RE: 25 size Bobcat  
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RE: 25 size Bobcat - 9/23/2007 4:28:02 AM   
opjose



Posts: 6144
Joined: 11/26/2005
From: Poolesville, MD, USA
Status: offline 		Tailspincharlie:

You should be able to do VERY well with your engine.

There is really no need to upgrade.

What you want is a higher prop pitch, preferably 8.

When that engine unloads using say an 8x8 or 9x8 prop, you'll get 100mph out of the small Bobcat.

Remember you don't need the higher thrust of a .32, what you are shooting for are high RPM's... the .25 and .32 can get up there equally with the right prop.



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RE: 25 size Bobcat - 9/23/2007 5:25:55 AM   
Tailspincharlie



Posts: 57
Joined: 1/11/2003
From: Bakersfield, CA, USA
Status: offline 		Clowdniner, I don't think a 10" prop will clear the ground. My 9x6 only leaves about a half inch clearence.

Tailspincharlie

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       Post #: 27

RE: 25 size Bobcat - 9/23/2007 5:31:38 AM   
Tailspincharlie



Posts: 57
Joined: 1/11/2003
From: Bakersfield, CA, USA
Status: offline 		Thanks for the tip on the prop. Maybe I will try a 8x8 pusher on it and see if that helps. The 25 I have is old and I don't know if I can get the RPMs that the newer ones have. I will give it a try though. Thanks

Tailspincharlie

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RE: 25 size Bobcat - 9/23/2007 11:27:55 AM   
opjose



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Joined: 11/26/2005
From: Poolesville, MD, USA
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quote:

ORIGINAL: Tailspincharlie

Clowdniner, I don't think a 10" prop will clear the ground. My 9x6 only leaves about a half inch clearence.

Tailspincharlie


I just finished my Bobcat .25

I have an APC 9x7 three bladed prop on it. There seems to be adecuate clearance with this prop.


Mine will be flying ( I hope ) with a 10oz 3900mAh 11v Lipo battery and a 1250KV motor.


To make the canopy easily removable I put a piece of wood just in in front of the existing former... accross the fuselage like the former.

This was epoxied in place.

I put two matched Carl Goldberg Angle Hold downs on the wood with screws, with the "C" clip side facing forward on both.

I then inserted a small metal rod accross the canopy in the correct position, and epoxied it in place.

To install the canopy, I push it backward from in front, until it latches into place.

To remove I just push it forward until it unlatches...

Very easy to install and do.


I also added small plastic air scoops just forward of the canopy, and cut the door "oval" out of the covering, to provide an airflow path to help cool the battery and ESC.



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RE: 25 size Bobcat - 9/24/2007 7:09:00 AM   
opjose



Posts: 6144
Joined: 11/26/2005
From: Poolesville, MD, USA
Status: offline 		I had a chance to fly the .25 extensively today.

It DEFINITELY needs a higher pitch prop.

I tried 9x6x2 APC, 9x7x3 MA Pusher, 10x7e APC and 9x8 APC standard.

The 9x8 standard is a great pitch speed, but the one I had with me was not an electric prop.

As a result it was pulling high AMPS from my battery w/o reflecting this in the performance of the plane.

A 9x8e prop would have been much better.

Like it's bigger cousin the Bobcat .52, this plane is a handful to land.

I finally got a good combination of up ailerons and down elevator mixed in that slows the plane down nicely.

I learned to kick this in only once the wheels touch the ground to act as a type of airbrake.

If I try this combo in slow flight I find the plane wallows around too much during landing attempts.



Quiet flyer had a review of a small Carbon Fiber Ducted fan unit designed for small electric 480 motors this month.

The reviewer put a 1 winding ( yes ONE! ) inrunner motor into it and was able to get 8 lbs ( !!!!!! ) of thrust out of the DF unit while drawing somewhere between 30 35AMPS ( !!!!! )...

WHOAH!!!!

I want one of these on my Bobcat .25

It would turn that plane into a missle!

Wings would be optional.




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RE: 25 size Bobcat - 10/31/2007 4:23:12 AM   
zachmccool


 

Posts: 197
Joined: 9/4/2006
From: , AR, USA
Status: offline 		I was looking at this model and wast thinking of using my OS 46 AX I have laying around.
Has anyone done this yet? Where is the cg located in relation to the nose and the engine mount? How big is the engine mount?
Thank you
Zachary McCool

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RE: 25 size Bobcat - 10/31/2007 4:34:32 AM   
opjose



Posts: 6144
Joined: 11/26/2005
From: Poolesville, MD, USA
Status: offline
quote:

ORIGINAL: zachmccool

I was looking at this model and wast thinking of using my OS 46 AX I have laying around.
Has anyone done this yet? Where is the cg located in relation to the nose and the engine mount? How big is the engine mount?
Thank you
Zachary McCool


That may be too big for it.

A .32 or at worst a .40 could be shoe horned in.



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RE: 25 size Bobcat - 10/31/2007 4:55:19 AM   
zachmccool


 

Posts: 197
Joined: 9/4/2006
From: , AR, USA
Status: offline 		The 46 i have is the same size as the 40s that os makes, i just have it laying around looking for a home. I'm mostly concerned about the cg of the plane. Thats why i would like to know how far it is from the cg to the motor mount and from the nose to the cg. That way I can do some moment calculations to see what the difference would be.


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RE: 25 size Bobcat - 11/1/2007 4:48:16 AM   
opjose



Posts: 6144
Joined: 11/26/2005
From: Poolesville, MD, USA
Status: offline 		The C.G. is two feet, 1/2 inch from the nose of the plane... 7.9 inches from the front of the wing along the fuselage.

It's 6 & 3/8" from the rear of the motor mount/bottom lip of the fuselage.

I've loaded the plane down almost 1/2 lb beyond it's stated weight, with batteries and it still flies fine... however it lands VERY hot.



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RE: 25 size Bobcat - 11/1/2007 5:24:08 AM   
gardenia


 

Posts: 49
Joined: 9/30/2007
From: watsonville, CA, USA
Status: offline 		bobcat 50 I'M GOING ELECTRIC WITH IT ANY MOTOR THOUGHTS?

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RE: 25 size Bobcat - 11/1/2007 6:10:21 AM   
opjose



Posts: 6144
Joined: 11/26/2005
From: Poolesville, MD, USA
Status: offline 		I would imagine that you need A LOT of power with the .50 going electric.

Remember that most people are putting in .75/.76 engines in it.

That would mean using the equivalent of a .90 type electric motor, since the way most motors are rated is quite, eh, conservative...

In turn you'll have a lot of battery weight... not that the airframe will not take it... it should handle it fine.

I'd love to see it fly this way though.





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RE: 25 size Bobcat - 11/11/2007 6:03:05 PM   
SavAxiInf



Posts: 66
Joined: 4/3/2004
From: Akron, OH, USA
Status: offline 		I have a .25 bobcat that I was going to go electric with.
An Axi 2826/08 1130kv motor and a Evo 4s 3700 20c lipo. AUW is about 4 1/2 lbs.
I hope it is not too much of a tank and I can get this bird tweetin right along.

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RE: 25 size Bobcat - 11/11/2007 6:44:07 PM   
opjose



Posts: 6144
Joined: 11/26/2005
From: Poolesville, MD, USA
Status: offline 		I'm flying mine with a 6S 300mAh ( 2 x 3S 3900mAh ) battery at the moment, at exactly that weight.

At 22V my 893KV motor does very well, but it is not blindly fast.


It's surprisingly "light" in the air at that speed. You shouldn't have a problem.


I'm going to install a .32 glow engine in it to see how it compares.



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RE: 25 size Bobcat - 11/12/2007 1:25:59 AM   
jetboy2003



Posts: 96
Joined: 12/31/2004
From: Rapid City, SD, USA
Status: offline 		Do you guys think a .40 LA would be a good fit for this plane? I am going nuts trying to find a fast plane to stick this in!!!

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RE: 25 size Bobcat - 11/12/2007 2:55:24 AM   
opjose



Posts: 6144
Joined: 11/26/2005
From: Poolesville, MD, USA
Status: offline 		It would probably fly well, but I don't think it will be a speed demon.

The .40 LA is about the equivalent of a .25 FX type engine... where-as the .46 LA performs closer to a .32 to .40 FX. ( somewhere in the middle ).


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RE: 25 size Bobcat - 11/12/2007 3:38:02 AM