Aileron attach screws

N170BP · Post by **N170BP** » Mon Sep 29, 2003 5:06 am

Folks,

I want to install the correct aileron attach hardware on
my '54 B model. The IP book says to use NAS229-8 structural
machine screws. None of the local aviation hardware suppliers
have those.... (niether do Aircraft Spruce or Wicks).

I have a Spencer's hardware catalog that says the MS27039 series
structural pan head phillips drive screw supercedes the NAS220-
NAS222 series screws (no mention of NAS 229 screws).

Is it OK to use MS27039 (or MS27039C / stainless) screws for
this application? For what it's worth, the MS27039 screws have
a tensile strength of 125K psi (the MS27039C / stainless has no tensile
strength value listed, but it says the material is "A286" corrosion
resistant steel).

Bela P. Havasreti
'54 C-170B N170BP

spiro · Post by **spiro** » Mon Sep 29, 2003 10:29 am

AN525 structural washer head screws is what I've always seen used.

Post by **GAHorn** » Mon Sep 29, 2003 9:00 pm

Mark your Parts Catalogs, the NAS229-8 screw has been superceded by the MS27039-1-08 priced at 20-cents each from Cessna distributors. Hill Aircraft 1-800-998-7832 is a good supplier as is Yingling 800-854-2647.
These are pan-head screws, not washer head, so the AN525 series is not correct.

spiro · Post by **spiro** » Tue Sep 30, 2003 1:42 am

>> These are pan-head screws, not washer head, so the AN525 series is not correct. <<

AC 43.13-1A has this to say:

"...several types of structural screws are available that differ from the standard structural bolts only in the type of head.
The material is equivalent and a definite grip is provided. The AN-525 washerhead screws ... and the NAS-204 through NAS-235 are such parts. ...

a. Structural Screws (NAS-204 through NAS-235, AN-509, and AN-525). This type of screw, when made of alloy steel such as SAE-4130, NE-8630, or equivalent, and heat-treated from 125,000 p.s.i., may be used for structural assembly in shear applications similar to structural bolts."

Language in the current AC 43.13-1B, Change 1 is similar except that NAS229 and AN525 (and MS27039) screws are not specifically mentioned.

C180's since '63 and all C185's call for NAS221 screws in this application. Since the NAS221 is a brazier head screw I believe the AN525 is an appropriate substitution.

N170BP · Post by **N170BP** » Tue Sep 30, 2003 2:18 am

spiro wrote:>> These are pan-head screws, not washer head, so the AN525 series is not correct. <<

AC 43.13-1A has this to say:

"...several types of structural screws are available that differ from the standard structural bolts only in the type of head.
The material is equivalent and a definite grip is provided. The AN-525 washerhead screws ... and the NAS-204 through NAS-235 are such parts. ...

a. Structural Screws (NAS-204 through NAS-235, AN-509, and AN-525). This type of screw, when made of alloy steel such as SAE-4130, NE-8630, or equivalent, and heat-treated from 125,000 p.s.i., may be used for structural assembly in shear applications similar to structural bolts."

Language in the current AC 43.13-1B, Change 1 is similar except that NAS229 and AN525 (and MS27039) screws are not specifically mentioned.

C180's since '63 and all C185's call for NAS221 screws in this application. Since the NAS221 is a brazier head screw I believe the AN525 is an appropriate substitution.

Thanks guys,

I think either screw (MS27039 or AN525) is a better choice than
what's on my airplane now (don't ask!).

Since we are talking a shear application (125K psi), both should work.

FWIW, Wicks Aircraft Supply has MS27039-1-08 screws for $.12
each (Aircraft Spruce has has them for $.13 each).

Bela P. Havasreti
'54 C-170B N170BP

Post by **GAHorn** » Tue Sep 30, 2003 4:10 am

Spiro, When I wrote correct I meant both in airworthiness and appearance. I certainly didn't mean to imply that substitution of AN525 screws were un-airworthy, only that there is a specified replacement part (the substitution of which technically requires some basis of approval.) In most instances an internal-wrenching bolt could also be used to replace a common AN bolt, or an AN3 bolt could be used to replace a #10 MS screw, but for the person to whom correct means airworthy AND appearance, ... (I know. I know. My airplane never left the factory with stainless PK screws on the cowling, either.) Anyway, I apologize if my use of the word "correct" implied less than airworthy... I didn't mean it that way.

Speaking of stainless:
Over at the Cessna Pilot's Association, it was once suggested to be good practice to substitute corrosion-resistant screws for the ordinary cad-plated ones which hold the aileron hinges of various Cessnas. The author of that recommendation also suggested that good practice dictates that nylon washers be installed under "stainless" screws to avoid corrosion due to the dissimilar metals. It all sounded good, until it was noticed by the IA that there was no basis of approval to install such washers, and that the corrosion-resistant screws would induce corrosion without the washers, and therefore in his opinion did not meet the"eqivalent" rule. The owner incurred increased annual labor costs necessary to change those screws back to the specified screws before the IA was satisfied. (I personally ran into this same problem with my Baron's aileron screws. First annual got the existing screws "squawked" for replacement with the approved part number.) Another micrometer/grease-pencil/hatchet story.

All I know is, all my stainless screws that hold my fairings/cowlings on have nylon washers under them and I'm not having it any different.

N170BP · Post by **N170BP** » Tue Sep 30, 2003 6:04 am

Since the aileron screws are loaded in shear (not tension),
I don't see a great big, giant problem with using plastic washers...
(not-withstanding anyone's IA's wishes/comments).

However (and maybe I'm all sideways on this?), as I understand
it, we use stainless hardware on our aluminum airplanes simply
because stainless steel is closer (on the galvanic scale) to aluminum
than cad-plated steel is.

In other words, since Stainless and aluminum are "closer friends"
on the galvanic scale, there is a less likely tendancy for dissimilar
metal corrosion to occur.

If there were no other issues at hand, plastic washers would, of
course, further decrease the chance of dissimilar metal corrosion.

Grumman (during & after WW-II) used some kind of barrier (it wasn't
plastic of course, but I'm not sure what it was.... cellophane?)
between cad-plated steel hardware and assembled aluminum
structures. If I'm not mistaken, they used this procedure on their seaplanes as well as their WW-II fighters.

Bela P. Havasreti
'54 C-170B N170BP

spiro · Post by **spiro** » Tue Sep 30, 2003 9:18 am

no offense taken, George - I actually appreciated the *correct* pn update. I've probably only looked that up once, the first time I installed an aileron, so it prompted me to look into it and make sure I still felt the AN525 was appropriate.

as far as appearance, I doubt my plane will never be "stock" again and I think the AN525 is by far the *coolest* looking screw. Pan-heads look ancient, like round head rivets...

- paul

funseventy · Post by **funseventy** » Tue Sep 30, 2003 3:41 pm

I am a firm believer in Stainleass screws for cowling, covers, and fairings. But I don't see where anyone has addressed Bela's first post about the use of stainless hardware for the aileron hinge hardware. You are talking correct part numbers but you don't ever come out and say, "Don't use Stainless Screws in Structural Applications." He mentioned later that he was going to use plastic washers under the head which sounds like he still wants Stainless Hardware on the Aileron hinges. Am I wrong? I think this needs some clarity. There is a reason that the catalog doesn't mention any strength properties on the Stainless Hardware.

N170BP · Post by **N170BP** » Tue Sep 30, 2003 3:50 pm

If I implied I wanted to use plastic washers with the aileron attach
hardware, I didn't mean to (I don't want to use plastic washers
there!).

I wouldn't mind using stainless hardware to attach the ailerons
though. My gut tells me the stainless has lower shear properties
(something less than the 125K psi of the cad plated hardware).

I think I will just use the MS screws, as they are readily available
at my local aviation hardware supplier.

Bela P. Havasreti
'54 C-170B N170BP

N170BP · Post by **N170BP** » Wed Oct 01, 2003 5:27 am

So, I ended up going with the MS27039 screws (I used MS27039C
stainless examples, with stainless washers and stainless nylock nuts).

I asked for, and got the spec sheet for the MS27039 series screws
from my favorite local aviation hardware supplier (Spencer's).

The cad plated steel examples have an ultimate tensile strength of
125,000 to 145,000 psi.

The Stainless examples have a minimum ultimate tensile strength
of 130,000 psi.

Long story short, I'm happy with what's holding my ailerons on my
airplane now vs what was there before!

Bela P. Havasreti
'54 C-170B N170BP

funseventy · Post by **funseventy** » Wed Oct 01, 2003 2:36 pm

I appreciate that response Bela. Mine is getting ready to go to paint and that answers some questions I'll have when I get it home.

Thanks

dacker · Post by **dacker** » Thu Oct 02, 2003 1:16 am

OK, now I am a little confused. I was waiting for someone knowledgeable of corrosion to reply to the use of stainless screws. I admit that the first thing I did when I bought my airplane was replace all of the cowling screws with stainless only to be chastised by my mechanic. It has been a long time since I had material science in college and I think I slept through it anyhow. I thought (and everything I have read) that stainless would cause corrosion of the aluminum. All I know is that I replaced all of mine with Cad plated screws.
I also had to find different screws for my aileron... we used the AN 525 washer head screws.
David Acker
9584A

Post by **GAHorn** » Thu Oct 02, 2003 4:48 am

funseventy wrote:I am a firm believer in Stainleass screws for cowling, covers, and fairings. But I don't see where anyone has addressed Bela's first post about the use of stainless hardware for the aileron hinge hardware. You are talking correct part numbers but you don't ever come out and say, "Don't use Stainless Screws in Structural Applications." He mentioned later that he was going to use plastic washers under the head which sounds like he still wants Stainless Hardware on the Aileron hinges. Am I wrong? I think this needs some clarity. There is a reason that the catalog doesn't mention any strength properties on the Stainless Hardware.

I don't think it's "disqualifying" to use "stainless" in structural applications, but this particular subject has some innuendos that are worth consideration.
Firstly, when we generally say "stainless" we are usually talking about those "stainless" screw kits sold in Trade-A-Plane, etc., that are intended for cowlings and fairings. Those are not structural components involving safety of flight, and "stainless" screws are commonly acceptable there.
The term "stainless" is widely used with regard to corrosion resistant hardware, but that term actually is not descriptive of any particular standard in aviation (or marine, or almost any other specialty field.) Stainless steel is a type of steel that has a high degree of nickle and other corrosion-resistant elements, ...and in varying percentages utilizing a variety of manufacturing techniques,...with the expected results with regard to strength. Using such hardware in non-structural (i.e., cowlings, fairings, etc.) is usually not a compromise of safety. (Notice that comment does not address legality. Also, with regard to your mechanic's aversion to using "stainless" on your cowlings, many mechanics are opposed to the practice simply because that kit-type hardware doesn't stand up to repeated use of electric screwdrivers because it's softer and the screw-heads deform so easily.)
So-called "structural" stainless steel actually is a different animal than that commonly considered "stainless" down at the hardware store. In many cases, a part number (i.e. MS27039) will have as a suffix the letter "C" (meaning corrosion-resistant) in it's designation if the article is what we commonly intend when we refer to "stainless". So a part designation of MS27039C would be a corrosion-resistant item which usually, other than it's resistance to corrosion, is identical or superior in strength to it's ordinary MS27039 brother. The specifications of alternate parts should be checked in critical applications.
But back to the concept of substitution of parts: If there is a specified part in a particular application, then there can be no substitution without some basis of approval. That basis of approval might be via the manufacturer's superceded part designation (such as in this thread where a MS part number has replaced a NAS number), or it might be an industry-standard which is recognized by the regulatory authority (such as when substituting an AN bolt with a NAS or MS bolt of equivalent standards, or it might be found in an STC, field approval, or other basis. But the point is that, when a part number is specified by the mfr., then that is the only part number which may be used as a replacement without some basis of approval, (be it industry standard, or otherwise.) When an old PN is superceded with a later PN (such as an AN part being superceded with a particular MS part number), then the use of ANY part other than the specified replacement part, ...must have a basis of approval,...or it's simply not the correct part. Just because another piece of hardware is stronger than the original, or is a commonly-used replacement out in the field, does not obviate the requirement for a basis of approval. (In some cases it's even possible the "stronger" part might cause unacceptable damage to the objects it is supposedly holding together exactly BECAUSE of it's different strength.) The only "safe" way, without another basis of approval, is to use the correct, specified part or superceded part in the application.

N170BP · Post by **N170BP** » Thu Oct 02, 2003 5:01 am

I did a little digging, and I was flat wrong about Stainless Steel
being closer to aluminum (on the galvanic scale) than cad-plated
steel. The opposite is true.

I did read/find that 316 series stainless is closer to aluminum
(galvanically) than 304 series stainless (doesn't help us much with the MS screws in question being manufactured from 200 series stainless steel....).

For those of us with painted airplanes, perhaps the stainless hardware
is a viable option because the hardware has a barrier (the paint) between
the aluminum and the hardware surface. If you "remove" the dissimilar
metals from the equation, no doubt stainless hardware will last longer
outdoors than cad plated steel will.

I apologize for the mis-information I posted.

Bela P. Havasreti
'54 C-170B N170BP