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Nitro models pusher Bobcat?

Old 01-05-2008, 10:28 PM
  #2751  
Capgains
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Default RE: Nitro models pusher Bobcat?

Great... can't wait to see what you find out!!!
Old 01-05-2008, 11:11 PM
  #2752  
Stick Jammer
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Default RE: Nitro models pusher Bobcat?


ORIGINAL: Capgains

I'm looking for a plane to do my 50 required logged flights, as part of my turbine waiver. A guy in my club just put one of these together with retacts, and a OS 61 (I'm not sure which model) and has offered it for sale. Is this thing capable of 100mph?

Several have posted awhile back of 100+MPH readings with a radar gun. I do believe this airframe is capable of that but probably not much more with a glow engine. The added weight with too large of an engine creates the need for lead in the nose. This along with the limited prop clearance (and selection for pushers) seem to be the main factors governing maximum MPH. The retract ready version also has a thicker wing than the non-retract flavor. The aerodynamic advantage of retracts is probably cancelled out by the thicker wing. I think the non-retract version that has been fitted with retracts along with the best engine/prop/low AUW combination probably has the greatest speed potential excluding turbine power of course.
Old 01-05-2008, 11:39 PM
  #2753  
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Default RE: Nitro models pusher Bobcat?

Hi I got my bobcat complete a while back have a old supertigre 61 on it (Italian) turning a 11/7 apc pusher prop at 28000 rpm I havent clocked it yet but I would bet it is 120 mph or so I have another plane that was clocked at 120 and thisone seems faster cant wate to check it for sure
Old 01-05-2008, 11:46 PM
  #2754  
keveaux
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Default RE: Nitro models pusher Bobcat?

forgot to add it tips the scale at 7.3# and cg is at 11'' and can hands off rt side up and inverted
Old 01-06-2008, 12:50 AM
  #2755  
Meekskin
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Default RE: Nitro models pusher Bobcat?

I would like to see a super tigre 61 with a 11/7 prop turn 28000.....those engines are rated at top end 16,000....no way it would turn 28,000....must be a typo.....
Old 01-06-2008, 12:56 AM
  #2756  
Stick Jammer
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Default RE: Nitro models pusher Bobcat?


ORIGINAL: keveaux

Hi I got my bobcat complete a while back have a old supertigre 61 on it (Italian) turning a 11/7 apc pusher prop at 28000 rpm I havent clocked it yet but I would bet it is 120 mph or so I have another plane that was clocked at 120 and thisone seems faster cant wate to check it for sure

28,000 rpm from a SuperTigre? Hmmmm.
Old 01-06-2008, 12:58 AM
  #2757  
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Default RE: Nitro models pusher Bobcat?

I swear its true I used a tac on my 9z tx sounded like a rabid bee not sure of the model but it has a blow threw pipe and blue head prob a df engine
Old 01-06-2008, 01:04 AM
  #2758  
Meekskin
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Default RE: Nitro models pusher Bobcat?

Lets see now....28,000 X 7(degrees pitch) equals 156 miles per hour.....I'm not sure about that.
Old 01-06-2008, 01:08 AM
  #2759  
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Default RE: Nitro models pusher Bobcat?

im sure thats what it said i will chek it again i might have had it set fot a three blade prop but i just looked at it on tx its set to two blade now
Old 01-06-2008, 01:15 AM
  #2760  
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Default RE: Nitro models pusher Bobcat?

sounds good to me...like to hear what you get this time.
Old 01-06-2008, 01:40 AM
  #2761  
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Default RE: Nitro models pusher Bobcat?

Not sure how you peeps are getting even close to 100 mph with this plane...I have one and so does another member of my club

On mine i have an Os 55ax 11x6 prop stock muffler a little over 11k rpm's, clocked at 54 mph

The other one has the same motor turning a 10x6 prop an ultra thrust muffler, rpm's 13.5k clocked at 65 mph
Old 01-06-2008, 01:44 AM
  #2762  
keveaux
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Default RE: Nitro models pusher Bobcat?

what is the weight? and do you have retract's?
Old 01-06-2008, 01:50 AM
  #2763  
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Default RE: Nitro models pusher Bobcat?

mine is 8.2 lbs no retracts.
the other I think is at 7 lbs (he thinks he has an older model) there where several differences between the to planes, when we talked about the building phase.
corrected weight typo..
Old 01-06-2008, 01:59 AM
  #2764  
keveaux
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Default RE: Nitro models pusher Bobcat?

are you at a high elavation? thiner air or somthing im at sea level havent clocked mine yet but it seems to be doing 100 +I have another plane that has been clocked at 120 and it seems close if not faster im turning a 11/7 at 28000 rpm but im going to have to tac it again to be sure begining to think that isnt to acurate
Old 01-06-2008, 02:08 AM
  #2765  
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Default RE: Nitro models pusher Bobcat?

flying at a very low elevation of 541 ft.
Old 01-06-2008, 02:15 AM
  #2766  
keveaux
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Default RE: Nitro models pusher Bobcat?

you might try a hier pich prop there is a thrust calc caled thrusthp to help yo figure it go to bmaps.net to get a free download
Old 01-06-2008, 02:35 AM
  #2767  
keveaux
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Default RE: Nitro models pusher Bobcat?

http://www.hoppenbrouwer-home.nl/ika...rusthpv20d.htm is the website to get thrust hp
Old 01-06-2008, 04:19 AM
  #2768  
Craig-RCU
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Default RE: Nitro models pusher Bobcat?

ORIGINAL: keveaux

are you at a high elavation? thiner air or somthing im at sea level havent clocked mine yet but it seems to be doing 100 +I have another plane that has been clocked at 120 and it seems close if not faster im turning a 11/7 at 28000 rpm but im going to have to tac it again to be sure begining to think that isnt to acurate
Unfortunately, probably not accurate. 2/3rds of 28000 is 18700 which is more in the ball park if you're running a tuned pipe. Thrust HP Calculator says that 28000 rpm with an apc 11x7 takes 16hp, produces a pitch speed of 186mph and 34 lbs of static thrust. The most powerful .90 size df engines produce 6ish hp. I calculate a tip speed of 916mph which is well above the speed of sound and the sonic boom coming off the prop tips would probably blow your eardrums out if you were within 10ft without ear protection. Mixing up the prop blade numbers on their tac. is a mistake anybody can make.
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Old 01-06-2008, 04:40 AM
  #2769  
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Default RE: Nitro models pusher Bobcat?

ORIGINAL: BillS

RandyM.

Canards may be next.
Canard has many intriguing possibilities. Appears that it would be easy to experiment. Hope you get an opportunity to experiment with the Bob Cat as a canard.

The possibilities for exchanging weight at the rear for front mounted weight are excellent. Moving weight up front partially solves issues with larger heaver engines.

Initial experiments could be as simple as servo operated aileron stock mounted to the front and bottom of the fuselage with no other airframe changes. A few flights would determine the size of the front mounted elevator. I often use screws on one side of the hinge so the control surface can be easily changed. For safety the airplane could be initially flown with both elevators operational but switchable at the radio.

Bill
This could be fun. The double-tail version could have a single power source centered on the middle wing. A tractor prop setup would even fit between the two fuses.
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Old 01-06-2008, 08:02 AM
  #2770  
Stick Jammer
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Default RE: Nitro models pusher Bobcat?

ORIGINAL: Wingspam

Not sure how you peeps are getting even close to 100 mph with this plane...I have one and so does another member of my club

On mine i have an Os 55ax 11x6 prop stock muffler a little over 11k rpm's, clocked at 54 mph

The other one has the same motor turning a 10x6 prop an ultra thrust muffler, rpm's 13.5k clocked at 65 mph

You're way low on RPM's. I have the same engine, stock muffler with an APC 11x7p and I'm getting 14,000 on the ground with 15%. My engine is still breaking in so it's even a little on the rich side. By the way, how'd you manage to have an AUW of 6.2 lbs.? Thats about a full pound lighter than everyone else who's posted including my own.
Old 01-06-2008, 08:12 AM
  #2771  
Stick Jammer
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Default RE: Nitro models pusher Bobcat?

keveaux,
How about a picture of your plane showing the engine. A DF engine would seem like a real PITA of an installation on this plane due to the rear exhaust and rear carb configuration. If it is indeed a DF engine I'm surprised it's not over heating as you wouldn't be getting nearly the airflow past the head that they're designed for.
Old 01-06-2008, 11:56 AM
  #2772  
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Default RE: Nitro models pusher Bobcat?


ORIGINAL: Stick Jammer
You're way low on RPM's. I have the same engine, stock muffler with an APC 11x7p and I'm getting 14,000 on the ground with 15%. My engine is still breaking in so it's even a little on the rich side. By the way, how'd you manage to have an AUW of 6.2 lbs.? Thats about a full pound lighter than everyone else who's posted including my own.
Stick Jammer, ThrustHP calculations aren't quite adding up for you either. If you look at the second case of the ThrustHP picture that I posted in post 2759, you'll see that an 11x7 APC prop spinning at 14K requires 2hp. The power rating of the .55ax stated on the Tower Hobbies website is 1.75ps(1.73hp) at 16K. If your numbers are right, you've exceeded this engine's rated hp 2K below its peak hp rpm. Is it possible that you are running a 10x7 instead of an 11x7? A 10x7 at 14K and 1.37hp seems more in line with the published numbers for this engine. Maybe ThrustHP Calculator is off?
Old 01-06-2008, 01:56 PM
  #2773  
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Default RE: Nitro models pusher Bobcat?

heree are a fiew pictures of my bobcat
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Old 01-06-2008, 02:37 PM
  #2774  
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Default RE: Nitro models pusher Bobcat?

Very nice. That doesn't look like a Supertigre crank case, head or muffler, but the carburetor is Supertigre.
http://www3.towerhobbies.com/cgi-bin...?&I=LXFV75&P=7
Old 01-06-2008, 02:42 PM
  #2775  
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Default RE: Nitro models pusher Bobcat?


ORIGINAL: keveaux

heree are a fiew pictures of my bobcat
Interesting idea for the gear...

But with the gear that far back is it able to rotate for take off?

I can't see the height of the nose wheel so I can't tell what the incidence would be.


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