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Thread: Bottom Cowl on a Pacer

  1. #1
    Stephen's Avatar
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    Default Bottom Cowl on a Pacer

    Has anyone while converting a PA22 to a PA20 or during a rebuild of a PA22/20 changed the stock PA22 firewall and modified the lower cowling to match the original PA-20? It looks fairly straight forward and has a cleaner look.
    "You can only tie the record for flying low."

  2. #2
    Todd's Avatar
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    Default PA-20 cowling

    My 22/20 had a PA-20 lower cowling on it before my rebuild. I was talked into using the deeper PA-22 firewall and lower cowling, which was supposedly developed to improve cooling with it's notched-in exhaust slot. I agree, the original Pacer is a less "jowly" looking set-up.

    I've got the old PA- 20 cowling and firewall if you want a look.

    Todd

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    mmmmm, let's do lunch. I should be finished with my current project...soon
    "You can only tie the record for flying low."

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    Sounds good to me. We've got a lot of notes to compare - might take two lunches!

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    Administrator Steve Pierce's Avatar
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    I talked to Jim Younkin who built the Mystery Pacer several years ago. The Mystery Pacer was built as a go fast cross country airplane. he used a tunnel in the bottom of the firewall and his intent was to build an adjustable cowl flap but I think his antique restorations got in the way and he never got it done. He also got a field approval to make the tube aft of the baggage compartment removable when not in flight so he could sleep in the plane. Very interesting guy.

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    Quote Originally Posted by Todd View Post
    ............PA-22 firewall and lower cowling, which was supposedly developed to improve cooling with it's notched-in exhaust slot...........Todd
    Does this mean that PA-22's run cooler (no pun here) than PA-16's or PA-20's??? My PA22/20 generally runs too cold. I block and wrap up my oil cooler in the winter.

    I always thought that Piper lower the cowling for the nose wheel gear..I does make sense that the increase out flow would help cooling...but does it????
    "You can only tie the record for flying low."

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    Quote Originally Posted by Steve Pierce View Post
    I talked to Jim Younkin who built the Mystery Pacer several years ago. The Mystery Pacer was built as a go fast cross country airplane. he used a tunnel in the bottom of the firewall and his intent was to build an adjustable cowl flap but I think his antique restorations got in the way and he never got it done. He also got a field approval to make the tube aft of the baggage compartment removable when not in flight so he could sleep in the plane. Very interesting guy.
    I wonder which way he placed his head...up hill or down???
    "You can only tie the record for flying low."

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    Well, there's a misunderstanding here. The only reason the PA-22 cowl is so "fat and bulbous" viewed alongside a Pacer is that there is the added "sugar scoop" under the main section of the "main part" of the engine bottom cowl. Actually, when you drill off the sugar scoop from the Tripe bottom cowl, what you have left is the same "shape" (viewed from the side) of the airplane profile. In fact, if you choose to "fabricate" a new bottom cowl when completing a 22 to 22/20 conversion... you can copy the exact shape of the 22 cowl (with the sugar scoop removed) OR you can trace a PA-20 bottom cowl. It the exactly same size and shape in every respect EXCEPT there is a slightly larger cutout around the carb area when the sugar scoop is used (putting a scab patch there is how the Univair conversion drawing "handles" putting that material back on there), and there is an additional inlet scoop added for the inlet air to the muffler (same location, except that the Tripe didn't need the little rectangular scoop, since the sugar scoop pressurized between the "base cowl" and the sugar scoop!) and the round air inlet hole cut in the bottom cowl is in exactly the same location. Since the elevator push-pull bellcrank (and the basic airframe shape and structure is identical "under there", the firewalls both wind up in the same location. It was an EXCELLANT idea (but, hahaha! you didn't "think of it", Piper did when they modified the Pacer to have a nose gear and ADDED the sugar scoop to the same cowl). The firewalls themselves MAY (or may not) actuallt be physically different (like in "part numbers") but they are [at least VIRTUALLY] identical in "shape". I would believe that you could actually install a PA-22 boot cowl on a PA-20 without modification (but I haven't actually ever done THAT!) except POSSIBLY for a very slightly changed "attach fastener pattern". But even then, probably "no more than from one TriPacer to another TriPacer" in variance.

    I would contend that if you "added a tunnel" under the engine bottom cowl itself, you would likely LOSE some of the effect of the low pressure area formed by the stock "tunnel" built into the bottom of the boot cowl BEHIND (and "cut into") the firewall (where the "cod piece" fillets the airflow where the elevator bellcrank would otherwise "hang out underneath"! The downturn formed by the "cooling lip" on the rear edge of the bottom cowl cutout leads me to believe this. Plus, you would "run into" clearance issues to be overcome with carb/air cleaner issues. Cleaning the area up to be like the Pacer is simply a matter of "removing the fat and bulbous sugar scoop", and what is left underneath that IS what the Pacer had, lock, stock and barrel. The only OTHER difference was the "hump cutout" at the front, when the TriPacer got the oil cooler "snout".

    Contrary to what the V6 mod fella "imagined", the TriPacer airframes where IDENTICAL to the Pacer airframes in basic structure, with the same size and diameter tubing, and the same structural analysis for carrying the load around the Warren Truss; a couple fittings "left off" and new "aft gear attach fittings" added on (and the tailwheel attach fitting omitted) and they had a "Girl's Version" of a very fine airplane (even with the MLG axle centerlines AT the WLE, rather than an inch and a half behind it). Only some "superstructure" (or "birdcage") and some "finish details" actually changed over the TriPacer's production run. But the engine bottom cowl...well, it was STILL THERE right where it used to be, just "hacked up a little" to get that sugar scoop on there too.
    Last edited by JohnW; 03-05-2010 at 10:24 AM.

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    I dug out my old PA-20 firewall today and laid it on top of my new "Cub Doctor" PA-22/20 firewall. In the attached photo notice the 2" difference in depth to the bottom of the 22 firewall. I inserted the lower motor mount bolt thru both for alignment. A PA-20 lower cowling won't wrap around the 22 firewall and reach the upper cowling latches. A fair amount less circumference.
    Attached Images Attached Images

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    Wow, I never put them on top of one another lie that. I didn't realize how much difference in length there was.

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