RE: Nitro models pusher Bobcat?
 

I was confused also but that is normal. My other Bob Cat has about the same flap area as hapyjac2's.

Bill

RE: Nitro models pusher Bobcat?
 

Ft it hurdy


Contact John Wright the editor of Jet International, He did his conversion about the same time I did mine. In fact he published his article in the Mag last year. He also employed flaps and has been flying his bird all over the United Kingdom and Europe.

Flaps properly installed and used are very efective, Especially on turbine powered aircraft. But I must admit on my BVM Bobcat I have no flaps nor are spoilerons set in my controls and that plane lands comfortably, but fast. Fortunately we have a long paved runway. I have considered adding flaps to that aircraft under the advice of the BVM rep that originally built the aircraft. Spoilerons were not even discussed as an option to slow it down furthur.

My 2 cents. Every option has it's adantages and disadvantages. I do not disagree with anyone. To each it's own. That what makes this hobby so much fun.

RE: Nitro models pusher Bobcat?
 

I'm not sure that everyone who refers to "flaps" on this plane is talking about flaperons or true flaps (split ailerons). I know for sure that with the stock aileron configuration, spoilerons are the way to go, flaperons will point the nose to the ground. An 1/8" of spoilerons will allow the plane to come in with a nose up attitude thus slowing it down nicely due to the higher AOA. I'm sure a true flap configuration would also work well but it's more work to do the mod and more weight for the extra servos.

RE: Nitro models pusher Bobcat?
 

Stick Jammer


I am refering to true flaps, I did split the ailerons, the extra weight was inconsequential with the use of a trubine for power. I would't recommend it for a prop pusher, not worth the bother.

RE: Nitro models pusher Bobcat?
 

The article indicated a landing speed of 29 mph with flaps. Suspect it might be more than a kitty walk for a doofus like me.

Bill

RE: Nitro models pusher Bobcat?
 

Bill,

That's not bad for a high performance plane. When my BVM Bobcat comes in it's a horror at first but it settles in and is a controlable landing. But my knees still shake a bit every time. Maybe that never goes away.

I had a GP Patriot that landed like a banshee, once the wheels made contact with the ground they were there, never a bounce, but you get used to it. Jets fly fast and land fast. Sometimes too fast. But I'd call those landing a crash. Had a couple of those too!

RE: Nitro models pusher Bobcat?
 

Thanks for pointing out the disconnect Jammer the whole split flap vs strip aileron thing makes both of our points valid.

RE: Nitro models pusher Bobcat?
 

You are operating in a league above my skill set. However as soon as I understand the flight characteristics of the lighter Bob Cat I'll start on the one with flaps.

Bill

RE: Nitro models pusher Bobcat?
 

I'm sure this technique is old hat to most, I do fly my KeeCat with flaperons, which need some programmed mix of about 25% up elevator to keep the plane in a constant attitude as the flaps deploys but allows a significant reduction in landing speed compared to no flaps. The KeeCat is slightly larger than the nitro version with some 730sq-in wing area, but at 10-Lbs all-up-weight, shud have slightly higher wing loading than yours. I will try the spoileron technique in the coming flying season.

Phil

RE: Nitro models pusher Bobcat?
 

[quote]ORIGINAL: Stick Jammer

RE: Nitro models pusher Bobcat?
 

Not sure what happened to the above post of mine, But my question was do you measure the aileron throw and spoiler throw from the wing root??
I hope to maiden today weather permitting.

RE: Nitro models pusher Bobcat?
 

Yes. Distance of control throw travel should always be measured at the widest part of the surface which in this case would be at the root. On the other hand, if you are checking control throw via degrees (angle) it doesn't matter where on the surface the reading is taken.

RE: Nitro models pusher Bobcat?
 

hey guys, I have the Newer Retract ready version............is pretty much everyone Bolting on the wings instead of glueing them like the instructions say....

and Mine has TWO small holes up fron (on the wing root) one for the small rod, and one with some beefed up ply and a blind nut epoxied on the back.......but the bolt that fits it is a rather small one for a wing bolt...



any help or advice would be great!

thanks, Jim

RE: Nitro models pusher Bobcat?
 

Flyboy 55

This is the method I used for attaching the wings. I measured on the wing root a spot approx 3/4" in front of the forward wing rod. There is a beefy section of ply there. Drill and tap a hole for a 1/4-20 nylon bolt. Reenforce the threads with thin ca and the tap them again when it is set. Measure the same distance on the fuse and drill a larger hole there fo the nylon bolt. The Box stores carry the needed nylon bolt and also a nylon wing nut. Cut some of the bolt length and ca the wing nut to the bolt end and wala you have a good firm attachment for your wings. You can add one of the plastic landing gear straps the the rear of the wings behind the retract well well for added support.

RE: Nitro models pusher Bobcat?
 

thanks sounds great! However- my kit did not come with any nylon bolts.....

RE: Nitro models pusher Bobcat?
 

I'm not a fan of gluing the wings or booms for the simple fact of maintenance and/or repairs. I used (2) 6-32 socket head screws and blind nuts per wing half. I did away with the small anti-rotation rod and used those holes for the rear bolts and then secured the second set close to the leading edge of the wing root. All were reinforced with 1/8" aircraft ply. I also secured a landing gear strap under the wings at the rear. Doing away with the anti-rotation rod also allows easy access to the fuel tank without removing the wings.

RE: Nitro models pusher Bobcat?
 

I glued mine in place.

You can do as Stick Jammer says and bolt them in.

In making my choice I decided that if I did so much damage to the wings that they could not be repaired in place, it would be time for me to purchase a new Bobcat anyway.

So far I've done some extensive repairs to the gear mounting areas and surrounding wood, w/o needing to deal with wing removal.

I left the booms bolted in however.

RE: Nitro models pusher Bobcat?
 

The Bob Cat would be difficult to repair if the wings cannot be removed.

I used 1/4-20 nylon bolts 1 3/4" back from the leading edge of the wing root. Stick Jammer's idea of doing away with the anti-rotation rod is a good idea. The tank sits on top of the anti-rotation rod which seems wrong and prevents removal for inspection. I am replacing the anti-rotation rod with bolts currently. Thanks Stick Jammer.

And after ground handling tests yesterday my tank needs inspection for leaks. The left wing also needs inspection. It may have bounced into the air before I was ready and I shut the throttle down. The ground was very rough.

Bill

RE: Nitro models pusher Bobcat?
 

Hi, a couple of questions for all you bobcat experts.
I have finished and just maidened my bobcat, a great stable airframe for sure once in the air........
Two problems
one, getting her airborne I tried three times to get it off the ground (not enough ground speed?)eventually succeded by forcing it off with full up elevator after a full 60yard run and catchig the expected stall to the right, what needs to be improved?, retract gear location and legnth are fixed due to wheel wells. Once airbourne elevator trim was spot on ?

two engie choice?
I tried a saito 91 with a reverse rotation cam, this was turning a 12*11 prop at 10200 rpm on the ground with a perry pump which I thourght would give a good mix of static thrust and speed, unfortunatly speed was Ok but not blistering and the static thrust was not enough for the take off run to be fast enought?

I'm guess ing a 10 or 11" dia by 8" going about 14000rpm would do it?

So I guess a two stroke is the way to go but what size? I can get a screamer of a 50 but again this wont turn a relativly large prop ie 11-12" to get the startic thrust up enough and I have read that 90 size motors are to heavy? Although my saito 91 and perry pump must weigh a bit.

What would you all reccomend?

RE: Nitro models pusher Bobcat?
 

AOA, AOA, AOA.

Make sure that when the Bobcat is level the front of the plane and the wings are a bit higher than the rear. You want the LE of the wing slightly high.

What you experienced indicates that your wing's angle of attack is negative during runup. Note that even if the plane is level, as it accelerates it can go negative, leading to problems at takeoff.

You want to get good RPM's with this plane.

I've flown it with both a Tower Hobbies .75 and a GMS .76. Either engine with a Graupner 11x8 pusher prop makes this plane a screamer.

Because the 11x8 will spin faster and maintain the RPM's, you'll find that you'll have plenty of thrust.

With either engine, your Bobcat will scoff at gravity. It has no problem maintaining a vertical upline.

Your Saito with an 11x8 will do well, though I'll bet not quite as well as the TH or GMS. But the difference will not be huge.

Since you already have it mounted, why not try the Graupner 11x8 then see how you like it.

RE: Nitro models pusher Bobcat?
 

My opinion is the take off roll should be about 28 mph before rotation for a 7 pound 7 oz. airplane (666 sq. in wing area) with 11 oz. fuel. Rotation should be slight with a flat climb out. The stock wheel location does not lend it's self to gradual rotation. I moved the wheels forward to 2" behind the 10.3" CG and even then it takes over a pound on the stab to rotate. A bumpy runway will bounce the airplane off the ground before it is up to speed.

I intend to experiment with elevator trim and with spoilerons to control the rotation. My opinion is the airplane should taxi at full speed without rotation and then with a slight amount of radio control the front wheel should lift.

Bill

RE: Nitro models pusher Bobcat?
 

Unfortunately if the plane does not have a postive Angle of Attach it will seem to "stick" to the runway even when it is moving at very high rates. Even if the plane is level the booms end up with a degree of negative AOA pushing the nose down until it is finally in flight.

Eventually it will develop so much lift because it is moving so fast that a touch of up elevator will cause it to climb abruptly vertically.

I saw this the very first time I flew mine with it almost level.

I redid the front wheel and establishing a postive AOA in the wings, the plane then lifted off with a nice gradual climbout even at lower throttle settings.

So YES I'm getting a nice gradual rotation at the stock locations even on my 9lb plane. It lifts off nicely now.

It really needs that positive AOA when it sits on the runway.

RE: Nitro models pusher Bobcat?
 

I agree with opjose on this but we need to call this what it is, positive AOA, not incidence. Incidence is the position of the wing in relation to the fuse centerline. With a slight nose up attitude while sitting on the gear the plane should develop enough lift as it gains speed to leave the ground at a nice shallow angle without much or any elevator input. This is pretty typical of most any plane as it reaches flying speed, it should be light on its feet when ready to fly. If the AOA is such that it "sticks" harder to the ground as the speed increases, watch out, your gonna have a handful if and when enough elevator gets it airborne.


Original: BillS

A slight positive AOA while on the gear will overcome the weight needed on the stab as the plane approaches flying speed. It sounds as though you have seen first hand what a bump on the takeoff roll can cause with the gear moved that close to the CG. I have my gear about 2 3/4" behind the CG and it has done the same to me when hitting a bump but so far it has been manageable. I almost wish I would have left the gear in the stock location.

RE: Nitro models pusher Bobcat?
 

morecashthansense,
Personnaly I think a good 2-stroke is better suited to this plane but you definitely have too much pitch with a 12x11. I don't think you want to turn 14,000 RPM's on that Saito though. I don't push my Saito's past 10,000 on the ground. Check your AOA as mentioned by opjose. It should be slightly positive when sitting on the gear.

RE: Nitro models pusher Bobcat?
 

Right on the money...

I used the wrong term.