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--- J H Webb <airmale@bright.net> wrote:
Dave
you should be improving the airplane that you
are testing not just writing scary stories.
Jack, I'm just reporting the facts of my flight test. I am surprised that a experience test pilot like yourself would take such offense to flight test results/facts.
Jack sez:
Aerobatics are fun but good
handling qualities are built in or added in flight test. I have
evaluated many vortex generator kits and discovered that if you have a
problem that cannot be improved by another means consider vortex generators
but keep in mind that if you put rivets, probes, or any thing that
protrudes on an airplane, if goes slower. Most of the heavily
advertised 'lower stall speed kits' take at least 5 knots off the cruise
speed.
Changing the angle of incident or flow strips
will improve low speed handling and stalls with little or no impact
on the cruise speed.
Dave replies:
I wasn't doing flight test for a major manufacturer. We didn't have an unlimited budget. We didn't have the opportunity to cutup the plane and glue anything in place. I'm not even talking about "lowering the stall speed", frankly, I just would like the airplanes to have a more effective spin recovery. Glasair had some similiar issues and came out with a larger rudder kit for it's earlier airplanes. It doubt they would "take at least 5 knots off the cruise speed". I normally cruise around 10,000 and 55% - 65%. The 5 knot impact more probably would be seen in top speed (1000' and 99% power). When Van's converted the RV-6 taildragger to the RV-6A trigear, they saw a loss of cruise speed of less the 5mph. Even so, if a fix was found that could be proved to vastly improve the spin recovery characterisitcs of the Lancair ES's or IV's and only cost 4 knots cruise, who whouldn't take that trade?
Jack:
In answer to your question, a rolloff is an
uncontrollable roll against full opposite aileron and rudder. If a
rolloff starts it is time to recover to avoid departures or spin entries.
Dave:
That's what I encountered. When I tried to recover, the plane continued to spin 3 revolutions.
Jack:
With reference to pitchups these have occurred
at CG's other that full aft, but they are far more common at the aft
limit of the CG range. these are not necessarily only uncommanded
in the sense of an abrupt rapid pitch up but gradual loss of ability to
pitch the nose down to the point that the nose is slowly pitching up and
full down elevator will not arrest it. We did deep stall tests and
achieved angle of attacks up to 65 degrees. These were power on stalls
and interestingly this caused rates of sink up to 3500 feet per minute
with full power at gross weight and aft CG..
Dave:
That's interesting, again, I bet you set the aft cg limit somewhat forward of where you encountered these uncontrollable situations. The F-4's I flew had a similiar characteristic called "Mach Tuck", but none of this is really relative to the subject.
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