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Nitro models pusher Bobcat?

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Old 03-28-2007, 05:11 PM
  #1401
Stick Jammer
 
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Default RE: Nitro models pusher Bobcat?

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ORIGINAL: countryshooter

no. I put about 1/4" shim under the stabuilizer arm that connects to the wing, on each side the back end of the wing is about 1" lower then front and the stabilizer is even front and back. I dont know what degree it is. yes I mean the tailboom and wing.
What you have effectively done here is negative incidence on the stabilizer. Adding shims to the rear bolts of the tail booms does not change the wing incidence. Incidence has to be measured with the center line of the fuse perfectly level. If you level the fuse and re-measure the incidence you will see that the leading edge of the stab is now lower than the trailing edge and the wing is most likely level (0 incidence). What this has done is almost the same effect as adding some up elevator to your trim, the air is pushing the tail down in upright flight. It also has most likely seriously affected inverted flight (nose will want to drop hard because the air is pushing up on the stab).
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Old 03-30-2007, 07:47 PM
  #1402
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Default RE: Nitro models pusher Bobcat?

Has anybody seen, or is anybody using a genisis pusher pipe? They make one special for the bobcat
http://www.westonuk.co.uk/index_090.htm
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Old 03-31-2007, 10:34 AM
  #1403
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Default RE: Nitro models pusher Bobcat?

The Weston Bobcat pipes look very good
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Old 03-31-2007, 10:42 AM
  #1404
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Default RE: Nitro models pusher Bobcat?


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ORIGINAL: Stick Jammer

You're welcome, glad it worked for ya. Did your range problems go away?

havent flown it yet. waiting for that perfect day. Almost everyday my field has a
sharp crosswind. dont need that on my setup flight.
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Old 03-31-2007, 10:59 AM
  #1405
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Default RE: Nitro models pusher Bobcat?


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ORIGINAL: timevac

Has anybody seen, or is anybody using a genisis pusher pipe? They make one special for the bobcat
http://www.westonuk.co.uk/index_090.htm
I have a Weston Bobcat pipe on order. I hope to test it in about a week or so. I will be using a OS 61FSR reverse rotation with a 11x10 pattern prop.
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Old 03-31-2007, 11:09 AM
  #1406
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Default RE: Nitro models pusher Bobcat?

Has anyone here tried elevon mixing on the Bobcat?
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Old 03-31-2007, 01:15 PM
  #1407
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Default RE: Nitro models pusher Bobcat?

Hi texan
Where did you find a reverse rotation motor??
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Old 03-31-2007, 01:39 PM
  #1408
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Default RE: Nitro models pusher Bobcat?

The OS 61fsr has a bolt-on front case. For reverse rotation, change the port timing by rotating the front case 90deg.

See post 745 in this thread for details http://www.rcuniverse.com/forum/fb.asp?m=5166752
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Old 04-01-2007, 08:50 AM
  #1409
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Default RE: Nitro models pusher Bobcat?

Quote:

ORIGINAL: Stick Jammer

What you have effectively done here is negative incidence on the stabilizer. Adding shims to the rear bolts of the tail booms does not change the wing incidence. Incidence has to be measured with the center line of the fuse perfectly level. If you level the fuse and re-measure the incidence you will see that the leading edge of the stab is now lower than the trailing edge and the wing is most likely level (0 incidence). What this has done is almost the same effect as adding some up elevator to your trim, the air is pushing the tail down in upright flight. It also has most likely seriously affected inverted flight (nose will want to drop hard because the air is pushing up on the stab).
Can this be achieved by adding downward thrust to the engine?
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Old 04-01-2007, 10:42 AM
  #1410
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ORIGINAL: Larry Legg


Can this be achieved by adding downward thrust to the engine?
That's what I was going to try/
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Old 04-01-2007, 01:42 PM
  #1411
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Default RE: Nitro models pusher Bobcat?

My new Bobcat should arrive this next week from Nitro Models. After reading through this thread, I have also ordered a Tower Hobbies 75 engine and 12x6 pusher props for this bird. From the information on this thread, this appears to give the best performance for the least amount of money. I am very interested though, in how well this bird performs with a DF setup. I see that at least two individuals have gone that direction but there does not seem to be any flight reports for the DF power as yet. A DF would qualify to fly at Jet Rallies but the pusher prop version will not. Can anyone tell me how the DF versions have worked out?

Best wishes and good safe flying.

Heli-NuBee (Roger)
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Old 04-01-2007, 02:48 PM
  #1412
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Default RE: Nitro models pusher Bobcat?


Quote:
ORIGINAL: Texan

Has anyone here tried elevon mixing on the Bobcat?
I have not, The bobcat 50 is not a delta wing where elevons are used and I have flown many deltas. You would have on the bobcat Flaperons. Two channels and correct mix required for this. My Bob cat will float in ground effect and lands easy no need for flaps.

bob
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Old 04-01-2007, 03:40 PM
  #1413
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Default RE: Nitro models pusher Bobcat?

Has anyone else experienced flutter with their Bobcats yet?
http://home.dc.rr.com/maurie/Flutter.wmv


Slow motion http://home.dc.rr.com/maurie/SloFlutter.wmv
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Old 04-01-2007, 08:02 PM
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Default RE: Nitro models pusher Bobcat?

I take it you got it on the ground all in one piece... what kind of damage, if any, did you find?
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Old 04-01-2007, 08:44 PM
  #1415
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Default RE: Nitro models pusher Bobcat?


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ORIGINAL: -Stevo-

I take it you got it on the ground all in one piece... what kind of damage, if any, did you find?

Unfortunately, it did not make it to the ground unscathed,...those nose wheel landings get ya every time. Canopy was smashed, ailerons were pulled out, he was lucky to have enough control left to get it on the runway. This blows,...it was only the 3rd flight on the plane. Maiden and the second flight today was good. http://home.dc.rr.com/maurie/FlutterSplat.wmv
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Old 04-02-2007, 02:28 AM
  #1416
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Default RE: Nitro models pusher Bobcat?

I bought this one for $80. I put my sc75 and pipe on it. Put a big header tank in ,2 aeleron and 1 elevator servo. Covered the rudder servo holes and the extra elevator servo hole. Took all the lead out and balanced it with its running gear.

The undercarriage is my idea after reading one of the posts explaining that the wires run parralel with the wing wich gives a torsion bar effect on most models , but not these. The loop has some give but not too much and it seems good as i have not bent it at all since fitting. I have had at least one bumpy landing that would have bent the old gear right back.

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Old 04-02-2007, 02:55 AM
  #1417
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Default RE: Nitro models pusher Bobcat?

Quote:
ORIGINAL: CrashPro


Quote:
ORIGINAL: -Stevo-

I take it you got it on the ground all in one piece... what kind of damage, if any, did you find?

Unfortunately, it did not make it to the ground unscathed,...those nose wheel landings get ya every time. Canopy was smashed, ailerons were pulled out, he was lucky to have enough control left to get it on the runway. This blows,...it was only the 3rd flight on the plane. Maiden and the second flight today was good. http://home.dc.rr.com/maurie/FlutterSplat.wmv
Interestingly enough, I think he would have landed better if he kept his course. This is a lesson to back seat pilots! You can see the pilot had a course of action in mind, yet listened to the back seat pilot yelling power power at the same time thereby causing a confused response. If he didn't apply power he may have floated the plane back down or land with less damage in the dirt and if he chose to apply power initially and kept it on he would have pulled out of that but seeing that he wanted that aircraft down after the flutter problem the guy yelling power at him cost him the heavy damage. Lesson to back seat pilots, fly your own plane and let the pilot dictate his own fate.
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Old 04-02-2007, 04:02 PM
  #1418
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Default RE: Nitro models pusher Bobcat?

I recently purchased a bobcat from an individual that had a GMS 76 engine with a 14X7 master airscrew 3-blade prop cut down to 11X7. Once in the air, in abougt 2 minutes it lost power and quit evidently from overheating. On the ground It would then overheat within a minute. carburator adjustment did not help. I replaced the engine with a Magnum 91XLS that I had used on a previous plane with no problems. I cut down a 3-blade 14X7 to 13X7. Everything seemed fine until like previously, after a couple minutes in the air, lost power and rpms evidently overheating. I am using 15% fuel that I was using on the engine when it was on the other plane. Very strange. I will try 30% next flight. I also had problems getting the nose to rise on takeoff. CG seems fine once in the air. I will add some height to the front wheel to add some lift from underneath . Question is, how much do I add? 1 inch, 1 1/2 inch, 2 inch? Anybody have any experience with this. I don't see many references to the overheating problems and I am suprised considering I am 2 for 2 for engine overheating. No other plane I have ever had has had this problem. Any other ideas other than the fuel? Thanks in advance for any advice you can give me. Quentin
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Old 04-02-2007, 04:09 PM
  #1419
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Default RE: Nitro models pusher Bobcat?

I did have overheating problems, with an OS 46 2 stroke. it seemed to do better when i ran 10% fuel instead of 15% (and I would think it would be the other way around). It could have been because of altitude, we're at 4400'. I adjusted it so it ran fine on the ground, then richened it up before taking off.

Mark
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Old 04-02-2007, 04:33 PM
  #1420
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Default RE: Nitro models pusher Bobcat?

I've run a Master Air Screw 14X7 three blade cut down on my Bobcat with Magnum .91 also, but I had no overheating problems at all. Its not cold here either, weather was in the low 80's when I had that setup. The problem with that prop tho is couldn't get any real speed out of it, best was 82 mph on the radar gun. I'm currently running a 14X6 APC cut down to 13". Its faster, but still not as fast as it was with the Tower .75 and 11X7 APC prop (110 mph).
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Old 04-02-2007, 04:37 PM
  #1421
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Default RE: Nitro models pusher Bobcat?

Mark, I am at sea level. Did you richen twice what you normally richen from peak rpm, or was it three times as much? I have a fear of a flameout at 10 feet..... Call me chicken. Thanks Quentin
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Old 04-02-2007, 04:47 PM
  #1422
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Default RE: Nitro models pusher Bobcat?

I think I turned the needle out about an eighth to one-quarter turn
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Old 04-02-2007, 05:00 PM
  #1423
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Default RE: Nitro models pusher Bobcat?

Quote:
ORIGINAL: qlacombe

I recently purchased a bobcat from an individual that had a GMS 76 engine with a 14X7 master airscrew 3-blade prop cut down to 11X7. Once in the air, in abougt 2 minutes it lost power and quit evidently from overheating. On the ground It would then overheat within a minute. carburator adjustment did not help. I replaced the engine with a Magnum 91XLS that I had used on a previous plane with no problems. I cut down a 3-blade 14X7 to 13X7. Everything seemed fine until like previously, after a couple minutes in the air, lost power and rpms evidently overheating. I am using 15% fuel that I was using on the engine when it was on the other plane. Very strange. I will try 30% next flight. I also had problems getting the nose to rise on takeoff. CG seems fine once in the air. I will add some height to the front wheel to add some lift from underneath . Question is, how much do I add? 1 inch, 1 1/2 inch, 2 inch? Anybody have any experience with this. I don't see many references to the overheating problems and I am suprised considering I am 2 for 2 for engine overheating. No other plane I have ever had has had this problem. Any other ideas other than the fuel? Thanks in advance for any advice you can give me. Quentin

Gl,

You should try 5%. You're overheating your engine. And with your current setup using higher nitro will cause more damage to your engine. You may also try shimming up your head with the 15%, your air in LA might high in humidity as well. On the ground you're engine won't unload as it does in the air. How's your pipe pressure setup, it may also cause a lean run.
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Old 04-02-2007, 05:13 PM
  #1424
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Default RE: Nitro models pusher Bobcat?

Quote:
ORIGINAL: CrashPro

I've run a Master Air Screw 14X7 three blade cut down on my Bobcat with Magnum .91 also, but I had no overheating problems at all. Its not cold here either, weather was in the low 80's when I had that setup. The problem with that prop tho is couldn't get any real speed out of it, best was 82 mph on the radar gun. I'm currently running a 14X6 APC cut down to 13". Its faster, but still not as fast as it was with the Tower .75 and 11X7 APC prop (110 mph).
The Tower .75/11x7 apc is the proven combo from the very beginning. and pound for pound the cheapest. Just make sure you reinforce the carb mount otherwise you're subject to the stamped metal arm failing in flight. If you're going to spend the $$ on an OS.91 put retracts in instead....
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Old 04-02-2007, 05:40 PM
  #1425
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Default RE: Nitro models pusher Bobcat?


Quote:
ORIGINAL: dragonpilot

Quote:
ORIGINAL: CrashPro

I've run a Master Air Screw 14X7 three blade cut down on my Bobcat with Magnum .91 also, but I had no overheating problems at all. Its not cold here either, weather was in the low 80's when I had that setup. The problem with that prop tho is couldn't get any real speed out of it, best was 82 mph on the radar gun. I'm currently running a 14X6 APC cut down to 13". Its faster, but still not as fast as it was with the Tower .75 and 11X7 APC prop (110 mph).
The Tower .75/11x7 apc is the proven combo from the very beginning. and pound for pound the cheapest. Just make sure you reinforce the carb mount otherwise you're subject to the stamped metal arm failing in flight. If you're going to spend the $$ on an OS.91 put retracts in instead....

Yea...I forgot to mention the needle valve arm weakness of the Tower engines.....see post #1094 and #1139 of this thread,..it happened twice to me.
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