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RV-8/8A Plans Gotchas

MIKE JG

Well Known Member
Those cool guys over on the RV-7 forum have their own stickied thread with gotchas for that airframe. Many of those for the empennage are applicable to building the RV-8 empennage but we don't have a similar thread for the 8 that I can find.

Is there one anywhere or has anyone kept a log anywhere? Or does anyone want to start populating one for the RV-8??
 
Not so much as "gotcha's" as little nit-noids that get overlooked. ...Like, leaving certain pre-punched holes open for nut plates to attach the empennage fairings. And, the order of operations for riveting the skins onto the skeleton for the Vert and Horiz stabs. If you don't have a plan to set every rivet before you start riveting, its really easy to "paint-yourself-into-a-corner" so to speak.
 
Firewall

And, the order of operations for riveting the skins onto the skeleton for the Vert and Horiz stabs. If you don't have a plan to set every rivet before you start riveting, its really easy to "paint-yourself-into-a-corner" so to speak.

Haha, I've "riveted myself into a corner" before too, recently actually. There's some nut plates on the firewall that just didn't make sense to rivet in that order, but I dutifully followed the instructions. Later on, I was unable to buck 3 rivets because nut plates were in the way. Ended up drilling out some nut plates, bucked the firewall rivets and re-riveted the nut plates. One firewall rivet I was far enough into, that I just stuck in a c/s Cherry Max and called it a day.
 
Tips and Tricks

1. Minimum Edge Distance for rivets. 470 rivets are 2 x the diameter and 426 rivets are 2.5 x the diameter.

2. Machine countersink only when material thickness is greater than rivet head. This doesn't mean the total thickness it means the sheet of material directly under the rivet head.

3. #3 Rivet hole is 3/32. When dimpling - drill the 3/32" hole, dimple and then if necessary ream to a #40. If you final drill to a #40 your holes will be sloppy when you dimple and they'll be too big for the rivet.

4. Cutting / Trimming. Always 2nd guess Van's on their cutting dimensions. When cutting something cut it long and then trim or file to fit. Otherwise you won't have the minimum edge distance for riveting. Especially see #1 and #5

5. R-710. Don't trim to Van's specs. If you do, you'll not have the edge distance along the edge you just trimmed. Go to the Search Box and simply type in R-710 - you'll see

6. R-802. There are punched holes in R-606 and R-405PD that line-up with each other, but no corresponding holes in the R-802 spar. The holes in 606 and 405 are holes used for alignment of the part during manufacturing. Don't use the holes and don't drill into the spar.

7. Circled Xs. Look on plan Drawing 3-8 of the horizontal stabilizer. On the inside edge of the left and right horizontal stabilizer you'll see circled x's over rivet holes and there's a corresponding note and arrow that reads leave Open on top side only for empennage fairing attach, 10 places. Well, don't dimple the skin or the understructure where these are depicted.

8. "Information acceptable to the administrator" Is Free. That means it's information promulgated by the FAA. Let's face it. We ask questions and opinions on an open forum because were curious, we like short cuts, we don't have any idea where to find the information or we're just too lazy to do our own homework. Van's publishes a lot of information in the beginning of the builder's manuals and that also includes some "tricks". But every bit of information on building aircraft, wood, fabric, metal, helicopter, balloon, their components, and the rules, regulations, minimum criteria etc. is free from the FAA. Especially useful are mechanic's handbooks. https://www.faa.gov/regulations_policies/handbooks_manuals/aircraft/

9. Drilling a hole. Drilling a hole is apparently an art. Different materials and different thicknesses require different speeds. Pushing too hard leads to a bent, malformed triangle. Drill bits are like dresses, there's a lot of differences. There are fractional, numbered, and lettered, angles are 90°, 110°, and 118° 140°. There's 0° rake angle, single cutting edge, double cutting edge. There's HSS, Titanium, Black Oxide, Cobalt, Carbon. They come in different lengths, some are double margin. Theres different speed drills. Then there's IPS. Drilling in Acrylic or Lexan or other plastic there's single cutting edge vs. 2 cutting edge Unibits. Then there's Rotabroach....Then there's about 50 different kinds of reamers.

10. Hole prep. Improper hole preparation facilitates cracks. Prior to dimpling or squeezing rivets the hole has to be clean, the correct size and round. When shooting or squeezing a rivet, the rivet expands into the hole with enormous force. Any inclusion in the hole is potentially a crack later on.

11. Bending Metal Just like there's a minimum edge distance for riveting, bending metal has a minimum bend angle. That depends on the material, the hardness, and the thickness. The overwhelming majority of A&Ps and I/As even when given the formula and charts can't tell you the minimum bend angle of a piece of metal - and of the 5% of those who can I'll bet 2% of them can't give you the set back. Take a scrap piece of aluminum and squeeze the daylights out of it and then put it under a 10x or better magnifying glass. You'll see where the clad plating starts separating from "work hardening" the material from excessive pressure. (I'm sure, I'm in the 95%)

12. Work Hardening Dimpling and bending metal and hammering on it via riveting work hardens the metal. Use as light a blow and as few blows as you can from a rivet gun.

13. Scrubbing the aluminum coating off AlClad. The Aluminum is there for corrosion protection but some people use Scothcbrite to scrub the protective surface off the AlClad so they can apply a protective surface (alodine). The pure aluminum coating is only 2%-5% of the material thickness so on a piece of .020" the pure aluminum coating can be as little as .0004" thick. Scrubbing the corrosion protection off to apply another corrosion protection never made much sense to me.
 
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"3. #3 Rivet hole is 3/32. When dimpling - drill the 3/32" hole, dimple and then if necessary ream to a #40. If you final drill to a #40 your holes will be sloppy when you dimple and they'll be too big for the rivet."

Is this true? They didn't teach this at Synergy, Van's doesn't say to do this, and wouldn't it be awful hard to debur the reamed, dimpled hole? If so, then I guess I'll ordering a new vertical stab.....
 
Strictly speaking it’s correct. Dimpling does stretch the hole slightly, so if you final drill before you dimple then the hole will be over size. Also if you use a reamer then the need for deburring is reduced.
However, doing it this way is not what Vans says is required and is not taught in the building classes here in the U.K. And loads of aircraft have been safely flying for years with out this level of accuracy.
 
I don’t think this is correct.. looking forward to the smarter guys on here to speak up. I feel if you drill 3/32 then dimple, you risk stretching the metal to the point you’ll get micro cracks around the hole. Sometimes I do drill #41 though before I dimple..
 
I don’t think this is correct.. looking forward to the smarter guys on here to speak up. I feel if you drill 3/32 then dimple, you risk stretching the metal to the point you’ll get micro cracks around the hole. Sometimes I do drill #41 though before I dimple..

I know some build centers will just dimple the holes without additional drilling. The dimple tool die acts as the reamer. If anything, this action slightly compresses the metal around the holes because the holes in the pre-punch RV8 sheetmetal are almost full size. You still have to fit the metal parts and to drill holes in the parts that are not perfectly aligned .
 
Plan Gotchas

Back to the plan gotchas rather than rivet hole preparation,

These apply to the kits before the matched-hole fuselage, and may or may not apply to the -1 matched hole fuselage kit - I don't know if these issues were corrected in the newer kits or not.

1) The recommended hole locations for the manual trim cable routing in the cockpit bulkhead (F-804) conflicts with the recommended hole location for the pushrod to actuate the rear seat throttle. It seems like the factory prototyping process installed one or the other in their prototype airplanes, but not both.

This conflict required me to install doublers on the two bulkhead panels to relocate the trim cable routing.

2) The vertical positioning of the fin on the fuselage: On the plans there were two different dimensions at two different revision stages, and IIRC, neither one was correct. Ultimately I put the rudder on the fin, and set the vertical position of the fin so that the rudder bottom lined up appropriately with a visual extension of the keel line of the fuselage.
 
"3. #3 Rivet hole is 3/32. When dimpling - drill the 3/32" hole, dimple and then if necessary ream to a #40. If you final drill to a #40 your holes will be sloppy when you dimple and they'll be too big for the rivet."

Is this true? They didn't teach this at Synergy, Van's doesn't say to do this, and wouldn't it be awful hard to debur the reamed, dimpled hole? If so, then I guess I'll ordering a new vertical stab.....

I'm not trying to tell anyone what to do, I'm just passing along information that was researched, tested, and peer reviewed by presubably, a team of aerospace engineers and a signed off by a PE with a PhD Aerospace Engineering and approved for the US Govt as a standard to use in Preparation for and Installation of Rivets and Screws in Rockets, Missiles, and Airframe Structures. Don't blame me for the contents - If you feel the information is inaccurate please contact the Commander of the U.S. Army Missile Command at Redstone Arsenal.

(Sorry, I don't know what Synergy is)

Anyway, the reference for #3 is MIL STD 403C Para 5.1. pg 7 and table I on pg 12. There are standards for everything in aerospace - and chances are those standards involve people much smarter than most and with a lot more money for testing. I am grateful to them for their hard work in getting their credentials and for passing along their knowledge for free.

You can also read AC 65-15A The whole book is worth reading, but you can read about drilling holes and dimpling at the top right of page 171 where it says to pilot drill the hole and dimple die.

Here is my procedure and the results. You may want to test things for yourself. I drill a 3/32 hole with a double margin bit then I debur, clean the hole and then dimple with a 3/32 die from Brown Aircraft Tool Supply, (the one identified as (made in the USA (I also measured the dimple die with a certified (calibrated to a traceable NIST standard) Starrett 3732 that measured the dimple stem to .09365)) the resulting hole is .1012 which is in the middle of the min/max on table I

If I final drill to #40 (also a double margin bit) and then clean, debur and dimple the hole at the end of the procedure is .106 which is at the max of the chart. So if I've got 50 holes on two or more sheets, the chances of the holes lining up is that compounded by a random dimple caused by a sloppy fit in the sheet metal

I'll also say that the dimple die will wobble around a lot more in the #40 hole so I can't imagine that 50 dimples would match as well.

So if things don't sound right that's ok - All I can do is qualify my statement and try to explain using objective reasoning - After all this is an industry where in addition to flying an X-15, people think its a good idea to fill their airplane engine's crankcase with Marvel's Mystery Oil or pull their airplanes parachute when they're low on gas.
 
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I'm not trying to tell anyone what to do, I'm just passing along information that was researched, tested, and peer reviewed by presubably, a team of aerospace engineers and a signed off by a PE with a PhD Aerospace Engineering and approved for the US Govt as a standard to use in Preparation for and Installation of Rivets and Screws in Rockets, Missiles, and Airframe Structures. Don't blame me for the contents - If you feel the information is inaccurate please contact the Commander of the U.S. Army Missile Command at Redstone Arsenal.

(Sorry, I don't know what Synergy is)

Anyway, the reference for #3 is MIL STD 403C Para 5.1. pg 7 and table I on pg 12. There are standards for everything in aerospace - and chances are those standards involve people much smarter than most and with a lot more money for testing. I am grateful to them for their hard work in getting their credentials and for passing along their knowledge for free.

Here is my procedure and the results. You may want to test things for yourself. I drill a 3/32 hole with a double margin bit then I debur, clean the hole and then dimple with a 3/32 die from Brown Aircraft Tool Supply, (the one identified as (made in the USA (I also measured the dimple die with a certified (calibrated to a traceable NIST standard) Starrett 3732 that measured the dimple stem to .09365)) the resulting hole is .1012 which is in the middle of the min/max on table I

If I final drill to #40 (also a double margin bit) and then clean, debur and dimple the hole at the end of the procedure is .106 which is at the max of the chart. So if I've got 50 holes on two or more sheets, the chances of the holes lining up is that compounded by a random dimple caused by a sloppy fit in the sheet metal

I'll also say that the dimple die will wobble around a lot more in the #40 hole so I can't imagine that 50 dimples would match as well.


From your reference material,

https://mmptdpublic.jsc.nasa.gov/prc/MIL-STD-403C.pdf

Page 12, table 1 states minimum hole size before dimpling should be no smaller than .096, which is a #41 drill bit. Your 3/32 drill bit would be .093, which may cause excess stretching and cracking when the dimple die spread open the hole. I do agree that sometimes it seems the #40 drill then dimpling feels a little loose, but your document would agree that a 3/32 hole before dimpling isn’t “milspec”

Sorry for the thread drift, but if this is to become a sticky, I would want the information to be accurate.
 
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