RE: Nitro models pusher Bobcat?
 

Yup I stole your GREAT idea...

It works VERY well... and elicits a few "wow"'s at the field...

http://image2-6.rcuniverse.com/e1/ga.../lg-111786.jpg

RE: Nitro models pusher Bobcat?
 

ok so were is the final SWEET CG spot? i flew my second bobcat with the gms 76 with the cg at 10.1/2 inches and it was tail heavie and i pankated it ? i had the fuel tank right at the cg so maybe that might have caused it. also my canopy flew of,,it had broke from the mount i made. im thinking that my battery got lose and was going everywere. the resson i say that is because the battery was the only thing out of the plane when i reached the crash site, there was no way it would have come unpluged.



i have ordered another one and it will be here tomorrow!:D

RE: Nitro models pusher Bobcat?
 

I've been building slightly smaller and not so precise copy of Bobcat 50. I made carbon fuse, foam core wings and went with Hobbico mechanical retracts.

Only thin to do before maiden is painting the canopy and adding a little nose weight.

Engine: OS 55AX with Weston-UK Genesis Pusher pipe and Perry VP-30 pump.

Radiogear: ailerons MPX Micro MC/V2, elevator and rudders Hitec HS-125, throttle Futaba 3101, retracts 2x MPX Profi 3BB

I've also ordered AX-18 smoke cartridges to be mounted on wingtips.

Here is couple of pics what she looks like at the moment.

RE: Nitro models pusher Bobcat?
 

damn! under $100 now...does anyone know why? dude, i just bought 2 more for spare parts just in case

RE: Nitro models pusher Bobcat?
 

I've had no problems flying it at 10.3" to 10 and 1/2 inches.

It is not tail heavy at this point, if anything it is still slightly nose heavy which is necessary with a delta...

If you haven't done so you really want to set up the plane for spoilerons for landings.

RE: Nitro models pusher Bobcat?
 

Do we really care as to "why"?

Isn't this a good thing?

RE: Nitro models pusher Bobcat?
 

hi guys

i am struggling with my bobcat, it is running with a J'EN 57 turning an 11x7 pusher prop

the tank is mounted with the bung facing forward and the fuel lines run back down the side and out to the engine

the problem is the engine i ssuffering from fuel starvation and cutting out, i manage to save it sometimes by throttling back, but 8/10 times i end

up dead sticking it, once on the ground the fuel pipe is completely dry

the engine has good compression, there is no leakage from the fuel system, the muffler vent is clear and providing pressure, and the carb is

sealed and not sucking air.

i have tried fitting a header tank just behind the engine, but the problem persists, upon landing the fuel line from the carb to the header is dry

please help as i can see ebay beckoning

i have got the weston bobcat pipe arriving to see if this solves the problem

many thanks

steve

RE: Nitro models pusher Bobcat?
 

I had a similiar problem.

It turned out that I had the clunk line too long, and the clunk would contact the back of the tank.

At idle this did not present a problem, but the engine would die when I ran it up and the lines would appear empty.

Make sure that the clunk is not hitting the back of the tank.

You also may want to connect a clean piece of fuel tubing to the muffler line and blow through it while holding the carb line over a receptacle.

You should have no problem pushing fuel out of the tank at a good clip.

RE: Nitro models pusher Bobcat?
 

thanks

done both of those things already

still no joy

RE: Nitro models pusher Bobcat?
 

I mounted my tank with the bung at the rear....towards the engine, and I am
not using a clunk or tubing for a clunk in the tank. Yes, I know it is unorthodox.
The set up is the same, but the pick up line (feed line) that normally goes straight
into the tank, is bent down as to pick up all the fuel. The other line, the vent line,
goes up to the top of the tank as normal.

Think about it....when the plane is flying, there is always fuel at the rear of the tank
at the bottom. Unless you are coming straight down, fuel will be there. If you are
coming straight down you will most likely have the throttle chopped, and there will
be plenty of fuel in the line when you bring the throttle back up.

However in this configuration, if you fly the plane inverted, you will starve for gas
after awhile....15 to 20 seconds is all you have fuel in the line. Not a problem, I don't
fly around inverted with the Bobcat.

Aileron rolls are not a problem either, it doesn't miss a beat.

Yes, it is different, and so is the Bobcat. This system made perfect sense to me, and
it works perfectly too. ;)

FBD. :D

RE: Nitro models pusher Bobcat?
 

Hairline crack somwhere?

Consider putting a one way valve between the muffler and the fuel tank.

This will increase the fuel flow so you may need to re-tune the engine.

Then try running it up on the ground to check how the engine behaves.



Had you been doing anything other than normal level flight when you get the deadsticks?

RE: Nitro models pusher Bobcat?
 

Keep looking and i am sure that you will find the problem

RE: Nitro models pusher Bobcat?
 

FBD,
If I understand you correctly all you did was take the metal tube on the carb side and bent it down on a 45 degree to the bottom of the tank?

I was wondering if you could put a T-fitting in there with one side of the T to the carb and the other side of the T with a tube and a clunk for the rear of the tank which is facing forward. Then on the bottom of the T have a line with a clunk toward the bung facing the engine. Seems like one side or the other would always be in the fuel. question is, would the side not in the fuel cause the engine to sag.

RE: Nitro models pusher Bobcat?
 

Been there, tried it, didn't work...

What happens is the uncovered clunk offers the least resistance to the lower pressure of the carb... so you still end up sucking air.

RE: Nitro models pusher Bobcat?
 

thanks opjose. I was just curious.

RE: Nitro models pusher Bobcat?
 

....yep. ;)

RE: Nitro models pusher Bobcat?
 

interesting concept. thanks....

RE: Nitro models pusher Bobcat?
 

It had me going enough to try it on a problematic plane..

RE: Nitro models pusher Bobcat?
 

Blue - you need to use the fuel tank the same way everyone else does, and also the way it was designed for - clunk towards the REAR of the plane. The inside plumbing - clunk should come about 1/8 - 1/4 to the end, but not touch - it should flop around to the "bottom" of whatever angle you're holding the tank. There's no other correct way to do it without using a pump.

If you're not just leaning out the motor too much - this is easy to do with a pusher, BTW, because you're not getting the prop-blast you're used to with a tractor setup. You can't tweak it to "max rpm" on the ground - you have to find that spot, then open the needle a bit more. When it's in the air, it will be moving forward, thus creating less resistance on the prop, allowing it to "unload" and acheive higher RPM. This is when it heats up and you get into trouble. The fact that sometimes when you throttle back you can save it is another BIG hint - you throttle back, the motor cools and begins to run properly again.

If you cannot get it to quick going dead stick even with a rich ground setting, I'd look into the following things:
1. Make sure all the head bolts are tiight.
2. Make sure there's no fuel leaking out under compression around the glow plug
3. Use an external fuel tank - just for testing - to verify it's not a fuel tank or line issue
4. When you're testing for a good setting, have your helper hold the plane vertically, with the nose DOWN (leanest cast conditions) and re-tune.
5. Change to brand new fuel, and put in a GOOD recommended glow plug.
6. When it's running, if you tap on the needle valve, and the motor changes, it may be that you have a bad 0-ring in the needle, or the o-ring sealing the carb to the motor. Unscrew the needle valve and try to see if the o-ring is damaged, and also try blowing fuel backwards from the exhaust feed, fuel should come out of the needle valve.

If none of these work, I'd say it's time to get a new piston and sleeve for the motor, or perhaps just get a new motor. It's not worth risking a nice plane for an unruly motor. Spend $90 and get the Tower - that's the deal according to some of the guys posting here. I'm running the OS 55AX, and I love the motor, but I've paid probably $150+ for it. (Can't remember now - but it's RELIABLE and has excellent power).

Whatever you do - don't fly it unless it will idle for a good 30 seconds without shutting down, and can also run at full throttle for 30 seconds without slowing down RPM's.

Finally, I do the "pinch test" when I think it's tuned properly - while at full throttle, I pinch the fuel line to the needle valve. It should make the engine INCREASE in RPM, if it sags or shuts off, you're too lean - open the needle a few clicks, and try again.

Hope that helps :)
Mark

RE: Nitro models pusher Bobcat?
 

Sage words!

Right on the money IMHO.

RE: Nitro models pusher Bobcat?
 

Anyone going to the jet rally in Cape Coral, FL on Oct. 20-21?
I'm not sure if I'll be allowed to fly my Bobcat there (does it count as a "Jet"?) but I should have my F20 (HET) done by then.

My wife actually suggested I take them along (has Hell frozen over????)

Anyway, if you're going to be there, let me know - I'd like to meet you guys.

Cya!
Mark

RE: Nitro models pusher Bobcat?
 

[link=http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXRHS9&P=7]Deflector[/link]In case anyone else is interested in adding a passthrough exhaust for their Bobcat .52 with a TH .75 or GMS .76 engine here is a simple way to do this... no muss no fuss...

I obtained one of these exhausts : [link=http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXRHS9&P=7]Deflector[/link] Left most image below.

These are longer than standard Dubro, Hobbico or GP deflectors. They permit the exhaust tip to stick out 1/4 to 1/2" below the wing...

I then used two of these: [link=http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXRHP4&P=7]Seal[/link] Middle Image Below.

To act as seals on the top and bottom of the wing.

Finally after gluing the seal in place and installing the longer deflector I installed one of these effectively upside down.

It was installed with the bigger end out, and the smaller end glued to the long deflector AND/OR the bottom wing seal...

One of these : [link=http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXRHR9&P=7]Exhaust Coupler[/link] Right Most Image Below.

This vents the exhaust fairly far below the wing.

RE: Nitro models pusher Bobcat?
 

Hi Mark,
I have my fuel tank set up as you described. I just thought that Dave had an interesting concept with the metal fuel tubing bent with no clunk. I was just curious about the other as I did not know if that one work, thinking one side is always in the fuel.

Thanks for the tuning tips on the engine and I will keep them handy, but I think scoobystig had the motor problems. I have a Jett SJ-50 with the stinger modified Jettstream muffler on mine. She should really move....

I am getting close to being done. Just need to hook up the air lines on the retracts, secure the receiver and run the antenna wire, mount the canopy, and balance it. The canopy looks to be another problem. I trimmed it along the lines they had marked on there. When it sits on the fuse there is not much room on the side of the fuse underneath the canopy to secure it witth screws. I can do one on the top front and top rear but the sides do not have much to grab.

RE: Nitro models pusher Bobcat?
 

Hello Guy's
Just a thought, when i bend my tube for air i use the round spring for bending tube's with out crimping them also i always put a inch of fuel line on the end of my tube so that it is at the top of the tank also can be done at the bottom to take the fuel out. I have never seen one of them fly but i bet they have some get up and go. Do they start easy the way it is set up.

RE: Nitro models pusher Bobcat?
 

Check out the "quick release" canopy mount I made for the Bobcat .25. Very easy to do.

You could use two instead of one like I did.

The magnets are totally unnecessary.

http://image2-6.rcuniverse.com/e1/ga.../lg-113288.jpg