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Nitro models pusher Bobcat?

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Old 09-01-2006, 10:27 PM
  #301
Mods-R-Me
 
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Default RE: Nitro models pusher Bobcat?

As far as engine choices go, you might want to try a Jett 90. Its' the same size as a OS 61 and turns an 11x7 prop 2000-16000 RPM. All engines are hand made in the USA to the customers specifications. They even make counter rotating crankshafts (engine runs backwards). This allows you to use any regular prop in the pusher configuration (more choices). Only reason I say this is because I'm designing a kit version of this very aircraft and, performance wise, the Jett 90L is an excellent choice.

I also have a thread documenting the progress while it's in the CAD stages: [link=http://www.rcuniverse.com/forum/m_4588489/mpage_1/key_/tm.htm]CLICK HERE[/link]

More info about the Jett brand of engines can be found [link=http://www.jettengineering.com/]HERE[/link]

My $0.02,

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Old 09-02-2006, 02:52 AM
  #302
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Default RE: Nitro models pusher Bobcat?

Turbine power is in no way similar to prop power, but adding the weight to the plane(of a bigger engine) can be an advantage if your looking for clues in helping with a turbine upgrade.

I must say I think a Jett engine would be a good choice also, this plane needs a high RPM engine. From my experience the zinger props aren't very effiecient, and a 3-blade prop will just lower effieciency (in a model anyway).
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Old 09-02-2006, 07:47 AM
  #303
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Default RE: Nitro models pusher Bobcat?

hehe....problem for me is that we have noise restrictions here which I have to take in acount. That realy sucks, and keeps my engine choices and performance down.
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Old 09-02-2006, 07:57 AM
  #304
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Default RE: Nitro models pusher Bobcat?

It would be hard to kit this thing for what the first kits sold for. Next shipment will be a bit higher I bet. Bob
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Old 09-02-2006, 10:20 AM
  #305
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Default RE: Nitro models pusher Bobcat?


Quote:
ORIGINAL: B58

It would be hard to kit this thing for what the first kits sold for. Next shipment will be a bit higher I bet. Bob
You would be surprised [X(]. I really depends on how greedy the designer/manufacturer is. The plan is not to stress about getting the price under the kit, but providing quality laser cut parts and a well designed aircraft at a reasonable cost. All I'm doing is making a kit I'd like to buy and build. The 3 blade prop is less efficient but, aerodynamically, I've never noticed much of a difference when flying propjets.

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Old 09-02-2006, 10:47 AM
  #306
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Default RE: Nitro models pusher Bobcat?

Has anyone successfully flown this model with the Wren 44. I have seen the photos of the install but no flight reports.
I am considering an EDF unit, with a 90mm fan and the new brushless motors, I think enough thrust could be generated to push this puppy nicely.
I have one of these kits and really do not want to go the glow engine route.

Any comments??
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Old 09-02-2006, 12:10 PM
  #307
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Default RE: Nitro models pusher Bobcat?

It'll be a while before I'm ready to fly mine. Although I have made some progress. I received my real Bobcat XL back from the painter and am doing the installation on that so it has slowed down the work on the mini bobcat. I did finish the canopy and the fuel tank from Jettech fits nicely.
Thanks to all of you who have done the preliminary work on the CG. That helps a lot.
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Old 09-02-2006, 06:44 PM
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Default RE: Nitro models pusher Bobcat?

Quote:
ORIGINAL: mugenkidd

yeah, I think thats enough French bashing, should be against RCU rules... anyway English is obviously his second language, and the truth of the matter is Turbine power is in no way similar to prop power, but adding the weight to the plane(of a bigger engine) can be an advantage if your looking for clues in helping with a turbine upgrade.

I must say I think a Jett engine would be a good choice also, this plane needs a high RPM engine. From my experience the zinger props aren't very effiecient, and a 3-blade prop will just lower effieciency (in a model anyway)... well good luck to everyone. And can we please keep from bashing others. RCU is not a means to voice your political opinions.
You noticed that, too? The Zinger props are lame. So are the Master Airscrew. The APC is lightyears ahead, really a big difference. Not sure what APC makes in the way of pushers...finding the right props is a big deal with pusher engines...on my last pushers, a Republic Sea Bee and a Saab J-21, I ended cutting down larger pusher props by hand and re-balancing them to get better performance.
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Old 09-02-2006, 09:01 PM
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Default RE: Nitro models pusher Bobcat?

Well I maidened this little jet with a Tower .75 and an 11x7 APC. I was running 10% fuel with shimmed head. I had the engine laying around so I figured it was a good candidate. I had just rebuilt it so it still needs run in so I was running very rich setting. Unlike some members speculation about what to use and what's right for this plane, I recommend this proven combo. I had unlimited vertical and it was truckin. On take off I went straight up. I flew at half most of the time even with the rich setting. 5 clicks of trim and it was flying like a dart on rails. I didn't install retracts yet.
As far as CG I balanced it at the recommend 260MM with 2 battery packs in the nose compartment but that actually proved too nose heavy. I would also recommend scaling down aileron throws as it gets sensitive at speed but I was nosy heavy.
I lost my muffler in flight and dead sticked into a small bush and grass. Damaged the wing a bit but this is a tough jet. I did reinforce the mounting locations for the booms and blocked the wing and fuse and installed a carbon plate across the bottom of the fuse/wing to hold them together. This proved and effective and easy install for that. Just plywood blocking, carbon plate and 4 screws.
For the fuel system I added a 2oz hopper tank for extra fuel and good fuel delivery, both tanks mounted in reverse with reverse clunk, bubbless clunk in main tank.
I hope this information is a benefit to anyone building the jet or looking into it. I hope they keep the price the same. I would buy another for a spare.
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Old 09-02-2006, 09:13 PM
  #310
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Default RE: Nitro models pusher Bobcat?

Looks great. Sounds like a good engine, never run a Tower 75 myself.
Reverse clunk...well...been there, done that. The clunk must be going towards the rear of the plane, or you WILL dead stick, sooner or later. Best of luck with that.
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Old 09-02-2006, 11:59 PM
  #311
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Default RE: Nitro models pusher Bobcat?

I am having trouble loading pictures and I left
the video camera at home today, but with that said,
I was able to maiden my Turbine Jetjoe JJ1400 with
just minor problems. The flight was fast but I could
not trim out for a smooth flight. The plane weight
9 1/2 lbs dry and carry 70 oz of fuel. I moved the
landing gear 2 inches forward to help rotation and
it rotated perfect. A turbine is the way to go. The
problem turned out to be bad rudder servos that
would not center and in fact failed in flight off
center causing the nose to always drop. I will
correct this and try another flight sunday.

Johnny
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Old 09-03-2006, 12:50 AM
  #312
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Default RE: Nitro models pusher Bobcat?

Quote:
ORIGINAL: EASYTIGER

Looks great. Sounds like a good engine, never run a Tower 75 myself.
Reverse clunk...well...been there, done that. The clunk must be going towards the rear of the plane, or you WILL dead stick, sooner or later. Best of luck with that.

Yes, you must install the tanks in reverse direction and reverse clunk. In other words, your tank is mounted front side back and your clunk has to also be reversed or looped around to front of the tank (which is now facing the rear of the plane). Sorry for the confusion on this, I can send you a diagram if you need one, it's quite simple.


and yes, with the new rebuild the engine, the Tower engine is great, plenty of power for the size plane/prop.
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Old 09-03-2006, 07:57 AM
  #313
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Default RE: Nitro models pusher Bobcat?

Test flew my Bobcat yesterday. Flew great but had to dead stick land it. Used a SuperTiger61 that I had laying around. Found one of the main gear blocks broke loose. Cut into the wing and found a very weak mounting installation. Suggest cutting both wing panels open and reglue the gear blocks and add more framework to support the load and shock of grass runways.
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Old 09-03-2006, 08:07 AM
  #314
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Default RE: Nitro models pusher Bobcat?

Well,

I maiden-ed mine today and it flys fine. CG is at 9and 1/2 inches and still a tad nose heavy but otherwise OK. Next flight will try 10 inches. I powered mine with a China made outrunner brushless on a 3 blade 12 x 6 prop with a 5s1p 4000mah battery pack. Enough power for my style of flying but a bit slow for speed demons. The main gear being so far back from the CG did not allow the plane to ROG without elevator input, but once elevator is pulled it leaps into the air. However, this layout did allow me to have a super smooth landing and once on the ground the plane did not have any tendency to bounce. I did tend to come in a bit hot though !! Hope all of you that have this kit to have as much fun as I did !!
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Old 09-03-2006, 01:33 PM
  #315
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Default RE: Nitro models pusher Bobcat?

Glad to see the electric conversions are working. When the larger "kee kat" arrives I plan on powering it with an outrunner of some sort. I would be interested in hearing some more details of your setup.
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Old 09-03-2006, 02:00 PM
  #316
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Default RE: Nitro models pusher Bobcat?

Today I broke in the Dub Jett BSE.50
It lit right up and has a great idle without adjustment.
Tomorrow the Bobkat goes out for its flight.

5 cell pack all the way forward and 2.0 in front of and .5 oz lead at F2 (nose gear mount) put the C.G. at 10.0-10.1"

bob
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Old 09-03-2006, 04:28 PM
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Default RE: Nitro models pusher Bobcat?

Quote:
ORIGINAL: wilerbee2

Well,

I maiden-ed mine today and it flys fine. CG is at 9and 1/2 inches and still a tad nose heavy but otherwise OK. Next flight will try 10 inches. I powered mine with a China made outrunner brushless on a 3 blade 12 x 6 prop with a 5s1p 4000mah battery pack. Enough power for my style of flying but a bit slow for speed demons. The main gear being so far back from the CG did not allow the plane to ROG without elevator input, but once elevator is pulled it leaps into the air. However, this layout did allow me to have a super smooth landing and once on the ground the plane did not have any tendency to bounce. I did tend to come in a bit hot though !! Hope all of you that have this kit to have as much fun as I did !!


To clarify between the Point of balance or the Neutral point and the CG.

If your models point of balance is at 9 1/2" and it flies nose heavy, This tells you your NP is further forward. If the CG of your airframe is 10" and you are trying to balance at the CG then you are even more nose heavy than at 9 1/2" considering not moving any weight around. If you move weight further back from the nose from a balanced aircraft, your NP will be aft.
Here is a useful diagram to help.
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Old 09-03-2006, 08:16 PM
  #318
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Default RE: Nitro models pusher Bobcat?



If you're nose heavy at 9 1/2 you'll want to move the CG forward, not back to 10"!
[/quote]


Hmmm.... something doesn't sound correct here!
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Old 09-03-2006, 09:11 PM
  #319
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Default RE: Nitro models pusher Bobcat?

If your nose heavy move the CG aft not forward![/b]!!!!!
Matty
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Old 09-03-2006, 09:13 PM
  #320
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Default RE: Nitro models pusher Bobcat?

Is the 10" CG with fuel tank empty or full?
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Old 09-03-2006, 09:26 PM
  #321
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Default RE: Nitro models pusher Bobcat?

Quote:
ORIGINAL: MattyC-130

If your nose heavy move the CG aft not forward!!!!!!
Matty
Balancing the model at the manufacture's recommend CG of 10.3" proved too nose heavy during my flight. The CG of the aircraft is determined by the design, however, the point of balance is changed depending on your style of flying and how you want the aircraft to handle, Refer to my posted diagram above.
..going to do some shots now.
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Old 09-03-2006, 10:42 PM
  #322
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Default RE: Nitro models pusher Bobcat?

For you guys that have flown it. Roughly, how much runway are you using. I want to buy one but, I fly at 9,000 ft msl and I am cocerned about getting one airborne up here. Any feedback would be appreciated.
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Old 09-04-2006, 08:34 AM
  #323
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Default RE: Nitro models pusher Bobcat?

60-70 meters on rough grass.
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Old 09-04-2006, 09:16 AM
  #324
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Default RE: Nitro models pusher Bobcat?

Flight Report Wren MW44:

I flew mine with the MW44 yesterday. The performance was very similar to the one I saw with an OS 61 on it. On the first flight it was nose heavy and I did not have enough up in the elevator but we got it up and down okay. The second flight was perfect except for a flame out on the turbine. It dropped in from about 15-20 feet but only bent the landing gear. This is a pretty strong little bird.

Two suggestions, turn the wheels outward on the main gear. It needs a wider stance. It was very unstable on takeoff. Second, make sure you have plenty of elevator.

Otherwise it is going to be a fun airplane to fly. I think it will be even better with a MW54 or P60 and retracts.

Hal
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Old 09-04-2006, 09:19 AM
  #325
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Default RE: Nitro models pusher Bobcat?

We have a 40 x 600ft paved runway, but I am still concerned. It would stink to put one together and not be able to fly it. I would put at least a .61 in it. Maybe a turbine on down the road.
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