I just bought CH 701 built in 1995 and an upgrade set of plans, would someone know what needs to be improved on the airframe to bring it up to acceptable. My registration is showing max gross at 1040 and the plans are showing 900 lbs.

Thank you for any assistance

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Michel, My understanding is that it can be done but is a lot of work to bring an older 701 up to the current SP standard with a GWT of 1100 lbs. There have been minor tweaks over the years to just about every area of the 701 airframe. Basically, you will end up doing something to just about every major component.

If there are no major structural issues at this time and you are just looking for the increased capacity, you might want to tackle it one upgrade at a time. I don't know if there have been any upgrades in the rudder but I know for sure there are new H-stab mounts called out. I expect there are some changes internal to the wings. There was an improvemnt in the C channel that goes between the rear spar mounts. I think there was a thickness increase in the upper channel on the firewall (could be wrong on this one). You get the idea. You will end up completely building the plane over again to do the upgrades all at once.

Hope this little bit of information is of help.

Doug MacDonald
CH-701 Scratch Builder
NW Ontario, Canada
Thank you very Doug

Will look in the major issues

Salut Michel,

I have the older plans and a set of newer ones. I would say that materiel Thickness is mostly what changed.
This is mainly due to increased weight/power of the engines used to move the 701's. Doug is right, there was a thickness increase in the rear channel that goes between the rear spar (cabin top). Heck, there was a modification to ADD another part there (shaped as a 'Z') to make this thing stronger. Also the upper channel in front that holds the TOP of the gear leg was always too flimsy. With a Subaru just hanging in there that part was buckling !

If I were you , I would look up the differences between both sets of plans and decide which mods to do.

Keep in mind that some of those mods are for people that go over GROSS WEIGHT with their 701's which might not be your case (that would never happen - right ???).

Keep us posted.


As you have the plans you should be able to register and enter the builders sections on the ZAC website.
Look for plans updates and print out the rev-4 update listing of the 40 material changes made to the wing structure and wing attach structure, mostly.
The original had a gross of 880 lbs and required engines 45-85 hp up to 130lbs wt.
Your build most likely is a 960lbs gross. That version met the design rules with up to 100 hp and was routinely fitted with the 912 80hp powerplant. Higher weights are flown as experimentals with amended operating limitations rather than 'advanced ultralights' to which they were designed.
The 1100 lbs spec allows 100 hp with 200 lbs total powerplant intallation wt. whilst meeting the design rules. There are many builds with heavier and more powerful engines that are flown as experimentals, or an alternate class appropriate to the country.
The more recent change to the H.Stab brackets thickness is only an issue with the 912S engine intsallations, which shake at startup and shutdown a lot more, cracking the brackets.

If you can live with the lower payload & fuel limitations, it would be easier to stick with your original airframe and just fit the better H stab brackets which require de skinning the stab to acomplish.



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