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Nitro models pusher Bobcat?

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Old 04-02-2007, 06:02 PM
  #1426
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Default RE: Nitro models pusher Bobcat?


Quote:
ORIGINAL: qlacombe

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?
I haven't flown mine yet but I can tell you two things on this plane that I feel contribute to this problem. One is gear height as you mentioned. The plane needs a small amount of positive angle of attack. The nose wheel needs to be adjusted so the leading edge of the wing is slightly higher than the trailing edge when sitting on a level surface. A degree or two of positive AOA should be enough. The second problem is the stock location of the main gear. If your mains are in the stock location and your CG is around 10.3" from the leading edge of the wing at the fuse, the main wheels are over 5" behind the CG. This makes it tough to get the nose off the ground for a nice smooth takeoff. That's why you will find many flight reports of this plane wanting to jump into the air at a steep angle. I rebuilt my main gear blocks side to side instead of fore to aft and bend my own fixed gear from 3/16 music wire. My main gear is about 3" forward of the stock location, about 2 1/2" behind the CG. This should help the plane to takeoff at a nice shallow angle and also benefit the landings by making it easier to keep the nose up after the mains touch down. As far as your over heating problem, it sounds like it's leaning out for some reason. How is the fuel tank orientated and plumbed?
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Old 04-02-2007, 06:39 PM
  #1427
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Default RE: Nitro models pusher Bobcat?


ORIGINAL: Larry Legg

Quote:
Can this be achieved by adding downward thrust to the engine?
Not sure what it is that you want to accomplish. Generally a good way to check if the engine needs up or down thrust is to trim the plane for hands off level flight at moderate speed. If the plane tends to pitch up with full throttle, it could be a CG issue, an engine thrust angle issue, a positive AOA issue, a stabilizer issue, etc............ If the plane stays level at varied speeds, take it straight up vertical at full throttle and see if wants to pitch. If it pitches, go staight down with the throttle chopped and see if it pitches. If you have pitching problems with vertical flight but not horizontal flight, it's usually an indication of incorrect engine thrust angle, usually. Add to the mix of things that this plane has a semi-symmetrical wing (some call it flat bottom) and a flat bottom airfoil for a stabilizer. This complicates things as far as fine tuning the flight performance. All this can make it tough to figure out exactly what needs tweaking.
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Old 04-02-2007, 06:41 PM
  #1428
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Default RE: Nitro models pusher Bobcat?

for those of you who have not run pusher engines before, you need to keep your ground running to a minimum, because there is no prop blast blowing cooling air over the engine, they will over heat. If you have to do some running on the ground, throw a tractor prop the same size on, do your tuning, then switch the props back when you are ready to fly.
Also keep the engine fairly rich...the excess fuel and oil help carry heat away from the engine when it is running..If you feel you need to tweak it to get every last RPM out of it, your engine is too small..go for more cu in, and run it a bit rich....if they lean out in the air, it will overheat quickly...Again, no prop blast over the cylinder... If the cooling demands are more than relative airflow can disappate, the engine heats up...

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Old 04-02-2007, 06:47 PM
  #1429
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Default RE: Nitro models pusher Bobcat?

Quentin,
I think you should just sell it! I am willing to meet you half way to help on travel expence!
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Old 04-02-2007, 07:21 PM
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Default RE: Nitro models pusher Bobcat?

Jynx, I am not ready to give up yet. It will stay with me for a while. This is a lot of information. I have a stock muffler on the engine with an exhaust deflector cut off to prevent air from entering the muffler in flight. My landing gear are upgrades but are at the stock location. I have many things to try now. I appreciate all of the information. Thanks to everybody for the help. Quentin
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Old 04-02-2007, 07:27 PM
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Default RE: Nitro models pusher Bobcat?

Stick Jammer, about the fuel tank, it is installed fuel lines to the front of the plane with the fuels lines running back along the tank to the engine. Quentin
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Old 04-02-2007, 09:32 PM
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Default RE: Nitro models pusher Bobcat?

My Bobcat arrived today from Nitro Planes. The quality looks quite good. I'm very pleased at this point. I have several other projects that I need to complete before I start this one, so it will be a while before the o'l Bobcat flies.

Best wishes and good safe flying.

Heli-NuBee (Roger)
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Old 04-02-2007, 10:27 PM
  #1433
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Default RE: Nitro models pusher Bobcat?

Guys,

I put 4 more flights on my Bobcat with SpringAir retracts this weekend. I don't know how this thing flys stock, but with the retracts, it is really neat! I don't know what the top speed is, and I really don't care too much - its fast enough. It takes off easily with just a bit of backpressure (the retracts are probably 2"+ ahead of the stock location), flys and tracks straight, doesn't have any really nasty slowspeed habits (although it will drop a wing sometimes in a stall, but it stays controllable with aileron), and actually lands quite well. I bounced it on the first two landings, but after I figured out how to get it slow enough, that's not really a problem anymore.

Its a really fun plane to fly and makes a great jet trainer for my son Louie!

Bob
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Old 04-03-2007, 05:50 PM
  #1434
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Default RE: Nitro models pusher Bobcat?

Original: CrashPro

Quote:
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.
I didn't see the video, was it aileron or elevator flutter? Seems odd that the ailerons would pull out due to the crash.
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Old 04-03-2007, 06:09 PM
  #1435
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Default RE: Nitro models pusher Bobcat?


Quote:
ORIGINAL: qlacombe

Stick Jammer, about the fuel tank, it is installed fuel lines to the front of the plane with the fuels lines running back along the tank to the engine. Quentin

If you haven't already, I would check the vent and clunk lines in the the tank to make sure everything is in order. You mentioned earlier that adjusting the needle didn't help so it still sounds to me that the engine is running lean for some other reason. You also mentioned that you had two different engines act the same way and one of them previously ran fine in another plane. This also points to possible fuel delivery problems.
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Old 04-03-2007, 06:33 PM
  #1436
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Default RE: Nitro models pusher Bobcat?

Hi all I have been reading these comments re the Nitro Bobcat ,

I would like to add that I have had over 30 flights with the the Bobcat and apart from replacing the undercarriage wires due to quality I am very pleased with the model .
It sits level on the ground ,take off is almost hands off on a grass strip with a small bump from the nose wheel when airspeed Is reached , climb out Is smooth with no real Input required, quickly reaching a very high climb out rate

landings are nose high touching down on the rear wheels then settling onto the nose wheel as it should .. there are no real Issues taking Into account that It Is a pusher model with common sense being applied re the set up

engine Is an OS 50 Heli using an 11*6 prop but I do feel that 11*7 would be an Improvement,
CG is where the Instructions suggested .
Position of the U/C is reversed as it should be closer to the CG,

Muffler is a standed OS muffler with mods made as per page 22 In the Instruction manual,
It will be one that that I will keep in my stable and looks cool in the air ,
comments are that it needs retracts to look even better which I agree and I know others are getting one after seeing mine perform
Cheers G
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Old 04-03-2007, 07:01 PM
  #1437
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Default RE: Nitro models pusher Bobcat?

Quote:
Muffler is a standed OS muffler with mods made as per page 22 In the Instruction manual,
Hmmmm my manual is only 10 pages long. Could you share what they are recommending?????
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Old 04-03-2007, 07:13 PM
  #1438
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Default RE: Nitro models pusher Bobcat?

whoops Page 9 Item 22 muffler has the rear half removed and a replacement end fitted .mail me and I will send a pic
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Old 04-03-2007, 09:04 PM
  #1439
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Default RE: Nitro models pusher Bobcat?

put 2 flights on my bobcat last night. flew awesome! had no problems with radio this time.
first flight was a hand full until I got it trimmed out. landed awesome. slow and smooth.
Had no problems with plane jumping off ground, but I removed stock wire gear and installed
aluminum landing gear. cant wait to fly again!!!!
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Old 04-04-2007, 04:38 PM
  #1440
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Default RE: Nitro models pusher Bobcat?

Awesome! Glad your radio problems are gone. Not knocking anyone's preference on antenna choice but I really don't see the need for a whip style antenna on this plane.
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Old 04-04-2007, 06:57 PM
  #1441
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Default RE: Nitro models pusher Bobcat?

Hi Gents
My Bobcat with Wren44 power.
Regards Craig Dyer
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Old 04-04-2007, 07:01 PM
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Default RE: Nitro models pusher Bobcat?

More pics...Dry weight is 3.6kg and springair 301 retracts.
Regards Craig
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Old 04-04-2007, 07:57 PM
  #1443
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Default RE: Nitro models pusher Bobcat?


Quote:
ORIGINAL: craigdyer

More pics...Dry weight is 3.6kg and springair 301 retracts.
Regards Craig
Craig,
If it would not be too much trouble, can you show us some pictures inside and out of how you installed your retracts in the nose ?

Thanks,
Michael
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Old 04-05-2007, 06:31 AM
  #1444
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Default RE: Nitro models pusher Bobcat?


Quote:
ORIGINAL: Stick Jammer

Awesome! Glad your radio problems are gone. Not knocking anyone's preference on antenna choice but I really don't see the need for a whip style antenna on this plane.
There isn't a need for a lot of stucff we are putting in this cheap little plane. I think that is part of the fun, seeing all of the neat mods done to this bird. As for the whip, it is the best way to place the antenna for optimal signal capture, you could argue a whip should be on every plane.

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Old 04-05-2007, 11:19 AM
  #1445
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Default RE: Nitro models pusher Bobcat?

Craig

Do you have a close up of your motor mount? I like the way you did it with the aluminum. I used blocks on mine.

I flew mine three times last weekend. It is a blast with a 44. I don't have retracts on mine but plan on putting them on the kitbashed version I posted earlier in this thread.

Hal
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Old 04-05-2007, 11:30 AM
  #1446
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Default RE: Nitro models pusher Bobcat?

Country shooter,

Have you posted pics of the modification you are talking about? I haven't found them. I'm a little confused by what you are calling the stabalizer arm and where you did the adjustment.

Thanks,

flying_Phil
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Old 04-05-2007, 02:38 PM
  #1447
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Default RE: Nitro models pusher Bobcat?

Sorry, havent had time to test fly this week but once I get her going the way I like it Ill post a vid. I'm still waiting for my bubbleless tank(tettra tank) cause I'm alittle nervouse flying inverted.
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Old 04-05-2007, 02:52 PM
  #1448
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Default RE: Nitro models pusher Bobcat?

Original: MMallory

Quote:
There isn't a need for a lot of stucff we are putting in this cheap little plane. I think that is part of the fun, seeing all of the neat mods done to this bird. As for the whip, it is the best way to place the antenna for optimal signal capture, you could argue a whip should be on every plane.
Other than the whip possibly being a cosmetic choice, I really don't see the advantage. I'd be interested in reading any hard data that proves a whip antenna gets better reception than a properly installed stock wire. I would think that if this were true the radio manufacturers would supply a whip instead. At any rate, I've never had any range problems whatsoever by using the stock antenna on all of my planes including several that are fully concealed within the airframe.
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Old 04-05-2007, 03:01 PM
  #1449
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Default RE: Nitro models pusher Bobcat?

countryshooter,
Just curious if you read my view on your stabilizer (booms) adjustment, post 1392.
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Old 04-05-2007, 04:14 PM
  #1450
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Default RE: Nitro models pusher Bobcat?

yes I did and I'm learning alot here. but the reason I'm moving things around is when the plane is flying straight and level my elevator is pointing upward meaning nose heavy but yet doing a turn it does a tip stall very easy. and flying inverted lots of down elivator is need for level flight. now its flying much better but still elevator is up alittle and inverted are almost hands off.
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