RV-3 Rear Spar

We have just finished fitting / drilling the Rear Spar for the RV-3.

Rear Spars, particularly the setting of sweep and incidence, cause much stress to RV builders, with limited room to keep ED and get the wings set correctly - as urged by Vans after the earlier RV-3 issues.

Some RV-3B builders even suggest using an oversize (hence overweight ) spar to keep minimise the issues - given the lack of matched holes etc., it would seem a good idea e.g.

Do not use the rear spar supplied by Vans! It leaves no room for error when you drill the wing attachment hole. After mounting the wing and drilling the hole I realized the hole violated the edge distance requirements by 1/16". It doesnt sound like much, but at least one RV-3 pilot has died as a result of rear spar failure. I recommend replacing it with a 2" wide piece. It only costs about 40 bucks, you will be glad you did.

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We approached this from the other direction:

• We made the fuselage "slots" for the rear spar
• We clamped the rear spar into the fuselage to set the rear / front spar distance as measured from the wings, during fuselage construction
• We drilled the wings for the rear spar bolts as per plans i.e. with good ED
• Drilled one end of the rear spar for the bolt - again "in the middle" so no ED issues
• Fitted the wings, and trimmed the rear spar length so the wings could establish the correct sweep, then drew a line on the rear spar where the other hole should go
• Drilled this hole centered vertically in the spar.

We now had wings fitted at the front spar, and tied together at the rear spar points, but the rear spar able to move laterally and vertically within the fuselage. It now just took:

• Lightly clamp the rear spar to the fuselage and adjust laterally until wings square, and vertically for correct incidence.
• With undersize holes drilled in the rear spar, match drill into the fuselage bulkhead
• Final Drill holes through rear spar fuselage
• (After priming, will rivet Rear Spar into fuselage) This should not be an issue - there is good access to set these rivets.

All in all, went as expected, and I would offer up as an option to consider for future builders - certainly for the RV-3. Comments of course welcome...

I think that yours is a clever solution Andy. Clearly, the factory rear spar is adequate size-wise - you just have to make sure it ends up in the correct place. We went with a SLIGHTLY larger rear spar (couldn't find 2", went with .25" wider than stock) and had plenty of edge distance. We basically had our fuselage complete when we mounted the wings and set incidence, so it would have been inconvenient to set the center section that late.

Either solution is a good option.

Rear Spar Attach Bolts

Unless I am blind, I cannot actually find in the RV-3 plans the Rear Spar Attach Bolt specification's.

The hole is detailed as 1/4" hence AN-4. On the assumption the spec is as for the RV-8, I would conclude:

1. AN4-X Bolt
2. AN310-4 (Castle) Nut
3. Cotter Pin
4. AN960-416(L) Washers as required

I'll update this post if I get better info I could ask Vans, but they are tending to run a mile when they see RV-3 in the subject line

RV-3B Rear Spar

I'm about to start the wing construction, then I saw the thread, regarding the rear spar attach hole issue.
I'm not sure whether I understood the whole subject. For me it will be impossible to adjust the fuselage spar to the rear wing spar with the mounted wing because my shop is too small (maybe some kind of template or "dimension-dummy" might work).
What do you mean with a 2" larger spar? Does it mean to enlarge the W-306B and W-306C in the way, I marked with red in the picture below?



The provided 0.125 sheets are slightly longer but the width is exactly as wide as shown in the drawing. Are these the parts to re-order for 40$, Rob Holmes http://www.myrv3.com/Fuselage.html mentioned?



By the way, I spotted another issue regarding the sandwiched W-306D. The provided bars are not as wide as the drawing calls for, creating another minimum edge distance issue when placing the rivets according to the plans (o.k. I know it's an RV-3 ). I'll open another thread later.

Peter

The 2" bar recommendation applies to the rear spar carry-through in the fuselage, not the parts on the wing spar.

If you read Andy's OP carefully, he describes a process where that fuselage part is installed last. The stock part is shown on Drawing 21, View E-E.

I think he located the slots that goes through with a jig; I know another builder used a jig for that assembly too.

Dave

Ok, now I finally understand.
Because I'm so busy with the wing spars, I thought it regards these.
Nevertheless I'll write another thread for the W-306D

Peter

Rear Spar Edge Distance

I could not proper edge distance on the rear spar attach points on my RV-4. I drilled out the two, rear fuselage spars and replaced them with 1 3/4" pieces and drilled of the spar attach bars on the rear of the wings with 2" pieces. I had no trouble with edge distance after setting proper incidence and sweep.