Citabria 180 hp STC's thread drift new thread

Old Blue

Old Blue

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Feb 13, 2020
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Location
Peterborough, NH
I may have posted this on the wrong thread, sorry 'bout that.

Hi all
If you're interested in 180 hp, there have been two STCs out there for twenty plus years. One is for the 7KCAB, but when I tried to track it down, I could get copies of the paperwork but could not track down the STC holder. As I recall he may have passed away and no one knew where the original was located. Dead end.
I then found Ron Emond (3 Elm Street, Tyngsboro, MA 01879, his business is located in Nashua, NH on Boire Field, 125 Perimeter road 4E)
STC# SA 00096BO. It is for the 7GCBC, issued in 1999. Basically making the 7GCBC a Scout from the firewall forward with an O-360 C2E, Scout motor mount, Sensich 76EM8S9-0-56, cowling, air box, etc.
I converted my 7GCBC back in 2002 and couldn't be happier
 
Thanks for the info Old Blue .
A few questions if I may …..
did Mr Emond do the conversion work for you and if so , is he still around and doing that type of work ?
 
I wonder if there is any potential for a wood spar Decathlon STC that addresses the current AD issues at a lower cost than the metal wing upgrade?
 
We did the STC conversion as part of a total rebuild/recover, including Milman spars in Keene, NH in 2001. I can't remember if Ron Emond would have done the work in Nashua. His business is Air Direct Airways • 83 Perimeter Rd. • Nashua, NH 03063 • (603) 882-5606
 
The AD is painful, especially if one has to pay shop rates. It alone is a grand a year if done according to the instructions, and yet it really cannot be done the way the AD specifies without uncovering, or at least installing Rainbow Ron's window in each bay.

The Decathlon really ought to be excluded - as far as I know there have been no Decathlon spar failures. Part of that may be due to most of us not trying to play bush pilot with our birds, but it is a more robust spar. Barring that, a Milman-type STC for the Decathlon would be optimum. Factory metal spar wings are now over $40K, which is almost a half-century of AD spar inspections.
 
Big Ed said:
I wonder if there is any potential for a wood spar Decathlon STC that addresses the current AD issues at a lower cost than the metal wing upgrade?
Click to expand...
I suppose if you could do a detailed analysis of a solution like Rainbow's improved/extended plywood doublers that shows they're less prone to cracking in some measurable way you might be able to negotiate an exemption from the AD with the FAA. Or come up with another solution that prevents compression cracks at the top of the spar where the doublers end and which could be added to an already assembled wing.
 
The problem is the FAA wants every square inch of all four sides of each spar inspected with a Bend A Lite and mirror. There is no "emphasis" on the critcal area in the sense that you do not have to inspect the rest of it quite as carefully.

So nothing you would do in the critical area, including Ron's window, makes the AD easier.

There were comments trying to make the AD reasonable (doable?) during the runup, but the FAA had made up its mind.

I do my own, and back it up with these incredibly good Chinese TV snakes. I am tempted to watch, when a truly good mechanic gets in there with Bend A Light and mirror, especially around the fuel tank area.

I am afraid the cure is metal spar. I am not delighted with the factory design, but I can tell you that the aircraft I am aware of with 1998 metal spar wings and 150 C/S, while ugly, handles so well and is so agile and light it makes my 180 wood spar feel like a truck. If you go metal spar, beware of corrosion. They must have used a different alloy.
 
Hi all

In order to keep the STC's sub forums posts on topic I've pared off a few posts that drifted off topic and they've been dropped here into a new thread. No big deal, carry on.

@Bob Turner after seeing the state of affairs in my 7ECA wood wings when they were disassembled for the Milman conversion, I fee a lot of the difference comes from fittings and such being loose in wood spar wings that haven't been disassembled since their original manufacture date. There were a lot of loose fittings in my old Citabria wings and it was obvious from the metal surfaces that had been rubbed shiny by the wood after so many years. It's hard for any wing to be spry and responsive if stuff isn't tight inside.

Regarding the wood spar AD, the problem is exacerbated by higher HP engines (Champs, with their lower hp engines and wood spars aren't affected by the AD) so a 180 hp STC might also demand a pretty good assessment of what's going on under the wing fabric before pulling the trigger on the project, IMHO.
 
I thought the problem was impact with the ground or a fence post. The current fad of attempting landings in questionable areas (bush pilot syndrome) would seem to lead to such impacts. Decathlons don't generally get subjected to such things.
After a compression fracture, I suppose a higher horsepower engine might make separation more likely.

It is my impression that this is peculiarly a Scout or 7GCBC problem, but was extended to all the Champs above 90 hp?
 
bob,
watch Rainbow Ron's video of his spar test cell experiments, very eye opening.

i don't know the answer but to remove the AD you will probably need a very big pile of paper/data.
 
Can you give the results out in a sentence or two? Does he crack Decathlon spars? He told me the Decathlon spars were way better than the Scout. I hate videos.
 
Ron demonstrates that the spars fail where everybody already knows they fail, in compression at the upper/outboard corner of the plywood doubler plates where the lift struts attach. He also demonstrates his spars with the improved and expanded doubler plates. They withstand more stress and appear to fail in shear along the neutral axis of the spar.
 
Thanks. That is why the AD is so silly - it is like incredibly long checklists - make them long enough, and folks just read and respond.

The feds need to go back and tell us to look at that particular area with a magnifying glass. A Bend A Light just doesn't cut it. And they probably never fail inboard of the strut fitting, so why not just make it part of an annual, and leave the AD to the important places.
 
I haven't read the AD in a long time so I'm not up on the specifics but, as I recall, the ribs are also subject to inspection as they have been shown to come loose and rub depressions into the spars. After watching the video I'd bet an engineer could make a case for removing the AD from wings that have been assembled using Ron's spars and rib-attach-screws STC's but the cost would be huge and who would want to take that project on? Ron also wasn't in the room when the original AD was being designed so it's an uphill fight without anyone to lead. Then there's the question of how to monitor/assess damage and abuse to wood spars in an aerobatic airplane over the course of time, do you just keep flying them or is there an inspection regiment that is imposed? That isn't an issue I'd want to debate!
 
I think that was a different AD - a one-time inspection. I shall check in a bit.

You were correct - here it is for group 2 aircraft - AD 2000-25-02R2, higher horsepower ACA:

(1) Inspection Requirements: Inspect (detailed visual) the entire length of the front and rear wood wing spars for cracks, compression cracks, longitudinal cracks through the boltholes or nail holes, or loose or missing rib nails. We will refer to these conditions as damage throughout the rest of this section.

Note that it does not single out the critical areas. Service letter 406 does, and it is incorporated by reference.

Inspection: The only area where it is possible to positively identify a compression crack is on (Bottom/Top) the top and bottom surfaces of the spar. Both front and rear spars need to be inspected. The key areas to be concerned with are shown in figure 1. Additional inspection holes may be necessary to do a thorough inspection. Service Letter 417, Revision C, may be used as a guide for installing additional inspection holes. Warning: Compression failures are often difficult to detect with the unaided eye. Do not expect an open crack or gap. Compression failures start as barely visible, minute, jagged series of lines running cross grain on the top or bottom of the spar.

Of some interest to mechanics - The Bend-A-Light is required, and a high powered flashlight is expressly excluded. I own a Bend-A-Light, and do not have a dog in this fight except to say that a high power flashlight would probably be better, and a TV scope would be best. I have a difficult time believing the Government is allowed to demand a sole source piece of test equipment - but have not researched that, since I just do as they say once a year. With a new battery, and once in a while a new bulb.
 
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Actually, the easiest way to detect a crack in sealed wood is to swab the area in question with a penetrant. I prefer using mineral spirits. Just like doing a dye penetrant inspection on metal surfaces, the spirits will wick into any crack and make it stand out and be quite visible. That, along with several rubber door stops (the wedge type) make the inspection of the top surface of both front and rear spars with an articulating borescope about a two hour project for a Citabra or Decathlon...
BTW; if wood spars are kept varnished/sealed and are not subjected to a really hard, sharp blows they're service life can be indefinite. Wood is much more tolerant of vibration, load cycles and spot deformation than aluminum or steel. It's not as strong as well engineered composite structures in the same purpose but wood is, when properly cared for, a better material for light aircraft spars. The ride is better too!
The reason for SL 406 and that asinine AD was simple. Because most A&P/IA's experience with wood airplane structures is limited or non existent companies that have such aircraft have to try to expiain the hows and whys of something that USED to be simple common knowledge...
Same thing as trying to find a car mechanic to rebuild a Quadrajet carb today...used to be a two hour job at any corner gas station. Not today...☹️
I take care of a 1939 65C pre war Chief. It's wood wing spars and the wood ribs are from 1939. Still pretty, probably with more coats of varnish than it needs but still solid as a rock. It flys about 80-90 hours a year with maybe a dozen or so different pilots. Wood lasts a long time if taken care of...
Yes you have to check/replace a nail or two every year. Not a big deal. The old Areoncas had itty bitty nails that can be replaced by 14 gauge ringed nails available at Univar or Aircraft Spruce.
I suspect the Service Letters from ACA (and maybe the AD itself) had more to do with wanting to get rid of the wood spar liability than it did with airplanes falling out of the sky with broken wings.

JMPO
Chris
 
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