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Building tip #1

jim plaster

Well Known Member
I didn't build my RV 6a but feel 34 years in aircraft maintenance could help a new builder out there. My advise in building any airplane is locate your components so they'll be accessed for maintenance in the future! I've seen items from a J3 thru a Boeing 757 located in horrible places when it comes to maintenance. So far one of the smartest RV mods I've seen is having access panels aft of the firewall for maintenance on avionics. Mine has a electrical load center that appears the airplane was built around! The vacuum filters , as well as the starter relay are mounted so high up on the inner firewall that removal/replacement is extremely difficult. A removeable panel here with nut plates would have been extremely helpful without too much time added to the build. I may modify mine in the future. My advise is take your time and do it right...it will payoff later!
 
Jim, Just remember that the RV is a "stressed skin" design and any time you cut holes in the skin, you are subjecting the aircraft to untested load points.

Although your suggestion has been done before, I'm not aware of any {approvals) from the designer.
 
Mel,

I was planning to cut these access panels up front. Does this need a call to Vans?
 
Mods

Mel,wasn't planning on cutting holes in mine. My future plan is to install nut plates where the existing rivet holes are,then replacing the aluminum rivets with either stainless or titanium screws. These are suitable substitutions per ac43-13 on certified airplanes.
 
Removable skin

I'm taking a different approach. Because I installed my VPX and my Skyview transponder, ADS-B, VHF slave, and EMS up forward between the firewall and sub-panel, I decided to fasten the forward skin with #6 screws, thus making the skin removable. Rather than rivet the skin on, I'm adding platenuts for #6 screws on all the ribs and bulkheads. I'll tap the longeron holes along the left and right edges. This adds about 6 ounces while keeping me from having to crawl up under the panel on my back for minor maintenance.
 
I'm taking a different approach. Because I installed my VPX and my Skyview transponder, ADS-B, VHF slave, and EMS up forward between the firewall and sub-panel, I decided to fasten the forward skin with #6 screws, thus making the skin removable. Rather than rivet the skin on, I'm adding platenuts for #6 screws on all the ribs and bulkheads. I'll tap the longeron holes along the left and right edges. This adds about 6 ounces while keeping me from having to crawl up under the panel on my back for minor maintenance.

I'd be very careful about trusting the strength of steel screws in tapped holes in aluminum longerons! In the RV-3, this skin is removable, but the plans call for nut plates to vary the loads.

In general, any mod (or design) should be designed with future maintenance in mind - that is VERY true. However, every design is a trade-off in some regard, and designers need to keep that in mind. I personally have gone with removable instrument panels - especially convenient in the age of electronic instruments - to gain access. Big holes, works great - no structural issues. Also - easy to retrofit, and no worries about water leaks into the expensive goodies!
 
I'd be very careful about trusting the strength of steel screws in tapped holes in aluminum longerons! In the RV-3, this skin is removable, but the plans call for nut plates to vary the loads.

In general, any mod (or design) should be designed with future maintenance in mind - that is VERY true. However, every design is a trade-off in some regard, and designers need to keep that in mind. I personally have gone with removable instrument panels - especially convenient in the age of electronic instruments - to gain access. Big holes, works great - no structural issues. Also - easy to retrofit, and no worries about water leaks into the expensive goodies!

Excellent advice, Paul. I will also add that any hole that a screw/nutplate goes into, has reduced fatigue properties compared to a driven rivet. While I'm not as familiar with the design of the 3, there are a BUNCH of rivets, all in a row, through the longerons picking up the top skins on a 7/9 fuselage. This means a lot of open holes in the longeron, a major load and thrust bearing structural member.

In short, there are rivets here for a reason. Replacing 100% of the rivets in this joint may, or may not, be a recipe for disaster. Please get a proper stress analysis performed by a competent aerospace structural/stress engineer before going this route.
 
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Bugsy,

Must say I am thinking about doing the same on my 6 ... But I will ask VAN's before I do ... mine is a tip-up 6 ..
 
I addressed this on my 8 by doing the following.

1. Added an removable access plate on the bulkhead aft of the firewall, this allows access to back of instr panel through the fed baggage compartment.

2 designed my instrument panel itself to be easily removed. I use Mgl avionics iefis, it is basically modular. To remove my instrument panel involves the screws, two 1/8th in hoses, one db9, two db25, two ant cables and one LAN cable. And the entire panel can be set aside. It takes about 10 min. And I then can access everything in there.

My fuse skins are riveted on as per plans and the acces panel in the fwd bulkhead is attached with nutplates and 8/32 screws about 2 inch spacing.
Pics on link below.

Bird
 
Structure

"I'd be very careful about trusting the strength of steel screws in tapped holes in aluminum longerons! In the RV-3, this skin is removable, but the plans call for nut plates to vary the loads."

Excellent advice, Paul. I will also add that any hole that a screw/nutplate goes into, has reduced fatigue properties compared to a driven rivet. While I'm not as familiar with the design of the 3, there are a BUNCH of rivets, all in a row, through the longerons picking up the top skins on a 7/9 fuselage. This means a lot of open holes in the longeron, a major load and thrust bearing structural member.

Paul and KRW,
Thanks for telling me this. I gave the Mothership a call and described my intentions: They were concerned. If I tapped the longeron holes, they were worried about the slightly enlarged holes for the #6 screws, plus possible further weaknesses introduced by the tapping process. If I instead used platenuts on the longerons, they were concerned about the doubled number of holes in the longerons. Both cases will possibly weaken the longerons, and they have no idea how much.

Vans has not conducted any sort of engineering study of how well that top front skin will fulfill its stressed skin structural role if it's screwed on vice riveted. This is too far into the unknown for me: I'll stick with the plans and rivet the skin on.
 
I am building a tipper and many things I don't want wet are located under that forward skin. I think everything can be accessed and removed from below. Screws have heads down. Nut plates uses so one hand can remove a screw.

Other components that are fastened to the sub panel are mounted so one hand under and one hand with screwdriver in front can remove it. Nutplates were added to avoid loose nuts, washers etc. and still have some fastener retention.

I will still have to lay on my back, but all should be able to be reached.

Full disclosure: I have no idea how this is going to work, so draw your own conclusions.
 
I've seen it somewhere years ago. I remember the builder said he installed nut plates and screws instead of rivets because he had no bucking help on the farm. 100% of the plane he built solo.


 
530 hrs...

...on my RV-6A this way. Lots of screws - keep plenty of replacements on hand. I purchased the aircraft flying, so the choice was made for me. However at 6'4" and 215 lbs. and 65 years of age, I have found the modification to be useful. I am reasonably certain that the shear strength of a steel screw is greater than an aluminum rivet.

I am not giving you advice, just reporting.

Larry Tompkins
N544WB -6A
W52 Battle Ground, WA
 
...on my RV-6A this way. Lots of screws - keep plenty of replacements on hand. I purchased the aircraft flying, so the choice was made for me. However at 6'4" and 215 lbs. and 65 years of age, I have found the modification to be useful. I am reasonably certain that the shear strength of a steel screw is greater than an aluminum rivet.
I am not giving you advice, just reporting.
Larry Tompkins
N544WB -6A
W52 Battle Ground, WA

I think the strength of the screws in this case are not in question.
The biggest factor is how many extra holes have been drilled in the longerons at a fairly high stress point.
 
I think the strength of the screws in this case are not in question.
The biggest factor is how many extra holes have been drilled in the longerons at a fairly high stress point.

The number of holes and the additional removal of material due to countersinking for the screw head dimple instead of the rivet head dimple. Also the machine countersinking for the added rivet holes. Overall, there are now 2 #40 holes and countersinks and a #27 or #19 hole and countersink for each #40 hole and countersink called for. That's a lot of extra holes in a longeron.

If the screws are held into tapped holes in the longeron, the holes are still bigger than called for. The sheer strength would increase, but what are the differences in tensile strength of a 3/32 rivet and tapped threads in an aluminum longeron?
 
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