cappaj1

My Feedback: (1)

I just checked my order with Tower and I'm using a 11x6 [link=http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXZ971&P=ML]prop[/link] with a OS Max 46AX engine and my instructor said I should change to a different size (I can't remember if he said larger or smaller - we couldn't see the size I was using as it's stamped on the hub underneath the spinner) as at full throttle the rpm's are too high.

OS recommends the following prop sizes - 10.5x6, 11x6-8, 12x6-7
What size would be a good one to switch to in order to bring my rpm's at full throttle down a little?

Thanks in advance.

MinnFlyer

My Feedback: (4)

11x7

bingo field

I "Make haste slowly!" (Only 1 change at a time, and test it for several flights before making a judgement).

cappaj1

My Feedback: (1)

Will 11x7 make the airplane go faster or slower than 11x6, taking into consideration the rpm's should drop since you are suggesting it. Just wondering.

jetmech05

Are you using a tach to get RPM..or your instructors ear?...You are in the prop range recommended by the manufacturer..the RPM range is 2000 to 17000..if your in there, then leave it alone...unless the airplane is giving you problems on approach with too much speed..or floating...then a bigger prop will help slow down the airplane....
I'd check idle trim to make sure the RPM's are low enough...before I'd go with an 11x7 or 11x8....APC
Next you have to consider ground clearence..depends on whether you're flying a trike or a tail dragger
Good Flyin

RCVFR

My Feedback: (7)

If you are using the OS 46AX on a typical trainer, it doesn't make much sense to fly at full throttle, anyway. It's way too much power for training purposes. Most rationale for that engine on a trainer is so that you will have it for the "next" plane, whatever that may be. In short, learn throttle control. That engine should easily take off most trainers at 1/2 throttle, and come down from that when you are flying. Or just bolt on a 9X6 and have at it.

Jetdesign

My Feedback: (8)

Mine was running at 13000 rpm with an 11x5 and ran fine, though was a bit loud. I switched to a 12x5 and get 11,000 rpm, and is a bit quieter. If you like the way the plane flies with the 11x6 then stick with it. OS has a new muffler system and maybe your instructor is not used to hearing the sound of the AX. Your prop is well within suggested range.

Now if you're having spped or pull issues, then I would suggest changing props. But again, if the plane flies fine, keep the prop. I was told by my instructor to change props after I was able to do touch-and-go's with no problem, which showed I had decent command of throttle control.

Charlie P.

There's a 20 year gap in my model flying but that is the first time I've ever heard of anyone having too many RPM with an engine . . . ever.

That's why it's called a throttle and they don't just use an on/off switch. ;-)

If you're beating 17 grand with an 11 x 6 I'd say the 11 x 7 is a good next step. That will make you faster but less torquie all else being equal vs. the 11 x 6 choice.

Personally, I'd lower the top end with a end-point adjustment from the servo. Cheaper.

j.duncker

My Feedback: (2)

11x6 is fine on that engine.

jetmech05

Jim: while I agree with you that the 46 AX is plenty of engine on a trainer...I always teach full power takeoffs and go arounds....better to have the power and not need it, than to need the power and not have it.....What I have my students do is go full power then once a positive rate of climb has been established with 10 or 15 ft altitude throttle down before the first turn...on go arounds basically the same..as sonn as you have a climb established throttle down...
I have seen idle trim set so high that the airplane just floated...
Good Flyin

combatpigg

My Feedback: (3)

The 11x6 will make the planes' speed easier to manage than if using a 11x8, easier to needle, less chance of running too hot, provide better vertical, better throttle response, etc. Just a better all around sport prop. A 12x5 might pull the plane around better, but would be easier to damage on the runway. I've got a Rossi .45 with a tuned exhaust and it won't turn any 11x6 prop anywhere close to the point of failure......IIRC 15,500 rpm is about all that sucker will deliver.

jaka

Hi!
I haven't run an OS .46AX but suspect that it is as powerful as the New ASP .40/ Kyosho GX.40 engines, and those swing a 12x6 with ease.Could not believe it first when I heard it but when I saw it myself the large 12x6 APC or RAM is the prop to use in a high winged trainer using 10-15% nitro. 11x6 is too small prop at least for the above engines when used in a high winged trainer.
10x6 or 10x7 RAM or APC is the prop to use if you want more speed in Q-500 type airplane with the above engines. Think the same applies to the OS .46 AX.

Mikecam

cappa, I use a 11x5 on my 46 on my nexstar. Tried a 11x6 and a 12x6 and I'm set with the 11x5. Shorter take off's and power to get out of trouble. Yes it will rev more but I don't do full power dives with it. 13300 rpm tached peak. The 12x6 runs 11800 rpm's and the plane just feels sluggish. With my rubber wheels it is closer to 7 pounds so take the weight of your plane and the thickness of your trainer wings into account.

n19htmare

My Feedback: (1)

11x6 is perfect on that engine, well atleast on my 4*40

hurk1

I have two 46ax engines. They both have 12x4 props and both are in the low 12000 for RPM's. The 12x4 is quiet, better torque ( pull or the aircraft) and you can slow the plane down for landings faster. Yeah you don't get the fast blistering air speed that you would get with the 11x6 but I like the torque and the ability to slow the plane down for landings much better.