wazzbat

Hi guys

Just getting started in this hobby and am putting together an ARF trainer (Seagull - Boomerang 40) and am in the process of building a Sig Kadet LT40 kit (which is taking forever due to lack of spare time to work on it). I went to the LHS today to buy an engine and a few bits and pieces for the Boomerang and the guy talked me into buying the 55ax instead of the 46ax which I was thinking of doing anyway. He picked up an APC 13x6 prop from the shelf and said that that's the one I want. But just having a quick look around the forums, it looks as though it could be too big for the 55ax? Will it be OK or should I swap it for something else?

Also any tips for setting/running in the 55ax?

Cheers

Switch_639

the 55ax is an awesome little engine... it could pull my 46size GP Revolver up to 160km/h (measured with GPS) in a declined dive... I did use a 11x8 prop though for revs... but a 13x6 would be a great sport prop... will have no troubles pulling your plane what so ever...

ameyam

Recommended prop as per manual is 12x8 & 13x6 so the APC 13x6 would be good. But you will need to fly it to learn if its the prop you want. Every airplane and every pilot like a different prop

Ameyam

Augie11

I've got 13x6's on my OS .55AX's. Turns them about 9700rpm. 12x6 gives a few more rpm (10,300).

Bax

My Feedback: (11)

You can also go as small as a 10 x 8 to get more power from the engine. O.S. suggests larger propellers to cut down on noise. However, you do lose out on overall power. For 3-D operation, something like the APC 12.25X3.75 Sport Prop works out very nicely. The engine will run very well if you prop it so that you're turning in the mid-12,000's when on the ground at full throttle and leaned rich of peak RPM. This, though, will be quite a bit noisier than with the larger props turning much lower RPM!

jimmyjames213

My Feedback: (2)

i use 11x5-6, 10x7-8, 12.25x3.75 and 12x4, honestly the 11x6/10x8 are the best props for sport engines
some use 13x4 but its alittle big unless your engine is totally broken in (3-4 gallons through it)
13x6 is waaaayyyyy to big thats a prop for .75 engines.....unless your in japan and have big noise regulations...it kills the hp your engine puts out

RCKen

My Feedback: (9)

Directly from OS specs on this engine:

You can never go wrong staying within what the manufacturer recommends.

Ken

HighPlains

My Feedback: (1)

This is no miracle engine, it has a very ordinary bore/stroke ratio. When you over prop an engine you end up with much less power and a needle range that becomes overly critical and much more difficult to adjust to a good setting that it will hold.

Airplanes fly on power, the top speed is directly proportional to the cube root of the available power. Matching the prop load to the engine's horsepower curve is how you achieve this. Since this engine makes it maximum power at 16,000, you would want to prop it to turn in the 12K range, with the knowledge that it will unload one to two thousand in the air in level flight. It will unload a bit more when in a dive, so a 12k ground rpm keeps you well below the maximum rpm.

The 55 will be much happier and easier to operate with a 12-6 or 12-5 with your trainers.

As far as OS and their recommendation - it's either to hold down noise for some markets that they serve or pure marketing hype.

As far as tips on running, this is a easy to operate, smooth running engine with a great idle and transition.

ameyam

I tried props ranging from a 11x9 (yes my LHS had one) to a 14x4 (from my 75ax) on this engine. My observation is that a 11x9 is too speedy and a 14x4 too large. I would suggest 11x8 / 12x8 for sports and 13x4 for 3D. I currently have a 13x6 on my Reactor but that is just becuase I want to have a absolutely balanced prop and the MAS 13X6 S2 I have is just that

Ameyam

Ed_Moorman

My Feedback: (1)

I have 2 of them and I like a 12-5 for sport planes like Sticks and low wing sport planes. I always set mine to leave a little smoke trail. Great engines.

wazzbat

Thanks guys. 

A few different views there.  I think I might get myself a couple of smaller sized props and see what the guys at the field think when I get down there?  Might try a 12x6 or 12x7?  Would it be better to run it in with a 12x7 over a 13x6 or it wouldn't matter?

wazzbat

Just looking on the Prop Chart Sticky and it shows I should be looking at anything between 11x4 to 12x6?  Do you think OS have overstated the correct prop size selections?  As Ken stated - they recommend 12x7-8, 13x6-7.

KWJ48

13x6 is not too big for the 55, but my personal preference is a xoar 13x4.

HighPlains

My Feedback: (1)

Three guys with a total experience of 161 years suggest 12-5 or 12-6 or keeping the rpm range around 12,000 ground rpm. Never mind.

Gray Beard

My Feedback: (-1)

The prop chart is great but it's just going to give you an idea of where you can start your testing. You still must keep the engine in it's working RPM range then it's a pilots choice. Ken posted up the OS sheet and Bill Baxter gave you more ideas. You will find over time you will have a very big box of props, Just look at John Buckners shop wall!! You will never walk into any hobby shop with as many props as John has.

JimmyZep

My LHS recomended 13x4 so thats what Im starting with.

Jimmy

jaka

Hi!
Problem is that the engine is too powerful for your plane! (Don't listen to those saying that throttle down is an option ...it's not!)
A .40 engine would have been much better. Better in this case means more suitable for newbi in a high winged trainer!

hllywdb

I've been flying mine for a few years now. I have great performance with an 11-7 on clean pattern style planes. For a sport plane, they have given you great advise on a 12-5 or 12-6. The engine will make plenty of power, run nice and cool, and give you nice, controlable power on your plane. The larger props are too big for that motor and will make far less power and needlessly over work the motor.

ameyam

You may want to do the run-in with the manual recommended prop and then experiment. I would

Ameyam

wazzbat

Thanks for your advice guys.  Sounds like a 12x6 might be the best place to start.  I hope the 55ax isn't too powerfull for my plane jaka?  If it is a bit too powerfull, could I not just set the servo to open the throttle a maximum of, for example, 3/4 when the throttle stick is at it's maximum?

mike109

G'day

I'm with Jaka. A friend and I were flying his Boomerang 40 yesterday with an AX 46 in it. With that engine it is on the overpowered side but not grossly so. With the 12 x 6 prop on a 55 I suspect you may find the plane hard to land AND you will have to watch the torque on take off too.

I have overpowered several trainers "for fun" and landing has always been a problem. The larger prop will still be producing quite a deal of thrust even at idle and with a new engine which is not yet idling perfectly, the thrust from a slightly high idle can keep a plane flying when you really want it to land.

The simple solution is to make sure you can cut the engine reliably in flight so that in the event that it just does not want to land, you can cut the power and glide in.

The other problem can be torque. Go easy on the throttle when taking off and things should be OK. Slam it open and you may find you have rather a hand full of plane.