1QwkSport2.5r

This engine is one of two I got from a buddy NIP from an old military mig-27 foamie target plane kit. The backplate has the "91" stamp. The carb is horrible. Only useful at 3/4-WOT. Midrange and idle are junk. The crankshaft bushing race has worn some (even using all castor brew) but I flogged it with a bunch of props for lack of anything better to do.. It used to idle okay and just had a crappy midrange but I think the more-noticeable crank leakage might be causing the crappy idle. I'm not sure.

58°F, breezy, low humidity.
5% nitro 20% castor homebrew fuel
McCoy MC59 hot plug

MAS K-series props:
11x6 = 13,700 with muffler pressure
11x7 = 13,080 with muffler pressure
12x6 = 11,010 with muffler pressure, 11,070 without muffler pressure
12x8 = 10,900 without muffler pressure
APC props:
13x6 = 10,940 no muffler pressure
13x7 = 10,290 no muffler pressure

The 11" props must be just a smidge off-balance because they vibrated a bit. The rest of the props ran pretty smooth considering.

This engine would run a lot better with a better carb. I was going to change the mixture disk to a current-production piece but I'm not currently using the engine for anything so I'm not going to bother. Down the road if I find a plane that I want to fly extra slow, I'll clean the cobwebs and oil scum off and find a carb for them.

turbo.gst

My Feedback: (8)

Those are good numbers for a K&B 65. I have always liked the 12 x 8, 13 x 5 and 13 x 6 props on mine. I have had great results using stock carb. I never got ahold of a drone carb. I would love to play with one.

turbo

flyingagin

I have a K&B .65 that has ssen a few hours, not yet worn out. It was a later date I think like 95 +- a year or 2. idled and transition well. OEM carb. Going in my current rebuild project. I have proped more like a 4 stroke and in it's current ride propping it just the same. I have hade 2 K&B .20s and 2 .45s. All that is left is the .65.
I have used 12x6 and 13x6 on mine perfer the later
They get a lot of direspect, but I find those who do just don't understand the engines or try to use them in planes that they are just not suited for.
I remember seeing thos drones in the mags way back when.

1QwkSport2.5r

If this were an engine other than the "91" designation, it would have a better carb. These were specified by the military to run at a certain rpm (Randy at Mecoa wasnt sure what the spec was but guessed 5000rpm which is way lower than what its capable of obviously) on 12x6 wood props. Each engine came with a bag of 10 maple or beech props. I ended up with 3 bags of these props which I sold to an RCU member last year.

The problem with the drone carbs has something to do with the idle mixture disk. I think the "cats eye" is mis-machined or something. There was a rumor floating around awhile back about a batch of sportster engines with bad spraybars. Perhaps the military got a deal on a big lot of these engines with the fubar carburetors... They were bolted to a plane, fueled up, and shot in the air at WOT and then shot down. Pretty sad when you think about it...

They run out at WOT fine. The engine I ran today is the only one of my two I've ran. The other one is still un-run but has the same junky carburetor that this one has. I imagine with a good spraybar, the engine would perform properly. Idling for more than 5 seconds gives a very snotty midrange. Give it 10 seconds at idle (I could only get mine to idle down to about 4000 before they loaded up and quit.) and it'll quit on transition. I had the engine on an airboat I built but after having to retrieve mid-lake enough times, I pulled it off and stuck a Super Tigre 90 on the airboat. No more problems.

I will not even attempt to fly this engine until I get a carb for it. Do you have a spare carb that transitions well that you'd be willing to trade? I'd swap you my new un-used drone carb for a good one just for testing purposes on my test stand. The spraybar/mixture disk is roughly $14 from Mecoa if they even have any left for the non-RNV engines.

On my airboat, I got the fastest speed with the 13x6 APC prop - 30mph. The boat flipped when the bow came up a little and the wind caught it. Took me an hour to get the engine to fire again because I didnt have an electric starter. (I had a very sore arm after this adventure... but I was happy with the speed it gave) My Super Tigre S90K turns the 13x6 APC at 13,600 on my test stand but I haven't GPSed it since I got the 'Tigre.

1QwkSport2.5r

I hadn't ran my sportster for a year or a little more. I had forgotten what it sounded like.. (They make noises you wouldnt think an engine should make, even after 2-3 gallons of fuel) I ran mine with 13" props after finding the 11 and 12" props didnt do the engine any justice. It'll turn faster than the MFG claims, but their good power is down low. Below 11k. I'm sure they will turn a 14x6 at 10,000rpm. Based on my runs today, I only lost 70rpm from the 12x6 MA-k and the 13x6 APC. This engine also has a high compression ratio and almost no blowdown period. Its got "poor mans 4-stroke" written all over it (along with burnt castor slime too)

It slimed the crap out of my test stand - bushing has a little wear on it. More than I remember, but the compression is still great and it has a good steady rpm at WOT. I peaked each prop, and then richened it 200rpm for about 2 minutes and swapped props.

My running .65 has no baffle in the stock muffler, and I found no muffler pressure to make it puke from the front bushing far far less.

flyingagin

funny got water wings
I can understand takeing that long to get your boat back. I have made 3 airboats. 2 for a St.40 and last one for a ST .90. that thing moved.
You could also use another brand carb. Finnding one that fits might give you fits. But I have done that on a buch of engines. I now have a little lathe so retrofitting will be easier.

1QwkSport2.5r

So far, the only aftermarket carb I've found that will fit is a Perry and it costs more than a K&B RNV carb does. Last I checked, Mecoa had parts for the non-RNV engines but I dont trust their site. I've tried finding anyone on RCU that has a non "91" carb from a .65 that they would sell me but nobody will give them up.

They have an odd size for the carb base. I figured my ST S90K carb would be a perfect fit but the S90K carb's base is smaller than the K&B carb on the sportster. I tried locating my old thread on my K&B with pictures of the spraybar but I think its so old its been archived. I'll have to look again.

Old thread I started awhile back. Bottom of page two are 3 pictures of the spraybar and barrel. http://www.rcuniverse.com/forum/m_10...m.htm#10068565

Either on page 2 or page 3 is a picture of a mix disk from a RNV engine (I think) that has a different orifice locations.. Take a look see if you want. The pictures are big, FYI.

flyingagin

Mine sure does need a good cleaning
Lost the muffler at some point during many moves. Yep that pepsi bottle is going to be my muffler.

flyingagin

My carb is stuck on the engine. Tried to get it off several times during this current rebuild I am doing. But it just wont come loose. Afraid to put any more pressur on it and destroy it or the engine.

1QwkSport2.5r

I remember posting with you when you first posted about needing the length of the muffler extension. Mine isnt as castor stained as yours, but you can tell its been run... I'll post a pic of mine in a few minutes.

1QwkSport2.5r

The draw bar on these engines kinks the edge of the carb neck a bit. I had a hard time getting my carb off when I took the pics in the other thread I linked to earlier. I loosen the screw and try pushing on the draw bar screw itself to push the back end of the draw bar away from the carb neck. After doing this, I was able to get the carb to wiggle a little and get it free. The two-piece draw bars dont need to be super tight to hold the carb in. If its got a lot of castor sludge around the base of the carb, try heating it up good and hot with a hair dryer or heat gun after knocking the draw bar loose.

Here's my running .65

flyingagin

Yep
I had to stack two togeather. I did intertaine thought of makeing my own muffler adapter, but common sense prevailed. Now I still gota bend the header pipe. That is a whole deferrent story.
I am hoping to lite this puppy up next month and fly it.

flyingagin

Thank's. I will try that. Be nice to remove the carb and clean the engine.

1QwkSport2.5r

Seems as though my computer won't access the forum part of RCU, but I can access other sites fine. Guess I gotta use my phone instead. Evidently Firefox didnt like the forum part of RCU.. I restarted Firefox and it works now.... Hmm...

Good luck. You might need to tap on the screw with a piece of wood or something soft to knock that drawbar loose. I think mine are both bronze.

flyingagin

bronze sounds right if my memory servs me well. I use google chrome But it seems all the browsers stumble with this site. I am more inclined to beleive it is the site that has proplems. I ahve expearnce that exact proplem more times than I can count, that and pic posting issues

HighPlains

My Feedback: (1)

As originally used in the drones, they ran 12-5 Rev-Up props that did not have the logos printed on the the blades that the commercial props had. The props had a 12-5 marking on the hub. One production run was for around 10,000 props.

1QwkSport2.5r

The two engines I have came from the most recent set of kits before they discontinued the program. The sealed boxes were dated September 1990. I still have 2 props somewhere, but they had no markings of any kind. I'm not 100% certain on the pitch, but they were 12" dia. If I can find one of them, I'll spin one up and compare the rpm just for the heck of it.

I'll have to see if I can find something to use as a sleeve and try my ST carb to see if my engine runs any better. The neck of the k&b carb is .623" and the st carb I have is .590".

HighPlains

My Feedback: (1)

I had worked part time for Chris Machin (Progress Manufacturing making Rev-Up props) back in the '70's, and he spent a considerable amount of time on the phone talking to other old time manufacturers like Axelrod (Top Flite), Goldberg, and K&B (Brodbeck). His Rev-Up line of props was started in 1949.

The Mig-27 drone foam airframe was made by Goldberg models, powered by K&B, propped by Rev-Up. It was known as the FQM-117 target drone. In this photo the prop has the classic Rev-Up shape, and the K&b .65

1QwkSport2.5r

Thanks for posting that. Thats pretty neat! These engines are definitely unique and have a useful purpose, and sometime I'd like to put one in an airframe and fly it... I have other priorities, so replacing the carb wont happen for awhile. I'd like to think they have the torque to turn a 15" prop, but I doubt I'll ever try it unless I borrow a prop from someone.

kloz

My Feedback: (44)

Picture 200 soldiers on line, each with a M16 on fulll auto and 10 magazines of ball/tracer ammo. Thats what we did in our intro to air defense at Fort Bragg in 1976. Even though cautioned not to fire at the drones if they were going down, the tracer streams always went into the ground.......

HighPlains

My Feedback: (1)

That must be why around 100,000 of these were produced. I seem to remember that 3 props were provided for each airframe, so the life expectancy was rather short.

1QwkSport2.5r

The kits I received from my buddy contained a bag of 10 wood props to each engine. I ended up with 3 bags of props, 2 bags being maple and 1 being beech. I use my airplane engines primarily for Airboats so I have not used any of the wood props on them. Wood props + water = bad things happening. I never even tried one on the test stand. I went right to Nylon and Nylon composites.

I am going to build a plane, so the purpose of my engines will shift somewhat to double duty. Air boats, and Air planes. (I like to not limit my options with RCing stuff. I'd RC my lawnmower so I could mow from my living room if I could afford the traction motors and servos..

The idea of a line of soldiers firing at one of those beasts using tracer rounds would be a sight to be seen.

There are videos on YouTube of these airplanes being flown by civilians. I heard awhile back since the program was discontinued, that some of these airplane kits are still around and had found their way out of the military and into civilian hands. I think my buddy that gave me the engines has 2 or 3 of these foam airframes laying around. I should see if he still has them when he returns from his Kuwait deployment in June 2012.

flyingagin

Combine both hobbies, i.e. Seaplanes,floatplanes. Yoi could even use a boat as a tug incase you end up dead stick in the water. Would need some kind of good prop shrould on the airboat though. Airboat prop + plane = ouch

1QwkSport2.5r

I've had thoughts of building a hovercraft using an air screw (prop) to power it. Inflatable bag underneath and the whole bit. I would just need to build it should the engine quit that it not sink.

I have too many ideas to put into motion all at once - my wife would never see me... I would like to build a glow powered rescue vessel, but I have other ventures that have priority right now.

Bill Rademacher

My Feedback: (77)

I was in armor in the Army, and we shot at these target drones when we did the defensive tables (TTVI for the tankers out there) and they were hard to hit with the .50 on the M60 and the M1 tanks.

The Bradley Fighting Vehicles could bring them down with their coax 7.62, as their turret slewed pretty fast to keep up with the drones. The local Air Defense unit flew them.

Here around Fort Knox, KY, we still have a number of them flying in the clubs. I have one I fly every new years day. Landing gear, flaps, and a Super tiger .91.

There were two that the army used. One was by Carl Goldberg, like in the picture in a previous post. The other was made by rs technologies.

The major difference was that the RS Technology bird has the motor mounted sideways on an aluminum frame. It also has an aluminum spar. We have tried to snap the wings, but she just hangs in there.

We don't use the K&B motors, for obvious reasons.

billrad