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Nitro models pusher Bobcat?

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Old 12-04-2007, 08:11 PM
  #2676
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Default RE: Nitro models pusher Bobcat?


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ORIGINAL: BillS

I am not all that surprised at a weight of 8 pounds 12 oz. Does the airplane stall abruptly or stall to the right or left? Are you using spoilers or flaps?
It doesn't stall abruptly, instead it begins to "wallow" around. The controls become very sluggish, the nose hard to keep up, and finally it will drop the nose quite hard.

With spoilerons the wallowing is more pronounced unless I lower the spoileron amount to say 1/4".

At that point it is far more controllable during approaches... but still rolls out quite a bit.

I'm going to try some of the suggestions here next season.


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Old 12-04-2007, 08:14 PM
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Default RE: Nitro models pusher Bobcat?

Mine is newly built, have not flown it yet it has a os 61 & 3300mha battery in the nose to balance, it comes in at 8lbs 3 oz. it sounds like it may have come in a little hot. I live in Michigan, it has been to nasty to fly ever since I got done with it, I hope to take it up for a test drive soon. Thanx to every one who gave some pointers on the build, I put a connecting rod to the rudders, & a through the wing exhaust, turned out sweet! All great idea's!!
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Old 12-04-2007, 08:14 PM
  #2678
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Default RE: Nitro models pusher Bobcat?


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ORIGINAL: Stick Jammer

Why so heavy?
Dunno.

I went with a stock setup, using the Robart retracts.

The battery pack is not that large at only 1400mAh.

The engine is the GMS .76 which does add a bit of weight.

I am using rather thick gear wire though. The wires are rather heavy.

My pilot must add a couple of ounces, because I had to anchor it down.

That's all I can think of though.
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Old 12-04-2007, 08:19 PM
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Mine is newly built, have not flown it yet it has a os 61 & 3300mha battery in the nose to balance, it comes in at 8lbs 3 oz. it sounds like it may have come in a little hot. I live in Michigan, it has been to nasty to fly ever since I got done with it, I hope to take it up for a test drive soon. Thanx to every one who gave some pointers on the build, I put a connecting rod to the rudders, & a through the wing exhaust, turned out sweet! All great idea's!!

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Old 12-04-2007, 10:08 PM
  #2680
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Default RE: Nitro models pusher Bobcat?

I think we should start comparing notes on CG. I think it may have a large effect on landing and or run out.

I have flown mine from 10-just over 10.5, 10.5 is a no-no and 10 was nose heavy. I sit at 10.3 right now.
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Old 12-04-2007, 11:15 PM
  #2681
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ORIGINAL: AGR413

I have flown mine from 10-just over 10.5, 10.5 is a no-no and 10 was nose heavy. I sit at 10.3 right now.
What happened at 10.5?

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Old 12-05-2007, 01:32 AM
  #2682
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Default RE: Nitro models pusher Bobcat?

It was so tail heavy the the slightest elevator input at slow speed was a drastic pitch movement. I barely saved the airplane when I landed. However, at speed it flew great.
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Old 12-05-2007, 06:54 PM
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Default RE: Nitro models pusher Bobcat?

opjose,

Thanks for the information about the Bob Cat's stall characteristics.

At 9 pounds or 31 oz/sq ft wing loading a minimum flying speed of approximately 28 mph could be expected. Add a small margin of error and landings are 30 mph which will seem fast. High angle of attack, power on, harrier type landings are likely to be entirely different.

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I am wondering if variations in the manufacturing process of the ARF is leading to a different angle of incidence of the stab and wing. Does anyone that is achieving great flight performance have a Incidence Meter to compare the angles? I think CG along with stab and wing incidence information would be beneficial. The only other factor (that I can think of) would be engine incidence.

Thanks,

Larry
Larry makes a good point which might account for the differing reported landing and flight characteristics.

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Old 12-05-2007, 08:48 PM
  #2684
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Default RE: Nitro models pusher Bobcat?


Quote:
ORIGINAL: BillS

opjose,

Thanks for the information about the Bob Cat's stall characteristics.

At 9 pounds or 31 oz/sq ft wing loading a minimum flying speed of approximately 28 mph could be expected. Add a small margin of error and landings are 30 mph which will seem fast. High angle of attack, power on, harrier type landings are likely to be entirely different.

Larry makes a good point which might account for the differing reported landing and flight characteristics.

Bill
I hadn't figured out what the wing loading would be, and stating it as you've put it makes perfect sense.

It it's moving at around 28+ mph when it touches down it will indeed take a looong time to slow down.

So I either need to drop the weight or make it more draggy on the ground.

In the air it's great however... I just need to not fear that I'll run off the asphalt upon every landing.

In contrast I have no problems with my more lightly loaded Bobcat .25. It lands and slows down as I would expect.


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Old 12-06-2007, 12:09 PM
  #2685
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Default RE: Nitro models pusher Bobcat?

Quote:
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
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Old 12-06-2007, 07:40 PM
  #2686
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Default RE: Nitro models pusher Bobcat?

Guys - does anyone know what size the stock fuel tank is?

I'm building a Top Flight Cessna 310, but powering it the same way as I did with the Bobcat - OS55AX's. The tanks that come with it are such a tight fit that I can't get any foam around the tanks...and I know how long I fly on the Bobcat tank, just don't know how many OZs it holds.

I want to put a smaller set of tanks in the new plane, but I'm trying to get an idea of flight times based on tank size.

Thanks guys
Mark
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Old 12-06-2007, 07:54 PM
  #2687
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Default RE: Nitro models pusher Bobcat?

marktur,
The stock fuel tank is 350cc which translates to 11.83 ounces.
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Old 12-06-2007, 08:12 PM
  #2688
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Default RE: Nitro models pusher Bobcat?

Thanks!
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Old 12-07-2007, 10:47 AM
  #2689
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Default RE: Nitro models pusher Bobcat?


Quote:
ORIGINAL: Stick Jammer

I'm going to be putting together one of the latest retract ready versions over the winter and was thinking of splitting the ailerons to create flaps. I know a few have done this and was wondering how the landing performance is as opposed to using spoilers with the full length ailerons. It's obvious that this plane doesn't need those huge ailerons for flying and I would think the addition of flaps is probably worth the effort. Info from anyone who has done this would be appreciated. Also the amount of throw on the flaps. Thanks.
I purchased a Bob Cat with flaps and have the same questions. In addition it would be interesting to know if flaps push the nose up or down. The flaps are currently disabled for initial flights (need servos).

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Old 12-07-2007, 11:01 AM
  #2690
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Default RE: Nitro models pusher Bobcat?

Bill - I have the retracts version - no flaps in it. I use spoilerons - about 1/4 up MAX, mixed with about 8-9% of DOWN elevator. I tried Flaperons, and it will not settle down for landing properly. With the spoilerons, you will get slow, nose-high landings every time. I can land, and keep the nose off the ground for the length of the runway and takeoff again (with throttle-control of course).

Don't split the ailerons, and you don't need extra servos, and it WORKS. Trust me on this one.

OPTJOSE and Terry showed me the light in this regards, and backed it up with a G3.5 version to prove it on the simulator.

Cya,
Mark

PS. Did you ever build the TF Cessna 310? I'm working on mine now. I think the high wingloading numbers do not tell a complete story on how this plane will fly. The wing is THICK, and has a semi-symmetrical airfoil. Also the Nacelles are huge, and also in a high-lift airfoil shape and this area does not get counted in regards to wing loading. Also the fuse is also a lifting body as well. I think it's going to fly like sweet!
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Old 12-07-2007, 11:38 AM
  #2691
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Default RE: Nitro models pusher Bobcat?

Quote:
Don't split the ailerons, and you don't need extra servos, and it WORKS. Trust me on this one.
Mark,

The flaps existed when the airplane was purchased but your comments are the reason they have been tied down.

I didn't attempt the TF Cessna 310. The high wing loading numbers indicated the airplane would be above my skill level and require 38 mph or so landing speeds. Most of the 310's are finished at about 20 pounds. But I also would avoid a .46 engine in a 10 pound single. I fly twins and the engines will quit occasionally in spite of every precaution. I saw your note about tank foam. My experience is that twins are at least an order of magnitude more sensitive to foaming probably because of harmonics in the airframe.

With your flying skills the Cessna 310 will be fun. It is a beautiful airplane.

Bill
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Old 12-07-2007, 12:05 PM
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Default RE: Nitro models pusher Bobcat?

Bill, I'm not sure if you're a "builder" or not, but this is an quick and easy fix. I'm sure there's a gap now between ailerons and flap...you'll need some thin sheet balse to glue in between and make them one again. (Remove the monocote from the edges so you have wood-to-wood). Sandwich as much balsa as you need between them, and then once you have everything aligned, use thin CA to glue. It will wick itself into the balsa. Then you can use a sanding block to shape the new balsa to the same airfoil as the ail. and flaps. It's truly a 15 minute job.

Then just monocote over the holes where his flap servos were...now you're lighter, and you'll like it for sure!

Take care.
Mark
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Old 12-09-2007, 01:39 PM
  #2693
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Default RE: Nitro models pusher Bobcat?

Bobcat sold.

Mike

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Old 12-10-2007, 08:54 PM
  #2694
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Default RE: Nitro models pusher Bobcat?

this is the same price they are selling it on NitroPlane. Is it the retract ready ver. fix gear.
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ORIGINAL: nrthwing


Hey guys I just put a new in box Bobcat 50 up for sale $100.00
Purchased November 2007

Decided to build an Extra.

Check the classifieds

Mike

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Old 12-10-2007, 10:33 PM
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Default RE: Nitro models pusher Bobcat?

It was the retract ready version.

It has been sold.

Mike
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Old 12-11-2007, 04:32 AM
  #2696
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Default RE: Nitro models pusher Bobcat?

Hi all,

I've read through the entire post, but don't recall if the mounting of switches was ever mentioned. Where and how did you mount your switches? I recall reading about the routing of receiver antennaes, but what is a practical way to do it? If I don't use servo reversers for the rudder and elevators, is there a practical way to mount the servos? Thanks for your help, my plane is on its way, and I need some help on these matters.
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Old 12-11-2007, 11:22 AM
  #2697
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Default RE: Nitro models pusher Bobcat?


Quote:
ORIGINAL: cyborg1

Hi all,

I've read through the entire post, but don't recall if the mounting of switches was ever mentioned. Where and how did you mount your switches? I recall reading about the routing of receiver antennaes, but what is a practical way to do it? If I don't use servo reversers for the rudder and elevators, is there a practical way to mount the servos? Thanks for your help, my plane is on its way, and I need some help on these matters.
Re: Switches

I mounted mine right on the fiberglass in the more curved areas to provide strength. No problems thus far.

Re: Antenna

Mine comes out of the fuse right at the wing root, and I've taped it right along the LE of the wing. Works great.

Re: Reversers

I eliminated my reversers by changing the orientation on one of the elevator servo linkage and control horn.

I haven't had any problems with this.

To implement spoilerons ( a very advisable thing ), you need to put each aileron on a seperate channel.

Re: Mount servos

I went with the "stock" installation of the servos.

I would recommend that leave plenty of extension on the servos so you can easily remove/replace one w/o having to take everything apart... especially if you are gluing everything permanently as I did.

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Old 12-11-2007, 03:12 PM
  #2698
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Default RE: Nitro models pusher Bobcat?

You should not need a reverser for the Rudders, If you have an extra channel you can put one of the elevator servos on that channel and reverse the direction of travel and then synchronize as best you can the two servos to work together, which is probably a better option than the reverser anyway.

The other option would be a separate slaved channel but split the elevator as at least one other has done.
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Old 12-11-2007, 06:46 PM
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Default RE: Nitro models pusher Bobcat?


Quote:
ORIGINAL: cyborg1

Hi all,

I've read through the entire post, but don't recall if the mounting of switches was ever mentioned. Where and how did you mount your switches? I recall reading about the routing of receiver antennaes, but what is a practical way to do it? If I don't use servo reversers for the rudder and elevators, is there a practical way to mount the servos? Thanks for your help, my plane is on its way, and I need some help on these matters.

Plenty of room for the switch in the fuse around the canopy area. For the antenna, I fastened a nylon push tube inside the right wing panel. There is an oval shaped hole in the ribs close to the leading edge, it's quite easy to thread the tube right down to the wing tip. I used a small square of light ply to glue the tube at the wing root with a about a 1/2" sticking out to insert into the fuse when the wing is attached. Just thread the antenna wire into the tube after the wings are secured. Works great and completely hidden. As mentioned, you WON'T need a servo reverser for dual rudder servos but you will need a spare channel or a "Y" connector. You WILL need a servo reverser or a spare channel for dual elevator servos. Another choice though is to modify the servo bays and go with one standard servo for rudders and one for elevator. I made the tail boom inner servo bays larger to accept standard size servos and went with a single HS-475HB on elevator and a single for rudders. I made up a carbon fiber tie rod with ball links to couple the rudders together. Much easier (and cheaper) setup than four tail servos and the weight stayed the same. Plus I prefer the durability of standard size servos over the mini's.
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Old 12-13-2007, 10:50 PM
  #2700
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Default RE: Nitro models pusher Bobcat?

I got my Bobcat the other day, put the main wings on bar and pushed up against fuse and they did not line up, one hit the front first and the other hit the back first with a gap on each. The holes in the fuse is at an angle. Has anybody had this trouble.
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