Bigdaddy1963

I have a Patriot XL with retracts and using a O.S. 95 AX with the stock power box muffler.I'm on a budget so need to use what I have.I'm thinking about bench testing a 14 x 8 for breakin,then a 13 x 8 followed by a 12 x 12.5 checking rpm. each time.The motor runs between 2000 and 16000 with peak HP. at 15000.Can you guy's help me in choosing the proper propeller with what I have without hurting the engine?
Thank You
Bob

SitNFly

My Feedback: (54)

You probably won't have clearance for a 14" prop; even a 13" is pushing it. I would think a 12" with as much pitch as you can stand will be what you wind up with.

lfinney

My Feedback: (44)

it would be much better if you used a smaller prop to run the engine in during break in, such as a 11x9 or a 11x8 and use a tach to keep rpms aound 14-15k during first runs, it allows you to keep it sloppy rich and be at the rpm you are targeting for flight, watch the muffler during these runs...as the higher rpms tend to loosen them up creating nasty black splooge, which is a distraction, its the muffler making the ugly stuff usually.[:-]

MJD

My Feedback: (1)

Ditto what LF said - big propellors are of no value for break-in, the opposite is the way to go - a light load it can spin up to operating rpm at a rich 2C setting. Big propellors increase mechanical loads and operating temperatures, not what a 2-stroke wants when new. A typical option is to reduce pitch 1-2", or go down about 10% in diameter from the planned flight prop - so that at a rich 2C it's running at operating rpm. Have faith, the RPM is not your enemy during break-in, but heat and friction are. And the dreaded black spooge of course.

MJD

Bigdaddy1963

I have made the rear legs shorter with 2.25" tires and am using a 2" tire on the front so it fits all the way up in wheel well. This leaves Me about 11/16"clearance from prop to groundusing a 14",But I do agree that I should use a smaller prop and more pitch to get maximum speed
Bob.

combatpigg

My Feedback: (3)

It's nice to have targets and goals. The Thrust HP program is handy so you can plug realistic numbers in to see what speed to expect. I don't know anything about this engine, but I plugged in a 12x8 prop at 14,000 rpm. The speed was just over 100 mph and it would require 3.25 HP. Now to see if this is realistic I could go to the RCU product reviews to find out what HP this engine is rated at.

Bigdaddy1963

2.9HP. @15000
Where can I find this program at?
Thank You
Bob

combatpigg

My Feedback: (3)

The prop that meets the 2.9HP at 15,000 criteria is a 12x6.....not exactly a hot sounding prop for speed but this gives you an idea of what the engine is limited to for load.
A 12x6 would be OK for getting the plane dialed in for takeoffs and landings.
A 11x8 would get you up over 100mph, be somewhat harder to land.
A 11x9 after the engine is well broken in might make the plane faster, but at this point you would need measuring equipment or an "enemy" plane flying to compare to.

Bigdaddy1963

Thank You very much for your help with this.
Bob

Mike Connor

My Feedback: (5)

ThrustHP? It has it limitations but good for comparison.
http://www.hoppenbrouwer-home.nl/ika...rusthpv20d.htm

Bigdaddy1963

Thank You Mike
Bob

Michael Beckman

My Feedback: (1)

Of course you could always follow your friends advise and get a JETT 90!

combatpigg

My Feedback: (3)

What RPM will a JETT 90 turn a 11x8?

daven

My Feedback: (1)

I know were the extreme speed group, but a 12x6 on a .95 2 stroke??

That's a bit small for the AX motors which are designed for max power at lower RPM numbers.

It may be ok for breakin, but don't think RPM is the only way to go fast. I'm betting you could put a pretty big load on that motor and get speed just as easily as letting it rip with a small prop.

smoknrv4

My Feedback: (11)

If I remember correctly CP, my Jett 90L turned about 15500-16000 w/ an 11x8, although its been a year and a half or so since I've run it, I love that engine.

lfinney

My Feedback: (44)

i know that os lists their engines as making more power down low, but they havent really reduced carb size, nor seriously reduced exhaust timing, most of the testing results of ax engines dont seem to be much different from the fx series, i think maybe they have dropped the compression slightly and maybe tiny bit of crank timing, but i think the newer powerbox mufflers have more to do with being more torque biased, plus being quieter.
using a 12 or 11 inch prop isnt a big deal , this is about speed, not towing power...

combatpigg

My Feedback: (3)

Is this the same plane as Speedboys? IIRC he had it going pretty good with a 10 inch prop.

Mike Connor

My Feedback: (5)

I believe the XL is a size bigger then Speedboy's

combatpigg

My Feedback: (3)

Outside of a few exceptions shown here at RCU, like Robs' Komet and the .90 powered delta shown recently, I've never seen anything .90 powered in this area that you could say was fast. Most of the fields have 300 feet or less of runway, with all sorts of evil stuff in the background to contend with. It would add a lot of variety to see big speed projects around here but they're as rare as hens' teeth.

freakingfast

My Feedback: (3)

First off, I don’t think you’ll get anywhere near the 2.9 hp advertised by OS, even on a tuned pipe. In fact, Id bet it won’t be very happy at 15K either, especially considering it’s an AX series, that is if it lives up to the recent pattern of lowering its peak hp speed compared similar sized former OS models. By no means does this mean it’s an inferior engine, you just need to realize where it makes its power.

The only engines that I have found to live up to OS’s horsepower rating are the Heli and DF engines.

Real world I’d expect the best power around 11000 rpm with 1.8hp on stock muffler and on tuned pipe 12500 rpm with 2.3 hp from the data that I used to extrapolate the numbers. These Rpm's will leave room to unload into if everything is matched right.
Incidentally, it’s very close in performance to the older 91FX, just think lower RPM for the AX (more pitch).

The props I’d try for the Patriot XL are the APC pattern 12X10, 12X11, 12X12 pattern and Master Airscrew 12X8 S-2 series.

Consider shutting off the engine to land.

The best program I’ve found to help is the “Prop power calculator”
http://www.mvvs.nl/ Left column, click on “utilities”.

I find it far more accurate than “Thrusthp”

Some links that may help get you an idea where the power is:

http://www.rcuniverse.com/forum/m_87...mpage_4/tm.htm

http://www.rcuniverse.com/forum/m_8169105/tm.htm



Hope this helps Bob.

Bigdaddy1963

Ithank all of You for Your input on this subject.I will let You know what I ended up doing and how it fly's.
Bob

Mike Connor

My Feedback: (5)

First glance looks good. At least it considers pitch when calculating thrust.

nexxa

I don`t remember the exact RPM I was getting with my OS.91FX on a Ultratrust muffler, but it was between 13 000 and 13 500 on ground with a APC 12X8 and APC 11X10. It was unloading a lot in the air.
My sundowner 50 was doing well over 100 mph with this setup, maybe 110/115 mph. (no retract and 8.5 pound)

The OS 95AX as the same spec, it is just a little bigger... A good starting point without tune pipe or tune muffler is 12x7 - 12x8 or 11x8 to 11x10.

After break-in process, a small tune muffler like an Ultratrust or a Jett muffler (± 75-90$) will give a real boost, and the engine will finaly came alive.
(fit it on your next budget, next year!)

Regards,
Seb

Bigdaddy1963

Thanks Seb
Bob