omega-RCU

To AGR413:

Please try to find the spreadsheet it would be must helpful.
Have you done any thinking of what electric motor to use?

I found in this thread someone flying it with a Welgard C5055-06.
Am planning to use a Hacker A50-12S or a Neumotor 1912/1.5Y.

Cheers
// Johan

AGR413

My Feedback: (1)

It's in my laptop I will try to remember to get into it tonight, I intended to do it last night but after feeding the rug rats and doing all the dishes last night I sat down for a rest and woke up when my wife came home from work...still stittin in the chair.

I don't remember what motocalc said but I can send you the motocalc profiles I worked up also.

Aero D

Bob,
I noticed you have your air filler valve in the cock pit so you'll have to remove the canopy to fill the air tank, correct? So how did you attach the canopy so that it can be easily removed?

Aero D

Bob, disregard my last post, I didn't go far enough into the thread.

AGR413

My Feedback: (1)

I found the figure in the other Bobcat thread it was 66.7 oz. This is all the contents that come with the plane no servos or batteries etc.

Stick Jammer

That was sorta my point. How much of a mess does it make on the tail booms directly in line with the prop arc?

Stick Jammer

While this theory sounds logical it would be interesting to see what actually takes place on a super slow-mo camera. At 12,000 RPM,s the prop blades would be in the exhaust path 400 times per second. The chance of something passing through the prop without contacting a blade is relative to the speed of the prop. It’s not as simple as saying the prop area is clear 330 degrees of each 360 degree rotation. Imagine a six foot fan blade turning at one RPM. It would be pretty easy to throw a baseball right through it and clear the blades. Now speed that fan up to 12,000 RPM,s and try throwing that baseball. As far as positioning the prop to the exhaust cycle, I’m not so sure that would matter at all. While the exhaust cycle is somewhat of a pulse, one of the purposes of the muffler is to even out the flow to create more power and better efficiency. The exhaust coming from the outlet doesn’t stop and start with every cycle. Over analyzing….. maybe. I might just have to buy one of these pusher mufflers to see which one makes the bigger mess.

fw190pilot

Stick a turbine on it and you won't have to worry about goo.

Stick Jammer

3 G's can buy a lot of Handy-Wipes!!

Wayne22

My Feedback: (2)

...yeah, you are....

The prop disc is mostly air - 91.3% of it in this example. Even if the exhaust stream was a constant flow (which it is not..) 91.3% of it would miss a prop blade regardless of the RPM. Because of the slender design of our prop blades, this system should have a good chance of shooting the majority of the exhaust through the propellor disk without impinging either of the blades. ( now if was a household fan blade, then yes it would make a heckuva mess...)

Anyways we are just talking theory here. It is not a critcal issue one way or the other. It would be interesting to see some real world results (although I'm encouraged by the one users comments..)

fw190pilot

Isn't the niose, smell, goo, and a 17k meatcleaver that goes with it at least half the fun.

Clean

Just paint those Red 'Danger Prop ARC' lines on the tail booms and go fly. I really have to clean my bench off and get back to it. But I've got 3 planes to test fly and every weekend for the last 4 has been nasty weather. This weekend however is supposed to have 45 degree temps, hopefully the winds will be under 20 mph.

Stick Jammer

You may be right on this. I bolted a 10x6 prop to my dremel and fired it up. A quick check with my tach said it was turning 6000 RPM,s.
I shot a stream of Brake Clean directly at the prop disc and most of it did indeed seem to go right through undisturbed. A pusher type muffler may be the cleanest way to go. More testing is needed. [sm=71_71.gif]

Clean

I sprayed water out of a garden hose into an electric fan once when I was a kid to clean it.

You're right, I should be dead. Unlike our propellors, electric fan blades take up MOST of the prop arc and although the water should have gone out to the sides when impacting the blades, it didn't do it when you sprayed the motor.

The parents wondered why the circuit breaker blew.

I was proud at having cleaned the fan AND produced a whole bunch of cool sparks.

serge760

i have a OS91fx two stroke in my bobcat,the only problem is they don't make any pusher prop for that size engine,i had a three blade 14x7 cut down to a 13x7 to clear the booms,i flown the plane we takd at 75mph.could y put a 11x7 on that engine and keep it under 15.000rpm's with out the engine to overheat??????????

AGR413

My Feedback: (1)

Serge,

Zinger propeller makes a 13x8 pusher two blade, I have heard you can order direct just by contacting them.

http://www.zingerpropeller.com/index.htm

Model Size Price
P703 13-8 6.35

The 13x8 is a recommended size for that engine right off the OS web site.

serge760

thanks for your help

Stick Jammer

serge760,
Just curious, what's the AUW of your Bobcat with that .91? As someone mentioned earlier that while this plane does move out with the right combination, it really isn't an all out speed platform for glow. I'm sure the fixed landing gear is robbing some speed. A turbine and retracts seems to be the only way to go ballistic with this plane. I'll be plenty happy if mine does 75-80 with an OS .55AX

serge760

what do you mean by AUW

bigsky_99

Just received my nitromodels bobcat. Took 5 days to come to Canada from California. Question, manual states c of g about 10 inches back from leading edge, a friend who got one says in his manual this is overwritten with a sticker stating c of g is about 4 inches back from leading edge. Big difference, which ones correct? BTW someone stated they were going to install an OS 91, I was going to use an OS 46, am I underpowering or is the OS 91 overpowering?

B58

My Feedback: (43)

10" is correct. I have a OS .91 on mine, and the props I can fit inside the booms won't handle the power. I really think a good .61 or .75 would be about right. It is not overpowered with the .91 though. The .46 will be a little weak. Bob

countryshooter

My Feedback: (21)

I just got my nitromodels bobcat yesterday and it said 10.3 inches back. In the earlier pages of this forum it was stated the correct cg was around 10". I was planning on putting a OS 91 in mine

AGR413

My Feedback: (1)

I started at 10.3 and moved to 10.5 and it is still a little nose heavy. I would not be afraid to start at 10.5

With a Tower .75 the wing loading is high enough to allow you to generate some pretty good speeds.

If you are after a sport flyer go with the OS .55 lots of good reports using this engine. If you are after a little more speed go with the .61 or .75. I don't know much about the .91 performance.

ExcaliburIII

Acronym for all up weight, BTW CG FUBAR and hundreds more many with more than one meaning and all because we are too lazy to say or write the whole word.
Rich

NM_Mark

My Feedback: (8)

I'm flying mine with an OS 46, and it is a little underpowered. We fly at 4400' altitude, so that does drain some of the power away from our motors.

Mark