Beauty and the Beast

[Dave Moritz]

Shown below is an un-run KMD 2.5, likely from the Soviet era. To me, it is the prettiest motor ever made, maybe in a steampunk sort of way. Machine work in and out is also beautiful!

But..., this beauty pulls the scale down a whopping 6.6 ounces (187 grams). Yet it is capable of 19,000 RPM on an APC 7x4. So, what to do with it? I'll field any CL suggestions here for a model (short of stooge weight or a boat anchor!). I'm not averse to mounting a fuel tank inboard or in the outboard wing. FYI, it was apparently manufactured as a team racing engine. So, any suggestions either stunty or fast & fun would be appreciated.

All the best to the brethren over the holidays!

Dave Mo...

[David_Ruff]

The Soviets launched the first successful satellite.  They put the first man in space.
Never think Russians are inferior.
Quantity is Quality.

[Paul Smith]

Perky Speed.

[Brian Hampton]

There are two versions of the KMD and the photo above is of the second version. I have an unrun first version. The first obvious difference is that the first is finished with a plain as cast cylinder, later is black anodised as are the prop driver and spinner nut. Compression adjustment on the first uses a screwdriver slot, later uses an as supplied special tool. Backplate on first has an as cast fixed venturi while second has 3 removeable venturis.

Edited to add a photo showing the differences,

[qaz049]

Shown below is an un-run KMD 2.5, likely from the Soviet era. To me, it is the prettiest motor ever made, maybe in a steampunk sort of way. Machine work in and out is also beautiful!

But..., this beauty pulls the scale down a whopping 6.6 ounces (187 grams). Yet it is capable of 19,000 RPM on an APC 7x4. So, what to do with it? I'll field any CL suggestions here for a model (short of stooge weight or a boat anchor!). I'm not averse to mounting a fuel tank inboard or in the outboard wing. FYI, it was apparently manufactured as a team racing engine. So, any suggestions either stunty or fast & fun would be appreciated.

All the best to the brethren over the holidays!

Dave Mo...

Lots of these around when you look in the right places. Quality can be quite low if you actually get around to running them. There have been "fixed up" versions capable of reaching the design's potential available from a reliable source in Ukraine even during the present unpleasantness. It's more or less a training F2C engine. There are better choices as a sports engine. A more robust front induction version has also been available from the chap in Ukraine. Pic below.

[Brett Buck]

The Soviets launched the first successful satellite.  They put the first man in space.
Never think Russians are inferior.
Quantity is Quality.

    Beg to differ with you there, the USSR Russian space efforts were, are, and always have been inferior. They were briefly ahead in missile technology because they were trying to loft gigantic thermonuclear weapons, and had to build giant boosters. We decided not to go that direction, so they were able to jump ahead briefly. Sputnik did nearly nothing, we already had a program putting a photoreconnaissance satellite that successfully flew slightly more than a year later.  I know the guys who built it.

    Their later space efforts were laughable compared to the USA, take a look at the interior of their lunar lander or read the history of the Apollo-Soyuz Test Project. Their "moon rocket" was similarly pathetic, there wasn't a chance in Hades they were ever going to succeed. They couldn't do it *now*, much less then. Note Elon Musk more-or-less copied it for the super heavy booster, which has the same success rate as the Soviet N1 - 0%. Musk also managed to trash a nature preserve, the Soviets also blew up their own launch pad.

    The current Russian capability is comparable to our Gemini program. That ended in 1966.

      Brett

[frank mccune]

     Well said Brett!

[Dave Hull]

Curly Moe,

Here are few ideas you can check out:

1. Make a Goodyear racer and use the diesel. We might allow it at our local races (which are pretty casual, Run-Whut-U-Brung, affairs) but you better check to see if anyone within the nearest 5 states might be running such a thing.
2. Make a better Goodyear and run it in AMA Scale racing, if they manage to run the event anywhere.
3. Make an F2CN profile racer. These can be real easy to build--or much harder, depending on your attention to winning details.
4. Make a nostalgia F2C racer and just have fun sport flying it. This can be more fun that you might expect. Find the mfg date of your engine, then find the record speed (national and international) for that year. Then "race" against that time and see how you are doing. Trust me, it will be challenging, even with your tremendous advantage of flying "one-up."
5. Invent a nostalgia FF event limited to pre-1970(?) 2.5cc diesels for no-auto-surface, polyhedral-only, tissue-covered, no-glass/no-carbon designs with a DOM rule. (Designer of the Model) Three wheels are required. A fuse for DT can be used, but you must carry an excess insurance policy of at least $25M. Anyone with a net worth over $5M is required to buy the contest fuel. Or at the very least, the ether....

Anyway, I personally might try idea 3. Picture attached.

The Divot

[Paul Wescott]

Here’s a bit of vintage info from a respected international engine man:

http://clamf.aerosports.net.au/newsletters/ACLN/Issue81.pdf

[Paul Wescott]

In June of 2020 you could buy brand new ABC and AAC versions…

[jerry v]

Shown below is an un-run KMD 2.5, likely from the Soviet era. To me, it is the prettiest motor ever made, maybe in a steampunk sort of way. Machine work in and out is also beautiful!

But..., this beauty pulls the scale down a whopping 6.6 ounces (187 grams). Yet it is capable of 19,000 RPM on an APC 7x4. So, what to do with it? I'll field any CL suggestions here for a model (short of stooge weight or a boat anchor!). I'm not averse to mounting a fuel tank inboard or in the outboard wing. FYI, it was apparently manufactured as a team racing engine. So, any suggestions either stunty or fast & fun would be appreciated.

All the best to the brethren over the holidays!

Dave Mo...

Dave, you can use this engine in the simple profile stunt model. Ready to fly weight no more than 26 oz. NIB engine comes with three venturi sizes: 3.0 mm, 3.2 mm, 3.4 mm. If you ream 3.0 venturi to size 3.6 mm it will increase the power and fuel consumption. Diesel has a good torque, it will turn MAS 8x4 - 8x6 prop, even 3 bladed. Engine doesn’t have the muffler,  and for steady stunt work it requires the pressurized tank. Kerosene will disintegrate the bladder. Typically engine can be tapped with the 3-56 fitting (m2.5x.45) in the 3 rd port to run the crankcase pressure to the tank. Or make custom muffler just for tank pressure.

Jerry

[Dave Moritz]

Hello All:

As expected, I got some good responses here. Will keep an eye peeled for Perky speed plans, Paul. And the Divot’s scary-looking Goodyear racer.

So many versions of this vaunted mill, judging by all of the shots so kindly posted. Those newer versions with the front venturi are very tempting, but likely I’ll abide the one I have on hand first.

So the Divot provided us an exposition into the gray matter on his creative side. So be it! Number Three it will be. But I’ve never understood the meaning of those alpha-numeric codes in the competitive circuits (F2CN, etc.). Must be something on the interwebs I can peruse so will get on that.

Thanks, Paul, for the reminder of the Dissler article. About as good as any information that can be had.

Finally, Jerry really laid out some encouraging parameters on using the KMD, especially the need for muffler pressure. By the way, I once had a sweet running engine just like the one Brian showed above. I really goofed up in that I installed a makeshift muffler with steel mounting clamps. In over tightening the clamps, the cylinder distorted, and I ended up ruining it. Jerry’s muffler suggestion is appreciated with the caveat that something gentler such as mounting springs springs (ha!) to mind.

Thanks to those of you who replied to the topic at hand.

Best for holiday seasons!

Dave Mo...

[Lauri Malila]

Long ago I used КМД’s quite a lot, for all kinds of fun-fly models, combats and such. KMД is one of the better quality  Soviet mass produced engines. Simple metal tank and never needed pressure feed. I don't remember which venturi I used but there was always enough power.
because of the old style intake drum system (non-reversed), I'd advice at least 20% full-castor fuel, otherwise you may wear out the conrod big end too soon. L

[Dave Moritz]

Lauri

Your experience was just what I was hoping for! A thousand thanks.

Dave Mo…

A PS to anyone who ends up with this Soviet beauty in NOS: the too tight contra piston can be loosened a bit by judiciously exercising it in place. Much easier than Dissler’s technique.

D…

[jerry v]

Here is some nostalgic memories. In Soviet Union it was prohibited to use glow fuel engines by the school kids. Methanol is a poison. To keep kids busy building and flying there was a good variety of Diesel engines for different hobby categories. KMD-2.5 started to come in big numbers after 1979. Originally it was designed for the team racing. But it was used in the trainers, speed , combat, stunt and the free flight. KMD has rear intake with the system making the smallest possible crankcase volume. It create the best pressure to move the fuel mixture up the ports. The bad part is - the fuel mixture is going mostly in one port above the intake window. To help spread the fuel mixture to the port closest to the front end there is a notch in the piston skirt facing the engine front. The notch also clears the rear bearing housing. This original intake style also requires 24 percent oil because the conrod  is running in the “shadow “ from the fuel mixture. Original fuel recommended by the factory is 45 % kerosene, 31% ether, 8% castor oil, and 16% MC -20 aircraft oil. The rear intake can be made in a different way - like in the earlier racing engine “Rytm 2.5”. If modified backplate will be made, if venturi wil be opened up to diameter 4.1 mm, if conrod will be fitted with bronze bushings - then model was capable to reach the speed of 190 km/hr. The stock KMD will fly 120 km/hr or 75 mph.
On my picture there are two combat KMD with tapped fittings into third port. KMD will work flawlessly in race or speed without tank pressure. But for combat it needs pressure for steady run.

Jerry

[jerry v]

Here is the better rear intake print to improve the KMD performance. It will allow to use fuel : 53% kerosene, 30% ether, 8.5 % castor oil, 8.5 % synthetic oil.  Anti detonating components - up to 3% if less kerosene.
One KMD was abused and piston lost its top. The head lost one mounting bracket. The engine is heavy, it has solid crankshaft diameter 8 mm, cast iron piston and contra piston and the steel sleeve. It’s a diesel!))

Jerry

[qaz049]

Rather than spending time and money on old Soviet era model diesel engines a much better deal is the Fora Junior 2.5cc engine. These are made in Ukraine and have been on the marker since about 2012. They have been available this year despite the war. They cost USD100-150 depending on how you buy them. Made in Diesel and Glow and AAC or ABC. They can also be converted from one to the other. They are quite powerful.

Very popular in Australia for Goodyear27 and Vintage Combat. Best small diesel available for the price.

Maris Dislers did an engine report in 2016. Available at: https://sceptreflight.com/Model%20Engine%20Tests/Fora%20Junior%2015.html

[Dave Moritz]

Doggone nice looking motors you’ve tempted us with, qaz!

 For any diehard here who wants to stay with the Soviet version: I’ve a one-page write up distilled from all the “received wisdom” from this and other sites. PM me with your email address and I’ll fire it off to you.

Dave Mo…

[jerry v]

Dave,
You can use your new KMD as is, out of the box, it should have the venturi 3.2 mm on it from the factory. New engine need the break-in run on the low compression and rich fuel mixture for 15-20 minutes. If you want to change the venturi, pay attention to the spray hole location on the NVA . It have to be toward the venturi body. The pivoting nipple can be rotated for the best position of the fuel line from the tank. The metal tank can have a “mesh” wall. This wall will have a series of  diameter 1/8 inches holes, and half holes around the wall perimeter. Mesh wall located parallel to the back of the tank wall spaced 3/8 inches from it. Pickup tube end located in the vee between two walls.
If you want to add the muffler just for pressure - make something simple. Diesels don’t exceed the rule noise level even without muffler. Here’s the pictures of Norvel .061 engine muffler details. It’s being held by the .031 piano wire. The pivoting rear end with exhaust has a groove and wire hold it together. Just add a tank pressure fitting and  fly!

Jerry

[jerry v]

Engine with no muffler will spray exhaust all over the model, and leaking muffler is not a big deal in this case. It doesn’t have to be tight to distort the engine head, and no gasket required. Maybe some silicone to prevent rubbing metal on metal.
More pictures:

Jerry