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Folks, there is a mystery here to be solved. I finally got my Harer STC paperwork today, and I would like to hear from EVERYONE who has done this upgrade to solve the big mystery. I make no apologies for the long length of this post, since it is a very specific problem and it would be too easy to misunderstand the details.
PART of the Harer spar drawing (G-108) says that there are _no changes_ to the forward spars at the mid-span strut attach point. Period. There are no additional parts, plywood doublers, etc. mentioned on this drawing, the parts list, etc. ANOTHER drawing (G-110) says that the distance between the front strut fittings (when bolted to the spar and after welding) is 1 and 1/16 inches. This is NOT how far apart the fittings are now on my supposedly stock airplane.
Don e-mailed me with his understanding to clarify and help me out (thanks Don). Don thinks that the extra 1/16" of thickness difference (between the 1" width of the existing spar/doublers and the 1 and 1/16" of the modified strut fitting) means that you are supposed to put 1/32" plywood doublers on each side of the existing spar/doubler lamination to take up the space.
In my humble opinion, this would mean that you'd have to shorten the compression strut at that location by 1/32", or have it not fit properly. None of this is mentioned in the STC either.
I just made an hour round trip to the hangar to measure what I have. My airplane has a 3/4" spruce spar, with 1/8" plywood doublers on each side of it at the strut attach point. By contrast, the plywood doublers at the root (butt) end are only 1/16". So my finished spar is one inch thick at that location, and the strut fittings are indeed one inch apart exactly. Since my spars are relatively new (damage 1995), whoever built these replacement spars MAY have put in thicker doublers than what were there before.
I am now faced with figuring out whether the Gilberti STC drawings from Harer are missing parts and missing instructions, or whether they made an unintentional error suggesting that the space between the fittings is 1/16" MORE than the actual width of the spar (with existing doublers).
Here is the e-mail that I sent to Don, Forrest, and Rob Lees this evening. I can't believe this is the first time this question has cropped up, but if there is an error on the drawings then it has not been corrected. Others will have to grapple with the same awful quandry...
I'd like to know the opinion and experience of ANYONE and EVERYONE who had done the Gilberti / Harer STC. (I spoke to Mr. Harer once to ask about another tech question, and got information that conflicted with what is shown on the drawings. He sounds like he's getting up in years. So I'd rather hear the opinions of actual field users and any engineering geniuses lurking in these waters)
(note to Don, I corrected my fractional math since the orig. e-mail)
---------------
Don, I think you might be mistaken about this. I got my STC today, and I
looked at the drawing closely. There is no 1/32" doubler (at the mid-span
strut fitting) noted anywhere on the drawing. There is no notation on the
drawing that says anything about adding another plywood doubler anywhere on any spar for that matter.
I am looking at drawing G-108 which I just got today.
If you put in another doubler on the back of the existing strut attach
fitting doubler, then your compression struts will not fit properly anymore.
The whole wing would have to be tweaked a little, and nothing would fit
right. OR, you'd have to shorten that one compression strut by 1/32".
The ONLY mention of anything with a 1/32" dimension that I saw, was the
mention of a + 1/32 and -0 tolerance at the top of the spar butt end view
drawing, right next to the 3/4" total width dimension. This has nothing to
do with adding a doubler, it is simply the tolerance for the spar thickness.
My understanding is that this Gilberti - Harer conversion IS INDEED the
original factory 85HP conversion. So that whatever extra parts, doublers,
bushings, etc that the factory did on THEIR original 85HP airplanes, is on
these drawings. Gilberti was the Taylorcraft factory engineer who designed
the 85HP upgrade for the factory, I understand. The STC also says that this
is a conversion to another model, which also indicates that this should be
the original factory upgrade.
I do indeed see the lines on the drawing that show something on the outside
of the spar out at the strut attach area. There are no call-outs and no
nomenclature associated with these lines at all. I can therefore only
believe these are the normal 65HP stock airplane doublers.
These lines on the drawing cause some other questions. If you add 1/16 to
both sides of a 3/4" spar (for the normal plywood doubler), you get a total
width of 7/8". If you add 3/32" worth of plywood (factory 1/16 plus another
1/32) to both sides of a 3/4 spar, you still only get 15/16" total, not one and
one sixteenth.
In order to go from 3/4 spruce to 1 and 1/16", you'd need to add 5/32"
doublers on both sides of the spruce, OR you would need to add a pair of
3/32" doublers ON TOP of the existing pair of 1/16" doublers.
As such, there is no way that a 1 and 1/16" gap between the strut fittings
would fit the existing 3/4 spar, plus 1/16" regular doublers, plus another
pair of these mystery 1/32" doublers. That still adds up to only 15/16",
which is still one-eighth of an inch shy of 1 and 1/16.
I briefly thought that perhaps my pre-war spars were not as thick, but the
Gilberti drawings clearly show that the spar is 3/4 thick (the width of the
little C shaped "clevis" welded to the butt fitting straps).
If there is SUPPOSED to be another 1/32" doubler on either side of the
existing doublers, then Gilberti and Harer have provided drawings that do
not describe all of the needed parts. They would have had to forget the
call-out, forget actually pointing to another doubler on the drawing, forget
putting it into the parts list, and then they would have had to purposely
write "no changes" instead of "add doubler". After looking at the other
drawings, it appears they they were pretty thorough, and a big structural
mistake like this is not likely.
That being said, I have no idea what is supposed to take up that extra 1/8"
between the strut fitting plates. I'm going out to the hangar tonight just
to re-measure all this again.
Forrest and Rob, do either of you know what the answers to this mystery? I
am doing the upgrade, and just got my papers. If there is supposed to be
another pair of doublers in there, I'd sure as hell want to know about it
now. If there is not supposed to be more doublers in there, then Don might
want to peel his off before he tries to install the compression struts and
trammel up the wing.
I think this is an issue that should be posted on the forum as well, and I
will do this tonight after one more measurement.
Bill Berle
----- Original Message -----
From:
To:
Sent: Tuesday, July 12, 2005 4:55 AM
Subject: Re: Spars
> Bill,
>
> I may have confused you again but I hope not.
> Take a look at your Front Spar at the strut attach point again.
> The Factory installed a 1/16" doubler that is full width (5 11/16) by
about
> 20" long.
> The doubler I'm talking about is on top of the 1/16" doubler and is 1/32
> thick and only 3" wide right under the Strut Fitting Strap. I assume its
> T-Crafts 85hp spar reinforcement and thats why my T-Craft didn't have it.
> The total width of the spar at that point is 1 1/16.
> Let me know if you have the 1/32" doubler.
>
> Don
PART of the Harer spar drawing (G-108) says that there are _no changes_ to the forward spars at the mid-span strut attach point. Period. There are no additional parts, plywood doublers, etc. mentioned on this drawing, the parts list, etc. ANOTHER drawing (G-110) says that the distance between the front strut fittings (when bolted to the spar and after welding) is 1 and 1/16 inches. This is NOT how far apart the fittings are now on my supposedly stock airplane.
Don e-mailed me with his understanding to clarify and help me out (thanks Don). Don thinks that the extra 1/16" of thickness difference (between the 1" width of the existing spar/doublers and the 1 and 1/16" of the modified strut fitting) means that you are supposed to put 1/32" plywood doublers on each side of the existing spar/doubler lamination to take up the space.
In my humble opinion, this would mean that you'd have to shorten the compression strut at that location by 1/32", or have it not fit properly. None of this is mentioned in the STC either.
I just made an hour round trip to the hangar to measure what I have. My airplane has a 3/4" spruce spar, with 1/8" plywood doublers on each side of it at the strut attach point. By contrast, the plywood doublers at the root (butt) end are only 1/16". So my finished spar is one inch thick at that location, and the strut fittings are indeed one inch apart exactly. Since my spars are relatively new (damage 1995), whoever built these replacement spars MAY have put in thicker doublers than what were there before.
I am now faced with figuring out whether the Gilberti STC drawings from Harer are missing parts and missing instructions, or whether they made an unintentional error suggesting that the space between the fittings is 1/16" MORE than the actual width of the spar (with existing doublers).
Here is the e-mail that I sent to Don, Forrest, and Rob Lees this evening. I can't believe this is the first time this question has cropped up, but if there is an error on the drawings then it has not been corrected. Others will have to grapple with the same awful quandry...
I'd like to know the opinion and experience of ANYONE and EVERYONE who had done the Gilberti / Harer STC. (I spoke to Mr. Harer once to ask about another tech question, and got information that conflicted with what is shown on the drawings. He sounds like he's getting up in years. So I'd rather hear the opinions of actual field users and any engineering geniuses lurking in these waters)
(note to Don, I corrected my fractional math since the orig. e-mail)
---------------
Don, I think you might be mistaken about this. I got my STC today, and I
looked at the drawing closely. There is no 1/32" doubler (at the mid-span
strut fitting) noted anywhere on the drawing. There is no notation on the
drawing that says anything about adding another plywood doubler anywhere on any spar for that matter.
I am looking at drawing G-108 which I just got today.
If you put in another doubler on the back of the existing strut attach
fitting doubler, then your compression struts will not fit properly anymore.
The whole wing would have to be tweaked a little, and nothing would fit
right. OR, you'd have to shorten that one compression strut by 1/32".
The ONLY mention of anything with a 1/32" dimension that I saw, was the
mention of a + 1/32 and -0 tolerance at the top of the spar butt end view
drawing, right next to the 3/4" total width dimension. This has nothing to
do with adding a doubler, it is simply the tolerance for the spar thickness.
My understanding is that this Gilberti - Harer conversion IS INDEED the
original factory 85HP conversion. So that whatever extra parts, doublers,
bushings, etc that the factory did on THEIR original 85HP airplanes, is on
these drawings. Gilberti was the Taylorcraft factory engineer who designed
the 85HP upgrade for the factory, I understand. The STC also says that this
is a conversion to another model, which also indicates that this should be
the original factory upgrade.
I do indeed see the lines on the drawing that show something on the outside
of the spar out at the strut attach area. There are no call-outs and no
nomenclature associated with these lines at all. I can therefore only
believe these are the normal 65HP stock airplane doublers.
These lines on the drawing cause some other questions. If you add 1/16 to
both sides of a 3/4" spar (for the normal plywood doubler), you get a total
width of 7/8". If you add 3/32" worth of plywood (factory 1/16 plus another
1/32) to both sides of a 3/4 spar, you still only get 15/16" total, not one and
one sixteenth.
In order to go from 3/4 spruce to 1 and 1/16", you'd need to add 5/32"
doublers on both sides of the spruce, OR you would need to add a pair of
3/32" doublers ON TOP of the existing pair of 1/16" doublers.
As such, there is no way that a 1 and 1/16" gap between the strut fittings
would fit the existing 3/4 spar, plus 1/16" regular doublers, plus another
pair of these mystery 1/32" doublers. That still adds up to only 15/16",
which is still one-eighth of an inch shy of 1 and 1/16.
I briefly thought that perhaps my pre-war spars were not as thick, but the
Gilberti drawings clearly show that the spar is 3/4 thick (the width of the
little C shaped "clevis" welded to the butt fitting straps).
If there is SUPPOSED to be another 1/32" doubler on either side of the
existing doublers, then Gilberti and Harer have provided drawings that do
not describe all of the needed parts. They would have had to forget the
call-out, forget actually pointing to another doubler on the drawing, forget
putting it into the parts list, and then they would have had to purposely
write "no changes" instead of "add doubler". After looking at the other
drawings, it appears they they were pretty thorough, and a big structural
mistake like this is not likely.
That being said, I have no idea what is supposed to take up that extra 1/8"
between the strut fitting plates. I'm going out to the hangar tonight just
to re-measure all this again.
Forrest and Rob, do either of you know what the answers to this mystery? I
am doing the upgrade, and just got my papers. If there is supposed to be
another pair of doublers in there, I'd sure as hell want to know about it
now. If there is not supposed to be more doublers in there, then Don might
want to peel his off before he tries to install the compression struts and
trammel up the wing.
I think this is an issue that should be posted on the forum as well, and I
will do this tonight after one more measurement.
Bill Berle
----- Original Message -----
From:
To:
Sent: Tuesday, July 12, 2005 4:55 AM
Subject: Re: Spars
> Bill,
>
> I may have confused you again but I hope not.
> Take a look at your Front Spar at the strut attach point again.
> The Factory installed a 1/16" doubler that is full width (5 11/16) by
about
> 20" long.
> The doubler I'm talking about is on top of the 1/16" doubler and is 1/32
> thick and only 3" wide right under the Strut Fitting Strap. I assume its
> T-Crafts 85hp spar reinforcement and thats why my T-Craft didn't have it.
> The total width of the spar at that point is 1 1/16.
> Let me know if you have the 1/32" doubler.
>
> Don
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