I have a used old K&B 61 I wanted to try to fly tomorrow. I have the right size props, but woodenyanowit they're reamed 5/16" for my ST61 and the K&B uses 1/4" .

The closest 1/4"-reamed prop I have is an 11x5. Is this too little? What would I expect if I tried it?

Thanks! flianbrian

why dont you bush them out with a piece of aluminum tube
to center them up????(then you can use thr right ones)

Higher revs than what the engine was designed to work EFFICIENTLY at.

Don't get misled by the popular conception that more useful power can be gained by running even higher rpm. Every engine has a design RPM range at which it delivers its maximum torque, which, (in the case of a model airplane engine) when the right prop is fitted, will give best performance.

An 11 x 5 will make it rev its head off with little benefit for the model its powering.

You'll have to open your wallet and buy a more suitable sized prop.

For this sized engine try an 11 x 6 or 11 x 7 or a 12 x 6, but it all depends upon what model it will be powering.

My vintage ST .60 powers a Kyosho .40 sized Cub and spins a wide bladed 11 x 6 at about 11,000 rpm max. Fine for the Cub.

11-7 is good....11-7 1/2 MAS is the best prop for the K&B.

most of my props are of course 1/4 shaft size having some smaller
engines 10 size (smaller shaft) KS metals has aluminum tubing
and the sizes telescope into each other so 2 or three sizes will
make a bushing.. stuff is soft and cuts easily so you can center
up the props on almost any shaft smaller than 1/4 US or metric

Well! Guess I'll have to put off running this thing tomorrow .
Not important enough to drive 40 min. to the hobby shop for a couple props. (Though maybe there's some other stuff I just NEED, too ). I had thought about a bushing, but there's nothing in the house suitable.

Would a nice neat wrap of tape work, or is that a known bad idea?

do not use tape you may wind up with a concentric fit--granted
the prop is squeezed between front washer/nut and rear driver
but no soilid fit between prop bore and shaft this might be ok
on a little 10 or 15 small prop but I would not chance on a 60

Ask one of your flying buddies, or someone at the field
if they have any of these plastic spacers. They come with
new spinners....so that the spinner will fit on all engines.

They are very common....ask around....

....don't get hurt by a silly mistake with a propeller....

Dave.

See that ////spinner insert brillant idea some one always has a
better solution not even any cutting and hacking if you had tubing

Brian,

Most "normal" muffler equipped, .60 class engines make their maximal horsepower at around 13,000 RPM. Please see the .60s shootout that was aired in MAN of May, 2003, by David Gierke.

This means that at maximum level speed they must spin around this RPM. Translated to static ground RPM, this would mean propping them to spin around 11,500 RPM.

Using a large prop that will spin more slowly on the ground, will never allow the engine to utilize its maximum available horsepower output (Unless it goes into a very steep dive). Somewhat like using a smaller engine.

Using a smaller prop, that will spin faster on the ground, will cause the engine to spin too fast, again producing less horsepower than it can.

For most normal .60, an 11x8, or a 12x6 are closest to this target.
With the 11x7 almost any .60 is under-propped.

Stronger .60s, that attain their maximum HP ratings at different rpm levels (don't believe the engine manufacturers...) can be propped differently.

On occasion I have used shrink tube, pushrod housing and the spinner bushings Dave mentioned with success.

....if he gets desperate....he might be able to cut a ball-point
pen....and make a spacer....

....I might have something that would work....

wow now I can get that 20x14 on my 09 just bush it down

....just hang onto the prop, and let the .09 spin....

We used to free flight .049 motors with no plane....just hold
them in your hand....start 'em up and let them go....

....they go up about 50 feet or so, and then they auto-gyrate
so bad, the fuel flow gets interrupted, and they die....

(don't try to catch them, they're hot !) :stupid:

ok guys looks like the prop bush thing has been solved --out of
here time to go flying..if I just get them home in the same condition
as they left in

I was really thinking about a 049 powered ceiling fan--now to solve the smoke and noise problem 20* nice size for small room

Good one Daver, I luv it.

Ditto Hobbsy's comments.

Hmmm-- would make a lovely present for the mother in law!!!

The K/B 61 is listed by the manuf. as 1.32 horsepower-definitely not nearly as powerful as any of the modern 60's. Just about any modern .46 has more horsepower.

I fly my late 80's K/B 61 on a R/C Special with an 11 X 7 prop, and it runs like a dream. The prop and the engine seem a perfect match.

Copterdrvr

Copterdrvr,

The K&B makes about 1.32 HP at about 13,000 RPM. Right?

Spinning an 11x7 APC at 13,000 RPM static required 1.46 HP (according to the Reivers prop calculator). So the K&B will spin it at about 12,500.

Unless you intend to use this engine to fly a 15 MPH Goodyear Blimp model, which will allow the engine to unload very little, the 11x7 is TOO SMALL for efficient use on this engine.

Any medium speed, sport plane will require the engine to be propped to a static, ground RPM of 11,500 RPM, so it can unload in top speed, level flight to the 13,000 RPM of maximum output.

The props which closely answer to this are the 12x6 and the 11x8.

The 11x7 will unload to about 14,000. Read my previous post, as well as this thread:
http://www.rcuniverse.com/showthread...+to+prop+a+.60

To see why this is not good..

.....theories look good on paper....and the MAN .60's
shoot-out was good reading....but it's beginning to look
like you perhaps, have not owned a K&B .61, or flown with
one for period of time.

I've been flying them for over 30 years....I have five or six
of them. My original one has been rebuilt 5 times, and is on
the third crankcase. I could say, that probably, I'm
as experienced as just about anyone (except Clarance).

flianbrian ....(who started this thread) said....
Quote: "I have a used old K&B 61"....

The fact of the matter is....the 6550 series perform very well
with the 11-7 prop. The very best prop for a nice crisp one
is the 11-71/2 MAS. The last ones....with the smaller muffler
Kicked off at a slight angle....calls for one prop to be used.
The 11-8. And they pull 'em really good. The older ones won't
pull the 11-8.

The K&B .61's don't like the 12-6....too much lumber, and
not enough pitch.....they're just "doggy" with the 12-6, and
don't perform well. I've flown the 6550's at sea level for
18 years, and at 3000 feet for 12 years.

Trust me, if you don't have an 11-71/2 MAS in the box....
the 11-7 is THE PROP....the motor will dog-out with the
12-6, or the 11-8....all my running is with 15% nitro, and
I've had them in all types of planes. I've flogged every oz.
of power from those motors since I started flying.

Here's one from about 20 years ago....

Dave.

I thought this was the old original cross baffled K&B? If so it it rated at 1.2 HP. Which is only .4 HP less than the FX as reported in the MAN shoot off!

IMO it won't blow up with a 11x5 if you had to use it. But a 11-7 would be much better.

Flyboy Dave,
Your prop selection is based on pattern flying. If you want to use it on a 3-D plane then a 12-4 or 12-5 is probably a better prop. I know its not common to use this engine that way. Recently I saw one on a Sig Senior Kadet, he liked the 12-5 the best.

Hi Dave,

I personally don't own a K&B.

If what you say is true and it probably is, then the K&B 6550 is not making 1.32 HP at this RPM.

It is either making less, or getting this figure at higher RPM.
If the muffler is the high noise variety, then the second is more probable.

With all the different engines out there, my MVVS .49 is spinning an APC 11x7 too, at about 13,200, or so.
And it peaks at about 15,000 RPM.

Yes the K&B is more of an easy going engine, not a screamer.
It is also a 30 year old design, loop scavenged rig, not a Schneurle scavenged ABC.

Yeah. Easy going. LOL