Im looking for a small 4stroke but smallest one i can find is a .30, is there anything out there smaller?

nutn2it, there is plenty of os 26 surpasses around but the smallest was the os 20 4 stroke but not many around - you'll find the new 30's are great as well. Brian

A .30 is a bit to big. Im trying to get one for my .15 size glider. Only reason I can think of getting one for it is the sound, I just love the sound of a 4stroke over a 2stroke
Seen a few old OS FS .20 4stroke but, I was hoping there would be newer ones around.

[b]Nut:

The OS FS-20 is a nice running little engine. Don't be afraid of it.

There are smaller 4s engines, but to get one you will have to greatly expand one of your nostrils as you'll pay through the nose for it. They are all hand/custom made. Far less expensive to get a boosted glider big enough for the little OS.

Bill.

HP VT-21, designed and originally made in Austria, now made in the US by Mecoa. Here's the link: http://www.mecoa.com/hp/vt/21.htm

[b]Chuck:

The HP VT-21 is a nice choice, it's been available in a 0.25 size also. MECoA now sells only the 21 and 40 sizes, as memory serves. Picture is the smaller one.

Bill.

Bill...
The pic of HP with big cooling fin and difference carb than model engine for airplane, belive it is made for model car and maybe more heavy. true?

Jens Eirik

[b]Jens:

Caught me. Yes, that is the car version, look again and you'll see that it also has the "Slide" carb on it.

Never found a decent picture of the aero version, but here's a 3-view and dimensions of both the 21 and 49 engines.

Bill.

I've got an HP 21 and one thing you'll have to watch out for is the fact that they're *heavy* -- over 9 oz from memory.

They're also pretty weak.

Mine is presently in a small Piper cub that is desiged for .10 to .15 two-strokers. It turned out *very* nose-heavy with the HP in it so I had to put a 4-cell AA-sized battery pack as far towards the tail as I could get it (and the CG is still a little too far forward for comfort). It also flies *very* scale-like -- which means that it has only just got enough power to climb gently at full throttle.

These are *very* sweet motors but they are incredibly expensive, as heavy as a plain-bearing .40 2-stroker and put out less power than a good 0.10 2-stroker.

You'll love the noise (there's almost none) but you probably won't be impressed with the effect of the extra weight on your glider.

Here's a pic of the one I had. It was the original Austrian version. According to what I've read, the new one has more power.

Complete agreement on the weight and power. However, since he's looking for a 4 stroke, I assume he's already thought through this issue. No small 4 stroke is going to be as light or as powerful as a 2 stroke.

Since he is looking for the smallest engine, would he also mean the lightest, either a Saito 30 or OS 26-30.

Forgive me for throwing cold water on your desires, but why is the sound of an engine of concern with a motorglider? The aim is to climb high (no one will hear it up there) and then shut down the engine to glide. And adding all of that extra weight (compared to a 2-stroke engine) won't help the glide phase.

Hi!
Agree!
Forget about the fourstroke on a glider. Get an OS .15 LA and prop i right (8x5 - 9x3 APC ) and it will be much more quiet than any fourstroke and ligher.
Regards!
Jan K
Sweden

The first, and only HP-21 4-stroke I ever saw run was on a Tiger Moth that had been converted from a large rubber powered kit. Man, what a sweet flying little model. I seem to remember the wingspan being around 30". It was covered in Monokote in a semi-camo scheme. It looked, and flew, fantastic. The only complaint the owner had about the engine was that the idle was fairly high 3K+ so landings were a bit tough with the engine running.

If you want quiet in an engine try a 2 strk diesel many choices and 09 gives the power of a 15 glow.I plan on using my Enya cx11d
in a ripmax coyote already have a coyote with a brushless elctric motor am getting an other for the Enya martin

The secret to getting a good idle with the HP is to use the right plug and let them *really* warm up before you try to idle them back.

The one in my Cub is mounted inverted and won't idle very well when first started but after a minute's running at full throttle it will idle forever -- and so slow you can almost see the prop turning. In fact it idles better than any of my other 4-strokes.

My little OS26FS is really nice and cute! I think getting a simple 15 sized 2C is okay ... there are not all that bad.

I picked up a VT21 at a swap meet a couple of years a go, the chap never got it running because of the fuel line hook-up . I benched
it had in running in a few minutes it was quiet and good idle (and Bill it did have the aircraft head) In a moment of weakness I sold it
to a guy in the UK because I thought it did not have a lot of power for its size. It would have been perfect for a small cub or
similar and it was the Austrian version.At idle all you heard was the prop swish. One of the advantages of the diesel however is you can use a tank of half the size to get almost the same run time as a glow martin

In order to get the idle down, the application of silicone rubber around the carb base is necessary (stop the air leak). The HP49VT has exactly the same problem and is an otherwise excellent engine. Yes, this comes from first hand experience. <G>

This particular series of engines utilizes a tapered shank on the bottom of the carb, so an o-ring doesn't work reliably. The silicone or butyl rubber seal works perfectly. You won't believe the difference this makes on these engines.

Also, be careful not to use glow plugs that stick down into the cylinder even the slightest bit. It will collide with the rotating valve and damage the engine. The plugs made by McCoy that look like normal non idle bar glow plugs work perfectly in this engine. These are the four-stroke McCoy plugs that I am referring to. Under no circumstances should you ever put an idle bar plug or an OS Type-F in these engines. Damage WILL result.

I liked my HP four-stroke. Sweet engine.

Ed Cregger

Dear Piper_Chuck & Bill Robison:

The PIPE here once more...and I'm about to get one of the Austrian made VT-21's myself within a month or two!

I've got the RCM 1980s era book on four stroke engines, and Clarence Lee did a review on the VT-21 for the magazine, which also showed up in the book I've got.

What JWN reported with the VT-21's idle he had observed is something Clarence mentioned in his article, too...

"The only blemish on the whole engine performance was the idle. I could not get the engine to idle reliably below 3500, with 4000 being a safer figure."

He did try using a homebrew fuel mix using ONLY 10% Klotz oil, 10% nitromethane, 2% propylene oxide igniter and 78% methanol, and got the idle down to "only 3500 rpm"...so perhaps a "high idle" MIGHT be expected. The idle DID stay lit as low as 2700 rpm with glow power connected with that fuel mix...so, perhaps a LIGHTWEIGHT glow plug power system might be advisable? Perhaps, if Clarence could have heard the advice that Ed Cregger was telling us about the need for a silicone sealant around the carb's entry into the cylinder head...most likely the brick-red-colored "copper-bearing" high temperature type, that I've seen in auto parts shops...maybe any possible air leaks (a BANE of four stroke engines!) cold have been avoided, and the VT-21 Clarence was testing might have idled a bit slower...!

The VT-21 didn't SEEM very "picky" about just what glow plug was used with it, in Clarence's review...K&B, Fox, Fireball (Swanson Associates), and the old GloBee plugs were tried and all were found to work...and from what Ed Cregger was saying, Clarence was TRULY "tempting fate" in trying an OS Type F four stroke plug in the VT-21 (which he DID do successfully)...I'm hoping that Clarence had a STACK of glow plug washers (in addition to the 1.6mm-or-1/16th inch thick "special spacer" that HP has provided for this engine) keeping the "hose-nose" business end of the Type F plug AWAY from the rotary valve's outer surface! I'd stick to trying short reach Fox 1.2 volt and Fireball units first (unless K & B plugs are still available) when I try firing up the slightly used VT-21 I'll be getting...later this autumn...either with the special HP washer, OR two or three stacked "regular" glow plug washers!

Clarence's article also mentioned the "proper plumbing" relating to the apparent need for a fuel line between the muffler pressure fitting and the similar fitting on the cylinder head on the VT-21...and then the crankcase vent under the engine's nose section was hooked up to the FUEL TANK??? Clarence just hooked up the muffler pressure fitting up to the tank, and advised periodic oiling (with Marvel air-tool oil, I suppose?) of the gears driving the rotary valve in place of the curious factory advice on those unusually connected fuel lines. Clarence stated that he was worried about possible metal powder (from engine break-in, etc.) getting back into the engine through the fuel tank with the factory hookup in that article.

Just wondering, Ed, DID your idle get better (hopefully with a lower minimum RPM) with silicone sealant around the carb's entry into the cylinder head?

The Balsa USA Swizzle Stick 30 plans I got last spring from another RCU member will be the recipient of the VT-21 I'll be getting soon...it was said by the seller of those plans that the VT-21 should be a "perfect" engine for it.

It will be interesting to see HOW the VT-21 does on my engine test stand...Clarence's prop RPM top end tests went like this...all with OLDER style round-tipped Top Flite props...with Cool Power 10% nitro fuel (not stated if it was 2 or 4 stroke fuel)...

7 x 6: 14700 rpm
8 x 6: 12700 rpm
9 x 5: 10800 rpm
9 x 6: 10200 rpm
10 x 6: 8200 rpm
11 x 6: 6500 rpm
...and even a 12 x 6: 5600 rpm...!

Now a "Swizzler" is a slow flying bird (basically a crutch with a box stuck atop it for a radio enclosure and wing mount, the engine stuck on the "top" and a tail stuck on the "bottom" ), so I'd most likely be using a 9x6 or 10x4 prop on the VT-21 for the Swiz-30.

I've heard one of the VT-21's run before, many years ago...and it IS a VERY QUIET four stroker...at idle it's "almost inaudible", even only a few feet away from the engine...so THAT should make it a very desirable engine to power an "early flying" aircraft, that could be possiblly flown at 7:30 AM...when my club's ( http://www.wingbusters.org/ ) field opens for "fueled flying" needs, I suppose that I COULD take it up even a little earlier, and fake people out into thinking the Swiz-30 MIGHT be an electric...the VT-21 COULD be that quiet of an engine!

I'll use all this advice in setting up my VT-21 on the test stand that I've got in this thread...as well as what Clarence had to say himself (EXCEPT his perilous attempt in trying an OS Type F plug in it!)...can't wait to pick up the engine later this autumn!

Yours Sincerely,

The PIPE!

Mine was the 49VT, not the 21VT. I'm extrapolating.

But to answer your question, yes, the idle was lower and reliable after the application of silicone rubber around the tapered shank of the carburetor.

Ed Cregger

Saito .30

How is the Saito .30, Hobbsy?

A friend of mine bought one and wasn't happy with it. He is a pretty good engine man in his own right. Did he have a bad example?

Ed Cregger

I'm sure that Clarence has wonderful credentials but when it comes to the VT21 he appears to not know his arse from his elbow.

My VT21 idles like a Swiss watch at just under 2,000 RPMs once it's warm on 10% fuel with 20% oil (half castor, half synthetic).

Connecting the crankcase vent to the fuel-tank is a big no-no and will stuff up the engine's lubrication system by not allowing sufficient oil blow-by between the piston and liner.

Likewise, connecting the nipple on the muffler to the fuel tank will also risk *major* engine damage because this is where the top-end (rotary valve and gears) gets its lube from.

Unlike a regular 4-stroke, you can't just rely on residual oil from a quick squirt with the oil can to keep a VT21's top-end lubed. The rotary valve is subjected to combustion temperatures and spins in the head. If the oil film decays or breaks down then the engine will suffer significant damage!

Likewise his use of 10% synthetic oil was a big no-no. These engines must have 20% oil with a good percentage of that being castor -- it says so in the manual and a quick inspection of how they work would show that the rotary valve assembly needs lots of *good* oil that will hold up at high temperature.

It sounds like Clarence was unfamiliar with these engines and got a bit out of his depth when reviewing them.

Mine is now 25 years old and still runs like a well maintained sewing machine. I replaced the bearings a while back but apart from that it's needed no work and is still running on the *original* glowplug!