PA24 180 Carb Air Box

[lawrence mueller]

HELP!
I am presently rebuilding my O-360 on my Comanche and while I have the front of the plane apart I decided to manufacture a new carb air box. Mine is in very poor condition and all of the people that I know local have big engines, my question is when looking down from the top of the air box the base is rotated about 3 degrees clockwise. It appears to be built that way (factory) I have a pic of it. Anyone familiar with this air box?

Larry

[Pat Donovan]

Hi Larry,

What year is your bird? Mine is a 1964 and the box appears to be straight, but I'll take a closer look tomorrow.

PatD

[lawrence mueller]

Mine is a '59 and after stepping back and looking at it again it makes sense because the engine has right thrust for torque. After some more careful measurements it is actually more about 1.5 degrees which is about .1" measuring back from the front edge side to side. It would be difficult to tell while the lower cowl is installed. I did not even notice it until I sat down to program the various parts of it.

Larry

[skipsouthernsky]

Dear Lawrence,

It seems to me that if you are fabricating/rebuilding your carb air box, then what you need to do is tack the lower part in place and then put it on the carburetor and install the lower cowl (just a few screws will hold it in place temporarily). At this point try to make sure that the part that attaches to the bellows is in alignment. I personally think that trying to measure 1 1/2* is way too cumbersome. Just get the bellows and carb air box inlet in alignment and whatever that degree is will be fine. I think you are making this way too complicated.

Sincerely,
Skip Dykema

[Ray B]

I agree with Skip. I sent mine to WebCo . Had it back 5 days latter, looked brand new, fit perfectly. Ray B

[lawrence mueller]

Like I said... I'm in the manufacturing business... Thanks for the replies!

Larry

[skipsouthernsky]

Dear Larry,

Very nice. The flapper door looks new. Did you get that door from Webco or make that new? Did you use a new shaft assembly with new end bushings as well? It all looks new and tight in the picture. Just curios. I'll bet it'll go 1000 hours without needing any attention. After flying and maintaining a Comanche 180 for 5000 hours, I know most of the stuff that wears and cracks over time.

My motto is "you fly them for a while, they fall apart, you fix them, you fly them for a while, they fall apart, you fix them, you fly them for a while.................."

Sincerely,
Skip Dykema

[lawrence mueller]

Hey Skip,
Yes everything is new, mine was totally shot, over all my plane has been neglected for years. After checking prices on this air box I decided it would be one of my idle time projects. the shaft even has replaceable bushings. When I bought this plane last March in Dallas,Tx the annual had been signed the day before, and the sad part was I think it was mostly a pencil job other than a new left fuel bladder (only because it started leaking on their hanger floor before they could finish signing the logbooks!). The engine has been a total basket case (case cracked beyond repair, bad crank, leaky fuel pump, hose all 20 plus years old, the Bendix mags had over 1600 hours on them with no maintenance!) Not really sure how it made it back to GA! While the engine was off I rebuilt the nose gear (plenty of surprises there, broken wheel, very bad bearings, etc.) I'm really looking forward to getting back together and flying (it will be just in time for the next annual!) So far I really enjoy flying it compared to a Piper Arrow that I used to fly.
Sounds like you have some serious Comanche time!

Larry

[skipsouthernsky]

Dear Larry,

If you fix the rest to the same level of airworthiness as the air box, then I'm sure your plane will be highly regarded at some expensive point in the future. You'll never get that money back out of the plane, but I'm sure it will be worth every dime to you as you fly it for many years and enjoy Comanche experiences along the way.

I have to wonder about the pre-buy inspection. Did you go in with your eyes open? I hope the selling price was commensurate with the overall condition of the airplane. Welcome to airplane ownership. You might end up older and wiser. Let me know if I can help in any way.

Sincerely,
Skip Dykema

ps: About 5 years ago, before Hurricane Katrina, the Horton's and Don Johnsen had a heavily attended fly-in at Diamondhead near Gulfport. Comanches were there from all over the US. There were many Comanche heavy hitters there. I won most time in a Comanche award at that time amongst the group. I've owned my 180 since 1979.

[DAVEG24]

Larry,

From what I can see in the picture, you have done an excellent job of recreating the original box, with at least one novel feature, the round tube inlet. I presume the opening into the box itself is still oval, so that you're not drawing warm air when the flapper valve is in the off position. I do have one suggestion that will improve on the longevity of the box. The original configuration, which you have made, has the mounting flange welded to the box, exactly as the original box was made. There is a lot of vibrational torque on the box, and the result is the box invariably shows cracks around the box where the flange extension attaches to the mounting flange. After about twenty years and a couple thousand hours of operation, I felt that there had to be a better way to improve the box. The answer was simple. I took a piece of angle aluminum and welded it front and back from the edge of the flange to the box itself. This increased the rigidity markedly, and I haven't had a crack in that area for many, many years. The other thing that I have done is to heat treat the shaft in the bearing area. The original box wasn't a great design to begin with, and they were relatively inexpensive 40 years ago. So when one broke, you just replaced it with another one, that would do the same thing. Now they're pretty dear, so anything you can do to make them last longer is money in your pocket. I've now had the plane for 42 years, and several thousand more hours accumulated. About the only thing I have to do now is replace the bearings, and that's not very often.

I also notice that you have not put the vanes in the heat box that are there to help in the distribution of air/fuel to the cylinders. The only box that was made without the vanes was for use in the 250. There was a service bulletin pertaining to the removal of the vanes, but it was only applicable to the 250. Whether the vanes actually do anything is subject to conjecture, but they are supposed to be there.

Dave Gitelman