bogateer

Of the "old style" Killer Bees meaning high-performance versions unlike todays repckaged renamed version which engine was more powerful....the .049 or the .051? Commmon wisdom dictates there is no replacment for displacement but I'm not sure and have never read that the same mods that made the .049 Killer Bee high performance (such as the lightend crankshaft) were incorporated into the .051 version. Just out of curiousity what other mods were done to increase performance? I'm guessing a lighter piston, the venturi, and probably something with the cylinder porting but this is only conjecture...the only thing I distinctly read was the lightened crankshaft. Finally....stupid question of the day....what makes the difference between an .049 and an .051? Is it bore or stroke or both? I know the .051 allows you to compete in different classs for certain contest events (I know nothing of contesting) but wouldn't it seem to put one at a disadvantage to run the smallest possible engine in a certain class? What am I missing?

Thanks,

Rob

PS For those curious enough to have red this far my latest project is a Frakenviper. A Cox Hyperviper with as Killer Bee engine. Not finished yet. I have both the .049 and .051 Killer bees available to use. I am going to cover the wings in Ultracote for strength. I'm hoping the engine more than makes up for the added weight. I get miixed reports s to whether the original Surestart engine wa adequate enough or too anemic. The other mod I did was to completely rehinge the elevator...the stock system binded like crazy so I removed it and glued in good-old fashioned cloth hinges....works smooth as silk...or cotton....or what ever. When I get it flying I'll give a report.

ffkiwi

The whole point of having 'twinned' capacities or 'under and over' displacements is that under normal fuels, props and conditions there should be NO difference in power between the two variants, to allow competition in two displacement classes by a simple engine change.
In the case of the Cox, the difference is merely in the bore-0.410" for the 051 versus 0.406" for the 049. You cannot pick this up by eye-which is why the 051 piston has the shallow groove in it-it is there solely as a distinguishing mark.

AFAIK, the original Killer Bees got their performance from a twin ported cylinder, a lightened piston, lightened shaft and a high compression head, plus an enlarged venturi. The lightened piston and shaft were the innovations-all the other design aspects had been used before in various reed valve models. I am not aware that there was any change as such to the actual cylinder porting from what had gone before (ie TD or Black Widow)

The other variation you get on a related theme with other manufacturers-is where the came crankcase is used to produce a range of engine capacities-eg K&B 29, 35 and 40 and Super Tigre G20/15, G20/19 and G20/23-where the increased capacity may arise from an increased bore, increased stroke-or both. Sometimes it works, sometimes it doesn't-depending on the case size-the ST G20/19 and G20/23 were not very successful-but the original G20/15 remained in production from the early 50's right through into the 70's. In K&B's case the early 60's 29 case proved capable of handling the 35 and 40 capacity increases very well-in fact the K&B 40 was probably the most successful engine-commercially-that K&B ever manufactured-and is still around!

ChrisM
'ffkiwi'

kersplat

The Killer Bees have had the following features. Tapered "Tee Dee style" type cylinders, Lightened pistons, Sub- piston induction, crank shaft with cutouts in the crank pin area of the shaft, Relieved crank case bore for a faster turning crank shaft with less drag, High compression head "TD style", A large bore venturi, An oil groove in the lower piston skirt and a low drag spring starter. Oh , and also a steel washer behind the thrust washer to allow the use of a starter.

The Killer B 051, had a larger cylinder bore. The stroke was the same. The RPM was identical in both. I believe the .051 had a minutely,"and I mean real small difference" better torque curve.

bogateer

Thank you Chris,

I appreciate you taing the time to reply and explain that to me. Never having contested I don't understand the rules but what is the "advantage" of being able to compete in two classes with what I presume is the same plane (via an engine swap)? Wouldn't the "higher" class have amongst it higher performance engines putting the "Barely made it" engine/plane combo at a disadvasntage? Kinda the opposite of wrestling and boxing where you want to be the most powerful in the lightest class possible. Just curious...it's sometihing I've wondered about for years but never brought it up as I never had the occasion to.

Thanks,

Rob

bogateer

Thanks Kersplat for taking the tim to explain the differences in the engines to me. I appreciate it.

Rob

ffkiwi

It's very much a traditional thing Rob-you have put it in the context of F/F and the early days-or rather the 40's when the different size classes were evolving-and the concept of Class A,B C and D etc evolved [bear in mind that the class limits changed over the years-1/2A as we now know it didn't even exist until 1950 (and even now the name is a misnomer-Class A goes up to 0.199 cu ins!) I suppose that engine outputs were largely a lot closer in the early days-and models were a lot larger-so it was feasible to swap engines and compete with the same model in a higher or lower desiplacement class-depending which way you swapped! The theory at least has always been that you shouldn't have to retrim the model as a consequence of the change.
In the 50's various manufacturers started producing 'twinned' displacement engines-K&B with their 19&23, their 29 and 32, O&R with their 29 and 33, Forster with their 29 and 31, Atwood with their 49 and 51 (that's .49 and .51 cubes by the way!) As the 1/2A revolution took off in the early 50's a few manufacturers saw the benefit of doing the same thing with the smaller motors. Atwood were the first with their 049 and 051-follwed by Holland with the Hornet 049/051. Cox were not innovative in this respect-they merely followed the crowd-and waited until 1962 until they did so (the TD 051 was the last model in the TD range to be put on the market)

The various classes still exist-but only in US FF rules-so the incentive is no longer there for this practice to be widespread-it still seems to go on in 1/2A and A a bit, but not much else-though K&B in recent times (ie in the last 25 years-have produced the 3.25 version of the K&B 3.5 FR, and a 41 version of the schneurle 40 to allow this class 'twinning' to go on-but usually only to special order-these oddball sizes have not been a regular production item.


You are quite right in that there is little advantage in using the smallest size on engine in the next class up-but people stillseem happy to do it. There is one other example-in the past a few UK fliers have used over size FAI team race engines such as the Eta 15 bored out to a 2.6cc capacity, to compete in Class B team race-which has a 5cc limit (.305 cu ins) here they are competing against racing glows-but hoping that the diesel's economy will allow it a chance against the glows speed by having far fewer pit stops-or perhaps none at all, in the race.

In R/C we are seeing a different trend-that of capacity creep in engines above 099. it is a small step from a 10 to a 12, 15's are becoming 18's, 21s are becoming 25's, 28's growing to 32s-, 40s to 48's-all without increasing the physical size of the engine. Even the Indians have produced a 1cc version of the mills 75, a 1.5cc version of the 1.3, and a 3.5cc version of the 2.4........

ChrisM
'ffkiwi'