Vintage K&B 61 power RPM
 

Hi, I have a Sig Kadet that performs well with the OS 46AX, I needed the 46 for another airframe so the Kadet now has my K&B 61 mounted.
The 61 will turn the 11x7 prop 12,200 RPM
The 46 was turning 10x6 15,000 RPM
Am I correct in thinkling the 61 is going to be sluggish comapred to the 46?

I was hoping for the Kadet to become a handful of fun with the 61 but not unless it makes a bunch more torqe because the RPM just doesn't come close to the 46.

RE: Vintage K&B 61 power RPM
 

I think you'll find that, assuming the K&B isn't wore out, that you'll have a much better flight, especially at low (landing) and medium throttle. I doubt if the top end changes at all because the plane's speed is dictated by it's design. I think you made a good choice, and will probably not go back to any 46.

RE: Vintage K&B 61 power RPM
 

The larger prop results in more efficiency so that will make for a improvement.
Based on the numbers you provided, the .46AX engine develops about 1.5hp and the K&B .61 develops about 1.4 hp. The speed difference is under ideal conditions the .46AX might go 85mph whereas the .61 might go about 81 mph.
So you may not see a difference between the two engines but the larger prop on the .61 engine may feel like it pulls stronger though. Even though the static thrust is about equal for the two engines and their respective props.

RE: Vintage K&B 61 power RPM
 

I'm hopeing for verticle straight up power over speed as it's just a trainer type plane, I think the 11x7 prop is about small as the KB can do.

RE: Vintage K&B 61 power RPM
 

Reaults. K&B with header and pipe 11/7 prop @ 13200 RPM vs OS 46ax with muffler turns 10/7 prop 15000 RPM
I couldn't hardly notice any difference in power, the plane flew about the same with either one.

RE: Vintage K&B 61 power RPM
 

I doubt either one will pull it at 80 MPH. 60 VS 64 perhaps.

RE: Vintage K&B 61 power RPM
 

Try a 12 x 4 for verticle.

RE: Vintage K&B 61 power RPM
 

My gut feel is that if you use a 12 X 6 prop you will get the ultimate thrust from the engine.  Turning high RPM with a smaller prop makes a lot of noise.  Using a prop more fitting the power band of the engine will produce the best performance.  A bigger prop at a lower RPM more than off sets all the extra RPM (and internal wear and tear) on your engine. 

But, alas, it is your airplane and power plant, do what you want with gusto.  Have fun!

RE: Vintage K&B 61 power RPM
 

The engine bogs down a bit on a 12x6, the RPM is not that much more on a 12x4.

RE: Vintage K&B 61 power RPM
 

Way back then the common propellers to use on the .60 or .61 engines were 11x7, 11x7.5, 11x7.75 (seven and three quarters) and the 11x8 sizes. 12x6, 12x7 and 13x6 props were used too. Usually the engine had to be really well broken in good to run the bigger props though, but it depends on the engine brand though. The engines that liked to rev up more used the smaller 11x7 or so props and the other slower rev'ing engines used the higher pitched props (11x8). But I remember quite a few guys running the 11x7.5 and 11x7.75 props a lot, myself included).
The 12x6 props of that era were quite popular on the engines too. But back then it was Top Flite, Rev-Up, andf Zinger mostly. We didn't have fiber filled plastic props at the time, the nylon props were quite questionable as to whether they would come apart on you or not.

I haven to have a old Fox .60 Blue head engine (with the dual plug head on it) and it is using a 12x6 prop at present too.  I used to run a 11x7 prop on the Fox Hawk .60. But with a Fox Eagle .60, it tended to like the 11x8 props.  If I remember correctly I used to run a 11x7.75 prop on a K&B .61 a long time ago.

RE: Vintage K&B 61 power RPM
 

I always thought my K&B .61's ran the best with a TF 11 x 7.75, but that was on the airframes I was using. Years later I played with it on .40-.45 sized aerobatic planes and found the I preferred larger props in that role.

RE: Vintage K&B 61 power RPM
 

Clarence Lee emailed me that he suggested an 11x7 as the most rpm out of the engine due to crankpin limitations. I can't remember the rpm limit he quoted, but it was around what we're talking about here- 12k.

RE: Vintage K&B 61 power RPM
 

I just installed a somewhat similar engine, the old Super Tigre V60, on my .40 size Escapade. I think you will notice the acceleration is greatly improved and the top speed somewhat better since there is a lot more torque to pull the plane.

RE: Vintage K&B 61 power RPM
 

I recall the K&B .61 running really well on a 11x6 with the stock muffler, RPM was in the upper 13,000 range. Most of the 12x4 props are also wide blade props and should run only slightly higher than the 11x6.

RE: Vintage K&B 61 power RPM
 

Ithink later engines had this area strengthened. About the time when they came out with the pumper versions.

RE: Vintage K&B 61 power RPM
 

Here is a thread that has some good info on the K&B .61, along with the CF Lee PDP version, and current K&B Twister 61. Earlier in the thread they speak of the older version having a pressed in crank pin that limits the rpm to 13000. Some good info....

http://www.rcuniverse.com/forum/fb.asp?m=5433641

RE: Vintage K&B 61 power RPM
 

The older PDP version one is what I have. Thanks. I should have remembered to mention this.

RE: Vintage K&B 61 power RPM
 

Ithink they all have pressed in rods except perhaps the very latest version and the Twister. But even with the pressed in pin CL says the engine runs well on a 10x8 prop with plenty of nitro at 14,000 RPM.</p>

RE: Vintage K&B 61 power RPM
 

Did we decide that the stock K&B 61 is better on big lumber ? So what size prop goes well with it? I am in the process of rebuilding mine and plan to install it on the front of my 40 size Great Planes Escapade in place of the Super Tigre V60 that is on it now. The Super Tigre V60 is very impressive on that plane and it is a similar engine to the K&B 61.

RE: Vintage K&B 61 power RPM
 

Here is a old review done by Peter Chinn with a K&amp;B .61 Lee Custom with pump engine.
http://sceptreflight.net/Model%20Eng...tom%20.61.html
He did get the best results using a 11x7.5 and 12x6 size prop at the time.

I think for the Escapade a 11x7.5 to 11x8 size prop would do the trick or a 12x6 if you wanted more thrust. You just may have to try them all to see which prop works best with that engine and plane combination.

If anyone happens to have the old back issues they did magazine reviews for the K&amp;B .61 in the March 1991 Model Airplane News, and in the November 1975 issue of MAN too.

RE: Vintage K&B 61 power RPM
 

Although the engine may get the best power with an 11-7 or a 12-6. You don't need that much power for a Kadet, and both have too much speed for a Kadet. You need a higher thrust and lower speed prop, if you think a 12x4 is too light then perhaps a 13x4, or a 13x4 cut down 1/2".

RE: Vintage K&B 61 power RPM
 

I have a old Kadet Senior that I built up many years ago and it would fly fine with a .35 engine on it. I had a old OS .60 open rocket four stroke engine on it and it had way too much power for flying the plane. Thus it wound up at 1/4 to 1/2 throttle most of the time for flying the plane around.

But the ARF Kadet Senior planes seem to need a .60 engine on them, as they seem to build up more more heavy in weight in comparison to the kit built versions.