster do you think the airplane will be with the 90 over the 60? I'm sure it will be faster, but will it be worth the extra weight? I'm sure you can't give me an exact speed comparison, but your best guess would be helpful.

Thanks,
Fred


Hi Fred,
Thanks for writing....

Ive never attempted to install anything larger than a "40" size engine on the Juno (dc) F-20. As it is stock, it is difficult to get the balance right with a .46 up front.

I think you real limiting factor here is how much fuel you can carry on board. The 90LX is a thursty animal. With either engine, using a bubble-free fuel system is going to be a requirement in this plane - very tight quarters, not a lot of room available, and no way to properly isolate a decent size fuel tank to avoid foam/bubbles. The bubble tanks will give you more effective fuel capacity, and no worry of foam/air and a burnt up engine.

A well built, well trimmed DC F-20, gear up, level flight, SJ-50 engine up front with a 9x8 prop was once well documented at 135 mph in level flight. My guess is you can do a bit better than that with the 60LX. Probably a bit more than that with the 90.

As for actually using the 90LX ...... your guess is as good as mine as for an actual speed. The engine will not mind the installation. A shorter nose will help with the CG a bit .... and anything you can do to get the wing loading back down will help. Install a stock APC 10x10 on it, and be sure to bring a clean pair of shorts in the field box.

The weight will not really effect the speed, but in the end, you want an enjoyable and controllable aircraft - not a brick.

Bob


_____________________________

Bob Brassell
Jett Engineering - Engine Mfg Support Forum Host

(in reply to fred685)
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All Forums >> Glow Engines, Gas Engines, Fuel & Mfg Support Forums >> Engine Manufacturers Direct Support Forum >> Jett Engineering Support >> 60 or 90 LX?
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