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psm(at)att.net
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 Posted: Mon Jun 15, 2009 4:08 am Post subject: Kit plane design safety. |
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Hi Jay,
I think you have made a very important point here and I want to
amplify it. Kit planes, and E-AB certified planes in general, give
builders the option to have Spartan interiors, instrumentation, and
paint jobs to keep the initial flying cost minimal. This type of
choice should not have a negative impact on flight safety. We can
also use inexpensive engines which do have some impact on flight
safety, but even this freedom should not lead to structural failures.
I believe kit plane designs should be stronger and safer than
certified planes rather than weaker and less safe. There is nobody
who disagrees with this notion when considering designs intended for
aerobatics. I don't see why anyone would be happy to accept a design
that is so delicate that a little rough air will make the wings fall off.
The Zodiac is designed to similar limits as Normal and possibly
Utility category certified planes. This kind of strength is adequate
for all but the most violent weather when flown as a normal airplane
rather than as an air show performer. In addition, the Zodiac is
designed to be built by first time builders. Hopefully, that means
there is a certain amount of "Fudge factor" built into the design to
allow for differences from one plane to another and one skill level
of builder to another..
When a knowledgeable person like Rick admits the Zodiac is not really
safe in marginal weather conditions (as opposed to flying through
thunderstorms) I think he is really saying the design is
deficient. Any plane that can only be flown on smooth days without
risking structural failure doesn't even come close to having a safe design.
Because the Zodiac is a light sport aircraft it has certain weather
related limits that simply cannot be exceeded without risking big
problems. The most obvious of these is the crosswind capability of
the plane. The common rule of thumb for crosswind ability of any
airplane is 1/3 of the stall speed in the flight configuration being
used. Since LSA have very low stall speeds that means they also have
very low crosswind capabilities. Of course the penalty for exceeding
this limit probably extends to landing and taxiing accidents that are
unlikely to include serious injuries to occupants. Industry wide
accident statistics suggest LSA are more difficult to land than
heavier planes - especially for pilots new to this class of
planes. Transition training is a serious issue here. My own
experience is that approach speeds and roundout speeds need to be
considerably higher, based on stall speed, than for heavier
planes. On the one LSA I am experienced with (Tecnam Echo) a final
approach speed of at least 1.3 times VS works well while heavier
planes call for an initial approach speed of 1.3 times VS and slower
final approach speeds.
The Zodiac is designed as a cross country airplane. If it is not
safe to operate unless the air is completely smooth then it would be
very difficult for it to complete any long distance trips. The design
load limits are similar to certified planes of this genre, so the
plane should survive normal use just as the certified planes do.
Paul
XL grounded
At 04:13 AM 6/15/2009, you wrote:
| Quote: | assuming that the Zodiac
need not be as safe as certificated aircraft is highly destructive,
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d.goddard(at)ns.sympatico
Guest
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| Posted: Mon Jun 15, 2009 4:42 am Post subject: Kit plane design safety. |
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Hi Paul, it's not that I disagree with the sentiment but you know this
wording is going to generate another sh**storm from people who cannot
separate their aircraft from their ego. I think the XL is probably OK as is,
although it appears that aspects of it could be improved. Old news now
anyway. Zeenith has moved on to the 650, which so far has not had issues.
| Quote: | I believe kit plane designs should be stronger and safer than certified
planes rather than weaker and less safe. There is nobody who disagrees
with this notion when considering designs intended for aerobatics. I
don't see why anyone would be happy to accept a design that is so delicate
that a little rough air will make the wings fall off.
|
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tigerrick(at)mindspring.c
Guest
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| Posted: Mon Jun 15, 2009 5:40 am Post subject: Kit plane design safety. |
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I agree with you, Dave. I certainly wouldn't turn up my nose at a factory approved retrofit that beefs up the center spar and wing attachments. Even though the airframe still fully meets the design spec for negative G loading, a little extra margin certainly wouldn't hurt the confidence factor. I'm looking forward to the UK results, as posted by Clive.
As for "...going to generate another sh**storm from people who cannot
| Quote: | separate their aircraft from their ego."
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Et tu, Brutus? 
Rick Lindstrom
N42KP
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bryanmmartin
Joined: 10 Jan 2006
Posts: 1018
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| Posted: Mon Jun 15, 2009 7:50 am Post subject: Kit plane design safety. |
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On my way from Michigan to Sun'N'Fun this year, I ran into some
turbulence south of Knoxville that was so severe that I almost thought
it would knock the fillings out of my teeth. Holding altitude was
impossible, all I could do was slow down and ride it out and try to
find smoother air. If I hadn't had my seat belt pulled tight, I would
have been bouncing off the canopy. It wasn't much fun, but got through
it OK and so did the airplane. I found no damage to the airframe after
the flight.
If I had been flying a King Air, It probably would have been
considered light to moderate turbulence. In an LSA class airplane like
the Zodiac, I would call it severe turbulence. You have to realize
that an LSA is not going to handle weather as well as most normal
category aircraft can because, most normal category aircraft are much
heavier and have higher wing loading than an LSA.
I don't believe the Zodiac is unsafe in marginal weather, but you do
have to respect its limitations and the pilot has to have the
necessary skills and experience. I would not consider a Zenith an
ideal IFR airplane, but then, it wasn't intended for that.
I have found that the Zodiac has better crosswind landing capability
than the Cessnas I have flown previously. This is due to the all
flying rudder. I have found that I can fly the airplane crabbed into
the wind all the way down into ground effect and kick out the crab
just before touchdown.
| Quote: |
Hi Jay,
I believe kit plane designs should be stronger and safer than
certified planes rather than weaker and less safe. There is nobody
who disagrees with this notion when considering designs intended for
aerobatics. I don't see why anyone would be happy to accept a
design that is so delicate that a little rough air will make the
wings fall off.
When a knowledgeable person like Rick admits the Zodiac is not
really safe in marginal weather conditions (as opposed to flying
through thunderstorms) I think he is really saying the design is
deficient. Any plane that can only be flown on smooth days without
risking structural failure doesn't even come close to having a safe
design.
Because the Zodiac is a light sport aircraft it has certain weather
related limits that simply cannot be exceeded without risking big
problems. The most obvious of these is the crosswind capability of
the plane. The common rule of thumb for crosswind ability of any
airplane is 1/3 of the stall speed in the flight configuration being
used. Since LSA have very low stall speeds that means they also
have very low crosswind capabilities.
|
--
Bryan Martin
N61BM, CH 601 XL,
RAM Subaru, Stratus redrive.
do not archive.
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_________________
--
Bryan Martin
N61BM, CH 601 XL, Stratus Subaru.
do not archive. |
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Juan Vega Jr
Joined: 13 Jan 2009
Posts: 157
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| Posted: Mon Jun 15, 2009 8:10 am Post subject: Kit plane design safety. |
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To look at it even more simply,
would you fly a piper cub or a cessna 170 in weather fit for a c-90? i think not. I would not fly the zodiac I wouldnt fly a 170 or a cub into. ZFit the tool to the situation.
JUan
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