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1. 11:02 PM - Re: N28697: Jaguar cowling (Gary L Vogt)
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Subject: | Re: N28697: Jaguar cowling |
During the initial cowling fabrication, I made the assumption that each engine
mount required one shim between the engine and the bushing. I installed a mockup
engine on new Lord mounts on a 78 Tiger, N28840, using one shim on each mount.
I laid up the new cowling using this as a starting point.
When I installed the first cowling, actually a fiberglass 'splash,' on N119ST,
it fit well using the same 'one shim per mount.'
When I installed the second prototype, the first one flown, on N119ST, it also
fit well with just one shim per mount.
I installed the splash on John Bunker's Traveler. It didn't have any shims. It
fit well.
The first complete cowling was installed on N28747. 747 required 2 shims on each
top mount.
Each of the first 5 cowlings was installed on each plane using a trial and error
method like that in the installation instructions. a lot of work.
It was at this point that I started asking for feedback regarding the number of
shims on Tigers. I also asked for the distance between the firewall and the back
of the aft spinner bulkhead. The answers I got were varied and inconsistent.
Ned wanted his cowling pre-fitted so he didn't have to wait very long. At that
time, I had a wingless Tiger, N29348, in a neighboring hangar. To save time, I
installed the cowling from N28747 onto 348. N28348 required 2 thick shims on
the left and one thick plus one thin shim on the right in order for the cowling
from N28747 to fit properly. After the new Jaguar cowling was completely fitted
to N28348, I fit the lower cowling of the new Jaguar cowling to N28747 just
to check. It fit fine. That cowling was installed on Ned's plane. Ned didn't
like the fact that his engine needed shims to fit the cowling since he thought
his original AG5B cowling was perfect and it fit well.
Fast forward.
I built a mockup for the Jaguar cowling using an AA1B, Cheetah engine mount, and
the same mockup engine used in the original Jaguar cowling fabrication. I fit
my cowling to the AA1B mockup and it required one thin shim on the upper right.
I measured the thrust angle at .3 degrees down on the left side (no shim side)
and .5 down on the right side.
I then took the cowling from N28747 and installed it on N28697. It required 2 thick
shims on the right and 2 thick plus one thin shim on the left. When done,
the engine was .6 degrees down on the left and .4 degrees down on the right.
The question that has been posed is: How well did the original cowling fit on N28697?
697 came to me with one shim on each mount. The engine was 1 degree up WRT the
fuselage waterline. (thrust angle was not the same for each side.). The cowling
fit OK. The engine looked like it was up just a bit, but not bad. Most people,
let's just say 'no one' except me, would ever notice.
So, why all the fuss? If the original cowling fit with the engine as is, what's
the big deal with where the engine is?
When I look at a plane, I see all sorts of poor fitting parts. Most, if not all,
of the cowlings don't fit worth a damn. With 3/4 inches (or more) between the
spinner bulkhead and the cowling, it can be off a lot and still look acceptable.
Most people don't care. I'm an obsessive compulsive so it does matter to
me.
The space between the rear spinner bulkhead and Jaguar cowling is just 3/16 inches.
The side-to-side location is less than 1/16 inches. The gap around the openings
and cowling halves is less than .065 inches.
Since my installation requirements are likely more stringent than most, I'm not
selling anymore cowlings that aren't pre-fitted to a known installation. It'll
cost more, but it will save the installer a lot of headaches.
Gary
Sent from my iPad
On Mar 30, 2013, at 12:18 AM, Bob Steward <n76lima@mindspring.com> wrote:
> What I am asking is: Did the engine line up with HIS cowling? Or was your reference
to "right place", saying that it did not match his cowl, and that once
you re-aligned the engine, your cowl also lined up with it?
> If you mean that the engine needs to be aligned differently for your cowl, how
can those of us that do not have your plane handy to test fit a completed cowl,
figure out the "right place", before starting to test fit an untrimmed cowl?
> I can measure the thrust angle of 1/2 degree down with my digital level. Not
sure about the offset to the (right) side. Could probably measure from firewall
to some points on the engine, if I knew what those measurements were.
>
> Given only the information in your instructions and your "right place" comments,
it seems that lacking your plane's cowl to prepare the engine position, I
should set the engine at 1/2 degree down, and then figure some way to align the
cowling to the spinner with 3/16" clearance all around, by shimming the engine
until the cowling lays on the fuselage smoothly?
> --Bob Steward
>
> Gary L Vogt <teamgrumman@yahoo.com> wrote:
>
>> I could rehash this again for the umpteenth time . . . . but,
>>
>> suffice it to say, all engines are not aligned the same. When you have 3/4
inches clearance at the prop, it's not such a big deal. When you have 3/16 inches
clearance, it makes a difference.
>>
>> When aligned to the cowling, the engine is down about .5 degrees wrt the canopy
rails.
>>
>>
>> ________________________________
>> From: "n76lima@mindspring.com" <n76lima@mindspring.com>
>> To: teamgrumman@yahoo.com
>> Sent: Friday, March 29, 2013 1:09 PM
>> Subject: Re: N28697: Jaguar cowling
>>
>>
>> Are you saying it was in the "wrong" place before, or did it match his cowling
location, but not yours?
>> --Bob Steward
>>
>> With the engine in the right place, fitting the cowling is pretty easy.
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