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RV-3 Spar Mods

L'Avion

L'Avion

Well Known Member
In the next couple months, a friend (tullypilot) and I will begin the spar mod on my RV-3, Type I wing.

I have all the fixins from Vans, and am looking for whatever advice anyone can offer before we start.

The RV-3 has wing fuel tanks (both need leaks fixed) which we plan to remove (both wings & tanks) to perform the mods. Interestingly, some mod was made years ago, but was not definitively entered in the logbook, so we'll be looking to see what might have been done as we begin. The logbook entry appears as though it may have been the first CN-I change, however we'll be working with the newer CN-301 TYPE I, making sure that all items from it are completed.

Lotta rivets to remove - advice on using, or not using, a rivet shaver?

My intentions are to make this aircraft as strong and safe as possible.

Thanks, in advance, for any helpful suggestions anyone may offer.
Barney
 
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L'Avion said:
Lotta rivets to remove - advice on using, or not using, a rivet shaver?
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A rivet shaver is not used to remove rivets. It is used to "shave" the top of slightly "proud" rivets for a smooth surface. I'm not crazy about the use of rivet shavers. I have used them, but I don't like the idea of taking material off of rivets.
 
Maybe I'm just stirrin' the pot, but do you guys feel you NEED to do the spar mod? Guess it all depends on your flying mission. Van will tell you not to do acro with the Type 1 wing, but they will also tell you there's nothing wrong with the original design as long as you obey the load limits (+6/-3G). I've read all the literature from Vans, as well as all the accident reports involving RV-3 wing failures (all gross stupidity) and wouldn't worry about my wing until the meter pushes 8G's. I do mild acro in mine and would really have to work to accidentally get anywhere near Vne and 5G's. But then, my airplane is slow with a top speed of maybe 160 mph (climb prop is rpm limited in straight and level). I obey the utility limit of 4.4G's in my airplane and pegged this one time on purpose. I am not questioning Van or his wisdom. BTW, if I tried the spar mod, I'd probably just make things worse:D
 
Eric,

I agree with your thinking, however, my -3 is 27 years old and I have no way of know who might have flown it, how hard, nor to what extreme in the past.

If I could have a plans built -3, I would have no reservations about flying it aggressively as per the original plans, but as things stand, I just don't know where what stress may have been applied by what stupido. So as long as I've had to dig in deep to fix leaking fuel tanks, I'll continue to beef things up, while inspecting for what some dumnorix might have pulled, not in accordance with good flying practice.

So far, we've got the fuel tanks out, canopy off, radio rack out from below instrument panel, seat & stick out, and main spar exposed. May get the wings removed tomorrow.

This will prove to be an interesting challenge. More as we progress.

Barney
 
Wise man.....

L'Avion said:
Eric,

I agree with your thinking, however, my -3 is 27 years old and I have no way of know who might have flown it, how hard, nor to what extreme in the past.


This will prove to be an interesting challenge. More as we progress.

Barney
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I'm with you on this one. I have a PT-6 turbine in my work airplane and even Pratt and Whitney mentions in their manual that your engine will "remember" every overtorque or no overtorque and will either reward you with faithful, reliable service or come back to haunt you with payback.

Good move,
 
All following discussion references a TYPE I wing, built prior to 1984 when a TYPE II wing was introduced. The main difference between TYPE I and TYPE II wings are that the spar flanges in TYPE I are 1/8" thick, whereas the TYPE II the spar flanges are 3/16" thick.

From CN-301 Type I Wing (CN-2-1):

"The CN-2-1 modification supplements the CN-1 modification, but does not supersede or replace it. Both are necessary to achieve aerobatic strength. Each addresses a different part of the wing structure. If any RV-3 has not yet been modified in accordance with CN-1, this needs to be performed before or in conjunction with CN-2-1."

Therefore to achieve aerobatic strength CN-1 must be accomplished on a TYPE I wing.

CN-1-1 (the second 1 designates TYPE I wing) states in part on page 4:

"3. All rivets attaching the spar flange strips to the spar web must be in place as specified in a staggered position. Aligning any of the rivets in the two rows in a vertical line will reduce the spar strength by as much as 10%.

4. Substitution of a larger than 1/8" rivets in the spar flange strip attachment will result in reduced strength. If a 3/16" bolt or rivet is substituted, a strength loss of up to 6% will result."

CN-301, Drawing CN-2-2 shows a 'single' row of 1/8" rivets in the lower forward spar flanges and suggests replacing most of them with 3/16" rivets; whereas my aircraft S/N 241, N90516, has a double row of 1/8" rivets alternately spaced as per early plans indicated in CN-1-1, #3. With no assumptions being made as to which row of these alternately spaced rivets might be replaced, any replacement would result in a reduction in strength of "up to 6%." Additionally, since a double row of alternately spaced rivets placed the 1/8" rivets closer to the edge of the flange than a single row of rivets would, one might reasonably expect an even greater loss of strength due to the closeness to the edge of the flange; and even this assumes that each replaced rivet had been exactly "center-bored" out.

It has made good sense to me to decide to not replace any of the 1/8" rivets in the lower spar flange, not being willing to accept any loss of strength from either the previously mentioned 6% loss, or even greater loss of strength from larger rivets replacing the 1/8"rivets closer to the outside edge of the flange, which is to say nothing of the probability that all the rivets to be replaced could be replaced without incurring an additional loss of strength due to a drill bit running off, or creating an out-of round hole in which to insert a 3/16" rivet, or bolt.

Deciding to not replace any 1/8" rivets with 3/16" rivets means that CN-301 incorporating both CN-1-1 and CN-2-1 can not be successfully accomplished and that N90516 cannot be returned to "aerobatic strength" per CN-301.

If anyone has successfully accomplished CN-301 on a TYPE I wing, made an appropriate entry into their aircraft log, and returned their aircraft to aerobatic strength, please advise as to how you may have gotten around replacing the 1/8" rivets in the lower, forward spar flanges with 3/16" rivets (per Drawing CN-2-2); or what other measures you may have accomplished to augment spar strength.

As always, all suggestions greatly appreciated.

Thanks,
Barney
 
Hello fellow rv3's I'm just starting on doing the same upgrades to my -3 with type I wings
Does anyone have any pictures of the CN 1-1 CN2-1 Mod?
thanks
Lee
 
CN2-1

Just opened up the wings on Both lh and rh sides, No cracks or corrosion
drilling out the tails for the 1/8 rivets is alot easier if you have a 45 angle or a 90 drill then use a 1/8 gun punch set in a rivet gun to knock out the old rivets.. helps to have someone with small hands to install the 3/16 bolts on the front side of the spar!:eek: I'll take some pictures if you want to see the Mod

Lee
 
jetmech said:
Just opened up the wings on Both lh and rh sides, No cracks or corrosion
drilling out the tails for the 1/8 rivets is alot easier if you have a 45 angle or a 90 drill then use a 1/8 gun punch set in a rivet gun to knock out the old rivets.. helps to have someone with small hands to install the 3/16 bolts on the front side of the spar!:eek: I'll take some pictures if you want to see the Mod

Lee
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Have you completed the mod? Any pictures?
 
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