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1. 06:52 AM - Re: Slats (ejessee)
2. 03:48 PM - Re: Re: Slats (JC Gilpin)
Message 1
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Thank you for your replies. At this moment, my 701 is advertised for sale, but
I will be damned if I will give her away. As time passes and I think about the
safety record of the 701 and 912 engine AND the hassle of selling AND the hassle
of buying another plane, I am beginning to question my decision to sell.
I wanted to get more of a "cruiser". My slat removal thoughts came from my trying
to figure out how to "have my cake and eat it too".
Thanks again.
--------
Ernest Jessee
N4931M
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=398801#398801
Message 2
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Gday,
As the guy who sparked of all this slats/no slats controversy, and
manufacturer of VGs, I usually don't post to the forum, in order not to be
thought to be trying to sell VGs. The portion of the VG market that goes
to replacing slats on 701's is so small that it makes no difference at all
to me.
But I do feel a need to balance various opinions with actual experience,
and state some of the facts that I now know by real-life experiment. I
still do have a keen interest in the aerodynamics of all this, and many
hundreds of hours of careful flight testing experience with published
results. There's lots of theory-based, and just plain second-hand, opinion
floating around, but none that I've seen backed by careful real-life test
results. I don't make any claims that aren't backed by numbers from
real-life flight testing.
- I would caution to be careful about just filling in the gaps on the
existing slats. I did try that early on, and didn't like the results, at
least not on the Savannah aircraft that I used. It moved the center of
lift forward, such that it felt like the aircraft was then flying near the
limit of of aft CofG. Very light and sensitive in pitch control, which
feels great but I know it to be a first symptom of an aft CofG..... Also,
the trim had changed, and now needed some nose-down trim to stay balanced,
not a lot but noticeable..... Most 701's seem to start off with a CofG
more toward the forward end of the range than the Savannahs, so this move
could then be beneficial, especially for float-equipped aircraft, but
still, caution advised......
- We have found many times, that removing the slats doesn't change the trim
at all. Which would indicate that the slats don't really provide any
significant lift at cruise attitude. This is contrary to what Zenith and
many books of theory claim, but our real-life testing shows otherwise.
This would also be borne out by flying aircraft with the retractable
slats, such as the Pegastol wing on the 701, and the Helio Courier, both of
which I have some experience. On those aircraft the slats self-deploy as
the aircraft slows to a slow cruise speed. Flying right around this
critical speed causes those slats to deploy and retract intermittently,
sometimes one wing at a time, but this causes no change in pitch of the
aircraft. Which would indicate to me that those slats when deployed aren't
providing any significant lift at cruise either, just lower stall speeds.
- It's not the smaller wing area after removing slats that gives increased
speed, it's removal of all that drag caused by the slats. Even if they're
positioned so there's little flow through the slot (and I don't think that
ideal is really attained in practice), there's still considerable drag due
to all the disrupting edges and gaps. The Savannah 'VG' model, with the
leading edge extended about 65mm to a profile more like the original NACA
65018 from which this wing was originally derived, increased cruise speed
by about 1.5kts, compared to the more blunt leading edge with just the
slats removed. The more blunt leading edge gave a stall speed 2kts lower,
and more gentle.
I've found the 701 to be a really fascinating aircraft to experiment with.
The construction is brilliant - very basic and easy to work with. Various
mods have been very tempting to try, and easy to do, and some gave dramatic
improvements - very satisfying to an experimenter. Hans just got back from
a 40hr flight to Tasmania and back in his much modified 701. Averaged 16.5
litre/hr (4.3 usgal/hr) at cruise speed about 84kts (96mph), fully loaded.
And did STOL landings at a couple of grass strips, one quite short and
behind powerlines. Just the greatest little aircraft for adventure flying!
JG
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