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Thanks for your reply, Paul.
Some comments below in context... "Paul Saccani" wrote in message ... On Sat, 24 Sep 2011 11:27:57 +1000, "Jeff R." wrote: I'm inclined to trust Chris Heintz, as the engineer/innovator, but at the same time he has (had - he's retired) a significant financial attachment to L.E. slats. Not just on the 701, but right up to th 850. Depends on your mission. The STOL performance of the 701 is such that most don't even need to use the flaps. The slats do dramatically steepen approach and departure, and if that's what you need.... Not so much need as "want". Catch is, I also "want" a decent glide slope and fuel economy. (yes, I know) I would note that unlike what CH states, the slatted wing does not act as though the chord is from the TE to the front of the slat, but rather, from the TE to the front of the wing. Which, if you look at the allowable %MAC for weight and balance, which uses the CH interpretation, those percentages are a little unusual compared with "regular" aeroplanes. Remeasure, using the front of the wing instead of the slat, and the %MAC values fall straight into the usual range. Thanks for that. I'd suspected as such, based partly on how well the de-slatted 701s seemed to perform. On balance, I'm inclined to favour VGs (Piper Cub didn't need slats), but I'm put off Savannah just simply because of their unethical poaching of CH's designs. They didn't poach a CH design. They made a slavish copy of a legitimate 701 cousin design by Max Tudesco, who has had a long involvement with CH's companies, and was involved in the design of the 701. He didn't like some aspects of the design and went his own way, whilst also making licensed quick build kits of the 701. The scummy Italian company was buying quick build kits from his company, and simply measured one for CNC copies to be made. They are actually more unethical than your first thoughts. Hehe International intrigue'n'all. I plan to cut the first stringers in about a year from now. As I recall, the stringers are all in the forward cabin, and all need solid rivets. You may find it worthwhile to buy those and the main spars from Zenith, with the solid riveting done. If you intend to build as per the edition 5, 7th revision, you will find that some items, such as the spar caps, are non-standard custom extrusions for Zenith. They will sell you a spar complete, but not the components to make the main spar. Still not decided on full kit or build from plans. I rather fancy myself at metalwork, but the cost of the raw materials makes the CNC cut kit awfully attractive. Now, if the US dollar would just oblige my falling down again... Personally, I'm happier using the slightly thicker alternative... Maybe I could build retractable slats? (joke) Well, it has been done, but the company was bought out, I'm not sure if they are in production again. PegaSTOL was the old company. Yup. Saw that, and like the idea (lots) but the weight? Most people don't know this, but at one time (late eighties), CH was recommending that some CH701 use VGs attached to the slat! ! Seems a bit greedy. I take it that didn't work... (?) What you lose if you use VG instead of slats, besides the steepness of approach and departure, is the "stall" controllability. With the slatted 701, you can go way on the wrong side of the lift/drag curve, so you no longer have enough lift to stay up, but aileron remains effective and there is no wing drop. It just gets "mushy". Sans slats, with VG, you get a conventional stall, and wing drop. Nothing nasty, but a little faster, with a little less control. Yes, and this is the main reason I'd like to retain the slats. Now, the slats are great, but there is an awful lot of drag, and you end up with an engine out glide ratio about the same as a helicopter, 4:1. It'll cost you fuel to haul their weight around, and fuel to counter their drag. IIRC, they weigh around 12 kg. 12kg. Hnh. I have main courses at dinner bigger than that. (anecdote edited for the sake of propriety) Still, the drag is a real bummer. I still don't know how much long distance stuff I'll be doing - I hope a lot - but then I suspect that good STOL will also be a significant factor in my dream "trip-around-Australia". Endurance - economy - STOL? Helluva balancing act. Having said that, I'm leaving mine on for the moment. With an EA81 and a 68" 3 blade warp drive at 16.5°, mine does 70 kts @ 13 litres an hour, @4,000 RPM for the engine, 1,820 RPM for the prop. Hmmm. None too shabby. 75hp? That enough for good STOL two-up? How's the rate of climb? In due course, I plan to fair my struts, but you could order the strut material for the 750, which is in an aerofoil shape, and save yourself a lot of bother. Fair them rather than remove them? Do you need the extra square feet, considering what you said above about the slat's contribution to total chord? VG for the elevator is a very good idea - you can get those from Zenair. I'm thinking of removing the slats and the entire mixer system and control for the flaps. If you look at the skyfox versus the kitfox, they removed the mixer system entirely - at CASAs request - and performance was still satisfactory. If you look at the 750 mixer, you will see that it is a much more elegant design. As I say, I am contemplating deleting the 701 mixer, but if I decide that flap is still necessary, I will install a 750 style mixer, which is far more elegant and lighter too. Also, having the elevator bell crank bracket on the aileron torque tube sucks. I have a part 35 engineered solution, where the bracket is mounted on a fitting that is fixed to the airframe, and allows the torque tube to rotate inside it. This gets rid of the elevator cable tension issue, where the aileron and elevator interfere with each other. Thanks again for all that Paul. It's good to toss this stuff around. (just had a quick look at your page at Zenith...) -- Jeff R. -- Cheers, Paul Saccani Perth, Western Australia. |
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