Dan Vincent

In 1968 Chuck Cunningham of RC Modeler magazine wrote an article suggesting a new racing class using plain bearing R/C carb .15 engines. This was meant to introduce folks to racing with the lower powered sport engines of the day.

The idea went over pretty well and soon .15 pylon racing became very popular. After much ado about rules such as the carburetor idle and tapered or non-tapered wings several racing clubs from various corners of the US held events and within a couple of years the AMA added Quarter Midget racing to their event calendar.

In the beginning the Fox and OS Max .15's were compact and would rev willingly so they were the obvious choices.

Soon after some performance oriented guys started adding carbs to the Supertigre G20/15 for a little more speed. World Engines then made the ST G-15 available and performance really jumped.

1) Fox .15
2) OS Max .15
3) Supertigre G20/15
4) Supertigre G15

Dan Vincent

Not to be outdone, K&B introduced their Schneurle-ported Series-72 .15 with rear drum intake.
All previous enignes could swing a 7 X 5 prop, the K&B had excellent torque and could easily handle a 7 X 6.

The K&B had a soft piston and the factrory soon upgraded with harder parts. With the new piston/cylinder came a solid crankpin. The early engines had a hollow crankpin.

In 1973 Taipan of Australia made their gold head rear exhaust .15. Here is a stock engine and another that had the head fins shaved. The Taipan was a willing revver but didn't have the torque of the K&B.

Taipan went through a succession of models with aluminum, grey plastic and black plastic backplates.

1) K&B S-72 .15 (right side)
2) K&B S-72 .15 (left side)
3) Taipan Gold Head .15
4) Taipan with modified head

Dan Vincent

In 1975 the Rossi .15, fitted with a Perry Carb, showed up and took over the Q/M racing scene.
The Rossi shown below came from George Aldrich and he said it was the fastest stock Rossi he had ever seen and he refused to modify it. It has a steel backplate on the spinner which George said was very unusual.

The Cox Conquest was introduced in 1976 and was very close in performance to the Rossi. This one is a "Ron Young Special" that has an ABC piston/cylinder.

Shamrock imported the HGK .15 which looked like a real contender for Q/M but poor piston fits put it out of the running. R/C versions of the HGK used a grey Perry carb.

The ultimate king of the Q/M class was the Nelson .15.

1) Rossi .15
2) Cox Conquest (Ron Young Special)
3) HGK .15
4) Nelson .15

matchlessaero

Thanks for putting up these pics Dan!

The .15 class was always my absolute favorite! Watching 4 screaming meanies taking off on mini pipes while pushing 6" propellers at 23k+ is a thrill I will never forget. When I raced Q500, the midgets always held my attention more than anything. Unfortunately, before I could get myself into the class, it began to disappear.......

I still one raced by 'Racer' Rick Landers, Mike Klutz and others. I picked it up from SpinDR in the late 80's for a speedplane project (modified QM with a tuned pipe that ran 157mph through the traps) Its somewhat different than the one in your pic, as it has had almost all the fins machined off both the case and the head.

Dan Vincent

Jeremy,

Yes, I always enjoyed listening to those screaming .15's. I saw one guy taching his Nelson at 28K...on the ground. It had to unload a couple more in the air.

Many of the racers here in Florida stopped racing when they did away with the QM-15 class and made it QM-40. I guess they didn't have enough .40 classes.

I still have a HOB "Miss Dara" and two "Shoestring" kits, plus a couple of fiberglass fuselages for "Rivets" and a DH.

Never did get the OPS .15 but they weren't that popular.

ajcoholic

My Feedback: (10)

Dan, I am still running one of those 75' Rossi 15's in a small plane of my own design (used a set of Ace foam wings that I glassed, and the fuse is a simple box with the full tuned pupe inside)

I was running it in a Sig Wonder before that. One heck of an engine! I did remove the brass ring on the crank however, after it split and shedded itself (luckily not harming the piston/liner!) one flight... but thats another story!

AJC

Dan Vincent

Andrew,

That Rossi was a class act all the way.

George said you could swap internals between the Rossi and the Cox Conquest. I never tried it but if he said so it has to be.

wild fred

My Feedback: (3)

I remember the q-midgets well! as a kid I used to go with a neighbor that raced them, and us kids got to flag the pylons; about 1975-76. tropic aeros r/c club in miami. rossi's were king. us kids flew c/l, as r/c kinda expensive. my neighbor flew pro-line. ran rossi's. I've owned cox conquests since, and remembered the rossi guys used to refer to the cox as a "turkey engine" , but it ran well...the old o.s. III 15 you pictured was my first c/l engine bigger than a cox 049. When I got a radio in 76, bought a muffler and r/c carb for it and it was my main r/c engine for a year! in fact, bought a bushwacker kit since it had a ply muffler so I could hold off on the muff. purchase; wound up having to buy one anyway! got a g-15 later (i think g-15, had solid head w/ 3 fins cut into exhaust side. a strong runner, had it in a doubler II and a flea fli+10 later on.

BobHH

My Feedback: (18)

Dan, how about that little Cox Conquest 15. I had one years ago. Bought it for a P39 1/4 midget racer but never finished it. I did fly the 15 in a little low winger. It was quite a screamer. I think RJL is making it now.


Bob Harris
Early RC Models
www.earlyrcmodels.com

Dan Vincent

Wilfred,

At least you got to see QM .15 racing before they dropped it.



Bob,

The Conquest had quite a run.

Cox sold it as a Cox Conquest in 76 and it was available in R/C and FF versions.

Then K&B added it to their line and added a Q/M Special to the line. It had the smooth head like the FF version but could be had with a straight venturi or an oversize bore RC carb.

After that RJL took over production.

I guess I need a stock RC version for my collection. I did have the K&B Q/M Spl but it ended up in The ECJ museum in Colorado.

gcb

I think initially there was a dollar limit on the retail price of an engine ($60.00?) which kept extremely hot...and expensive engines out. This was an attempt to keep it low key. Some held "claiming" races where you could claim another flyers engine for the $60.00 plus a few bucks.
This worked for awhile until the "need for speed" took over.
I think the initial rules called for a plain bearing engine also.
Anyone remember this more accurately?

George

William Robison

My Feedback: (3)

George:

In his first post Dan mentkioned the plain bearing restriction. That was just about the first rules change. Need for sped, you know.

Bill.

ZAGNUT

My Feedback: (1)

anyone looking for a good .15 at a reasonable price should check out the MVVS. similar design to the rossi and cox, big fat 12mm crank with a nicely flowed induction port and designed primarily as a rear exhaust (see pic)

the timing isn't what it should be though and needs a bit of work. after playing with mine it will turn an APC 7x4 at 23K on 10% nitro and open exhaust. this is also with the stock head button that has a lot of room for improvement

in my haste (or was it too many beers?) i didn't use my brain enough before porting it...parts are super cheap though and i now have a new cylinder/piston/rod to play with when i get the time. the head design man at MVVS is a nice guy and made sure i got a really tight set like i wanted. i'm hoping to get past 27K with a 6.5" pylon prop and pipe on the next try.


dave

Dan Vincent

George,

I'm not sure the plain bearing was ever a rule. It was just that Chuck wanted to use the standard RC engines of the day.

Competitors being competitors soon led to certain clubs adapting carbs to K&B Series-61 and Supertigre G.20/15 engines with BB shafts. The need for speed was on.

There were some real hot beds of Q/M competition around the country and Ohio, Kentucky and California were a few which had separate club rules. If you went from Kentucky to California chances are your model wouldn't meet their local rules.

When the AMA adopted Q/M as an event the engine idle rule was in effect. You had to have an engine which had the same manufacturers' carb and the model had to stand still at idle for a certain length of time. This would stop the super-tuners from mods which would cause more thrust at idle.

When a fellow from Tennessee started importing Rossi engines and fitting them with Perry carbs he was selling them for around $95. Even though this was a flagrant violation of the rule concerning the carb not being from the original engine manufacturer, the AMA rules committee said it was OK but they did rule that no engine used in Q/M could exceed a MSRP of $59.95. As you can imagine a furor arose because you were no longer competitive unless you had a Rossi but the price magically dropped to a more reasonable $59.95.

Remember when the Cox Conquest came along?.......$59.95.

ajcoholic

My Feedback: (10)

Funny I paid allmost $200 C for my Rossi NIB aboiut 5 years ago... and if I left it in the box, well, they go for a good buck today especially NIB with papers and accessories. But I tell you the engine was made to run,and run it does! I would never make a good collector, Dan, as I have to run the darn things. They call out to me "run me, run me"...

AJC

coffeemug

My Feedback: (6)

Dan, I'm really enjoying your history lessons. I recently picked up a K&B C/L speed .15 and it appears to be identical to the one in your picture minus the r/c carb and exhaust mod. Since its got an "A" stamped into the mounting lug instead of "B" can I assume it has the soft piston/hollow crank?

Nick

gcb

Nick,
I have the CL version also. K&B dropped the design when they bought the Conquest .15 from Cox.
I have never had a Rossi...too expensive.

AJC
When QM dropped the engine price rule, Rossi and others raised their prices immediately.
I still have some Fox .15 slant plugs (all CL) and some OS Max-III .15's (CL and RC). They are still good runners...but not nearly as fast as their BB race-bred brethren.

Dan,
Sorry I missed the plain bearing part of the first paragraph. Sometimes the old neurons don't shake hands.

Nick,
I agree with the MVVS .15 being an excellent engine. I have one RC glow and two diesels. One diesel was bought as a CL engine, the other I replaced the carb with a home-made venturi. All run well.

George

Dan Vincent

Nick,

Serial numbers can be very misleading.

Whenever K&B made a new competition engine John Brodbeck Sr. would take a group of engines, maybe 100 or 200 and number them "B" XXX for Brodbeck and the S/N. He would then pass them out to competitiors for testing and evaluation.

The A in your serial number probably stands for Airplane.

Here is a picture of a couple of K&B S-72 .15s. The engine on the Tatone Motor mount does not have a S/N as it was built for me at the factory with the hard piston/cylinder assy and solid crankpin. When K&B used a replacement case there was no S/N.

When K&B made the first 3.5cc outboards in 1976 I was supposed to get one of 12 prototypes. I got a little concerned when it didn't show up and called John. He said his son had accidently mailed it to someone else so I was to get one of the first production engines.

When the engine finally showed up I looked at the S/N which was O-1625.

A few months later John and I were talking on the phone and I mentioned they must be very fast at putting engines together. At first John couldn't understand why I had such a high S/N when he gave specific instructions to pull one of the first engines off the line and get it mailed to me.

John thought about it for a few seconds and said "I know what happened." He went on to explain that back in the days of the greenhead engines they built the engines and then stamped the S/N on their way out the door.

Later on they stamped the S/N on the case and then put them in boxes. They would move the boxes to another table for assembly. Sooooo....in my case when the put the numbered cases in the box the low numbers ended up in the bottom of the box and higher numbers on top.

This is why you will often see a K&B engine with obviously later parts with a lower S/N than an earlier version.

As far as I know K&B made the run of Series-72 engines and then stopped production because John knew they would be making the more modern Cox Conquest engine with its' rear exhaust.
The Conquest would rev higher and made almost as much torque as the K&B S-72.

There was also a problem in obtaining quantities of ball-bearings during that period and although the S-72 and Veco .19 took different bearings, John was forced to pick supporting the K&B/Veco .19 line over the K&B 72-S .15 as there were so many in use and demand was high.

Some of those K&B .15's were real screamers and there were many wins over the early Rossi .15s'

raddad

Hey I just found out what kinda engine i have it's a taipan gold head i purchased on a Q-midget fiberglass {little toni} I think it is for 25 dollars. thanks for the info Dan I'm looking forwards to flying this thing.

gcb

At one time I thought I would try a boat so I got one of the early K&B .21 outboards. Don't know what the SN is and it's currently packed under a bunch of modeling stuff. It was one of the earlier ones made when they used the Perry carb. Well, things came up and it got put on back burner, never to return to top priority. Hull incomplete in garage, engine still NIB...since about '76 or '77. (Sigh!!) Still haven't tried boats, but someday...

George

Dan Vincent

George,

The first time I started my original K&B outboard I threw a rod. It went from 0-to about 27,000 so quick I couldn't get to the throttle to cut it back. I also discovered you had to cut a notch for the lower end in your boat holder to keep the engine straight when you hit it with the starter.

I called John and he sent me a new rod, piston and cylinder. The replacement rod had a slit for oiling whereas the original didn't have the slit and they could run dry very quickly until fuel had a chance to lubricate the engine well.

Another weak link in the first version was the main lower prop bearing. It was one solid piece and had trouble with premature wear. John then made a two piece lead-teflon bearing with a little green thing in the center. John sent me a complete lower end with the new bearing to convert my original engine.

K&B quickly dumped the perry carb and went to an exhaust throttle setup on the second series.

Those K&B outboards were unchallenged for years and from what I here are still at the top of the food chain in 3.5cc outboards. I saw a Rossi 3.5cc powerhead on e-bay that bolts to the K&B lower end so that may be a runner.

OS makes a decent 3.5 outboard which is a fair runner but I understand the Thunder Tigre 3.5cc outboard really isn't competitive. Wonder why OPS never went into outboards.

Japanman

Dan,
Back in N.Z I have a K&B 21 outboard that my brother bought back from the U.S- IT was given to "us" by his brother in law- Not having it in front of me it is hard to give seial No.s or anything but it looked old to me when I first got it- and quite low run time I`d say (but seized up from sitting around forever). It had a very fine pitched bronze prop that looked standard. Well I was going to ditch the prop as it just looked far to low in pitch for fun, but that being the only one on hand the sunday afternoon the boat was ready, thats what it ran with. Boy, it was fast enough with that prop! those engines can rev can`t they? Both my friend and I thought it was a hot engine to go that fast with such a fine pitch prop- We`ve both seen other K&B 21`s running on tunnelhulls and while not having a side by side comparison there seemed very little in it. The engine didn`t sound like it was at the end of it`s power band , either.

Was there an early engine that was hotter than subsequent versions? Our one shows no rework marks.

You are probably THE man to ask this, The liner is frozen in the case- What would you suggest a good way to get it out to be?

J.M

Dan Vincent

Stefan,

If you have a bronze prop it's probably a J.G. look at the side of the hub it will probably have JG on one side and a size on the other side. J.G Props were very popular. My K&B outboards came with aluminum props.

If I were going after absolute speed between an inboard K&B and an outboard I would go with the Inboard every time. The outboard just makes it easier as everything you need is all in one unit.

Find a local R/C boat club and see what they recommend for props in their water. I remember a race I covered at Stone Mountain near Atlanta, Georga that had red, muddy water. The guys from out of state were getting so much bite in the muddy water they had to drop back in pitch to get their engines back up into the proper RPM range. Local conditions vary and the local guys are the experts.

I hear the latest K&B goldhead outboard is their hottest ever. I'm not into boats any longer so I'm not current on the latest goodies. The early K&B outboards had shorter turning fins below the prop which K&B later modified to get them to turn on a dime in a tunnel-hull.

R/C boats can be a lot of fun.

Oh yeah, the K&B outboards were ABC so it can't be rusted. Try heat or cold to unstick it or find someone who works on engines to help you out..

raddad

After looking at some pics i believe i bought a cosmic wind instead a little toni.

Thanks again for the info Dan

Japanman

Dan, How about the antifreeze trick?

J.M