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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Replies to This Discussion

In other posts on this blog, you suggest that you are favoring adding CH650-like L-angles to the 601XL's. You also state that you are concerned about wing strength if wing lockers are present. So, a relevant question is, "Might not the stringers add sufficient strength to compensate for wing locker cutout at about the same weight penalty as the L-angles?"

May I respectfully request that you ask Chris Heintz whether adding Z-angle stringers as shown in the photo would increase or decrease the strength of the wing considering the loads for conditions A, C, and D? It is my impression that stringers are very commonly used to increase the strength of wing panels in aircraft. See, e.g., Airframe Structural Design by Michael Niu, p. 147.
I am waiting for an answer from Chris on this.
Thanks, Mat!
Chris Heintz is not recommending that the rib be cut out as shown in the above photo as the load tests were not done to that. With aircraft that have more ribs, it is a good idea. Adding an angle from the Z-angle stringer to the rib would be good as to prevent bucking of the rib in the cut-out area.
Thanks, Mat.

I appreciate you asking Chris the question. I think I'll pass on the stringers.
while performing the up grades would it be advisable to upgrade the 601 wing to the 650 by install the span wise angle brace between the ribs.
Yes, I think we will be adding the angle braces ("L" angles) to the upgrade kit. We had done this as a marketing tool for the AMD SLSA aircraft as a few pilots questioned the skins bubbling between the ribs in flight.
Here are my concerns-
Even the best craftsman will not remove all rivits without having some or many damaged holes.
Not all builders(myself included)may not be capable of reinstalling solid rivits properly.
Now in addition to the 4 draft sheets, you are giving us MORE upgrades- elevator trim area and aileron trim area-"L" angles
between wing ribs-damper spring on elevator cable.
When will the upgrades end?
You also say hold off starting until drawings are available====Two to Three Months!
I think most builders and owners of completed planes would like to get the extra work completed.

Please comment on these items
Fred Schutt
Frederick -- Matt said: "We hope to have the upgrade drawings 100% finished next week."

You did not differentiate between the "upgrade" adjective and the later sentence discussing the "update" of the formal 650 drawings.

Personally, I think they are doing a darn good job and I certainly appreciate the open discussion on this forum. -- FJD
Thanks for the positive comment. We all need more of that.
You are correct. when installing the new solid rivets in the upper spar caps, it is important that the holes are not too big. If the holes are too big, you either go to the next size solid rivet or bolt. If you are bolting, bolt needs to be a snug fit. Zenith Aircraft has posted a simple method of removing the solid rivets without drilling the hole. blog part 3.

It is great that you want to start. If you can keep up with the Zenith upgrade, that is excellent. The drawings should be finalized early next week.
Hi Mathieu
Thankyou for putting an approximate time frame on the final drawings. I'm sure this is a question that many have been pondering. I for one appreciate the thoroughness of your answers and I'm sure many others think the same.

Phill Barnes


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