RE: Nitro models pusher Bobcat?

RE: Nitro models pusher Bobcat?
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RE: Nitro models pusher Bobcat? - 3/15/2008 3:53:00 AM

Stick Jammer

Posts: 2251
Joined: 11/21/2002
From: Crete, IL, USA
Status: offline

quote:

ORIGINAL: BillS

I used a 1 oz. header tank facing forward and behind the supplied tank. The standard tank faces to the rear and is vented to short fill to 8 Oz. The header tank was installed from the rear which required cutting a larger hole in the fuselage.

The fuel lines are considerably shorter. Both needles are easier to adjust. With full fuel anything over 35 degrees AOA draws only from the header tank. Working room is nonexistent and the fuel lines were difficult to plumb. After considerable ground testing (no flights) deceleration after a high speed run often shuts the engine down. Cause unknown.

Bill

I'm not sure a lot of full throttle ground testing of a pusher is the best thing for your engine, it's very possibly overheating. On the header tank subject, I'll go back to what I mentioned earlier, keep it simple. Really no need for all the extra plumbing on this plane. Hope you get it all worked out and in the air.

_____________________________

The more you fly, the more you buy.

(in reply to BillS)

Post #: 3026

RE: Nitro models pusher Bobcat? - 3/15/2008 3:12:59 PM

Overpowered

Posts: 96
Joined: 7/30/2002
From: Frisco, TX, USA
Status: offline

Whats the best choice of nose weight and how have you mounted/inserted it at the nose.

Plenty of room in the nose, but not a whole lot of access to get in there - so my receiver & battery are at the backside of the front LG bulkhead.

Eric

(in reply to Stick Jammer)

Post #: 3027

RE: Nitro models pusher Bobcat? - 3/15/2008 8:01:09 PM

opjose

Posts: 5830
Joined: 11/26/2005
From: Poolesville, MD, USA
Status: online

quote:

ORIGINAL: Overpowered

Whats the best choice of nose weight and how have you mounted/inserted it at the nose.

Plenty of room in the nose, but not a whole lot of access to get in there - so my receiver & battery are at the backside of the front LG bulkhead.

Eric

I used a long but thin Venom 1200mAh battery pack. I had no problems putting it into the nose. You could even insert two of them there... that way the weight is "working" weight for you.

_____________________________

-
Build em'', fly em'', crash em'' and build more.

(in reply to Overpowered)

Post #: 3028

RE: Nitro models pusher Bobcat? - 3/15/2008 8:02:10 PM

opjose

Posts: 5830
Joined: 11/26/2005
From: Poolesville, MD, USA
Status: online

quote:

ORIGINAL: Stick Jammer

I'm not sure a lot of full throttle ground testing of a pusher is the best thing for your engine, it's very possibly overheating.

Yup something I found out the hard way.

Until I understood this I had many problems trying to get the engine tuned up and trying to avoid it cutting out at run-up/takeoff.

_____________________________

-
Build em'', fly em'', crash em'' and build more.

(in reply to Stick Jammer)

Post #: 3029

RE: Nitro models pusher Bobcat? - 3/16/2008 1:36:58 AM

Stick Jammer

Posts: 2251
Joined: 11/21/2002
From: Crete, IL, USA
Status: offline

quote:

ORIGINAL: Overpowered

Whats the best choice of nose weight and how have you mounted/inserted it at the nose.

Plenty of room in the nose, but not a whole lot of access to get in there - so my receiver & battery are at the backside of the front LG bulkhead.

Eric

Velcro is about the best solution for holding the battery in the nose. My battery and Rx are in the same location as yours. I only had to put about an ounce of lead in the nose of mine. I glued some sheet lead to a piece of 1/4" balsa. I reached in with a long pair of forceps and epoxied the balsa into the nose. If I ever need to get it out I can simply reach in and break the balsa loose.

_____________________________

The more you fly, the more you buy.

(in reply to Overpowered)

Post #: 3030

RE: Nitro models pusher Bobcat? - 3/17/2008 3:35:18 AM

BillS

Posts: 3050
Joined: 9/6/2004
From: Greensboro, NC, USA
Status: offline

quote:

ORIGINAL: Stick Jammer

quote:

ORIGINAL: BillS

I used a 1 oz. header tank facing forward and behind the supplied tank. The standard tank faces to the rear and is vented to short fill to 8 Oz. The header tank was installed from the rear which required cutting a larger hole in the fuselage.

The fuel lines are considerably shorter. Both needles are easier to adjust. With full fuel anything over 35 degrees AOA draws only from the header tank. Working room is nonexistent and the fuel lines were difficult to plumb. After considerable ground testing (no flights) deceleration after a high speed run often shuts the engine down. Cause unknown.

Bill

I'm not sure a lot of full throttle ground testing of a pusher is the best thing for your engine, it's very possibly overheating. On the header tank subject, I'll go back to what I mentioned earlier, keep it simple. Really no need for all the extra plumbing on this plane. Hope you get it all worked out and in the air.

While I don't know the final outcome of the concept of drawing fuel from the main tank only when reasonably level, the concept seemed sound in the beginning and it still seems sound. Also I had fun with the implementation. Running an engine in a reverse configuration does seem to require different tuning techniques.

Bill

(in reply to Stick Jammer)

Post #: 3031

RE: Nitro models pusher Bobcat? - 3/17/2008 6:39:50 AM

Overpowered

Posts: 96
Joined: 7/30/2002
From: Frisco, TX, USA
Status: offline

There were a few suggestions on CG & Throw.

Should I start with the 10.3" from the front edge of the wing for CG or is there something better.

What about the throws.

I'd hate to have to re-read this all and have to pick from the posters.

Please someone chime in who flys this plane on a good flyable setting.

I'd hate to be overcontrolling and snaping or not having enough throw to bring it back in one piece.

Eric

(in reply to BillS)

Post #: 3032

RE: Nitro models pusher Bobcat? - 3/17/2008 6:30:20 PM

squidster

Posts: 51
Joined: 12/19/2007
From: oviedo, FL, USA
Status: offline

Have 2 being deliverd tomorrow

. Very much looking forward to digging in. A question for those of you that put the air retracts in: Most had to cut into the fuse to accomodate the wheels when the gear is pulled up. What does the idea of moving thegear further outboard on the wings and also moving the aileron servo outboard furhter seem like to you guys? If this can be accommodated, cutting into the fuse could possibly be elimintaed, yes?

I have read the entire thread (whew!!), but can't remember if I saw this addressed in here, has anyone started with the fixed gear and added the retract later? My concern is going to far with $$ on the retracts in the event this thing has a short life span (ie: midair with earth).

Thanks!

Sqidster's Dad.

(in reply to Overpowered)

Post #: 3033

RE: Nitro models pusher Bobcat? - 3/17/2008 6:46:35 PM

opjose

Posts: 5830
Joined: 11/26/2005
From: Poolesville, MD, USA
Status: online

quote:

ORIGINAL: Overpowered

There were a few suggestions on CG & Throw.

Should I start with the 10.3" from the front edge of the wing for CG or is there something better.

Yup that is optimal.

quote:

ORIGINAL: Overpowered

What about the throws.

Start by setting your high rates to the recommended throws, and your low rates to be about 65-75% of the recommended throws.

That way on your first flights, if you find things too fast or twitchy, you can dial things down, but DO NOT restrict elevator throw too much, or you will have a hard time landing the plane.

quote:

ORIGINAL: Overpowered

I'd hate to be overcontrolling and snaping or not having enough throw to bring it back in one piece.

Eric

Make SURE you have a positiive angle of attack on the wings.

Also plan on putting the plane on one end of the runway and quickly running up the engine then back down again, so you can see how it responds. Do this after the plane has sat on the runway for at least a minute to double check your tuning too.

Do NOT pull back on the stick hard at takeoff. Give it as much room to accelerate as you can and then pull up gradually... ( again assuming that the AOA is positive otherwise the plane will "stick" to the ground ).

Once in the air trim the plane, then start working the spoilerons and low speed flight characteristics at high altitude. Get a feel for how slow the plane will go, and make turns. The first time it starts to wallow around on you, you will be surprised... and you are too slow.

Dedicate two runs around the field to slow speed and spoilerons, then work on your approaches and landings.

This is a fast hot landing plane ( for a propped plane ). You need to get the sweet spot for landings.

You want to get it low and let the spoilerons/nose high attitude/ bleed off the airspeed until it settles in, in a very jet fighter manner.

_____________________________

-
Build em'', fly em'', crash em'' and build more.

(in reply to Overpowered)

Post #: 3034

RE: Nitro models pusher Bobcat? - 3/17/2008 6:52:28 PM

opjose

Posts: 5830
Joined: 11/26/2005
From: Poolesville, MD, USA
Status: online

quote:

ORIGINAL: squidster

A question for those of you that put the air retracts in: Most had to cut into the fuse to accomodate the wheels when the gear is pulled up.

No, not on the retract ready versions.

quote:

ORIGINAL: squidster

What does the idea of moving thegear further outboard on the wings and also moving the aileron servo outboard furhter seem like to you guys? If this can be accommodated, cutting into the fuse could possibly be elimintaed, yes?

This is not needed on the retract ready versions.

quote:

ORIGINAL: squidster

I have read the entire thread (whew!!), but can't remember if I saw this addressed in here, has anyone started with the fixed gear and added the retract later? My concern is going to far with $$ on the retracts in the event this thing has a short life span (ie: midair with earth).

I would not recommend trying to install retracts after the fact. If you install the fixed gear there are gear blocks which must be put in and epoxied. These will be impossible to remove later.

If you are going with retracts, do so from the onset.

If you lawn dart the plane, it is unlikely that the gear will be severely damaged.

The biggest problem is hard landings, and if you've gone with the recommended gear sets, most of the damage is to the wing or fuselage.

I have yet to even bend a gear wire, but I've yanked the gear out of the wing twice now with bad landings.

_____________________________

-
Build em'', fly em'', crash em'' and build more.

(in reply to squidster)

Post #: 3035

RE: Nitro models pusher Bobcat? - 3/17/2008 7:14:43 PM

squidster

Posts: 51
Joined: 12/19/2007
From: oviedo, FL, USA
Status: offline

Thanks for the quick response! Another question came to mind while reading. The Robarts, 520w1 set comes with wire gear as I recall. If I go this direction, can the wire be changed out to the shock absorber struts after the fact or does it need to be done initially and do you know what the model # is if I go with the struts instead of the wire set up?

Thanks again for a great thread and read.

(in reply to opjose)

Post #: 3036

RE: Nitro models pusher Bobcat? - 3/17/2008 7:20:21 PM

opjose

Posts: 5830
Joined: 11/26/2005
From: Poolesville, MD, USA
Status: online

Usually you have to do this from the onset.

The Strut ready gear have larger openings for the struts.

There may be some exceptions to this, but I am unfamiliar with them.

_____________________________

-
Build em'', fly em'', crash em'' and build more.

(in reply to squidster)

Post #: 3037

RE: Nitro models pusher Bobcat? - 3/17/2008 7:26:32 PM