"1/2 A" & "1/8 A" airplanes These are the small ones...more popular now than ever.

MDS F2A 2.5cc

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Old 01-22-2015, 07:33 PM
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MJD
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Default MDS F2A 2.5cc

My justification for posting this in the 1/2A forum, is that it will end up in a 1/2A size model. Otherwise what's the point. Plus, things are pretty quiet round these parts.

Here's a classic MDS speed .15 and pipe, which I think Crosscheck might recognize. I talked to Bill Hughes about it, not a surprise he knows plenty about them, they're well known. Out of the gate the advice was the same that applies to NIB Conquests - ditch the rod. I got a rod from Bill with some OPS bits a while ago. Check the bearings (they're fine to me) and see if it is the 172 or 180 degree timed version (an evolution at some point I guess). It appears to have 180 degree exhaust timing now that I've had it apart and gone over it. What I read about the engine brands it as a poor man's Rossi clone, but that well set up examples are fine runners. So as a sport RC engine this sounds like some good cheap thrills to me!

Apparently years ago you could get them for about $50. They are in current use, on the F2A forum there is an article for a speed trainer that uses one. 5.5"x5" was said to be the best prop they found, not an excessively fast model. You could pull a little bit more shaft load on a small RC model. Typical rpm for these on a single blade CL prop (typically like half of a 6x6 with counterweight) was quoted at 29k in one source. Bill suggested lightening the prop load and trying the Profi pipe on it, running it up towards 33,34k. Sounds like fun, okay.

It feels healthy - lots of compression, pop and bounce, and turns very freely. I chucked up the pipe and spun it with a cotton rag and some Mother's scratch remover. Now it looks more like fine machining marks and shiny sparkly.

Get a load of the bench prop! I knew it was going to be something special from the description.. and boy is it ever. It truly looks like the blank was whittled from a piece of scrap lumber from the floor. The airfoil looks like it was formed with an adze. I love it! It is designed to let the engine spin up pretty freely, and coax some cooling air over the cylinder. Appears to be about 5.5x2.5 to 5.5x3 in dimension but with that section I am not sure how much the number actually matters. When I got it for the Profi 2.5, Bill said " it will have no problem staging the pipe on that prop. Might startle you. You can hand start it with that prop easikly too." Cool.

So weather permitting I'll see if I can bench run the thing this weekend. Time to mix up some 75/25 break in fuel.

.
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Old 01-22-2015, 07:37 PM
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ps the head bolts are typically atrocious, shallow slots, soft metal, and they are an interference fit in the head. I skimmed them down and Dremelled the slots. They are not the standard metric thread pitch so I have no replacements around.
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Old 01-22-2015, 08:00 PM
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That's a nice acquisition..!
Even better if it is a drop in fit for your Profi.
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Old 01-22-2015, 08:08 PM
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Originally Posted by MJD View Post
ps the head bolts are typically atrocious, shallow slots, soft metal, and they are an interference fit in the head......... They are not the standard metric thread pitch so I have no replacements around.
Noticed that right away --- too bad about not being standardized. Socket head screws would have made a great replacement.

Nice job on the clean-up, BTW.
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Old 01-22-2015, 08:18 PM
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It doesn't make any sense for the mfg to use oddball threads.
Regardless, see if you can drill and tap to a larger size when the time comes.
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Old 01-22-2015, 08:18 PM
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Nope - this one is a regular beam mount, I'll whip up something for it. [CP that was regarding being a drop in for the Profi] I'm actually thinking of that stupid 24" span 1/4" SWR delta wing I made about 5 years back. It's got enough area. Actually, I drew up a design to laser cut the fuse from 1/16" ply - and was instantly reminded of the thread the other day where we talked about ugly flying wings and deltas..

The Profi is a dedicated mount pattern for F2A speed pans - two lugs forward, two lugs rear. That engine goes in a dedicated airframe. The MDS will serve pretty much the same purpose it seems to these days in CL - my practice F2A engine.

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Old 01-22-2015, 08:24 PM
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The prop nut is finer pitch than standard as well - M6 x .75. Normal OPS (and some other engines?) shaft thread is M6x1. Lucky I found the prop nut, I dropped it one day and it showed up much later.. which then inspired me to dust off and clean up the engine. The fatter and shorter pipe is the pipe supplied with the Profi F2A engine.
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Old 01-22-2015, 08:41 PM
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I've got a metric tap and die set that has some .75 threaded bits.....so what you've got is probably serviceable through a mail order bolt supply.
At our local bolt supply I recently learned that metric uses "half sizes" in the smaller diameters, too.
So, there is more metric weirdness that I never knew existed.
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Old 01-22-2015, 09:33 PM
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Oh sure there is. I know I am little more than weakly familiar with the handful of standards that are the metric equivalents of the common UNC fasteners. Then there are the variants..
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Old 01-23-2015, 01:17 AM
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I have a few of these engines too, but I have only run one of them though and perhaps I used a too large prop, 6.5x5 (if I remember correctly). I fitted an MVVS .15 carb to mine as I like to have throttles. Rod is still intact at least..

What rod did you get for it, an OPS one?

Are you tapping the backplate for pressure?
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Old 01-23-2015, 05:10 AM
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Someone had added a pressure tap to the backplate already, although it is a standard fitting so I will solder fill it and drill through a more reasonable hole.

There are a couple of YT videos of these, one of them shows someone confusing "break-in" with "breaking" an engine, it is struggling to turn a big prop at about 12,000 rpm. Bet it just loved that.

I think they fall off pretty drastically when you add too much prop load.. it is a speed timed engine.. so aim for 25+ and it would be happy I think. My first milestone will be getting it to run.
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Old 01-23-2015, 06:00 AM
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Niccccce engine you have there!!

I think anything less than.15 size or the power of keeps them in the small plane category and suits this forum as the design could be flown with .061 - .074 to.10 size engines.
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Old 01-23-2015, 06:17 AM
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Originally Posted by Mr Cox View Post
I have a few of these engines too, but I have only run one of them though and perhaps I used a too large prop, 6.5x5 (if I remember correctly). I fitted an MVVS .15 carb to mine as I like to have throttles. Rod is still intact at least..

What rod did you get for it, an OPS one?

Are you tapping the backplate for pressure?
Not sure on the rod - Bill just said "I have a good rod for it" and he said what from but forget. Rossi or another Rossi clone? Others would know more about this, but as I understand it there were several 2.5cc engines through the '70's and '80's that had interchangeable internals, I guess this is the "Rossi clone" crowd.
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Old 01-23-2015, 07:26 AM
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Wow, I go to sleep, and there are 13 posts. I have a couple of these. Sad to hear they need new rods, I likely won't bother getting them, although I need another one that is probably the same for an old X .15. Mine ran ok on a 7-5. About 15,000 with or without the pipe. I am sure they will spool up with the pipe in the air when propped right. I just bought mine on two separate occasions for $50, just to get the pipes. The motors were just a bonus. The screws were tight on a couple holes, and I retapped them. Turns out there was sand in the holes, and I ruined the tap. I thought it was a standard metric thread. The crank gap is pretty big, and it spits out fuel from the front bearing. I was told by Alex that this is a good thing, to lube the front bearing, but it seemed pretty excessive to me. http://f2aspeed.org/node/17 This may be the article that was referred to.

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Old 01-23-2015, 07:33 AM
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I'll take a wet nosed one over one that cooks the front bearing. Rods are cheap and takes all of ten minutes to swap.

So, you wouldn't happen to have an extra X-15 rear intake venturi and needle would you? I am in the market for one, I have a nice example but for that missing detail. Has the extractor megaphone, but the timing has been bumped from the looks of things so I may detach the expansion cone and turn it in to a pipe header. If.. I find a venturi assembly. There has to be one somewhere. I posted a wanted as on the speed forum but got crickets, except in e guy said he had one then evaporated. It is such a sweet looking engine it deserves to breath alcohol again.
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Old 01-23-2015, 07:42 AM
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https://www.youtube.com/watch?v=a9ZAOyJ834U

MDS 15 on a proper prop size for a change. There are YT videos on oversize props and they predictably run like dogs.
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Old 01-23-2015, 07:46 AM
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Here is a pic of the earlier combat one. Much cruder casting. It is only about 500 rpm less than a real Rossi which it was copied from. I use it whenever a field doesn't require a muffler. I believe they were $35 US around the mid 1980's, and worth every penny. I sorted through about 5 on the table at Toledo before I found one that was useable between bad cylinder fits and crunchy bearings. OK just looking for stuff. I can't even find the rear rotor at all for the X .15. I was going to change over another casting I found to make it a front intake, and then needed a rod too. The stock one has a crack at the bottom rod hole after one run, and hasn't run since. I think I may have been 14 when I got it. Nevertheless, if you want a venturi, I can make one up for you, the needle valve I am not sure of, but you could drill and tap a hole for whatever pressure fitting you may have, and then use a remote needle, or whatever. I will need all the dimensions as I cannot find mine, and don't know what kind of needle you may have. I would say to use a F2D combat needle, but they will only work with a bladder, and will not open up enough to run a pipe, or even suction. PM me with dimensions whenever you get them.
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Old 01-23-2015, 08:17 AM
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I read elsewhere that Tower was selling them for about $50 in the late 80's or early '90's. Makes sense, at that time MDS had no real distribution in NA - we had imported a few .40's and .61's late '80's and peddled them locally and I have a couple of those left and one FIRE 10cc. Estes looked at them at the time (and at Mutunuc which went nowhere, I have a .61 of those too I got for review and test - another decent OS clone is all), then they were picked up "for real" by.. Tower I guess or did someone else get in there first. forget. That was when they started getting general exposure in the US. And when people found out they ran strong but the carbs were leaky and they didn't tolerate much over 5% nitromethane, as opposed to being fine up to 15% or so as most folks were used to. So some folks had issues.

The machine screws in this are really just the metric equiv of UNF versus UNC. So one step off the normal beaten track I guess, enough that I can;t pick up a pack of spares from the Dubro/Sullivan or car department at the LHS. I'll order some.
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Old 01-23-2015, 11:45 AM
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Okay, here are some of my engines. There older ones came in polystyrene boxes and are marked Uctkam. While the newer ones came in MDS boxes and have the MDS markings on the case. I don't know anything about the relations between the two companies though...

The Uctkam ones are said to make their max power at 22000rpm, without the tuned pipe. Running in is supposed to be done at 6000-7000rpm, strangely enough...

The MVVS .15 carb is a direct drop-in for those who are interested in that. The Norvel .15 carb should also work but it is more restrictive. I have use a similar pipe on an MVVS .15 and it peaked around 23000rpm. I wonder if these engines where really meant to run around 30000rpm? Hence the rod might be good enough around 22-23000rpm?
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Old 01-23-2015, 06:13 PM
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Looks like we all have them, and no one flies the piped ones. I have flown the combat one about ten times. It really is pretty good so far. My box on the one looks like yours Mr. Cox, and it is marked as Ucktam or whatever. I think the U is really a C in the Cyrillic alphabet. I don't know, but the wife 'knew a bit' at one time. My pipe ones worked fine, the one didn't start real easy unless it was over primed. I think Alex mentioned they would go about 135 mph on a real speed plane. I timed the one in the picture that his son flew, and seemed to remember about 100 mph. I think his son was about 10 at the time. He few in the pylon too for an official flight.
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Old 01-23-2015, 06:15 PM
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Hi MJD,
I thought you would have fun with it !
Early 90s sounds about right. A club member imported some. My friend got it and some 6.5cc (.40)s in a trade.
I remember them in styrofoam boxes, with several head shims and hillarious Russian to English instructions.

We have countless jugs through the 6.5s. Got hex cap screws from HobbyHobby I recall. 15% with two head shims. The carbs leaked air badly, were repaced by various others. My current one has a Webra carb and a Rossi semi tuned muffler, so it now a 'UN engine' of sorts ! Great runner, mounted in a flying boat.

My freind moved north of Peterborough 25 years ago. I see him once a year in Feb. for a Cabin Fever Fly, from a beach area over the frozen lake. We barter and trade, and he knew I wanted the 2.5cc, so he kept 'the price' high... A few years back he gave it to me.

The box and shims were lost in a move. We did try bench running it 30 yrs ago. Old fuel and a dodgy glow battery. Got a few pops out of it on a 7-4. (no electric starter) While fiddling with it, it started pouring and we bailed inside. Engine has been sitting in boxes ever since. It deserves to be run !

I have a HOB Quarter Midget wing kit I was going to make something for it, yours if interested.
The clubs around here, hate the sound of 'real' model airplanes...

Gotta make some time to fly with you this summer...
Brewery expansions are nearly done...

Take care,
Have fun,
Dave'crosscheck'Fallowfield
Maac 6437
Unabashed Combat Team
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Old 01-23-2015, 06:31 PM
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It sounded very eager to run today. I got a handle on the incipient binding on the big end - yes it is tight and needs some clearance, but the bug end bushing is actually a bit thicker than the crankpin, and although it turned freely when assembled there was next to zero clearance, there were swirls/fret marks on the backplate. Maybe some fine swarf got in there too. Anyhow it tightened up just as it faded out, and did not seize. So it came apart and cleaned up fine. Piston and liner are peachy. This would mark the first time I have installed a non-original connecting rod in an engine before, so it didn't occur to me to check that dimension. This is definitely my speed trainer engine.
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Old 01-24-2015, 02:16 PM
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Here's a photo of my speed trainer, with Ucktam 15, only mods to the motor were to bush the big end and fit a new head insert to use standard plugs, uses an Irvine pipe.
It's for control line by the way.

Video clip here,

https://www.youtube.com/watch?v=sWlchWYBzmM

Made 189 kph.
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Old 01-24-2015, 03:52 PM
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That's a very cool looking plane and a great flight video...!
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Old 01-24-2015, 03:59 PM
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It is nice to have landing gear on those. Much better than a dolly, with shaft runs.
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