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Engine choice - 11/22/2007 12:01:23 AM   
MJD


 

Posts: 1509
Joined: 5/27/2003
From: Orangeville, ON, CANADA
Status: offline 		Hi Bob,

Supposin' I was to find a way (plans are afoot) to afford a pair of small block .90's or 1.00's for the Duelist 2/60 I just scored.

The specs for the .90 vs the .90 LX say, on a 12-6, 14,500 and 14,500+ respectively. I am not sure I see the difference there. Does the .90LX generate more horsepower than the .90L if you let it spin up higher?

Or, for an extra 10 bucks a motor, would the 1.00LX be a "better" choice?

One fellow told me his 2/60 came out to 14 pounds. It has an 84" wing span; as far as sport/pattern type birds it's a monster, at least by my standards. But with a pair of either of these it ought to plain haul butt.

Your thoughts on engine choice and setup of same? To me, a pair of the 1.00LX's on what, 11-9's or 10's would likely do the job. As to the referenced 12-8's, 14.5K on 8" pitch is "only" 109 mph. More would be nice.

Thx,

MJD
       Post #: 1

RE: Engine choice - 11/22/2007 2:43:05 PM   
RocketRob



Posts: 538
Joined: 12/27/2002
From: San Francisco, CA, USA
Status: offline 		Sounds like a nice project!
I would think the LX spinning the somewhat smaller diameter prop (faster)would be more forgiving of single engine adverse yaw?

(in reply to MJD)
       Post #: 2

RE: Engine choice - 11/23/2007 2:15:51 PM   
MJD


 

Posts: 1509
Joined: 5/27/2003
From: Orangeville, ON, CANADA
Status: offline
quote:

ORIGINAL: RocketRob

Sounds like a nice project!
I would think the LX spinning the somewhat smaller diameter prop (faster)would be more forgiving of single engine adverse yaw?



Possibly if/as the torque is reduced. But I understand the aircraft is not much of a problem with engine out. So I'd like to see enough disc area to suit the airframe - of course experimentation is in order.

Yeah, this would be a major project by my frame of reference, but why not? (Well, except for the cost of engines.. I just realized I have a few RRSP's from my past employer's plan, and thought I might be irresponsible and cash some in for toys. Not exactly what they are meant for but temptation is a wicked thing, as I am sure anyone in this hobby knows all too well )

MJD

(in reply to RocketRob)
       Post #: 3

RE: Engine choice - 11/27/2007 4:51:05 PM   
bob27s



Posts: 4637
Joined: 4/9/2002
From: Cleveland, OH, USA
Status: offline 		The 90LX engines trade off some torque for rpm. And yes, it does produce more power at the higher rpm. They also tend to be a tiny bit less user friendly - narrower prop selection - have to get the fuel system right - but not too bad.

They are timed to run about 500-1000 rpm higher than the regular 90L engine. And as such they are propped a bit lighter.

The 90LX prefers 11x7, 11x8 props - get the engine up over 15,000 rpm. It does run well with 11x9 and 12x6 props as well - but in most applications we have found the lighter props turning faster work best for balanced performance.

Don't go by the pitch number only for speed. First off, th engine will unload a bunch in the air. Second, the prop actually does work.

We know from a few sources, aircraft like the Alley Cat or Toni with 90LX power and 11x8 props fly well over 120mph. Same goes for the big Patriot XL - 11x8 seems to works best, and almost all reports are well over 120mph.

http://www.jettengineering.com/hall/je-patxl.html

Considering the twin dualist is not that much bigger than the PatXL, and would have twice the power, figure the speed will increase a bit. Will obviously not double - also has twice the prop disk drag - but you would definately have a very quick aircraft.

Something else to possibly consider.....
There was someone not long ago who powered a Duals 2x40 with FIRE-60LX engines.
There was a TON of power to be had there.
Firgure set up the engines with long pipes - 10x6 or 10x7 props - 18K+ rpm
Figure you will save a bunch of weight on the aircraft - easier to fit 12oz tanks....
And with the larger nacells you might very neetly tuck away the pipes into semi-open tunnels?

Bob


_____________________________

Bob Brassell
Jett Engineering - Engine Mfg Support Forum Host

(in reply to MJD)
       Post #: 4

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