Planning ahead again... what engine for a Yak-9

**RknRusty** Fri Apr 05, 2013 11:15 pm

I'm soon to be the owner of a Sterling Yak-9 kit, so I better start looking for an engine. The Thunder Tiger Pro 25 seems to fit my 30 ounce Shoestring well. I think the Yak is lighter, probably closer to 25 ounces. I was wondering if something like an OS 25 LA-S control line engine would suit it. Fox 35 engines are plentiful on the Bay but that seems awful heavy for this plane.

I figured I'd start the search now, so as to have time to shop for a good deal and get a nice one that won't bust the budget.

I s'pose I'll be building this while Ron builds his new Shoestring. Too bad we can't all get together to play with our toys.

Ken Cook Sat Apr 06, 2013 5:49 am

Rusty, it comes down to what do you want to spend. Many options are available and there's also different run styles. I'm a Fox fan. What the engine lacks in quality, it makes up for in enjoyment and can be had brand new for $50. Used, I probably wouldn't spend more than $35 sight unseen and parts are available and the engine is light. The Fox weighs in at 7-8 oz's depending on the version. I personally wouldn't go for the older Fox due to the newer case being a better design and stronger.

The LA series which is my staple engine in speed limit combat works, I just wouldn't want it on the Yak unless it had a bladder. I could certainly provide you a picture of remote setup for bladder. The engine really comes to life. The LA .25 weighs in at just under 7oz's which puts it in the correct weight category and it's modern.

You would also have other OS choices like the FP.20 and FP.25. which work but your faced with a out of production engine with very limited parts availability. These engines however last and are built remarkably well.

If period engines are to be used, my choice would indeed be the Fox .35 or one of the Fox combat engines like the .36x or Blackhead. The Mccoy works well and I fly 2 of my Yak's with Mccoy's. Keep in mind fuel choice is imperative with the Mccoy due to the possibility of catastrophic damage. I've had these engines last ONE run while others have been going strong since the 60's. It comes down to cost which would help assist you in a engine choice. Keeping the weight under 8 oz's with no muffler is imperative. As an example, the Mccoy .35 (non Lightning bolt case) weighs in at 7.30 oz's. The Lightning bolt case has a bronze bushing in it which is slightly heavier. The K&B series engines which I don't care for work but like the Mccoy's are subject to problems and parts breaking with no parts support. The K&B only had I believe 3 head screws which held the liner assembly on which would handgrenade.

Enya's in my opinion like the Enya .35 5224 are powerhouses which could be used but the weight penalty may be a factor. These take FOREVER to break in but once run in you have an exceptional engine.

The OS Max .35-S would be a great choice, but again it had some short comings like premature conrod wear which rods are unobtainable. The OS Max .35 needs 25% castor fuel. Piston liners failed due to the brass end pads on the wrist pins cutting grooves into the liner. Mind you this didn't happen as soon as you started it. I'm just making clear the current state of MOST used engines like this that you would find sight unseen from the auction site.
Many things to think about, but most importantly your budget which would assist the decision in what you would like to use. Ken

OVERLORD Sat Apr 06, 2013 6:45 am

Hello Rusty,

Just because Ken talked above about OS engines, I've bought recently via internet 2 new OS .25 FSR engines. I paid them 40 EUR a piece. They're R/C models but I'm converting them to C/L, so turning them into FSRS models. I was said that the standard venturi and NVA from a .25 LA fit straight on. I've ordered those parts and waiting to mount them on. A .25 FSRS weights according to OS 6.8 oz. without exhaust. It is true that parts are not available anymore and thus need searching when needed but this engine has twin ball bearings, is Schnuerle ported, and would be more powerfull with more torque than a .25 FP. Maybe Ken knows other (dis)advantages of this engine?

I hope this is of any help.

Lieven

Ken Cook Sat Apr 06, 2013 7:29 am

The FSR is a very powerful and well built engine. I was always under the assumption that it was heavier than you stated. A good engine indeed and many of these older engines can be found. Here is my take on these engines however. Seeing that a few here are new to the larger sized planes, I made my suggestions accordingly using plain bearing engines aside from the combat specials excluding the Blackhead Fox. If a ball bearing engine hits the ground, your basically done for the day. Washing the dirt off with fuel and restarting without proper cleaning is going to result in damage. I have this happen continuously in combat and as much as I don't care for doing it, I wipe out a set of bearings on a regular basis. This can not only get expensive, it can take the enjoyment out of the experience.

If however, one is inclined to use these engines which I'm not suggesting not to, keep that in mind. The FSR would have far greater power than just about any engine I included on my list BUT, your not going to get any kind of stunt run if so desired. The engine is timed for high rpm's and will not run the 4-2-4 which I don't subscribe to anyway. I'm just saying be prepared for extremely fast lap times and to tame this engine would require a lot of experimentation with props, head shims, and venturi sizes which one may or may not be so inclined to do so. Running and engine like the FSR on suction for control line use for the purpose of stunt would more than likely end up starting out rich and ending up in a screaming lean run to the end of the tank.

Many times these wild engine runs can be tamed by adding more castor, or not muffling the engine, or opening the venturi. I will say this, been there and done that and while I'm not against experimenting, this can become frustrating especially to one that has no experience in doing so. My vote would be to stick to what has worked and is simple. Please don't accept this as criticism, I'm just stating that keeping the simplicity in things makes the experience easier. When you have several weekends invested into experimenting that plane can get real old quick. Ken

**RknRusty** Sat Apr 06, 2013 8:34 am

Now that's what I call quality advice, thanks for the detailed information, guys. I did not know about the ball bearing engines being so susceptible to dirt damage. I'll keep that in mind when I fly the Shoestring with the Thunder Tiger, and I'll stick with bushed engines for now. Flying the SS is on the schedule for tomorrow. It sounds like the Fox, either regular 35 or stunt version, and the LA 25 are my best bets. As you know, I'm not at all averse to using a bladder if it suits the LA best.

**Cribbs74** Sat Apr 06, 2013 9:45 am

RknRusty wrote:Now that's what I call quality advice, thanks for the detailed information, guys. I did not know about the ball bearing engines being so susceptible to dirt damage. I'll keep that in mind when I fly the Shoestring with the Thunder Tiger, and I'll stick with bushed engines for now. Flying the SS is on the schedule for tomorrow. It sounds like the Fox, either regular 35 or stunt version, and the LA 25 are my best bets. As you know, I'm not at all averse to using a bladder if it suits the LA best.

That would be one big bladder! Probably have to be built into the wing.

Ron

SuperDave Sat Apr 06, 2013 10:01 am

Though I have high regard for Fox .35's, ever the rebel, I was drawn to K&B Torpedos and Veco .35's for the Sterling Ringmaster, P-51, Navion and Yak series.

All were solid performers IMO.

SD

OVERLORD Sat Apr 06, 2013 10:16 am

Ken Cook wrote: The FSR is a very powerful and well built engine. I was always under the assumption that it was heavier than you stated. A good engine indeed and many of these older engines can be found. Here is my take on these engines however. Seeing that a few here are new to the larger sized planes, I made my suggestions accordingly using plain bearing engines aside from the combat specials excluding the Blackhead Fox. If a ball bearing engine hits the ground, your basically done for the day. Washing the dirt off with fuel and restarting without proper cleaning is going to result in damage. I have this happen continuously in combat and as much as I don't care for doing it, I wipe out a set of bearings on a regular basis. This can not only get expensive, it can take the enjoyment out of the experience.

If however, one is inclined to use these engines which I'm not suggesting not to, keep that in mind. The FSR would have far greater power than just about any engine I included on my list BUT, your not going to get any kind of stunt run if so desired. The engine is timed for high rpm's and will not run the 4-2-4 which I don't subscribe to anyway. I'm just saying be prepared for extremely fast lap times and to tame this engine would require a lot of experimentation with props, head shims, and venturi sizes which one may or may not be so inclined to do so. Running and engine like the FSR on suction for control line use for the purpose of stunt would more than likely end up starting out rich and ending up in a screaming lean run to the end of the tank.

Many times these wild engine runs can be tamed by adding more castor, or not muffling the engine, or opening the venturi. I will say this, been there and done that and while I'm not against experimenting, this can become frustrating especially to one that has no experience in doing so. My vote would be to stick to what has worked and is simple. Please don't accept this as criticism, I'm just stating that keeping the simplicity in things makes the experience easier. When you have several weekends invested into experimenting that plane can get real old quick. Ken

Thanks, Ken, for the advice, I've learnt something as well.

Lieven

duke.johnson Sat Apr 06, 2013 10:41 am

Rusty
If it's the Sterling or Brodak Yak, it's only 38" and like 305'" sq. I think that's small for a Fox 35, I like the Fox 35 though and as Ken said quality, cheap, engine off the shelf. But My chose would be either the O.S. .25 FP and the .20FP, you can still get most f not all the parts from Tower Hobbies or the internet. They are great engines. I like them over the LA series, seem to run better and stronger, I have both in sizes .15, .25, .40, .46. Another great engine for the Yak would be the Veco .19, My son had one in his P-51, which is all but the same plane. It few awsome! The Veco is a real power house, I'm going to build a Ringmaster with a Veco .19 in it after I finish getting the carrier planes ready for the contest season. But that being said Ken is way better at this than I am. This is just my opinion and opinions are like armpits, everyone has at least two and some of them stink. lol!

Duke

SuperDave Sat Apr 06, 2013 11:02 am

Duke:

Certainly the choice is yours to make but anything less than a .35 on one of the Sterling series is to under-power it. But if you find that to be true in your syle of flying, moving up to a larger engine is always an option.

Simpler that than REDUCING the size of the engine. Laughing

SD

**RknRusty** Sat Apr 06, 2013 11:08 am

cribbs74 wrote:That would be one big bladder! Probably have to be built into the wing.

Ron

It would be the same circumference as the 3/4oz I use on the little ones but it'll look like an 8" Ballpark hotdog. If I put it on lengthwise, I think it will straddle the CG pretty well, just like on the 1/2As. I'll have to check that out to make sure.

Here's 2 ounces on the Baby Streak. The black sharpie line is the CG mark. 4 ounces would look the same, just twice as long but not fatter. And the plane is longer.
Planning ahead again... what engine for a Yak-9 Sam_1611

Planning ahead again... what engine for a Yak-9 Sam_1611

**RknRusty** Sat Apr 06, 2013 11:10 am

SuperDave wrote:Duke:

Certainly the choice is yours to make but anything less than a .35 on one of the Sterling series is to under-power it. But if you find that to be true in your syle of flying, moving up to a larger engine is always an option.

Simpler that than REDUCING the size of the engine.

SD

Dave, keep in mind most modern 25s will blow the doors off an old style 35.

SuperDave Sat Apr 06, 2013 11:14 am

Rusty:

Since I don't have experience with modern .25's I'll leave that to others to judge.

SD

Ken Cook Sat Apr 06, 2013 11:17 am

The bladder wouldn't need to be large, A fluorescent light guard is 1 1/4" in diam and it would only need to be 4" long. Putting balsa end caps on it would allow it to attach to the fuse in the same manner as a tank. If needed it could partially sit up on the wing. A LA .25 uses 2.25 oz's of fuel in 5 minutes. It could really be a cool to do. I prefer the run of a LA .25 on bladder but the LA runs completely fine on draw and can be used like that as well. Ken

duke.johnson Sat Apr 06, 2013 11:19 am

SD
This is Rusty's plane we are talking about. And I've talked to many that would put even a smaller engine it, tey fly way better than I though. I need power to fix my errors. Power is your friend. I can't remember the year, but the Nats were won with a Ringmaster powered by a Veco .19. And the Ringmaster is somewhere around 381sq in and the Yak-9 is around 305-320sq in.
The .25FP is just as strong as the Fox .35 and the P-51 and Yak-9 fly great onthe Veco.19 (no shortageof power).

Side note Dave, are you going to the swap meet next weekend? The offer to pick you up is still open.

SuperDave Sat Apr 06, 2013 11:41 am

Duke:

"Side note Dave, are you going to the swap meet next weekend? The offer to pick you up is still open"

Details please? Yes that would be muchly apppreciated, friend if we could meet up again.

Where,when, time etc? I've reached a "turning point" in modeling so I need to sell or trade-off my larger planes and RC equipment.

SD

duke.johnson Sat Apr 06, 2013 11:44 am

PM coming, we'll get off Rusty's post.

**RknRusty** Sat Apr 06, 2013 1:52 pm

I'd be right at home with a bladder. I expect my usual fishnet sheath would work fine too. When the bladder has any fuel in it the sheath conforms to its rounded lead edge shape, so it's pretty aerodynamic. The tail of the sheath is tightly secured so it doesn't flop in the wind. It's not an issue, especially with only 2.5oz.
Am I presuming correctly that the LA does not need a modified from stock NV?

OVERLORD Sat Apr 06, 2013 2:03 pm

Just one more remark about the OS 25 FSR while we're at it. Following Ken's point of view which is fully understandable, I had a closer look at the prop end in order to check this ball bearing configuration. To have peace of mind and for information to you, Rusty and everybody else, I took all washers and drive hub of the shaft. The bearing is not just an open ball bearing but a double Z type and thus shielded however not sealed. An intermediate washer is located between the drive hub and the bearing. The drive hub has a shoulder that sits over the machined edge of the engine casting with a very small clearance only. A well engineered part and now we know why. Unless you ditch a plane in a puddle, I think this ball bearing is well protected.

Lieven

Planning ahead again... what engine for a Yak-9 Imgp2410

Planning ahead again... what engine for a Yak-9 Imgp2410

Planning ahead again... what engine for a Yak-9 Imgp2412

Planning ahead again... what engine for a Yak-9 Imgp2413

Planning ahead again... what engine for a Yak-9 Imgp2414

**RknRusty** Sat Apr 06, 2013 6:28 pm

That looks a lot like the front end of my Thunder Tiger. I'll double check. Good to know, thanks, Overlord. I'm an engine guy and like to know things I hadn't thought of. This would be an equally good design for a bushed engine as well. I've lost front bushings in Coxes because they weren't well isolated from the elements.

andrew Sat Apr 06, 2013 6:39 pm

It's fairly common construction in most bearing engines. You'll get a little bit of a shield from the thrust plate. Rear bearings on most of these engines are open. Front bearings may have the rear shield missing or may have both shields in place, but normally are not sealed since they need to allow lube to pass thru.

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