ronreiter

Hi everyone I am presently in the middle of building my first propjet kit (Patriot XL) and wanted to put a OS 91FX in it however when i was looking at buying one I came across the new replacement for the 91 FX which is the 120 AX. I was wondering if it would be a good choice in a patriot or is it overkill? My plane will be a bit heavier since it has fully sheeted wings and Pneumatic retracts. ANy comments welcome. I am not considering a Jett since its beyond my budjet.

Any comments welcome

Ron

bob27s

My Feedback: (19)

The 120AX is not an rpm engine...... porting, carb and design is for lower rpm, big props. Real nice engine. Not an appropriate choice for the Patriot.

You would be better of with the OS91FX. Prop the engine to turn 12,500 to 13,000 rpm. Basic 11x8 or 12x7 prop to start with.

And if you want top performance, add a jett-stream muffler to it. 11x9, 12x8 prop.

ronreiter

Thnaks for the input I really appreciate it
ROn

vertical grimmace

My Feedback: (1)

Also, prop clearance is an issue with this design. Going with the 120 would most likely force you to increase diameter which would give you issues.
A guy in my club was flying his this last Sunday with a .91 FX in it, and it looked like a very nice flying plane. That seemed like a good combo.

Good luck.

Crazy4Flight

My Feedback: (540)

Ron,

add a dub Jett Muffler to the 91FX...Reports and what I have seen at my club ar well worht the money .

better mid range power/torque and more top end RPM
these guy fly Tiger 60 arfs with OS.91FX & JETT muffler.
surprizing performance!

Julian537

My Feedback: (9)

What about an O.S 1.08 FSR ? ? will it be to heavy? is it an RPM motor?

Cyclic Hardover

My Feedback: (3)

Nope. Your best shot is a 90 and a tuned muffler or pipe.

SitNFly

My Feedback: (54)

I would add that this plane builds very nose-heavy. Mine has a Jett Sport 90 in it and I have nearly 7 ounces of lead in the tail to balance it. I wound up making a balsa tailcone and adding lead to that. Fun plane to fly because of the flaps and retracts, but really kind of porker when all is said and done.

Julian537

My Feedback: (9)

Sit n fly,

That sounds terible that you had to add that much lead to the tail to make it balance.
do you have a full pipe on it, or mini pipe?
What prop do you fly on this plane?

kmtranmd

My Feedback: (71)

Try to keep it light for better performance. Don't forget to put in flaps to help take off and landing if you fly off grass like me. Prop clearance was a problem for me, having to stick with apc 11x9 on OS91FX with Jettstream muffler, plenty fast with that set up. OS 120 is a torque engine, more for 3d planes, not for prop jets. Also, for retracts consider getting the Cermark F16 retracts for $96, instead of shelling out $245 from Spring Air.

buzzingb

My Feedback: (2)

All this is why the 40 size patriot is the best choice if one can be found.

SitNFly

My Feedback: (54)

Mine has the stock Jettstream muffler that comes with the engine. I waffle back and forth between an 11x9 and 11x8. I fly at 5000' ASL which kind of aggravates the issues with this plane. I had to shim the nosewheel down to get the plane's nose up and make takeoffs a little more manageable. Otherwise, it's a bit of a stinkbug and, even with flaps, takeoffs are.....abrupt .

Bigdaddy1963

Im also building a patriot xl with robart retracts and a brand new os 120 ax and thinking about a jett tuned muffler and a 14 x 12 apc. am i wasting my time?

SitNFly

My Feedback: (54)

14" prop won't fit.

smoknrv4

My Feedback: (11)

I flew mine with Robart retracts and a JETT 90L also and was using the Apc 11x8 mostly, and yes ground clearance is an issue with retracts, a 14" prop would definately not work.
I also had to add weight to the tail, even with a 6V pack as far back as possible, all in all I loved flying the plane though, lots of fun.

bob27s

My Feedback: (19)

OS120 is probably not the best choice here. Great engine, but that prop selection will be a real bear.

Play with it on the bench. With the jett-stream muffler, you want to prop the OS120 for around 10,000-10,500 ground peak rpm. Upwards to 11,500-12,000 is ok (engine is ok with it too).

You can squeeze out a 12" prop and clear the ground, so look more into a 12x12 or the 12x14 that APC has.

Again, you will need to properly characterize the engine on the test bench - so you know what to expect in the aircraft.

And, as noted, you should expect to add a bunch of weight in the tail end. Plan ahead.

Bob

airraptor

My Feedback: (66)

get a 13x13 for the os 120 with a pipe i get 11,900-12,100 with it in my H9 miss america. also spins a 15x8 at 11,700

CARS II

My Feedback: (7)

I'm getting 11,600 out my ST 90 with a 12/8 APC prop and 15% nitro, mine came out at 9.5 lbs and I'm using a 5 cell batt. and only had to add 2 oz in the tail cone that I made out of ply and balsa, maiden it today with two flights after the rain, no aileron trim needed but since I got a 16 oz fuel tank it feels nose heavy, may go back to the original 12 oz. the TO run was some what insteresting it wound't rotate with the elevator low rate because it seats nose down, landing is sooo slooow and with flaps even more.