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GP cherokee 40 : Cutting Cowl ?

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GP cherokee 40 : Cutting Cowl ?

Old 09-18-2008, 11:08 AM
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The1User
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Default GP cherokee 40 : Cutting Cowl ?

Hello all,

I am about to cut my first cowl (ever) on a Great Planes Cherokee 40 build

What is the best tool / method for cutting?

I have to cut a round hole for the motor on the right side of the cowl

And then another hole on the bottom for my Pitts muffler exhaust and the nose gear

I really want to cut this the best way possible,

1) Least likely to ruin it
2) Nice clean edges

Thanks

Joe
Old 09-18-2008, 11:20 AM
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MinnFlyer
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Default RE: GP cherokee 40 : Cutting Cowl ?

Dremel tool
Old 09-18-2008, 11:56 AM
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ChuckW
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Default RE: GP cherokee 40 : Cutting Cowl ?

I use a Dremel with a cone shaped abrasive bit. I can use the tip of the cone for more precise stuff or push it in to the larger diameter area to remove material faster.

Try to start small and work up to the final opening size. It is easy to remove more material if needed but impossible to put it back.

One trick is to use cardboard taped to the side of the fuselage that extends out over the motor and other areas that need to be cut. Experiment with cutting the cardboard until you get it just right. Then remove the engine, put the cowl in place and trace the openings in the cardboard on to the cowl. This will get you very close and will likely only need some fine tuning. I wish I had some photos or drawings of this to post.

The Cherokee should be pretty simple. On my glow version, I made a large U-shaped cut out to clear the muffler and nose gear. Then a simple opening for the cylinder head and a round hole for the high speed needle.
Old 09-18-2008, 07:24 PM
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Default RE: GP cherokee 40 : Cutting Cowl ?

Remember that you should have at least 2 to 1 exit air to intake air for cooling. I like to use 3 to 1 . The above method is probably about as easy and accurate as you will find. ENJOY !!! RED
Old 09-22-2008, 04:22 PM
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Default RE: GP cherokee 40 : Cutting Cowl ?

Well I did it,

Not too bad for a first try.... I didn't like doing it !! I am 50 years old and between going blind and never doing it before I was a bit worried

As you can see I decided to mount my fuel dot back right behind the fuel tank where the wood is strong
I'm using the 3 line system so I just drilled a small hole in the firewall and sent the fill line back where it was needed



I have another question about the muffler (I asked this in another area but realized I was hijacking the thread)
Can I bend the left pipe about 1/2 inch? I don't want to cut it, I like how long it is. And I don't want to add a deflector

I was thinking to try bending it by clamping the square part of the muffler in a vice and then sticking something round
up the pipe to bend with, Has anyone ever done it (besides from landing hard )

As always Thanks For The HELP !!

Old 09-22-2008, 09:25 PM
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Default RE: GP cherokee 40 : Cutting Cowl ?

Great job. I have seen a lot of hacked up cowls (even ruined a few myself) but yours is excellent.

I've never bent the muffler tubes on purpose but I don't see why it wouldn't be possible. My main concern would be collapsing the tube or breaking at the point where it attaches to the muffler. Of course, a few flat spots or kinks in the tubes probably wouldn't hurt much besides looks. Maybe you could take the muffler off and pack the tubes with sand to make them bend smoother without kinking? Perhaps one of those spring type tube benders might work? Who knows, they may bend smooth just as they are.

Where abouts in the Philly area are you? My wife is from the Norristown area. We are going to visit her family in June and I'm going to try and sneak away to some flying fields in the area.
Old 09-22-2008, 11:12 PM
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Default RE: GP cherokee 40 : Cutting Cowl ?

About your exhaust tubes:

if you cut them or bend them too much, the bottom of your plane will get oily...it's kinda like 6 of one, half dozen of the other. But if you do decide to bend them, use a nice tubing bender, otherwise they will collapse in a hurry! If you don't have experience with bending tube, try to talk to some friends that have experience in that area. I'm far from a good fabricator and ask for advice and help from friends for doing stuff like this. Lord knows i'd kink those tubes beyond recognition!!

BTW: great job on the cowl cutting!! I've seen my fair share of hack job's when people take the time to do it nicely and it really detracts from the look of the plane...

I wonder if cutting the pipes tike shown in the pic would help things???
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Old 09-23-2008, 12:11 AM
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Default RE: GP cherokee 40 : Cutting Cowl ?

Thanks for the compliment on the cut, I couldn't "find" my Dremel tool so I clamped my drill down to the work bench in my shop and held the cowl in my hands moving it around (worked real nice that way)

I used a cone shaped grinding wheel as suggested by you, the 3 cuts took over an hour and a half (engine head, muffler, needle valve), filled the room with fiberglass dust to the point of having to use my gas mask and shower after the job was done.... NOT FUN

I know how cutting them will cover the plane with oil, thats why I don't want to cut them, I love how long they are, at the same time the left pipe is right above the wheel and covers the wheel in oil just running the engine for 1 minute

I am an old plumber and know a little about bending pipe but this pipe scares me, I think a "small" bend to the left (up high) would make it a "bigger" bend down low near the wheel, Maybe one of those coiled wire pipe benders as someone here suggested BUT I think the Aluminum pipe would be stronger than the coil and maybe not be able to keep the round shape, Thats why I was thinking of just sticking a round rod of some kind up the pipe, giving it a very small move and then pulling it out a little and doing it again lower (so as not to put all the bend in one place)

*JCB* LOVE the Photoshop cut on the Pipes

ChuckW: I live in Wayne (5 miles SW of Norristown) We fly at Valley Forge National Park, club name VFSS (Valley Forge Signal Seekers [link=http://www.vfss.org/]http://www.vfss.org/[/link]) The field is a 10 minute drive from Norristown, Just bring your AMA card and stop at the park office for a free day pass, Sundays Gliders only till 2 PM

When I can't stand looking at the pipe right over the tire anymore I'll post a picture of the outcome (that Bisson Pitts is only $27 member pricing from my favorite place [link=http://www.wholesaletrains.com/Detail.asp?ID=200438543]https://www.wholesaletrains.com/Detail.asp?ID=200438543[/link]

Thanks Guys

Joe
Old 09-23-2008, 09:02 AM
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Default RE: GP cherokee 40 : Cutting Cowl ?

How about this,

I am being told that in many cases it is necessary to block or restrict one of the outlets to ensure the motor runs properly and transitions well

Does anyone know if this is true using the Bisson pitts muffler designed for a 46 engine with a 46 engine?

Thanks

Joe
Old 09-23-2008, 08:18 PM
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Default RE: GP cherokee 40 : Cutting Cowl ?

I haven't had a single issue as far as "lack of fuel tank pressure" on my Cherokee. I am using a Magnum 46 motor and it runs like a top with this muffler. I have probably about 30 LONG flights on this plane and had only one dead-stick. That was because is was 110 deg F out and I didn't adjusted the needle setting since that previous time out when it was 80deg...I wouldn't worry about clamping off one of the pipes unless you are SURE you are having back pressure issues.
Old 09-23-2008, 10:45 PM
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Default RE: GP cherokee 40 : Cutting Cowl ?

Thanks for the info JCB,

It makes no sense why Bisson would design this muffler for a 46 with two pipes only for the user to have to block one

I am going to try and bend it right now (will post pictures)

BTW what was it like dead sticking the Great Planes Cherokee 40??

Seems a bit heavy to me and can't wait to fly it !!

Thanks again

Joe
Old 09-24-2008, 12:14 AM
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Default RE: GP cherokee 40 : Cutting Cowl ?


ORIGINAL: The1User

BTW what was it like dead sticking the Great Planes Cherokee 40??
Not sure on a glow powered Cherokee. Mine didn't last long enough to find out. My second is electric and I used the recommended motor, ESC and battery. Although, I never got an accurate weight to really compare the two versions, it seems like the electric is definitely heavier. That extra weight affects the flying quality in my opinion. Moving the CG back helped but I still liked my glow powered Cherokee better.

Regardless, it will stay flying at pretty slow speeds so dead sticks shouldn't be a big deal.
Old 09-24-2008, 12:35 AM
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Default RE: GP cherokee 40 : Cutting Cowl ?

Well that was way easy,

Just took a large Allen key up the pipe I wanted to bend and then held the other pipe real tight
(didn't even remove muffler, but made sure to keep all torque on the two pipes only)

Because the Allen key gave me more leverage the left pipe moved more than the right pipe



Before:



After:




Thanks Everyone

Joe
Old 05-27-2022, 02:00 PM
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Default

looking for a replacement cowl for the great planes. 40.Kiwi4

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