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Thread: CH 750 WOW!!!

  1. #16
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    Re: CH 750 WOW!!!

    The VGs in pic 3 are on the LE of the elevator.. Designed to be inside the hinge gap and out of the airflow at cruise, and exposed to the airflow at full up elevator. This was developed by stolspeed and recommended to Zenith. JG recommends building a tailplane with a symmetrical airfoil similar to the Savannah if you are building from scratch, but I don't think Zenith will support you on that. The VGs aren't needed on Savannahs.

    I like the idea of the adjustable seats... The more I look at this thing, the more I want to buy the plans! I'm even beginning to think I don't need to design my own aircraft to get the performance I want... This will come close enough.

  2. #17
    Registered User Joe Kidd's Avatar
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    Re: CH 750 WOW!!!

    Divad,

    I've got to agree with you on this design becoming more intresting the more one thinks about it. The 100MPH speed is a negative trade off but then again maybe not because airfoil changes are very possible should someone feel the need. The aspect I like most though is the ability to use more engines in this platform then were recommended in the 701. Time will tell.

  3. #18
    Registered User Kmccune's Avatar
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    Re: CH 750 WOW!!!

    More speed can be had, or better fuel economy, you choose. Just don't put on the slats. Before anyone jumps on me read the following pages.

    http://www.stolspeed.com/
    http://www.zenithair.com/stolch801/d...vg-design.html

    I have spoken with people who has done this and they completely back up JG claims. If your thinking of the 701, putting fairings ect.. on will clean it up enough for 100mph fast cruise too, still with the slats.

    I may build the slats, but not install them, just for resale.


    Kevin

  4. #19
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    Re: CH 750 WOW!!!

    I won't bother with building the slats... According to most of the builder's logs I've read, they are one of the most fiddly parts of the whole build, and require quite a bit of preparation before construction (ie: the press box for forming and fitting the skin).

    I'm still umm-ing and ahh-ing over whether to change the LE profile to match that of the Savannah VG. JG says it doesn't make a lot of difference to the way it flies and that people who have retro fitted it to existing aircraft have regretted it for the cost and effort. However, it does look better IMO than having the big blunt LE, and because I'll be building from scratch it wouldn't be too much extra work to implement it from the word go...

  5. #20
    Registered User Kmccune's Avatar
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    Re: CH 750 WOW!!!

    One thing to consider is that removing the slats does not effect the trim...CG But if you are not careful with the LE shape you could increase the cord and CG. I know sounds obvious, just be careful. Didn't JG have some neg comments about the Savannah VG wing, compared to a standard Savannah wing?

    Keivn

  6. #21
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    Re: CH 750 WOW!!!

    Not negative comments... Indifferent comments. As I said earlier, he said that builders who have retro-fitted the LE kits to their existing Savannahs have regretted the expense and effort for the particularly minor (almost non-existant) change in performance..

    The main reason I would do it is for the aesthetics.

    As for CG changes... With a modification like that, I would put particular emphasis on doing the maths to make sure its right before flight.

  7. #22
    Registered User Kmccune's Avatar
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    Re: CH 750 WOW!!!

    Sorry I guess negative was a little strong.

    I keep going back and forth on the slats, they weigh something like 11 or 14 lbs and a real pain to make. But they are a part of its "attractiveness"
    But the added idiosyncrasies,additional drag and low glide ratio sure are big motivators. The designer Chris H does not care from an engineering standpoint, but I wounder about a low time pilot flying a homebuilt that has modified wings... will I be able to get ANY insurance?

    Kevin

  8. #23
    Registered User Rhino's Avatar
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    Re: CH 750 WOW!!!

    Quote Originally Posted by Kmccune View Post
    Nope, the Zenith airframes are designed for continuous out door storage. The Canadian distributor has his 701 that he instructs in, tied out side all year long.
    Which means I'd still have to pay tiedown fees, like I said. The only reason I'd maybe consider a hangar is for the longevity of the paint job. But since an aircraft with foldable wings would be stored in my workshop, the comparison with hangar costs is valid. Either way, I'd still have to pay fees I'd rather not pay.
    Last edited by Rhino; August 11th, 2008 at 04:01 PM.
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  9. #24
    Registered User Kmccune's Avatar
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    Re: CH 750 WOW!!!

    Mine is going right beside my garage. If its not possible in your yard, maybe a friends yard. This is one of big the things that attracted me to the 701,I don't have to go to the airport.

    Kevin

  10. #25
    Registered User BSwift's Avatar
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    Re: CH 750 WOW!!!

    Interesting discussion. I've got the 750 spec sheet in front of me. Each of the pro's and con's for the 701/750 lead me towards the 701. The trade off for more engines/higher gph/more cargo area is where to keep it. The folding wings and low fuel burn is a long term positive for me. The slats just seem to be a big challenge but likely perform as claimed. The VG's are a interesting departure and if properly installed will provide nearly the same slow speed performance.
    BTW, fuel just hit $3.39 locally today. $.50 drop in 14 days.
    Dirtbikes and Airplanes, money to be spent, fun to be had!
    Brian

  11. #26
    Registered User Kmccune's Avatar
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    Re: CH 750 WOW!!!

    For me the VNE, Gross weight, and cabin volume/windows are the big deal that should have been addressed with the 701 instead of the 750. The Savannah (701 copy .. let the flames start) has a gross weight of 1230lbs and it uses the older non SP 701 wings. I do commend Zenith for doing it right. But mine may just be listed a bit higher then 1150lbs as I have a copy of the update published by ICP to increase the Savannah gross to 1230lbs. The windows are easy to install in the 701 baggage area, though the seats are not possible to duplicate. The engine for me is a standard Raven SVS1300 or a Corvair with a new forged crank and a 5th bearing. I probably will go with VGs, due to fuel burn. But over all, the cabin windows are its best feature for me.

    Kevin

  12. #27
    Registered User Rhino's Avatar
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    Re: CH 750 WOW!!!

    I've got two acres, so it would easily fit in the yard. But I don't have a runway. There is a field behind my house that my next door neighbor would likely let me use, but I'd prefer to have some proficiency in the aircraft before I attempted off airport STOL takeoffs and landings. My wife prefers the Zodiac, so I'm still not certain which aircraft I'll eventually build. Every time I think I have my mind made up, something new comes along to change it.
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  13. #28
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    Re: CH 750 WOW!!!

    I was thinking about the Zodiac a few weeks ago, until Orion pointed out the mysterious "wing fold" accidents that have been plagueing the type in the last couple of years. I had a bit of a look at how unsubstantial the mainspar is compared to other types in similar configuration (low wing, cantilevered, ultralight/light GA). Two examples of this comparison are the RV-12 and the sonex. Both of these types have the spar roots crossing right over each other inside the fuselage and bolted or pinned to each other at each end. I hope that makes sense. Watch the RV-12 assembly video on their website to see what I mean.

    I was holding a completed sonex mainspar not 4 days ago, and I was very impressed with the sparcap that they use. It is a solid aluminium "T" section, about 1/4" thick, 1" tall, and 2"wide at the root tapering to 1/4" at the tip. The top of the "T" is shaped to fit the airfoil.

    The Zodiac spar on the other hand looks (to me) more like it SHOULD be strut braced, not cantilevered. There is a center spar section about 4' wide running through the fuselage, and each mainspar is attached to the end of this with about 3" crossover, and retained by 6 3/8" bolts with nyloc nuts. Thats a lot of leverage on such a small area. And as for spar caps... All it has is strips of (about, IIRC) 3/4" X 3/16" allu strips running front and back, top and bottom of the spar web. It may only be front actually, with a strip of "L" angle on the back (3/4"x3/4"x1/8" thick) to support the skin. Not much there to stop the spar from buckling under load in my opinion.

    I think if I was going to pursue the idea of building a low wing light sport aircraft (I've now made a firm decision to go for a STOL type though) I would go for a sonex. I don't like the look of the canopy on a sonex, but it IS a very sound design structurally as far as I can tell. I would certainly feel safe in it.

    As for strut braced Zenith high wing aircraft, I can't find any instances of the wings falling off unexpectedly in level flight in searches on the net...

  14. #29
    river1
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    Exclamation Re: CH 750 WOW!!!

    Divad , another thing to consider ; the 600 series is much older than the 701 . The 600 , 601hd , hds and hd/ul none had the wing "problem" . Go to www.zenair.org the newsletter is now available in CD .

    PR

  15. #30
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    Re: CH 750 WOW!!!

    Yeah, I was aware of that the only model with the issue was the XL. I will bite my tounge now though and point out that I did say "was" in that last sentence. I've just noticed on the zenith site that the 750 isn't the only new aircraft in the line-up.. The 601 is noticeable by its absence. The CH-650 has taken its place. Not much info available at this stage, but from what I can see from the 3-views, there is no longer any forward sweep in the mainspar... This could well be the answer to the 601XL's problem.

    In the older design, the foward sweep on the spar was facilitated by leaning the spar forward somewhat. I've gone over this in another topic elsewhere (My design concept... and the previous page) Without the sweep, it doesn't need to lean forward. Therefore the load is a bit more linear, if that makes sense.

    I don't know if they've beefed up the spar at all... not enough info available yet.

    I'm still going to build a STOL aircraft though, and right now, the 750 is at the top of my list...

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