RE: Nitro models pusher Bobcat?

RE: Nitro models pusher Bobcat?
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RE: Nitro models pusher Bobcat? - 8/24/2008 12:01:50 AM

Boomerang1

Posts: 904
Joined: 6/24/2005
From: Sydney, AUSTRALIA
Status: offline

An airbrake will not lower the landing speed at all, the stall speed will not be altered by extra drag alone. What an airbrake does is make more drag, the opposite of thrust. What it means for me is the landing approach can be steeper without building up speed or, if I am making a flat approach, I have to fly in with some throttle on & can control the rate of descent better with the throttle.

With the engine I'm using it takes about 6 seconds for it to go from idle speed (55,000 RPM) to full speed (190,000 RPM). If I have to go round because I stuff up the approach & I already have some power on it takes only about 3 seconds to reach full power. Even 3 seconds is a long while if your model is descending towards the weeds!

I have drilled a heap of holes in my airbrake to hopefully increase the drag some more, I cannot make it longer because it will scrape on the ground or wider because it will hit on the engine support rails. I could not fit them where yours are because of the retracts. - John.

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Post #: 3401

RE: Nitro models pusher Bobcat? - 8/26/2008 8:17:59 AM

cyborg1

Posts: 61
Joined: 11/24/2005
From: Bangkok, THAILAND
Status: offline

Hi guys,

Maidened my bobcat already, and lost it on the same flight. I clipped the roof of a building on my landing approach, lost one of my retracts, and then it just didn't respond to any input after that. Result - broken leading edge of the left wing, cracked fuselage from the front to the center, elevator ripped out from the booms, both booms seperated from the wing. Anyway, fixed her up, and she's almost ready to fly again. I noticed a trait I found puzzling. When banking for a turn and grabbing the elevator to tighten the turn. the plane would nose up and start to climb mid turn. Has anyone experienced this? I found the trait to be unsettling, so I just opted for wide banking turns without elevator input. Any ideas on what causes this? BTW, I had a heck of a time trimming her out, as she required almost full up trim before flying level hands off. I had about 6 minutes of flying time, with about 3 of those minutes setting her up for landing in a crosswind. Happy Flying!

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Post #: 3402

RE: Nitro models pusher Bobcat? - 8/26/2008 8:21:10 AM

jrotor

Posts: 271
Joined: 7/24/2002
From: San Jose, CA, USA
Status: offline

may be this was already discussed, but
anyone used elevon to reduce servo count ?
I'm thinking about not using elevator and rudder.
Just 4 servos for throttle, nose steering, 2 elevons.
What do u think ?

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Post #: 3403

RE: Nitro models pusher Bobcat? - 8/26/2008 11:12:46 AM

Xairflyer

Posts: 313
Joined: 12/17/2002
From: Co. Donegal, IRELAND
Status: offline

quote:

ORIGINAL: cyborg1

I noticed a trait I found puzzling. When banking for a turn and grabbing the elevator to tighten the turn. the plane would nose up and start to climb mid turn. Has anyone experienced this? I found the trait to be unsettling, so I just opted for wide banking turns without elevator input. Any ideas on what causes this? BTW, I had a heck of a time trimming her out, as she required almost full up trim before flying level hands off. I had about 6 minutes of flying time, with about 3 of those minutes setting her up for landing in a crosswind. Happy Flying!

If a model points its nose up in a turn it says it is tail heavy, only other thing can be rudder deflection or boom alignment.
Does it do it if you turn the other way ?

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Post #: 3404

RE: Nitro models pusher Bobcat? - 8/26/2008 12:27:19 PM

Xairflyer

Posts: 313
Joined: 12/17/2002
From: Co. Donegal, IRELAND
Status: offline

quote:

ORIGINAL: jrotor

may be this was already discussed, but
anyone used elevon to reduce servo count ?
I'm thinking about not using elevator and rudder.
Just 4 servos for throttle, nose steering, 2 elevons.
What do u think ?

Don't know if this would work with the high mounted tailplane, why not fit a single servo in the tailplane like I done (see pics in previous posts) and no rudders.

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Post #: 3405

RE: Nitro models pusher Bobcat? - 8/26/2008 2:43:22 PM

Xairflyer

Posts: 313
Joined: 12/17/2002
From: Co. Donegal, IRELAND
Status: offline

Went to fly my Bobcat yesterday to try out the new split flaps/airbrake but my EGT probe on my turbine was'nt reading so had to go home again !

I have attached pictures of what I done below.

The flaps are made from 1/16" ply, how to hinge them was the biggest problem, finally went with using bullet tape first on one side then folded back and done the other, amazing how strong it is, I tried it on my dead bobcat, that I keep for reference (rib positions etc) and I had to apply a lot of pressure to rip it off. I super glued the edges and punched holes so it glued into the wood below as well.

Using my dead bobcat I was able to establish the positions of the ribs and wing joiner tube so I could fit the servos to the measurements shown. Covered the tape with film peeled off the dead bobcat and then some red on the flaps.
I can get about 70deg with the servo arms/travel fitted at the moment but I think these will work more like the flaps on the larger falcon version so don't expect to use more than 45deg.

Will report back on the results when I fly it

Attachments

Click for fullsize	Click for fullsize	Click for fullsize	Click for fullsize
Click for fullsize

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Post #: 3406

RE: Nitro models pusher Bobcat? - 8/26/2008 5:12:02 PM

BillS

Posts: 3077
Joined: 9/6/2004
From: Greensboro, NC, USA
Status: offline

Sure looks like the brakes should slow it down. What does the airplane weight?

I am finding a number of reasonably severe cracks in the fuselage between former # 2 and former # 3 in front of the servo tray. Probably should have reinforced the area with fiberglass before flying. Better landings would help.

Bill

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Post #: 3407

RE: Nitro models pusher Bobcat? - 8/26/2008 5:14:30 PM

TUMBLER

Posts: 462
Joined: 6/24/2002
From: Voorhees, NJ, USA
Status: offline

That looks great!!! That will really help! On my turbine powered KAngaroo, it came at mach 3 until I got the linkage right so the airbrake would not get blown back. I couldn;t believe how that little airbrake made such a difference!

Tumbler

quote:

ORIGINAL: Xairflyer

Went to fly my Bobcat yesterday to try out the new split flaps/airbrake but my EGT probe on my turbine was'nt reading so had to go home again !

I have attached pictures of what I done below.

The flaps are made from 1/16" ply, how to hinge them was the biggest problem, finally went with using bullet tape first on one side then folded back and done the other, amazing how strong it is, I tried it on my dead bobcat, that I keep for reference (rib positions etc) and I had to apply a lot of pressure to rip it off. I super glued the edges and punched holes so it glued into the wood below as well.

Using my dead bobcat I was able to establish the positions of the ribs and wing joiner tube so I could fit the servos to the measurements shown. Covered the tape with film peeled off the dead bobcat and then some red on the flaps.
I can get about 70deg with the servo arms/travel fitted at the moment but I think these will work more like the flaps on the larger falcon version so don't expect to use more than 45deg.

Will report back on the results when I fly it

(in reply to Xairflyer)

Post #: 3408

RE: Nitro models pusher Bobcat? - 8/26/2008 8:39:33 PM

Xairflyer

Posts: 313
Joined: 12/17/2002
From: Co. Donegal, IRELAND
Status: offline

It weighs now 9lb 13ozs empty.

Been wondering if I should use them as flaps or airbrakes, the guys flying the bigger version say it comes in at walking pace and they are set up as flaps with a max of 45deg.

I will try this first and then see how they work full down like airbrakes, but I think like this they will be too big and may need to be trimmed down. The airbrake on the boomerang is only about 30mm.

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Post #: 3409

RE: Nitro models pusher Bobcat? - 9/1/2008 1:30:53 AM

Xairflyer

Posts: 313
Joined: 12/17/2002
From: Co. Donegal, IRELAND
Status: offline

Flew it twice today, sorted my EGT problem, turned out to be that parameter 1 (gasper Fadec AU-540) was set at 252 instead of 49 ?? Speaking to gasper he said it can happen but very rarely, so if anyone has the same problem, check the EGT calibration parameter.

Well the flaps/airbrakes worked very well, I set them at 45deg with 20% down elevator (JR Tranny) makes a big difference on landing, a must do mod to help slow these things down on landing.

Going to try more movement on my second flap setting next day I fly it to see if it works even better.

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Post #: 3410

RE: Nitro models pusher Bobcat? - 9/2/2008 10:22:03 AM

Romulo

Posts: 4
Joined: 9/8/2005
From: LisbonLisbon, PORTUGAL
Status: offline

Does anyone have the Bobcat 50 manual in PDF format ?? I loose my paper manual !!

Thanks,

(in reply to G-ROOKIE)

Post #: 3411

RE: Nitro models pusher Bobcat? - 9/2/2008 1:45:30 PM

bob092

Posts: 7
Joined: 1/2/2005
From: Worcester, MA, USA
Status: offline

Romulo
Send me your email address I can copy my manuel and send it to you. Bob

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