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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.