Larry Legg

What is the best engine for a Bobcat 50 in the $100-$250 range?

I got a Bobcat 50 pusher jet for Christmas.

http://www.nitroplanes.com/usbojet5051n.html

I am looking at a Clarence Lee Modified K&B .61 engine with a Mac tuned pipe for power. Has anyone had any experience with this engine? Also a Tower .75 looks good.

What is the best speed for the $$$$

Thanks

Flyboy Dave

My Feedback: (21)

I think the Big Dog right now is the Tower .75 ....at $95.00 it can't be beat.

Look at this performance with the Tower and a 12-6 wood Zinger prop....

http://www.rcuvideos.com/view_video....0e5a00c1e221eb

russm

i was thinking about a rossi 40 w/ a tuned muffler. look on ebay for new in box engines. i picked up a tower 75 for about 60 bucks. i just syarted my bobcat an hour ago. let me know how its going. russm

MattyC-130

My Feedback: (5)

TOWER .75!, I have one on my Bobcat with Robart Spring Airs and Flaps. A true joy to fly and I think the Tower .75 with 11x8 prop is the perfect combo for the Bobcat.
Matty

Clean

And have you recorded it as it went by? What kind of speed we talking?

Flyboy Dave

My Feedback: (21)

MattyC....are you running the 11-8 Zinger ?

Larry Legg

I have been sold on either a Tower .75 or (if I can afford it) an OS .91. The .91 is $100.00 more but the post I am seeing say it will scream. It is not that much heavier than the Tower .75.

MattyC-130

My Feedback: (5)

FlyboyDave,
Yes it is a Zinger 11-8 from Tower. My friend has a Radar Gun and he clocked it at 120 MPH.
Here is a link to the Prop:
http://www2.towerhobbies.com/cgi-bin...?&I=LXLH17&P=7

Teedee

My Feedback: (1)

My Bobcat 50 has a OS 55AX with a cut down 10x8 APC pusher prop. It turns 14,500 on the ground and was clocked at a best time of 112 mph after a dive to level flight. I am using 15% Byron Premium Sport and the glow plug that came with the engine OS#8.[sm=teeth_smile.gif]

Flyboy Dave

My Feedback: (21)

I figured the 11-8 Zinger would be the best prop for the Tower 75 in the Bobcat, I was suprised at
the performance of the 12-6 as well. I flew mine today with the 11-8 Zinger, using the YS .63 FZ
4-cycle engine. THe wind was blowing about 15 MPH, so it was hard to get a good guage on the run.
It was satisfactory for a sport plane, but nothing like the stellar performance of the video with the
Tower engine.

FBD.

Larry Legg

Thanks for all the info. I think before I go out and purchase a tower .75 I will try a pipe on the K&B .61 and see what RPM's I get. If I can get 13,000 to 14,000 out of the engine--I might stick with the K&B. The lightness of the K&B would make it more desireable.

Larry Legg

I took a friends advice and went to the source (Clarence Lee) about the Modified K&B .61 ringed engine I bought from him.
I got a response back from Clarence Lee about the K&B .61 he sold in a week. It sounds like it will work for me and perform better than I expected. These are the facts about the engine he modifies. I thought this might be helpful to anyone else looking for and engine to run in the Bobcat 50. Below is his response.

You have been getting a lot of misinformation off the internet so it is easy to understand your confusion.

To start with, the engine I sent you will turn just as strong if not stronger than the "Twister" 61. If a Twister and older stok 61 are compared, the Twister will have an edge. However, this edge comes through the semi-Schnuerle porting and a larger carburetor intake. The Twister is not a true Schnuele scavenged engines as it only has one mixture transfer channel. The Twister uses the same case as the ringed 61 with notches cut at the top edges of the bypass channel and two extra holes drilled in the sleeve. I do the same thing when incorporating PDP in the engines I sell, except I mill slots at the top of the bypass and in the sleeve. In effect, both engines utilize the same type of porting. Sort of a combination of semi-Schnuerle and PDP. The engine I sent you also uses the Twister carburetor, crankshaft, and rod. The stock rods have far too much crankpin clearance (.004-.005") that results in clicking when turning the engine over and fellows thinking the rod is defective or owrn out. I rebush the rod for.002" clearance, so do not ever replace the rod. Also, I have modified the timing in your engine for higher rpm operation and pipe use. Didn't you read the letter that accompanied your engine?? Bear in mind that the engines you mention as possible alter native choices are not intended for higher rpm operation. The only two engines that I can think of, off hand, that would give you more speed would be a piped Rossi 61 or OPS 60 (if you could find one). And even then, the small increase in speed might not justify the cost of these engines.

There is no reason to install a counter-rotating crankshaft in the engine. Both APC and Zinger as well as Graupner and others make "pusher props". Install a 10 x 8 APC prop, 25-30% nitro fuel, and you will have plenty of speed. With this combination you should see in excess of 14,000 rpm on the ground with the pipe the proper length. Start with the pipe length about 12: from the piston face to start off the maximum dia. pipe section and shorten in 3/8" increments. When the rpm falls off, pull the pipe back out 3/8" and insert the cut off section back in the rubber coupler.

Something else to bear in mind-other than to make some "show off" passes down the runway, few jet pilots flay a full throttle all the time, usually flying at reduced throttle to conserve the fuel. Your engine should put in this same speed range.

I would appreciate hearing what kind of speed you do see.

Zacster

Is the tower 75 a fuel efficient engine. If someone uses this engine with
the fuel tank supplied with the bobcat, how much flight time do you get?
Does anyone have any problems with this engine such ans starting, tuning or
breaking in?

Thanks

Z Wheeler

MarvinE255

My Feedback: (10)

OS Max 50 Hyper heli motor with a Jett muffler set up for pusher prop use. Exhaust faces toward the rear of the plane. With 10x6 apc pusher prop gives 16,500 rpm on the ground with no overheating problems and lite weight. This is an expensive set up but works great with 30% nitro heli fuel.

patzane

I run my bobcat with 75 on the rich rich side due to the only air flow is from the air it's traveling. So keep in mind you don't have the extra air you well get from a tractor setup. So it all depend on your setting. I can say the TH 75 like to drink and with the stock tank I was getting 5 min flight with less than 1/4 tank on landing. I did go with a 12 oz tank and extened flight time of 9 mins.

z06kal

I think the 10" prop is not nearly enough disc for this very draggy plane. I spin a 12x12 prop at around 11,500 using E-power and the airplane still doesn't reach it's 130mph pitch speed (does about 120 in true level flight). I would say 11" is the bare minimum.

mscic-RCU

My Feedback: (6)

I fly mine a Webra .61 ringed 11X7 prop. Seems to be a real good match.

Dauntae

What muffler are you using on your Webra .61 I just put one on my Bobcat and took off the 55AX I had on it. I mounted a Tower 75 muffler to the Webra hoping to get decent performance on FIA fuel.

Dauntae

mscic-RCU

My Feedback: (6)

i use a mac's muffler with an adapter plate I made

Tailspincharlie

I have a Magnum 52 and run a 10x7 prop and we recorded it 125 level flight. The muffler I have is one that I ordered from England it's a special turned pipe that gets you 3000 more r"s. I was very surprised. My buddy has one just like the set up I have and are both great.

Happy flying, Tailspincharlie

tizer33

Hi is it this one?
I got this on a os55 hoping to get the best from it.

skowowski

Couldn't find much on someone actually flying a bobcat with a .90, so i bought one and took her up and it flies fantastically!! I had to reinforce the plane with lots of epoxy as the Chinese glue they use is terrible. Also put a support bar under the wing to the support leading to the rudder to really hold the thing together. I started with a .46, barely got it off the ground. Then a .61 and it was fun, but with the .90, take offs are very quick and the plane has some serious speed! I have tried only with an 11/7 APC pusher prop, i have a few larger pusher props i'll try, so i'll keep you posted. I'll get some footage this weekend and post it on youtube next week. Just type in "skowowski" and my vids are there. I have some footage there already but only with a .61.

Ciao.