Extreme Speed Prop Planes Discuss the need for speed with fast prop planes (Screamin Demon, Diamond Dust, Shrikes or any REAL sound breakin'''' plane)

Its Bobcat nice

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Old 12-12-2007, 03:43 PM
  #426
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Default RE: Its Bobcat nice

Thanks and it is definitely different than what I am working with.

Bill
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Old 12-12-2007, 04:10 PM
  #427
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Default RE: Its Bobcat nice

looks like they designed the retract gear installation robust enough ....

but from your photos... are those load bearing parts actually glued in place to the ribs ?? Sure would be nice to have solid glue joints and perhaps a fillet or two ...
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Old 12-12-2007, 04:19 PM
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Quote:
ORIGINAL: bob27s

looks like they designed the retract gear installation robust enough ....

but from your photos... are those load bearing parts actually glued in place to the ribs ?? Sure would be nice to have solid glue joints and perhaps a fillet or two ...
IMHO the ribs should be longer to distribute the load and there should be a couple of cross ribs...

I've broken them twice.

The first time the block ( which was glued in fairly well ) popped up with a piece of the underlying hardwood.

The second time, the rib broke, letting the block pop out.

Now the plane did hit harder than it should...

I installed form fitting cross blocks under the existing mounts and practically packed the surrounding areas with hardwood triange stock and epoxy.

Now I can't imagine the gear breaking without either taking the wing off at impact or demolishing the gear itself.

In the first picture you see things as it comes from the factory.

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Old 12-13-2007, 01:28 AM
  #429
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Quote:
ORIGINAL: BillS

Yes my gear location looks like your picture.

The front of the slot is 3 1/4" behind the CG and the rear of the slot will put the wheel CL 5 7/8" behind the CG. 10 1/4" CG. My experience with other types of airplanes indicates the airplane will not rotate. The airplane will need positive ground incidence and simply fly off the ground when it gets up to speed.

I will rely on your experience and see what happens.

Bill
Sounds like you know pretty well how things work! It has been stated many times in the two Bobcat threads that the nose gear should be set high which gives a slightly positive incidence. However, in my experience when this plane does "fly" off the ground it won't do so until it has plenty of speed so in my case I don't even notice it. When you get the CG set just right you won't even notice this characteristic anymore.
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Old 12-13-2007, 09:29 AM
  #430
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Default RE: Its Bobcat nice

Thanks for your comments.

The gear is not a huge issue but it appears that the front and main gear don't match. One or the other was intended for use on another airplane. The mains are 5" high. The nose gear is 3 1/2". With normal gear placement the incidence will be negative to the runway.

With negative incidence and mains well behind the CG the unsuspecting and novice flyer probably won't achieve rotation. I doubt if the elevator is large enough to force rotation.

I will probably use a longer nose gear and at first repair move the mains closer to the CG. The front to back mounting of the main gear wire also seems backwards and doesn't take advantage of the torsion of the wire to absorb shock.

The quality of manufacturing is worthy of the price but the design detail leaves something to be desired.

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Old 12-13-2007, 01:00 PM
  #431
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Default RE: Its Bobcat nice

Bill,

That just sounds bizarre, if that is the nose gear you got something is really wrong. Personally I would not monkey with the placement of the gear. I realize you are operating on solid normal procedures but after flying this plane many times I like the gear right where they are and can see how changing their location might produce some negative effects.

Here is a pic of my messy work bench, at the point where the Bobcat was finished. You can get an ideal of what the nose gear should look like.
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Old 12-13-2007, 06:34 PM
  #432
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Quote:
ORIGINAL: AGR413

Here is a pic of my messy work bench, at the point where the Bobcat was finished. You can get an ideal of what the nose gear should look like.

Messy work bench? Where? Looks normal to me......
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Old 12-13-2007, 07:03 PM
  #433
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Default RE: Its Bobcat nice


Quote:
ORIGINAL: BillS

Thanks for your comments.

The gear is not a huge issue but it appears that the front and main gear don't match. One or the other was intended for use on another airplane. The mains are 5" high. The nose gear is 3 1/2". With normal gear placement the incidence will be negative to the runway.

With negative incidence and mains well behind the CG the unsuspecting and novice flyer probably won't achieve rotation. I doubt if the elevator is large enough to force rotation.

Bill
That has been a re-occuring complaint about the stock gear, that the plane will not rotate.

Adjusting the gear length to give postive incidence fixes this.

Mine ended up with about 2-3 degrees of positive wing incidence and it has no problems lifting off.

Note: ( to anyone else following along ) then there is also the minor point of what constitutes elevator "neutral" on this plane, something that is not obvious.


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Old 12-14-2007, 06:10 AM
  #434
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Quote:
ORIGINAL: AGR413

Bill,

That just sounds bizarre, if that is the nose gear you got something is really wrong. Personally I would not monkey with the placement of the gear. I realize you are operating on solid normal procedures but after flying this plane many times I like the gear right where they are and can see how changing their location might produce some negative effects.

Here is a pic of my messy work bench, at the point where the Bobcat was finished. You can get an ideal of what the nose gear should look like.
In your picture the nose gear looks like it has been lowered about 1 1/2" which is like my gear. The distance between the spring coil and the axle should have been longer by about 1 1/2". Gear is more robust when the spring coil is close to the mounting block. It's probably a manufacturing shortcut but not good design. I am also laminating another thickness of wood to the former holding the nose gear.

Your work bench makes me feel at home.

I am proceeding with the stock location for the mains knowing it can be made to work with positive ground incidence.

However I normally set up airplanes with tricycle gear at a slight negative ground incidence. To have negative incidence the airplane should be able to rotate on demand. Location of main gear far behind the CG probably prevents rotate on demand on the Bob Cat. A slight negative incidence allows high landing speeds without bouncing. Rotate on demand allows jumping over the high grass if the airplane veers towards the weeds.

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Old 12-14-2007, 07:50 AM
  #435
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Default RE: Its Bobcat nice


Quote:
ORIGINAL: opjose


Quote:
ORIGINAL: BillS

Thanks for your comments.

The gear is not a huge issue but it appears that the front and main gear don't match. One or the other was intended for use on another airplane. The mains are 5" high. The nose gear is 3 1/2". With normal gear placement the incidence will be negative to the runway.

With negative incidence and mains well behind the CG the unsuspecting and novice flyer probably won't achieve rotation. I doubt if the elevator is large enough to force rotation.

Bill
That has been a re-occuring complaint about the stock gear, that the plane will not rotate.

Adjusting the gear length to give postive incidence fixes this.

Mine ended up with about 2-3 degrees of positive wing incidence and it has no problems lifting off.

Note: ( to anyone else following along ) then there is also the minor point of what constitutes elevator "neutral" on this plane, something that is not obvious.


The method of mounting the tail section to the wing could easily lead to manufacturing inconsistencies resulting in differing stabilizer incidences. A small amount of sanding or shimming at the wing mounting of the tail booms would greatly affect the stab incidence. A 1/64 ply shim at the front wing mount for the tail boom will change the stab incidence approximately 6 degrees. Manufacturing tolerances are likely to be 1/16" or so.

No problem exists to my knowledge. Those interested in maximum speed or fine tuning might want to be aware that small manufacturing inconsistencies result in large changes in the stabilizer and maybe also to elevator "neutral". Rotation would also be affected. It's all somewhat useless information.

Bill
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Old 12-14-2007, 11:05 AM
  #436
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Default RE: Its Bobcat nice

Bill,

Well at least we now know you have the same equipment as everyone else and it does work with the supplied equipment.

The one thing I must be sure to point out is that you need to beef up the nose gear pushrod (steering pushrod) if you use the stock pushrod. I have scuffed wingtips because of the pushrod flexing and allowing the nosegear wheel to buckle, I cut a channel in a length of dowel and secured it to the pushrod, no more problems.
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Old 12-14-2007, 11:41 AM
  #437
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Default RE: Its Bobcat nice

Heh... I placed a large metal washer on the bottom of the nose of my Bobcat just in case the nose gear fails to extend or if it buckles.

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Old 12-14-2007, 01:00 PM
  #438
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Default RE: Its Bobcat nice

Hello Bobcat Builders,

I started to build the 50 size when they first came out and was following a thread but then I had to stop due to back injury's, now I can not find the thread even with a search so I am kindly asking for some help.

I am now able to work a little each day but I have a few questions where I left off and hoping some one could steer me in the correct direction. Basically the plane is built and I used my MVVS 77 for power. I have also reinforced the landing gear block.

My questions are:
Fuel Tank, What is the correct installation direction, fuel lines exit pointing towards front of plane or pointing to the rear as shown.

Center of gravity, What would a good point to start at to get use to the plane?

Than you,
John
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Old 12-14-2007, 03:07 PM
  #439
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Default RE: Its Bobcat nice

The fuel tank should face toward the front of the plane with the clunk toward the rear. Just route the fuel lines around the tank and out the back. If memory serves me the CG should be 10.3" from leading edge at the fuse. Is [link=http://www.rcuniverse.com/forum/m_4588799/tm.htm]this the thread[/link] you were referring to? It is in the RC Jet section.

Blessings, Terry
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Old 12-30-2007, 04:42 PM
  #440
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Default RE: Its Bobcat nice

i am responding to the question about the bobcat calling for 4 channel 8 servos..now how does that work..and the instruction manual is very vague..is there anyway to get an in depth instruction manual??? please help..this is my first plane
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Old 12-30-2007, 05:27 PM
  #441
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Default RE: Its Bobcat nice


Quote:
ORIGINAL: allstardude17

i am responding to the question about the bobcat calling for 4 channel 8 servos..now how does that work..and the instruction manual is very vague..is there anyway to get an in depth instruction manual??? please help..this is my first plane
Here is more information than you wanted to know.

http://www.rcuniverse.com/forum/m_4588799/tm.htm

I used 6 standard servos.
1 rudder
1 elivator
2 aileron
1 throttle
1 steering

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Old 12-30-2007, 06:36 PM
  #442
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Default RE: Its Bobcat nice

so i bought a 4 channel transmitter..how do i control all those servos with 4 channels (mainly the 2 rudders, and the 2 ailerons)..may sound dumb but im new to this
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Old 12-30-2007, 07:52 PM
  #443
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Default RE: Its Bobcat nice

Allstardude17:

This is your first plane???????????? [:-]

Do yourself a favor.

Put it away.

Purchase a trainer, or at worst a low wing trainer.... ( hint: Pulse XT PNP, you will not tire of it... )

The Bobcat really takes an EXPERIENCED flyer to handle.

It is far more difficult than an average plane and flies differently.

Not to sound disingenuous, if you need more than the C.G. and throws to put the Bobcat together, you are NOT ready for it.

Wait until you have certified, and then elicit the aid of someone at your club to help you with the Bobcat.

I went to the MOST experienced and accredited flyers at my club for help with this plane, notably the "jet guys" who have 16K+ invested into each of their jets... these guys have to know their stuff, least they loose their investment...

They found the Bobcat to be an EXCELLENT "Jet trainer" as according to them, "if you crash it, you are not worried about the loss... ", eh.... ok. It's good to them because it flies much like their Kingcats for which they need far more training...

PLEASE don't try to fly it until you have a good bit of experience with other planes. I






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Old 12-30-2007, 08:07 PM
  #444
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Default RE: Its Bobcat nice

well i have been flying a simulator i bought for my computer with the transmitter hooked up to my computer...but i still want to know how i need to put this thing together..i understand how it works...i worked on planes in the navy and all...but i just dont understand having 4 channels controlling 8 servos...i dont plan on flying it anytime soon..i want to get it put together so my local hobby shop guys can help me learn to fly it..
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Old 12-30-2007, 08:12 PM
  #445
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Default RE: Its Bobcat nice

"Y" harnesses now if you need a definition then don't buy the plane.
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Old 12-30-2007, 08:16 PM
  #446
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Default RE: Its Bobcat nice

Quote:
ORIGINAL: allstardude17

well i have been flying a simulator i bought for my computer with the transmitter hooked up to my computer...but i still want to know how i need to put this thing together..i understand how it works...i worked on planes in the navy and all...but i just dont understand having 4 channels controlling 8 servos...i dont plan on flying it anytime soon..i want to get it put together so my local hobby shop guys can help me learn to fly it..
Do by all means put it together, just take your time.

I'd suggest that if you can, join a local club. Many have their own trainers which you can use for training session.
And of course you need your liability insurance, etc... so joining a club is practically a must unless you live in a very isolated area with "wide open spaces".

You really do not want to start out with the Bobcat.

Remember the simulator is NOT going to teach you to fly. particularly this plane. It only changes the amount of time required.

There are a bunch of experienced instructors at our field that I would NEVER let them fly the Bobcat, as I know they would crash it, since they do not have experience with it. It's that "different".

Unless you have seen you "hobby shop guys" fly one of their own Bobcats, you may want to stear clear.

Re: Servos.

You can use Y adapters on the ailerons, elevator, and rudder servos.

That will bring the number of required channels down to 4, assuming NO retracts.

However you will need either to use, servo reversers ( which I dislike ), a matched reversed servo ( good! ), or reversing one of the linkages on the elevator and rudder.

The latter is NOT problematic with this plane.... but not the best solution either.

With 4 channels and no mixing you will not be able to employ spoilerons which IMHO are almost a must with this plane.


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Old 12-30-2007, 10:25 PM
  #447
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Default RE: Its Bobcat nice

i get ya..thanks alot..no, i def want to just put it together..im very cautious on flying this plane..i have flown cheap little planes before but nothing this complex..it is def an experience though putting this thing together....now u said something about insurance??/ can u tell me more?? and yes i live in a place that has alot of open fields..lol
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Old 12-30-2007, 10:57 PM
  #448
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Quote:
ORIGINAL: allstardude17

i get ya..thanks alot..no, i def want to just put it together..im very cautious on flying this plane..i have flown cheap little planes before but nothing this complex..it is def an experience though putting this thing together....now u said something about insurance??/ can u tell me more?? and yes i live in a place that has alot of open fields..lol
You have certain liabilities flying these things.

That is why AMA provides insurance that supplants your home owner's insurance in case you ever have an accident with your plane.

RC clubs require AMA membership, and adherence to flying rules.

You pay dues to the clubs, and in return you get to use their flying fields ( once you certify ) and there are a meriad of other benefits...

Go to the AMA web site, and punch in your zip code:

http://www.modelaircraft.org/clubsearch.aspx

You'll get a listing of local clubs in your area.

IMHO this was the best thing that happened to me getting into this stuff.

Choose a club ( preferably one nearby with a nice field ) and take the time to go to the field and attend a meeting.

You'll pick up a lot, and you typically walk away with a whole new perspective, plus help when you need it.

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Old 12-31-2007, 12:08 AM
  #449
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Default RE: Its Bobcat nice


Quote:
ORIGINAL: allstardude17

well i have been flying a simulator i bought for my computer with the transmitter hooked up to my computer...but i still want to know how i need to put this thing together..i understand how it works...i worked on planes in the navy and all...but i just dont understand having 4 channels controlling 8 servos...i dont plan on flying it anytime soon..i want to get it put together so my local hobby shop guys can help me learn to fly it..
you may need to ugrade your radio 7-9 channels with P-mix. Or buy a JR matchbox / Futaba MAS-10. For you will need to drive 2 rudder servos and a servo to steer the nose gear. Most receivers can only drive 2 servos off any one channel. You could cheat and use only one servo on a rudder and link the rudders together mechanically and use the Y to drive the steering. But then you link may get in the way of starting the motor.
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Old 12-31-2007, 12:35 AM
  #450
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Default RE: Its Bobcat nice

hey thanks for that site..sounds like a good idea..i have talked to people that have been flying for years and say they still crash every now and then..so insurance is def a good idea..thanks for the help
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