I am finishing up a new ARF - the 27 oz. Sportsman Aviation Aero Princess. The manufacturer recommends the AP .15 engine for power. The two engines I am debating on for this plane are the Enya .15 IV (circa 1970s), and the O.S. MAX .25 R/C (1973 model). I have already broken in the Enya, and its spinning an 8x4 at around 12500. I haven't run the OS yet... I just LOVE the little Enya, but I'm afraid that it won't be enough since it can't rev nearly as high as a modern .15 can. These engines are both old tech (iron pistons, high castor, etc...) but I'm thinking that the old O.S. .25 will put out the power that a modern .15 can, right? Any thoughts?? Thanks!!!

The performance of the .15 sounds reasonable, I'd go with it. An old .25 is going to add alot of weight in the nose.

I'd go with the .15 too....[sm=thumbup.gif]

FBD.

Wow - this is unexpected (good) news! I really did want to put in the Enya, and now, I just might. BUT, the old .25 is actually the same weight as the .15 - is the Enya still the way to go? Also, I didn't think 12500 was anywhere near "good" RPMs for a .15 - was I wrong?

A "good" .15 should spin a 8x4 13500 to 14000 rpm. At 12500 rpm, the engine will certainly fly the plane but I would not expect unlimited vertical. A thousand more rpm doesn't sound significant but prop thrust is exponential, doubling the rpm quadruples the thrust.

The Enya will alst you until you get tired of it. They were good engines.

I had OS 35's back in the late 60's early 70's. They were good also.

I'd try to use the Enya in that plane.

Enjoy,

Jim

Many people get caught up in the HP thing, which is usually developed with a small prop at high RPM.

Don't underestimate your Enya.

If you run the Max .25 you might consider a 9x4 or so prop. An 8x4 is too small for it. BTW, a Max .25 is a strong runner, especially considering it's not schnuerle.

These are only opinions. Good luck with it.

George

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I run 7x4 to 7x6 props on my .15 size engines. Even the old ones. These little rascals need to rev up to begin to develop serious power.

I don't know if the .15 will be up to the task of pulling the model because I am not familiar with the model. But you can bet that the lighter weight of the .15 will permit the model to turn sharper and fly better, if there is enough power being developed.

I have an old Fun One that I have flown with both an OS .32F-H and with several .40 to .50 size engines. I prefer flying it with the .32. It is a completely different model with the smaller engine.

Fortunately, the .32 provides enough power to fly rather quickly and will just hover the model. The larger engines provide infinite vertical performance, but they also double the turning radius with their extra weight. I'll take the .32 for power every time.

Ed, the plane has a flying weight of under 2 pounds. A .15 should be up to the task. You're not suggesting that he try stuffing a .32 in the nose of such a plane, are you?

I have the same ARF kit, and I am planning to put a modern Fox .15 on it. It is also iron piston steel sleeve, but it will turn an 8-4 prop at almost 15,000 revs. Not sure it it will hover with that old Enya. What nitro fuel did you use? Some of those older .15's needed high nitro fuel, such as Cox racing or Missle Mist.

Thinking of reinforcing the plastic fuse on this model. Not sure how, but thinking of gluing some 3/16" square balsa, in four courners and top, to the rear former and gluing the stabilizer to that. Or maybe it will hold up fine without?

The 25 FP will put out more poop than the 25 LA. That one should have an aluminum piston. I still use two of them regularly. Just a light, reliable, tough engine. 9 in. prop is best for it. Have to take the spinner off to see if they're 4 or 6 in pitch, although either one would work fine.

Like Sport Pilot said, the Fox 15BBRC is VERY strong.. It also runs well throughout the entire throttle range.

turbo

A few personal opinions which may or may not be correct:

I do not have the Enya-IV .15, but my Enya-III .15 runs fine on 15% nitro, 22% castor oil, and an 8x4 prop. I think a 8x4 prop for a sport model will out-pull a 7x6. Were it a sleek, streamlined model I would go with the 7x6.

I think the Max .25RC in question is the older iron/steel with drop-in liner that replaced the steel fin Max engines. OS has always enjoyed a good rep to most. Same fuel as Enya.

I do not have an LA .25 but the FP .25 is a good engine. I think the porting was changed on the LA. My understanding is that they eliminated the boost port. This SHOULD give the similar power until you get to the higher RPM range, then the FP should have the edge.

As stated, these are only opinions, individual results may vary.

George

Thanks for the advice!

gcb - I'm not exactly sure what you mean whe you say "don't underestimate your Enya" - while I very well may end up using it, I think you are the only one I've heard of that said it was better than average.

Sport_Pilot - Concerning the plane - I was thinking about reinforcing it also (other people have mentioned this in other threads), but I don't think I should add any weight if I go with the Enya - I think it will have just enough power as it is...

Flypaper 2 - The OS engine I have is the MAX .25 R/C - it's older than both the LA and FP you mentioned.

gcb - What RPMs were you getting with your Enya .15 III? (Just curious).

Thanks for all the advide - can't tell you how much this helps with the decision!!

I'm not saying it's better than average by today's standards, I'm just saying that it is not a "puny" engine, and most seem to have good pulling power. As someone mentioned, the Fox .15 is a much stronger running engine...but you are comparing a BB schnuerle with a PB baffle. The current OS LA is also a good runner, as is the TT.

Bottom line is that it is your engine and your choice. I'm just saying I would not hesitate to use it.

I have no idea, I did not tach it.

George

Found an engine review that might help:

http://www.the.elmores.btinternet.co..._15_3_am0.html

Enjoy.

George

Based on the test report, I would buy some Fox Missle Mist fuel, or Cox Racing fuel and try it with an 8-4 prop.

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No. I am suggesting that I would try the .15 first because of the light weight. That should make the model fly much better than with a heavier engine.

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The Fox .15 ball bearing is a good engine, but it nearly weighs as much as a plain bearing .25.

Nitro doesn't hurt the small engines one iota, that's for sure. However, I don't think I would go with 40% nitro in it. IIRC, that's what the Cox Racing Fuel is.

When it came time to buy a bunch of .15's, I opted for two Thunder Tiger and two Enya plain bearing .15's, because of their light weight. With light engines, you don't need to worry as much about beefing up much of anything.

The Fox .15 BBRC weights 6 ounces with muffler. The Enya III weigh's 6.5 ounces with muffler and that is with a venturi instead of a carb. As I recall most plain bearing .25's weigh about 8 ounces. Did you really think any Fox weighs a lot? Some weigh a lot for a Fox but not compared to the market.

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Can you still buy a new Fox .15BB? I thought they went out of production.

I never weighed my little Fox .15 BB when I owned it. I'm sure it weighs more than the TT .15 and most likely the new Enya .15's I mentioned. I could be wrong. No pissing contest from me.

I have a pristine condition Super Tigre G20/15 that I bought new in the seventies and one in not so pristine condition that was a gift from Bob Adkins. It is a beautiful little engine that was designed for FAI 1/4 Midget Pylon Racing. Mine ran good, but it was never anything special in power production. My HB .15 would cream it any day of the week in peak rpm figures with the same 7x4 prop.

I used to run 8x6 props on my ancient Fox .15X when flying control line. It always felt like it was too much prop, but that is what everyone in the magazines said to use. This was in 1962, when the .15X was a brand new product. I was all alone in my flying back then, with no one more knowledgeable to talk with.

Years later, when I discovered an R/C model named the "Peppermint Pattie", a mini pattern aircraft of sorts, I started reducing prop sizes and I was amazed at how much more thrust the little engines developed. Pattie used to blow right by the several .60 sized piped pattern ships at the field. I be smilin'.