This Q&A is now closed and replaced with a new Q&A based on the latest upgrade drawings at

To all 601XL and 650 builders and aircraft owners. If you have a specific question regarding the upgrade, post it here and I will consult with Chris Heintz so that we can give you the best possible answer. Please be specific about your questions.

When posting a question or replying to an existing comment, PLEASE add it to end of the last page.

Zenith Aircraft is upgrading its 601 XL, so a lot of questions are answered on the step-by-step Blog Posts on this main page.

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Reply to Eric,
As an Aerospace Engineer involved in the design of airplane and missile parts, we had an often used expression, "every solution has it's problems", and it was generally true. You make the best decisions you can based on the available information using the best technology accessible and the problems will be minimized. I would like to think this is what Zenith has done and as a result, any residual problems encountered should be very minimal. We need to move forward because the existing "problem" is unacceptable. The folks at Zenith have a lot at stake and are doing their very best. The problem may simply be a slightly greater empty weight.
Hi Mathieu

When I built my XL I dimpled the wing skins and most of the fuselage.

Will it be acceptable for me to countersink the top of the L angle doubler that attachs to the top of the wing spar so that my wing skins can sit flat against this surface?

Eddie Seve
Yes, there is no problem to countersink the top "L" extrusion since it is 1/8" aluminum.
Good question. The only item that could affect the way the aircraft flies is the UK LAA aileron counter balance weight modification. We are using this modification as the LAA did flight test the aircraft with it installed. The German flutter specialist did confirm to us that there is no increase in potential flutter with the upgrade kit. As a general rule, the stiffer you make the aircraft, the less it is prone to vibrations / flutter.
I am building the CH 650 from a kit. I am ready to start on the wings, so I am in a good position to incorporate the upgrades. It appears that a few items you are specifying for the 601XL are already in the original 650 kit. It also appears that the upgrades are mainly pointed toward reworking the 601XL.

(1) Will there be two upgrade kits? One for the 601 and one for the 650?

(2) Will photos, videos, and detailed instructions be supplied with the kit? It looks like I will have to mark up my original plans very carefully so that I don't put something in that has to be replaced (unless revised 650 plan sheets will be available soon.

(3) I have seen comments about adding reinforcing around servos, etc. I assume these will be added to the final drawings (maybe sheet #5 ?).

Jim Snyder
CH 650
Will the solid rivets, AN bolts, NAS bolts, A5, AS5 rivets, etc. be included with the kit?
I need to order a partial kit, I will be fabricating many of the parts myself. Please post a parts list with cost of each item.

Bob Reinero
San Diego CA.

I scratch built the stuff and it isn't worth it we have about $600 in it now and that doesn't include hardware so you will be much better off just buying the stuff from Zenith. They have to be in the red on these parts and I think we all owe them a huge thank you. It isn't many companies in avation that would do what they have done. Most parts you buy that need a required upgrade in avation will get you racked over the coals.

Leaving the airport now
I am stopping the Q&A and replacing it with a new one, based on the latest upgrade drawings of Nov. 24, 2009: We've updated the draft Drawings 6-ZU-1, 6-ZU-2, 6-ZU-3 and 6-ZU-4, and LAA Aileron Balance.
Thank you for all your excellent comments.
Mathieu Heintz
After talking to Roger about solid Rivets and the different ways to extract them without damaging the hole I have found a almost mistake free way to remove them. I will post the video I made of it on here tonight.

One Note: Everyone in the forum or building a airplane has a local EAA chaptor near you and if you go visit them they will guide you to someone that has a 4X rivet gun so don't be scared of the driven rivets. In 10 mins with the proper teacher you will be a pro at it. To rivet the wing spar back together takes about 30 mins and you will see after watching the video I will upload that you can do it.



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