phildo

Giday Folks,

I am currently building a Top Flight Spitfire and I was just about to buy a OS 61FX as recommended in the destructions. However, I would'nt mind the extra pull of the AX 75.

My question is ...

1. Does the mount holes match up?
2. Will the muffler holes be the same width?

A quick look at the next located the OS 61 instructions with blue print measurements, but I cant find the 75.

Does anyone have access to both to measure and help?!?

RCKen

My Feedback: (9)

I did a review of the OS 75 AX for RCU. You can find that review here: [link]http://www.rcuniverse.com/magazine/article_display.cfm?article_id=920[/link]

I'm not 100% sure about the muffler bolts, but I do think that they are the same. But I can tell you that the mounting bolts for the engine are identical. In fact, in my review you will see that I installed the 75 AX into a plane that previously had the 61 FX in it, and it dropped right into the same mount holes.

Hope this helps

Ken

carrellh

I didn't see muffler info so I looked at Bisson Mufflers web site and it appears that the 91FX muffler fits the 75AX. Before spending any money you probably should call Bisson and confirm.
http://bissonmufflers.com/en/muffler...imageField.y=7

phildo

Thanks guys your info was very helpful. I now understand that the mounts are the same .... problem with the muffler is that I was going to use the Top Flight muffler designed for the spitfire that is available via Tower. I may just go with teh Bisson pitts for the OS 91.... Ahhhh ... the decissions of kit building!!!!

What cant kill me ... will only make me stronger !!!

Thanks again...

Phil

ChuckW

One thing is for sure... you will love the engine. I'm running this engine with an APC 13x6 on my Super Sportster and the power is amazing. The vertical is seemingly endless. I will definitely by another for my next .60 sized plane.

phildo

Chuck ... Yep, that's what I was thinking [>:] It would be cool to beat up the strip and pull up nicely to 400 feet and round out.
A real plus is that oblong shaped head fins .... it should be a nice look in the front lower cowl of the spit. I have been tempted to buy a brand new OS 60 FX that someone here in Australia has on Ebay for a good price (AUD $120) but for AUD$250 dollars for the new AX75, I just cant seem to be bothered to save the extra $100 or so. So,you think its worth it??

ChuckW

Here in the US, the .75-Ax sells for around $40-$50 dollars more than the .61-FX. From my experience so far, it is definitely worth it.

CustomPC

I Have the .75AX I agree it is a great motor.

I have tried 3 mufflers for it.

The standard muffler gives excellent performance if you can fit it. Can you rotate the motor so that the cylinder is on approx 45 deg down angle and the muffler is under the fuse?

I also tried the Bisson Pitts designed for the .61FX and it gave better performance on the test stand, but not enough exhaust pressure and the needle needed to be 1.5 more turns out than the stock muffler. I suspect the pitts made for the .91 may have even less exhaust pressure. You may have to restrict the outlets to get the right performance.

The Jett Engineering Turbo-Jett muffler works great too and works well with the motor mounted sideways.

jetmech05

everything is the same mount holes, muffler, and crankshaft...just put a .75 in my Ultimate, replaced a .61

phildo

Thanks Jetmech and Chuck ... just the info I was looking for. Chuck .. as to the motor turned 45 deg with the muffler under the fuz is a top idea. I dont know why I missed this. Could slove a few other probs as well. Only forseeable drama is the cuting up of a clow [&o] ... Oh well, At least I know if I get another muff, it will bolt on straight up.
Thanks guys.

Phil.

CustomPC

Phildo,

If the firewall has the thrustline + marked you could cheat a little by using the motor mount template from the Great Planes Venus II manual. There's a template in there that fit's the Great Planes motor mount and puts it at the correct angle to place the muffler under the fuse.

Also, if you haven't bought the motor yet, i have mine for sale. It's in great condition and had about 20 flights. There is some castor stains but that's only cosmetic. It spins an APC 14x6 at 10,000rpm or a 13x8 at 10,900rpm.

phildo

Custom, Great idea using the template. As to the engine .... sounds good. Could Email me at [email protected] with a photo or price maybe?

Thanks mate.

P.

phildo

AX.75 SOLD!!! ... to me!!!

Thanks CustomPC (aka Michael) ..... Fantastic. Really appreciate the engine and I have put it up against the plans for the TF spitfire and it will be an excellent fit.

Man, ... really need to hurry up with the build.

Thanks to all for your advice ...

Phil