RC Jets Discuss RC jets in this forum plus rc turbines and ducted fan power systems

Nitro models pusher Bobcat?

Reply
Old 12-23-2007, 08:06 PM
  #2726
Meekskin
 
Join Date: Jul 2007
Location: , CA
Posts: 442
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: Nitro models pusher Bobcat?

Thanks Bills,,,,I'm really looking forward to the maiden flight. I hope the top speed will be over 100+.....will let all know results.

lots of family in greensboro...I grew up just outside of greensboro so I know the area really well.....
Meekskin is offline  
Reply With Quote
Old 12-24-2007, 09:14 AM
  #2727
BillS
 
Join Date: Sep 2004
Location: Greensboro, NC
Posts: 3,312
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: Nitro models pusher Bobcat?

GRAMS one of the older clubs in the area moved to a new field about a year ago. The flight field is on City/County park property and is located in Brown Summit. Miracles never cease. Maybe you can visit sometime.

Bill
BillS is offline  
Reply With Quote
Old 12-24-2007, 11:46 AM
  #2728
Meekskin
 
Join Date: Jul 2007
Location: , CA
Posts: 442
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: Nitro models pusher Bobcat?

I do,,,,my brother, sisters and dad live there...so I try to come back once a year or so.
Meekskin is offline  
Reply With Quote
Old 12-28-2007, 11:40 AM
  #2729
BillS
 
Join Date: Sep 2004
Location: Greensboro, NC
Posts: 3,312
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: Nitro models pusher Bobcat?

Looks like I am going to end up slightly tail heavy. Anyone experimented with moving the tail feathers forward an inch or so?

Bill
BillS is offline  
Reply With Quote
Old 12-28-2007, 11:48 AM
  #2730
opjose
 
opjose's Avatar
 
Join Date: Nov 2005
Location: Poolesville, MD
Posts: 12,588
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: Nitro models pusher Bobcat?

How much is "slightly"?

Up to .75" is not going to have an adverse effect on the plane, and may even improve landings and rotations... however you may want to add a bit more expo to your rates to offset any increases in sensitivity.

opjose is offline  
Reply With Quote
Old 12-28-2007, 07:53 PM
  #2731
Stick Jammer
 
Join Date: Nov 2002
Location: Crete, IL
Posts: 2,251
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: Nitro models pusher Bobcat?


Quote:
ORIGINAL: BillS

Looks like I am going to end up slightly tail heavy. Anyone experimented with moving the tail feathers forward an inch or so?

Bill

A little lead in the nose is much easier and won't add enough to the AUW to matter.
Stick Jammer is offline  
Reply With Quote
Old 12-29-2007, 07:49 AM
  #2732
BillS
 
Join Date: Sep 2004
Location: Greensboro, NC
Posts: 3,312
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: Nitro models pusher Bobcat?

Quote:
How much is "slightly"?
As you may know I have two Bob Cats. One is stock and being built without retracts. The other one has been sheeted and painted and flown once with a turbine.

Today was balance day.

The stock Bob Cat without retracts needs 4 oz. of nose weight. It has a .45 engine.

The sheeted/painted Bob Cat weights 2 pounds more and is very tail heavy even without engine. It needs 11 oz. to balance w/o engine and 15 oz to balance with a .45 engine. A .45 is probably not enough engine.

Bill
BillS is offline  
Reply With Quote
Old 12-29-2007, 10:10 AM
  #2733
hapyjac2
 
Join Date: Mar 2002
Location: tamarac, FL
Posts: 113
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: Nitro models pusher Bobcat?

Bill,
Been reading your posts, I'm surprised that your turbine bobcat is tail heavy. I sheeted mine, wings and stab, and it was still nose heavy. I ended up puting both the radio/servo battery and ecu batteries as far back as I could to get ut to balance at 10.3". After about 1.5oz added to the tail.
Flys fine just had to decrease the ailerons and add a bunch of expo to smooth it out.
What Size turbine are you using?

Hapyjac

www.SouthFloridaJetTogether.com
hapyjac2 is offline  
Reply With Quote
Old 12-29-2007, 11:43 AM
  #2734
Stick Jammer
 
Join Date: Nov 2002
Location: Crete, IL
Posts: 2,251
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: Nitro models pusher Bobcat?

Original: BillS

Quote:
The stock Bob Cat without retracts needs 4 oz. of nose weight. It has a .45 engine.

Wow, that seems odd. Mine is stock, OS 55AX with stock muffler, fixed gear, 5-cell battery just behind the nose gear former and I only needed 1/4 ounce in the nose for 10.3" CG.
Stick Jammer is offline  
Reply With Quote
Old 12-29-2007, 04:05 PM
  #2735
csetting
 
Join Date: Jul 2005
Location: Windsor, CA
Posts: 33
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: Nitro models pusher Bobcat?

I have just started to work on my new bobcat 25.I am mounting a Lambert micro turbine and I wanted to know if there was a certain thrust angle that you guys were putting the turbine at .I know you guys are using the wren 44 on the bigger bobcat so I figure I would do it the same way as you guys are and should be good.
csetting is online now  
Reply With Quote
Old 12-29-2007, 04:44 PM
  #2736
BillS
 
Join Date: Sep 2004
Location: Greensboro, NC
Posts: 3,312
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: Nitro models pusher Bobcat?

Quote:
What Size turbine are you using?
The airplane had a Wrenn 44 set at 10 pounds thrust on it's first and only flight. After the first flight the airplane was retired and turbine removed. The previous owner considered the landing speed far too high for comfort. Based on the bare weight, wing area and landing description it is easy to believe the landing speed was over 40 mph. I think the landing was with flaps, which may have pushed the nose down requiring considerable power and speed to maintain elevator authority. The owner is not new to jets and usually flies two jets several times when he goes to the field . I received the airplane without turbine and returned the retracts. The airplane is glassed and has a beautiful paint job.

As a rough check the airplane was put in the balance cradle without engine and it needed 11 oz on the nose to get the CG correct. An additional 1/3 of the engine weight will be required in the nose to maintain CG.

This project is experimental and likely headed towards a prop engine.

Bill
BillS is offline  
Reply With Quote
Old 12-29-2007, 05:45 PM
  #2737
opjose
 
opjose's Avatar
 
Join Date: Nov 2005
Location: Poolesville, MD
Posts: 12,588
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: Nitro models pusher Bobcat?


Quote:
ORIGINAL: BillS

Based on the bare weight, wing area and landing description it is easy to believe the landing speed was over 40 mph.
Wow, and I though I had long rollouts...

Did he have brakes in it?
opjose is offline  
Reply With Quote
Old 12-29-2007, 07:22 PM
  #2738
Meekskin
 
Join Date: Jul 2007
Location: , CA
Posts: 442
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: Nitro models pusher Bobcat?

Hey Guys,

Anyone know what RPM boost the Genesis pusher pipe for the Bobcat will give for a Magnum 52 engine. Would like to know what to expect from someone who has used them.

thanks
Meekskin is offline  
Reply With Quote
Old 12-29-2007, 09:10 PM
  #2739
Stick Jammer
 
Join Date: Nov 2002
Location: Crete, IL
Posts: 2,251
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: Nitro models pusher Bobcat?

Original: BillS

Quote:
This project is experimental and likely headed towards a prop engine.

Might be a good candidate for doing away with the tail feathers completely and fly it with elevons. I don't recall anyone trying this but yours seems well suited due to the excess tail weight. It's basically a delta wing and it should work considering how pitch sensitive the airframe is to spoilerons and flaperons. In it's present state it sounds like you're gonna need more power than a glow engine can produce as prop size is limited.
Stick Jammer is offline  
Reply With Quote
Old 12-30-2007, 12:18 AM
  #2740
fw190pilot
 
Join Date: Jan 2004
Location: Mt. Vernon, IL
Posts: 481
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: Nitro models pusher Bobcat?

5 degrees downthrust on the turbine version is about right.
fw190pilot is offline  
Reply With Quote
Old 12-30-2007, 12:04 PM
  #2741
BillS
 
Join Date: Sep 2004
Location: Greensboro, NC
Posts: 3,312
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: Nitro models pusher Bobcat?


Quote:
ORIGINAL: opjose


Quote:
ORIGINAL: BillS

Based on the bare weight, wing area and landing description it is easy to believe the landing speed was over 40 mph.
Wow, and I though I had long rollouts...

Did he have brakes in it?
Unfortunately I did not observe the landing and don't remember brakes on the retracts. However scratches under nose and numerous breaks in the nose gear former indicate the landing roll continued into the high grass.

The pictures below show a fixed brake solution to long roll outs. The Bob Cat has not been flown but the brake solution is being used on 4 other airplanes.

Bill
Attached Thumbnails
Click image for larger version

Name:	Xv63775.jpg
Views:	16
Size:	32.2 KB
ID:	837321   Click image for larger version

Name:	Yt60929.jpg
Views:	10
Size:	31.9 KB
ID:	837322   Click image for larger version

Name:	Vb73853.jpg
Views:	11
Size:	33.5 KB
ID:	837323   Click image for larger version

Name:	Nh11442.jpg
Views:	13
Size:	29.8 KB
ID:	837324  
BillS is offline  
Reply With Quote
Old 12-30-2007, 01:55 PM
  #2742
Meekskin
 
Join Date: Jul 2007
Location: , CA
Posts: 442
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: Nitro models pusher Bobcat?

BillS,,,,that looks like a good fix, but I don't think it will work with retracts...The wheel well isn't deep enough to accomadate the rubber...Other than that, it look good.
Meekskin is offline  
Reply With Quote
Old 12-30-2007, 03:31 PM
  #2743
BillS
 
Join Date: Sep 2004
Location: Greensboro, NC
Posts: 3,312
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: Nitro models pusher Bobcat?


Quote:
ORIGINAL: Meekskin

BillS,,,,that looks like a good fix, but I don't think it will work with retracts...The wheel well isn't deep enough to accomadate the rubber...Other than that, it look good.
I only use rubber on one side of the wheel, sometimes on the outside collar and sometimes on the inside collar. Never tried a flat washer but it would probably work also. There is nothing precision about the brake and the slightest amount of drag is all that is necessary.

Bill
BillS is offline  
Reply With Quote
Old 12-30-2007, 04:13 PM
  #2744
BillS
 
Join Date: Sep 2004
Location: Greensboro, NC
Posts: 3,312
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: Nitro models pusher Bobcat?


Quote:
ORIGINAL: Stick Jammer

Original: BillS

Quote:
This project is experimental and likely headed towards a prop engine.

Might be a good candidate for doing away with the tail feathers completely and fly it with elevons. I don't recall anyone trying this but yours seems well suited due to the excess tail weight. It's basically a delta wing and it should work considering how pitch sensitive the airframe is to spoilerons and flaperons. In it's present state it sounds like you're gonna need more power than a glow engine can produce as prop size is limited.
Yes, power will be a problem.

I have an older ST 90 (removable front housing and hope it will run backwards) and a 12 x 8 three blade prop laying on the bench for consideration. It will probably fly with the .90 but minimum flying speed is likely to be in the mid 30's.

Your delta suggestion is interesting. The tail section weights 1 pound 7 oz or so with servos. Maybe the delta suggestion can be tested with the skinny Bob Cat first since I have zero delta experience.

What is really needed is more wing area. All recent military aircraft have supplemental wing area in front of the main delta wing. The cardboard mockup below of additional wing area might be easy to try. It also might not work. This type of conversation often results in serious breakage.

The heavy airplane is simply too pretty to retire.

Bill
Attached Thumbnails
Click image for larger version

Name:	Jh15217.jpg
Views:	14
Size:	58.4 KB
ID:	837487   Click image for larger version

Name:	Gb89359.jpg
Views:	12
Size:	64.2 KB
ID:	837488   Click image for larger version

Name:	Qv53916.jpg
Views:	10
Size:	44.5 KB
ID:	837489  
BillS is offline  
Reply With Quote
Old 12-30-2007, 10:26 PM
  #2745
patzane
 
Join Date: Nov 2005
Location: Glendale, AZ
Posts: 653
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: Nitro models pusher Bobcat?

would Robart 521w1 work on this baby. Looking to get another for retracts.
patzane is offline  
Reply With Quote
Old 12-30-2007, 11:06 PM
  #2746
opjose
 
opjose's Avatar
 
Join Date: Nov 2005
Location: Poolesville, MD
Posts: 12,588
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: Nitro models pusher Bobcat?

Yup I've got those Robarts in mine.

opjose is offline  
Reply With Quote
Old 12-31-2007, 10:09 AM
  #2747
Stick Jammer
 
Join Date: Nov 2002
Location: Crete, IL
Posts: 2,251
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: Nitro models pusher Bobcat?


Quote:
ORIGINAL: patzane

would Robart 521w1 work on this baby. Looking to get another for retracts.

I think the retract ready Bobcat is set up for rail mount nose gear, the 521W1's have a firewall mount. The 520W1's have the rail mount.
Stick Jammer is offline  
Reply With Quote
Old 12-31-2007, 10:34 AM
  #2748
Stick Jammer
 
Join Date: Nov 2002
Location: Crete, IL
Posts: 2,251
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: Nitro models pusher Bobcat?

Original: BillS

Quote:
Your delta suggestion is interesting. The tail section weights 1 pound 7 oz or so with servos. Maybe the delta suggestion can be tested with the skinny Bob Cat first since I have zero delta experience.

As long as the plane balances at 10.3" with the tail section removed (engine mounted and ready to fly of course) I see no reason why it wouldn't fly. Elevons are just a matter of radio programming. With any experimental test there's always a risk but your "GlassCat" is already going to be an experiment with a glow engine simply due to the weight. On the maiden flight of mine I had about 1/4" of spoilerons programmed in for landing and the test deployment at low speed (with altitude of course) nearly put the plane vertical and probably would have completed a loop if I hadn't clicked them off. There's no doubt in my mind this plane would fly without the elevator.
Stick Jammer is offline  
Reply With Quote
Old 01-04-2008, 01:54 AM
  #2749
Capgains
 
Capgains's Avatar
 
Join Date: Feb 2002
Location: Klamath Falls, OR
Posts: 277
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: Nitro models pusher Bobcat?

I'm looking for a plane to do my 50 required logged flights, as part of my turbine waiver. A guy in my club just put one of these together with retacts, and a OS 61 (I'm not sure which model) and has offered it for sale. Is this thing capable of 100mph?
Capgains is offline  
Reply With Quote
Old 01-05-2008, 06:30 PM
  #2750
Meekskin
 
Join Date: Jul 2007
Location: , CA
Posts: 442
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: Nitro models pusher Bobcat?

I will let you know next wednesday. My radar gun will be here tuesday and we will be checking the speed on 3 different Bobcat 52. This is a picture of mine with a Magnum 52, Weston Genesis pipe and retracts.
Attached Thumbnails
Click image for larger version

Name:	Pn36222.jpg
Views:	19
Size:	69.6 KB
ID:	843153  
Meekskin is offline  
Reply With Quote
Reply


Thread Tools
Search this Thread
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off



All times are GMT -8. The time now is 07:48 AM.