Online Community of Zenith Builders and Flyers
CH-750 STOL -> CH-750 Cruzer has the same wing structure behind the spar. The difference is the short front rib and slat vs a longer front rib.
So for the CH-750 Super Duty minimum conversion to Cruzer seems like using CH-750 Cruzer front ribs and a fresh leading edge skin, unless the holes somehow line up for existing skins from Cruzer. I am assuming that rib thickness (of material) from CH-750 STOL -> CH-750 Super Duty is the same.
Possible issues: Center of lift/CG and tail differences.
Tail span seems similar between the two, however, the STOL tail should be more effective. I would assume this causes no issues.
W&B for Cruzer is 18-32% of MAC or 1510mm +/- 15. (270 to 480 from leading edge)
W&B for STOL is 19-34% of MAC or 1480mm +/- 15. (280 to 500 from leading slat)
This makes me think the lifting moment is similar and possibly a difference in the chord. Careful testing of CG range would yield a safe aircraft.
The more I read about slats vs good VGs, I see that there is a slight improvement in STOL with slats, but at the cause of overall drag. I really wonder about increased safety when a better L/D could allow you to make a field with a slightly cleaner Cruzer style but land a knot or two faster rather than possibly not make it with a STOL slat wing.
Cruzer is a single strut with more ribs vs a jury strut with fewer ribs. There are significant differences in tail both in vert stab/ rudder & horozonal stab and elevator between the two. The amount of control authority difference and you would have to balance this from aerodynamic and CG or things could go badly wrong. To enhance my Cruzer for STOL activities I added VGs everywhere, bigger taller gear, nose gear spring, bigger tires and brakes and an electrically adjustable pitch prop, but left the wing and tail alone aside from the VG's. Thre is a lot of engineering in the combination of things and Zenith may very well make an SD Cruzer eventually. The struts and the Tail are the biggest drag improvements on the Cruzer, and they added counterweights to prevent flutter. If you are going to mess with it understand all the engineering that went into it before you mix and match and assume it will just work.
Great. This is the type of information I was hoping to get. It is hard to dive into this without buying up plans. Thanks for the detailed response. I do hope Zenith does the leg work for the SD Cruzer.
A SD Cruzer would be great! ...and oh I hope if there is any chance for a SD Cruzer coming out in the future they let potential buyers know so they can make an informed choice on which model to buy. I say this from experience with another kit plane manufacturer who kept their new model secret. They came out with a new (improved) model 3 months after I sunk big $$ into their current kit......ugh. Sure wish they had shared that!
Yeah, I'm worried about the same thing. But looking at 2 years out for build start or buy currently. How clean can the STOL tail be modded, etc. If I had to pull the trigger today, I think I would build stock and make fences if removing the Slats to make it look better but keep both options.
Zenith is very deliberate and takes its time in releasing new products. There is no reason to add a new kit type unless they find they can't sell as many of the current kits that they can build, or will have a higher profit margin on what they build. I think they are months of lead time right now which means there is no room in their production schedule to release a new kit. I don't think you are going to see it released any time soon, so holding up your purchasing decision based on that possibility may leave you not building for a long while.
That isn't the only factor in balance. The choice gets harder when the RV-15 is available to build. As someone who is getting back current, but flew only taildraggers, for the most part, I would love it. The advantage of Zenith at that point is lower insurance for tri-gear and a simpler build, but not as much as other RVs if they stay with pulled rivets.
I'm 2 years out from a build, so we will see how things go.
In looking through more on these, I still think there are gains to be had with only modifying the front ribs and skinning the front as if you filled in the gap of the slat. However, the time spent in this part of the build would probably take a LONG time to recoup in the better cruise speed you gain with the dual struts and jury struts still helping with drag. If the ribs from the Cruzer fit the airfoil the same, then the work may not be as extensive, but not having pre-drilled skins would still be a bit of work.