Harer STC Questions

[flyguy]

Re: Harer STC Questions

I have the STC, as said before, never used it (keeping for rainy day.) Turns out my 337 is legal per the FAA guy I talked to--anyway my comment is:

The story I heard was the plate was to prevent the strut fittings from being twisted by the strut. Supposedly twisting wrecks the through holes in the spar, or something like that.

I guess I can picture the outboard section of the wing doing some torsional movement under load, which would be resisted by the strut end, causing the strut-attached ends of the fittings to flex one up, one down. Perhaps someone found that type of crush pattern in the fitting-attach holes in a spar.

Couldn't agree more on all the weird venting methods, including the caps.

Darryl

[VictorBravo]

Re: Harer STC Questions

As Jimmy Durante famously said... "AND Furthermore..."

A real live engineer I know (big resume') looked at the little square plates welded across the fittings and said that he could not for the life of him figure out what Jack Gilberti was trying to accomplish by doing that. It certainly does not add tenslie or compressive strength to the system, and does not appear to stabilize anything that needs stabilizing. But it looks like it does something, and the FAA likes it. I wish Gilberti were available to discuss all this in detail.

Hank from the POV of watching out for your friend's safety, IMHO the "first-line" stuff to be concerned with is the thickness of the bolt lugs at the root attach fitting and the condition of the wood spar/doubler ass'y at the root end and the strut attach. I am assuming that the existing metal fittings are far overbuilt for even 1500 pounds GW at 6G, and the most common failure would be deterioration of the wood structure and/or corrosion someplace that degrades the structure below the original design.

After that, the -6 fuel line is easy enough to do although I have it on some authority that the 85HP engine will still be fed properly by the original size line.

The fuel venting monstrosity will not hurt anything, however I doubt that it is truly necessary. There should be a Cessna-style vent line that has nothing to do with the fuel caps, and be done with it. I'd like to know who authorized the fuel tank vent placed in the lowest pressure area on the whole airplane, above the leading edge of the wing!

The cross-vent lines, hot soldering irons near a fuel tank filled with vapor, poking holes in 60 year old tanks, running more fuel-related lines through the airplane... all that seems too much effort for not enough benefit IMHO. I "abbreviated" the process when doing my conversion.

Your buddy doing the upgrade should be 3X more concerned with the condition of his lower fuselage strut attach fittings and longerons, any looseness in the wing root attach bolts, the condition of the wood spars, etc.

Book 'em, Dan-o... Operating a calculator without a degree!

[Hank Jarrett]

Re: Harer STC Questions

Bill, you actually usually do a pretty good job impersonating an engineer. I know very little about the STC and am pretty excited that a fellow at the airport I use is rebuilding a Taylorcraft that is supposed to have the Harer STC already on it. The new owner is planning to go through the whole airframe as he rebuilds it and I just convinced him to join the Foundation. The STC is in the logs but he has no technical info on what it should look like. I am hoping to get very familiar with the Harer mods in the near future. Until then I really can't comment, but am looking forward to learning all about it. He is looking for a copy of the STC to use for information while he checks the implementation.
Hank

[VictorBravo]

Re: Harer STC Questions

STC areas of concern:
1. Engine mount- ---I know there are several mounts.
2. Engine baffles --- Does the STC have you use same baffles as the A-65 in a BC-12D? Or ?
3. Fuel lines -- LARGER fuel lines from Aux to Main? What size ?
4. Fuel line to carb. -- What size?
5. Brakes -- I believe the Model 19 must use Cleveland brakes. Does the STC require this as well.
6. Electrical System- -
7. Tires- Not part of STC ?

If the engine mount actually fits the engine, and allows room for the starter and generator, then you are on reasonably solid ground "assuming" it is correct for now.

Yes, you use the same baffles, they may have to be adjusted slightly, tapped, pounded, filed, etc. to fit the other cylinders which have more fins. That is normal and simply not addressed by the STC, which means whatever you do to get them to fit is OK.

There is no requirement for larger fuel lines from the wing tanks to the main tank... if you have both wing tanks and they adequately refill the main tank you are OK. The engine does not ever run directly off the wing tanks, all they do is refill the main tank.

If you have the fuel shutoff valves mounted at the tank outlet in the wing root, LEAVE them there and do NOT move them down under the instrument panel as shown by the STC. Refer the FAA, your IA, and anyone else who argues for the location shown on the STC drawing... directly to me and tell them to bring boxing gloves.

You DO need the -6 larger fuel line from the gascolator to the carburetor, and (on behalf of the group) we strongly recommend a "lifetime" teflon/steel braid hose with Firesleeve for safety. Make SURE the hose has room to allow the engine movement on the mounts!

The STC does not address brakes at all, nor could it. There is unfortunately not a Cleveland brake setup that easily adapts to the Taylorcraft landing gear without a lot of surgery. Your Shinn brakes will work perfectly well if you follow the care and feeding instructions kindly provided by Rob Lees here: http://taylorcraft.org.uk/Brake-issues.pdf

The electrical system that comes with the C-90 is acceptable, although there are now much lighter and better starter and alternator units that are approved for that engine.

The tires are really no problem. There are hundreds of T-crafts flying with 8.50 x 6 tires. I believe the original certification basis, CAR-3, states that you are able to use any tire that is approved for the speed and weight of the aircraft. The FAA folks and "by the book" IA types can argue it all day long, and will. But because you can change the tires back rather easily, fly with the 8.50's for now and worry about everything else.

There are a couple of other things you need to be aware of...

The Harer STC shows re-built wing ROOT fittings as well as the square plates welded to the outer fittings. To follow the STC to the letter, you have to replace the long straps of the fittings (essentially making new ones using the same small U-shaped bracket). You are removing the .065" steel straps and replacing them with .095" steel straps.

IMHO You could also add .030" steel doublers and achieve the same overall metal thickness, without cutting apart the fitting and making a mess. This also gives you a separate load path, so that in case the .065" strap cracks the crack will not travel across the .030" strap. The engineer types call this a redundant or secondary load path I think (sorry Hank, please don't have me arrested for impersonating an engineer ).

Now here's what they DON'T tell you...

If you put thicker straps on the fitting by EITHER of the above methods, your wing root fittings are now by definition .060" wider. But the gap between mating fittings on the fuselage has not been changed. Now your wings may not fit onto the fuselage, or will be very tight and possibly have to bend or deform to fit. Not good.

Miscellaneous fact #486 : The reason IMHO that original engineer Jack Gilberti wanted to increase the thickness of the metal at that fitting is to prevent the wing mounting bolt from "tearing out" of the fitting lugs at the attach point.

Miscellaneous fact #663 : The soft Spruce and plywood in the spar root would fail LONG before the original .065" thick steel straps would break. So adding more thickness to the straps where they bolt into the wood does not do anything useful.

Miscellaneous fact #155 : Gilberti designed the BC-12D-85 upgrade to the BC-12D at the Taylorcraft Factory, for the building of new airplanes. It was a LOT easier and cheaper for Jack to get his "tear-out" strength" by having them make the fittings out of thicker materials from the start, instead of only adding extra material at the bolt location only where it was needed.

Miscellaneous fact #2387 : During the building of these new BC-12D-85 airplanes, the factory welders could easily just move the fuselage attach fittings .060" further apart to accommodate the extra width of the wing fitting, due to the thicker metal. We can't do that easily at all!

Miscellaneous fact # 2140 : As an afterthought and a side project after the BC-12D-85 was designed, Jack Gilberti was allowed to use the data and engineering he did for the factory to become the basis of a modification for existing older Taylorcrafts. My guess is that Jack took the same drawings he did for a new factory-built airplane, showed them to the CAA, and they approved it for a field modification/STC without a second thought. I am guessing that Jack forgot (or simply turned the other cheek) about the many small discrepancies between BC-65 airplanes, BC-12D airplanes, and the BC-12D-85 / Model 19 airplane , figuring that the field modifiers would just figure out the details and make everything work using the common sense and skills of the day. Those skills are now frowned upon by far too many mechanics and FAA inspectors because of our "new" outlook on liability.

In my opinion, THAT is why we have several nagging inconsistencies, mysteries, and conflicts (in the spar thicknesses, in the fuel system venting, in the root fittings, etc.) when we upgrade an older Taylorcraft to the 85 horse engine upgrade. There have been many blazing gun battles in this forum that arose out of these discrepancies, with some feelings having been hurt (sorry Don) in the process.

And SO... this brings us back to WHY I mentioned all the miscellaneous facts above and have filibustered on this Forum yet again...

Although NOT in strict compliance with the STC itself, where it comes to the STC's discrepancies and the intent of the modifications, I personally recommend and take full responsibility for the following recommendation:

When you weld the square plates onto the strut fitting out on the wings, joining them into one fitting, weld them together at WHATEVER distance perfectly fits the actual thickness of your spruce spar/plywood doubler at that location. The STC drawings give a specific dimension, which must be ignored. Due to variations in the thickness of some spars over the years, and the SOMETIMES inclusion of paper-thin plywood shims to make up this difference, following the STC to the letter could result in the fittings being up to 1/16" loose on the spar, which is obviously wrong. Your fittings when welded together should have a gap of anywhere between ONE inch and ONE and One-SIXTEENTH inches, and should fit snugly over the wing spar and plywood doublers at that location.

When modifying the root fittings, measure the distance between the fuselage fittings to determine whether there is room for the increased thickness of the modified spar root fitting. If there is, then add the .030" strap doublers to the existing .065" fittings to achieve the STC's .095" metal thickness. If there is not enough clearance, then do one of two things: 1) Make up a new U-shaped bracket out of thicker 4130 steel and replace the U-bracket instead of the straps to achieve the same extra thickness at the attach bolt location where it is actually needed, or 2) weld 4130 washers to the inside of the un-modified fitting to achieve the required extra thickness at the bolt lug location.

Any qualified engineers who care to look at this and confirm or deny the validity of what I write above are free to do so, ASKED and WELCOMED to do so, for the benefit of the Taylorcraft community.

[Forrest Barber]

Re: Harer STC Questions

e-mail this to me direct and wait about a week..... I can answer most of the questions. I have four requests for clarification on the Harer STC. Bob Harer recently passed away and your Taylorcraft Regional Reps ahve drafted a request to the family once again to acquire the STC. WE of course ahve a pristine copy hee; remeber they should be issued by ser# for the aircraft they are going to be used upon. MANY times they were copied and used improperly. Just another thing we need to do here in Alliance.

[GallagerG]

Hello Fellow T-Craft Owners,
I have a bit of a problem and I would really appreciate your expertise in this field. I have a 46 BC-12-D that was upgraded with the Harer STC in 1973. The aircraft was wrecked since then. All I have for paperwork is the 337. I’m looking for the drawings, or a complete list of what is supposed to be done with this STC.
I got the engine, a C-90-12F, rebuilt and I’m ready to put things back together, but, my mechanic and I are not convinced the STC was appropriately complied with,,, from the legal standpoint. IE: The fuel vent system. I have short vent lines from all three tanks, but none of them are hooked up according to a drawing I was able to find for the STC. I’m convinced the 12” engine mount is what the drawings called for, but I don’t know that for sure either.
Also the engine, according to the 337, was adjusted and rigged to be equivalent to the C-85. What did they do? I’m pretty sure I understand the reinforcements to the wings where the lift struts attach: Larger bushings attaching to the spars, and a plate welding them together. Maybe?
I fear when it was damaged things were not repaired properly and or things left off or out… ? Partly due to the poor work preformed.
It also came with 6X850 tires with no paperwork… does anyone have a 337 so I could get mine approved?
Thanks so much,
Gallager B
STC areas of concern:
1. Engine mount- ---I know there are several mounts.
2. Engine baffles --- Does the STC have you use same baffles as the A-65 in a BC-12D? Or ?
3. Fuel lines -- LARGER fuel lines from Aux to Main? What size ?
4. Fuel line to carb. -- What size?
5. Brakes -- I believe the Model 19 must use Cleveland brakes. Does the STC require this as well.
6. Electrical System- -
7. Tires- Not part of STC ?