more rivet questions

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greentowtruck

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Jan 20, 2008
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70 miles north of Seattle WA
I have been looking but cant seem to find the thickness break between dimpling and countersinking for rivets. The plane I am building is mostly .025 and .032 skins which i assume will require dimpleing. my main question is the spars are .050 so would i dimple or countertsink for the dimpled skins??

the plans say nothing about countersunk rivets as they call out for USM pop style rivets or to use solid rivets (ms20470ad4-4 or 4-5) where ever possible.I really like the look of countersunk even though they are more work to install

There are some places that will require blind rivets although I am having trouble finding the USM rivet (AD42 and AD43) or an equivelant countersunk blind rivet. I considered Avex Rivets bit I am unsure about the strength of them versus the USM

by the way the plane is a late 70's design Durand MK V all metal biplane
 

orion

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Can you post a bigger picture?

If someone has a technically better spec please jump in - my rule of thumb for a typical 1/8" rivet is that you dimple through .032" or thereabouts and then you can start countersinking for .040" sheet.

Regarding the .050" spar material and the .032" sheet: This is a tough question to answer because we don't know the design spec that was used for the design of said spar. The countersink of course removes some material in the most critical portion of the spar, that being the flange. Furthermore, the countersink also introduces a higher stress concentration factor due to the increased void and the nearer edge distance (distance of rivet hole to nearest edge) the countersink forms.

I know it'll be more work with the thick gage but to stay on the safe side, I'd recommend dimpling both.
 

BBerson

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It depends on the rivet. The FAA Airframe handbook shows that countersinking is permissible to the bottom of the hole but no more (page 170).
The book says dimpling works best for .040 and thinner.
 

greentowtruck

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70 miles north of Seattle WA
I would post a larger picture if i could figure out how. the spars are a box spar made of two modified J beams formed from .050 2024 T3 when put together they form a box with a single top and bottom flange facing opposite directions away from the box top one forward bottom one aft. I would post a drawing but again I cant figure out how yet. It looks like the flanges are used only for attaching the skin as there are no rivets in the upper and lower portions of the box section



just looked at my plans again the wing skins are .020 except for the lower wing walk area which is .025
 
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orion

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Clever configuration - allows for sheet attachment without compromising the primary spar cross section. That's just a guess though.
 

Captain_John

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Feb 3, 2003
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KPYM
You won't find a spec on where to dimple vs. countersink.

Also, you will have a hard time dimpling anything thicker than 0.040" or so.

Given that, you should dimple any material that... when you attempt to countersink it... you enlarge the hole diameter or leave a knife edge on the countersunk hole.

Check out Van's section 5 of their manual. It is a free download and has lots of good tips!

Here is the first part:

http://www.vansaircraft.com/pdf/section 5r9a.pdf

...and here is the second:

http://www.vansaircraft.com/pdf/section 5r9b.pdf

Hope this helps!

:) CJ
 

Othman

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NOTE: CHECK WITH THE DESIGNER to confirm that the MS20470 domed head rivets can be replaced with flush head rivets (MS20426) in the area you are considering. The joints will have slightly different strengths.

Machine countersinking 0.040 sheet for a MS20426__-4 rivet will cause a knife-edge condition and should be considered for design. Cold dimpling 0.040 Al alloy (2024-T3) is possible however great care should be exercised to avoid cracks. Anything thicker should be hot dimpled.

Machine countersinking 0.050 sheet for MS20426__-4 rivet is ok; however, is not ideal for fatigue. Given that it's a recreational aircraft and won't be building up the hours a commercial airliner would in it's life, it will be ok.

For your particular problem, the 0.020 wing skins can be dimpled, and the underlying 0.050 flanges can be machine countersunk... but again, confirm with the responsible owner of the design.
 

jnorris

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The general rule of thumb is that you can dimple on anything up through .040 aluminum. Anything thicker must be countersunk.

Joe
 

PTAirco

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You guys sound like boilermakers to me - most of the stuff I'm working with on my single seater is 0.016" and 0.020"....
 

greentowtruck

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70 miles north of Seattle WA
thanks for all the information. I would love to talk to the original designer but unfortunately he has gone west and is no longer with us and nobody is supporting the design. That is why I have started asking questions here. This is also my first plane project.

I have not been able to find much information on the plane except what came with the plans and the very small builders manual that covered basic building standards along with weight and balance, a sample preflight checklist, and basic takeoff and landing procedures. I also got a couple of 80's kitplane articles about the plane.

the nice thing is that even though there are only about 5 that were known to be completed I have not been able to find anything in the NTSB database on any of them. the one that I have as an Avatar pic and that I have posted in my other threads as larger pics is located at the boeing museum of flight restoration center in everett. I am going to try to get down there to see it soon I hope. I am only abour a half hour from there.

If anybody has specific questions about the durand MK V please email me and i will answer them to the best of my ability
 

Topaz

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My recollection from the '80's was that the airplane was written up as "quite nice" by the press at the time. That was when it actually meant something, since the magazines were willing to do a 'this airplane sucks' review back then, as opposed to now.

IIRC, it was stuck in a rather awkward niche for the time - for its power range the early Glasairs and other early premolded, higher-performance airplanes were becoming all the rage in the kit industry (this was a tad before Lance Neibauer came along and made life difficult for them, too). For those who wanted a cabin biplane, the bigger-engined HiperBipe was The Thing To Buy, and some purists objected to the tri-gear, stating that a 'real' biplane can only be a tail-dragger. The scratch-builders were all into Eze's, KR's, early RV's, and the Sonarai derivatives. I remember this as being one of those 'nice airplanes' that never really caught on due to the market forces at that particular time.

Nice to see one still a-borning. :)
 
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greentowtruck

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70 miles north of Seattle WA
Both the articles i have wrote it up as a nice cruiser with docile handleing, and nearly impossible to stall. also being a bit different due to the spoilers for roll control instead of Ailerons.

We had originally planned on a bearhawk and I have the plans for that also but we really liked the all metal cabin bipe design. The information I got with it which included several letters from Bill Durand also stated it could take up to a O360. although I think my plans will put a Mazda rotary in it. I still need to do some calculations on fuel usage as it only carries 24 gal or 32 with the aux wing tanks
 
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