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Quality of kitplane designs?



 
 
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  #1  
Old May 20th 10, 11:52 AM posted to rec.aviation.homebuilt
Oliver Arend
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Posts: 41
Default Quality of kitplane designs?

After reading

http://www.faa.gov/aircraft/gen_av/l...dia/Zodiac.pdf

I'm wondering how much trouble is hidden in other kitplane designs?
Obviously, the RV fleet seems to be rather untroubled, but the others?
How much design work is really going into kit planes? Or is it
eyeballing/judging from experience for the most part?

Oliver
  #2  
Old May 20th 10, 02:49 PM posted to rec.aviation.homebuilt
Ron Wanttaja[_2_]
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Posts: 108
Default Quality of kitplane designs?

Oliver Arend wrote:
After reading

http://www.faa.gov/aircraft/gen_av/l...dia/Zodiac.pdf

I'm wondering how much trouble is hidden in other kitplane designs?
Obviously, the RV fleet seems to be rather untroubled....


Obviously?

http://www.kalinskyconsulting.com/rvproj/nosegear.htm

I've been looking at homebuilt accidents for quite a while now. I got
into it hoping to find, among other things, common threads in accidents
that might indicate design flaws. As it turns out, clear-cut cases are
rare.

One factor is probably the relative scarcity of most homebuilt types,
which reduces the sample size. Its hard to spot trends from ~5
accidents per year for a given type, especially when over half of them
are going to be due to pilot error.

Ron Wanttaja
  #3  
Old May 20th 10, 07:08 PM posted to rec.aviation.homebuilt
Stu Fields
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Posts: 87
Default Quality of kitplane designs?


"Oliver Arend" wrote in message
...
After reading

http://www.faa.gov/aircraft/gen_av/l...dia/Zodiac.pdf

I'm wondering how much trouble is hidden in other kitplane designs?
Obviously, the RV fleet seems to be rather untroubled, but the others?
How much design work is really going into kit planes? Or is it
eyeballing/judging from experience for the most part?

Oliver


Often the designs are performed by well meaning backyard designers that
borrowed a design from another ship that they saw flying and assumed it to
be good. In fact a noticeable test for reliability has been noticed
occurring so often that I've coined an ancronym for it: NHFY. None Have
Failed Yet. That is exactly the statement I've heard when reliability was
questioned. I've heard people say things like "Herby has been flying his
ship with that design for 5 years" A closer check shows that yeah Herby has
been flying on the average 10 hrs/yr. and has accumulated the total of 50
hrs on that design. In some cases the shafts had very sharp stress risers
machined into them but the NHFY said they were reliable. In one case a
simple seal w/o the normal spring insert, chewed a 0.020 jagged groove in
the shaft. The designer was aware of this problem for several years but
elected to use the NHFY reliability test.
It pays to look into the specifics of the design and might even pay to have
an experienced engineer take a close look. Vans anodizes the RV wing spars.
Anodizing aluminum reduces the fatigue life by as much as 50%. Van knows
this and takes it into account in his design to achieve a safe aircraft.
Other designers see the use of anodizing and use it without having the
technical skills evidenced by the RV crew. Numerous examples of violation
of "Good Practice" can be seen in numerous aircraft at various fly-ins. If
some of the judges used at these events could be of higher technical and
experience background, some of these things could be found and pointed out.
E.G. A Oshkosh Grand Champion rotorcraft had anodized aluminum control
tubes that failed in fatigue. The pilot survived. Up until then NHFY
worked.


  #4  
Old May 20th 10, 07:20 PM posted to rec.aviation.homebuilt
Jim Logajan
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Posts: 1,958
Default Quality of kitplane designs?

Oliver Arend wrote:
After reading

http://www.faa.gov/aircraft/gen_av/l...dia/Zodiac.pdf

I'm wondering how much trouble is hidden in other kitplane designs?
Obviously, the RV fleet seems to be rather untroubled, but the others?


It is not untroubled. Besides the nose wheel issues already mentioned by
Ron Wanttaja, about three decades ago the RV-3 experienced at least four
accidents in which in-flight wing separations occurred, and since some of
the causal chains were speculated or unknown, the wing spar design was
questioned, existing airworthiness certificates were suspended and new
operating limits were placed on any reissued ones. The designer employed
external reviewers who found no problems with the design, but nevertheless
made changes to beef up the wing. (Does some of this sound familiar after
reading of the Zodiac problems?)

You can find some history on the RV-3 problems he

http://www.romeolima.com/RV3hq/Info/info.html

Scroll down to the "RV-3 wing spar background" section and review the
documents at the three links provided for additional background and detail.
  #5  
Old May 21st 10, 03:39 AM posted to rec.aviation.homebuilt
rzzzwilson
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Posts: 1
Default Quality of kitplane designs?

On May 20, 8:52*pm, Oliver Arend wrote:

I'm wondering how much trouble is hidden in other kitplane designs?
Obviously, the RV fleet seems to be rather untroubled, but the others?


It's not just problems with the design (if any). Plenty of instances
of a design that has no problems *if built according to the plans* but
have problems when builders make changes (even if it's just to make it
'stronger'). For example, on Ron's Flybaby page (http://
www.bowersflybaby.com/safety/index.html) there is discussion of wing
departure accidents on Flybabys that builders changed. There appears
to be nothing wrong with the Flybaby design, yet wings did come off.
And others have mentioned the RV-3 'problems'.

So pick a design that has lots of examples flying and build it
according to the plans.

Ross
  #6  
Old May 21st 10, 02:44 PM posted to rec.aviation.homebuilt
Stealth Pilot[_2_]
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Posts: 846
Default Quality of kitplane designs?

On Thu, 20 May 2010 06:49:58 -0700, Ron Wanttaja
wrote:

Oliver Arend wrote:
After reading

http://www.faa.gov/aircraft/gen_av/l...dia/Zodiac.pdf

I'm wondering how much trouble is hidden in other kitplane designs?
Obviously, the RV fleet seems to be rather untroubled....


Obviously?

http://www.kalinskyconsulting.com/rvproj/nosegear.htm

I've been looking at homebuilt accidents for quite a while now. I got
into it hoping to find, among other things, common threads in accidents
that might indicate design flaws. As it turns out, clear-cut cases are
rare.

One factor is probably the relative scarcity of most homebuilt types,
which reduces the sample size. Its hard to spot trends from ~5
accidents per year for a given type, especially when over half of them
are going to be due to pilot error.

Ron Wanttaja


oliver's thread should be titled 'quality of kitplane design' because
this really hits the black hole in most of aviation.

nobody ever publishes the design calcs so you have absolutely no way
of knowing what assumptions the designer made, you have no idea where
they may have made a calculation error and you have no idea what the
designer simply forgot to do.

of course even if you actually saw the calcs would you even recognise
a problem?

as it happens I have seen chris's design calcs for the UL. they are
many pages of tightly written calculations. I didnt fully understand
what he'd calculated. it took a very experienced and schmicked up aero
engineer to say 'hang on a mo' there's a calc error there'. ' gee that
bit of the structure looks a bit flimsy'.'hang on that isnt the way to
calc that'.
in the meantime dozens had been built.

the schmicked up aero engineer tells me that the corrections the poms
made and the corrections described on the EAA website dont actually
fix all of the problems that he is aware of.

the short answer to oliver's question is that you will never know.

calculation competence isnt the full answer either.
The W8 Tailwind had no design calcs done that I'm aware of and yet the
TLAR approach has produced a competent aircraft.
My copy of Wittmans W8 is 25 years old. 750 or so hours and decidedly
airworthy.

The truth is that this design competence problem wont go away until
design calcs are published so that some sort of peer review can occur.
can anyone see that happening anytime soon? I cant.

we also need a history of published design calcs out there so that
people can build up the competent review skills.

the solution in the meantime is to wear a parachute during test
flying. actually fly a full test program including a dive to VD and a
60 degree banked turn both to the left and to the right at Vne.
it wont prove everything but it will give you some increased
confidence.

btw I saw a really beautifully built RV6 landed a kiss on greaser on
its test flight then go plonk on to its nose as the nose leg broke
off. vans denied a problem. tisc tisc.

Stealth Pilot
  #7  
Old May 22nd 10, 05:47 PM posted to rec.aviation.homebuilt
[email protected]
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Posts: 1,130
Default Quality of kitplane designs?

On May 21, 7:44*am, Stealth Pilot
wrote:


btw I saw a really beautifully built RV6 landed a kiss on greaser on
its test flight then go plonk on to its nose as the nose leg broke
off. vans denied a problem. tisc tisc.



Yeah, and a buddy of mine saw an RV land on its nosewheel when the
pilot made a bad approach and forced it on. Porpoised down the runway
and broke the wheelpant. That sort of piloting is really common and
regularly breaks nosegears on Cessna 150s and 172s. That RV pilot flew
away again with the busted nosehweel in the baggage compartment, but
what damage has been done to the leg now, and when is it going to snap
off and cause a serious accident? And who will get the blame? Van's of
course, not the clumsy pilot who failed to get the thing NDI'd after
the incident. How often are RVs flipping over busted nosegears that
were abused by their owners? Can Van's be expected to produce idiot-
proof airplanes? Aren't we supposed to learn to fly so that fragile
structures like airplanes don''t get broken and don't need redesigning
to the point they're too heavy to fly?

Dan

  #8  
Old May 22nd 10, 07:47 PM posted to rec.aviation.homebuilt
Ron Wanttaja[_2_]
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Posts: 108
Default Quality of kitplane designs?

wrote:
On May 21, 7:44 am, Stealth Pilot
wrote:

btw I saw a really beautifully built RV6 landed a kiss on greaser on
its test flight then go plonk on to its nose as the nose leg broke
off. vans denied a problem. tisc tisc.



Yeah, and a buddy of mine saw an RV land on its nosewheel when the
pilot made a bad approach and forced it on. Porpoised down the runway
and broke the wheelpant. That sort of piloting is really common and
regularly breaks nosegears on Cessna 150s and 172s. That RV pilot flew
away again with the busted nosehweel in the baggage compartment, but
what damage has been done to the leg now, and when is it going to snap
off and cause a serious accident? And who will get the blame? Van's of
course, not the clumsy pilot who failed to get the thing NDI'd after
the incident. How often are RVs flipping over busted nosegears that
were abused by their owners? Can Van's be expected to produce idiot-
proof airplanes? Aren't we supposed to learn to fly so that fragile
structures like airplanes don''t get broken and don't need redesigning
to the point they're too heavy to fly?


My understanding of the nose-gear issue is that Van's fix was a slight
change to the angle to give a skoosh more clearance. Hardly a
"redesign," and certainly little or no weight penalty

The primary difference between the owner of a certified airplane and
that of an Experimental Amateur-Built is that the guy who owns a
certified airplane has a right to expect a certain level of quality,
both in design and construction. The Amateur-Built owner has no quality
assurance beyond his or her trust in the aircraft designer.

However, in my opinion, this does not give the aircraft designer a
"pass." If there are features of the design which tend to trip pilots
up, the designer should consider altering the design to make it safer.
Certainly, there has to be a balance between performance and safety, but
often the changes don't hurt that much.

Do I blame Vans' for the original nosegear design? No. It was adequate
to the mission. However, service in the field indicated that *typical*
RV-6A pilots were having trouble. They averaged over 1,500 hours total
time. One had over 500 hours in RV-6s. In no cases did the nosegear
"just break"; there were pilot factors, there were environmental factors
(a 15,000-hour ATP hitting a rabbit, for instance...).

Vans looked at the accidents, and decided to alter the nosegear design
to give a bit more clearance. Wouldn't (probably) have helped with the
rabbit, but there were several bounced landings or soft fields where it
might of helped.

*That's* the right response...not just blaming the pilots. The fact is,
pilots are going to have trouble. More and better training helps, but
all of us can probably relate events in the past where we screwed
up...but didn't suffer any consequences because the plane pulled us
through. I accidentally stalled/spun carrying my first passenger after
getting my license; I got too slow on an approach and dropped the plane
in with an impact greater than four Gs.

If I'd crashed in either case, there's no doubt the NTSB would have
ruled it "Pilot Error"...and rightly so. But the Citabria was tolerant
of a ham-fisted ex-student scared out of his wits; Pete Bowers put a lot
of beef into laminated spruce gear legs and the fuselage structure
supporting them.

Every accident is "pilot error," but sometimes the only error the pilot
made was getting out of bed that morning. Tom Wolfe wrote about pilots'
tendencies to automatically absolve the aircraft in most accidents; that
a "good enough pilot would never have let it happen/should have been
able to recover/should have be able to recognize the situation early
enough to bail out."

It's an attitude still rife. Sadly, it tends to blind pilots from the
potential for beneficial changes.

Ron Wanttaja
  #9  
Old May 22nd 10, 08:03 PM posted to rec.aviation.homebuilt
Stu Fields
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Posts: 87
Default Quality of kitplane designs?


wrote in message
...
On May 21, 7:44 am, Stealth Pilot
wrote:


btw I saw a really beautifully built RV6 landed a kiss on greaser on
its test flight then go plonk on to its nose as the nose leg broke
off. vans denied a problem. tisc tisc.



Yeah, and a buddy of mine saw an RV land on its nosewheel when the
pilot made a bad approach and forced it on. Porpoised down the runway
and broke the wheelpant. That sort of piloting is really common and
regularly breaks nosegears on Cessna 150s and 172s. That RV pilot flew
away again with the busted nosehweel in the baggage compartment, but
what damage has been done to the leg now, and when is it going to snap
off and cause a serious accident? And who will get the blame? Van's of
course, not the clumsy pilot who failed to get the thing NDI'd after
the incident. How often are RVs flipping over busted nosegears that
were abused by their owners? Can Van's be expected to produce idiot-
proof airplanes? Aren't we supposed to learn to fly so that fragile
structures like airplanes don''t get broken and don't need redesigning
to the point they're too heavy to fly?

Dan
Dang. As a pilot with a few hours in the Cessna products which included
hauling sky divers with an avg of 15min between landings, I never saw or
even heard much of people losing Nose gears. The Cessna was just very easy
to land without getting the nose gear in the way..


  #10  
Old May 23rd 10, 10:36 PM posted to rec.aviation.homebuilt
Dan[_12_]
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Posts: 451
Default Quality of kitplane designs?

wrote:
On May 21, 7:44 am, Stealth Pilot
wrote:

btw I saw a really beautifully built RV6 landed a kiss on greaser on
its test flight then go plonk on to its nose as the nose leg broke
off. vans denied a problem. tisc tisc.



Yeah, and a buddy of mine saw an RV land on its nosewheel when the
pilot made a bad approach and forced it on. Porpoised down the runway
and broke the wheelpant. That sort of piloting is really common and
regularly breaks nosegears on Cessna 150s and 172s. That RV pilot flew
away again with the busted nosehweel in the baggage compartment, but
what damage has been done to the leg now, and when is it going to snap
off and cause a serious accident? And who will get the blame? Van's of
course, not the clumsy pilot who failed to get the thing NDI'd after
the incident. How often are RVs flipping over busted nosegears that
were abused by their owners? Can Van's be expected to produce idiot-
proof airplanes? Aren't we supposed to learn to fly so that fragile
structures like airplanes don''t get broken and don't need redesigning
to the point they're too heavy to fly?

Dan


The day someone invents an idiot proof system someone else will
invent a better idiot.

When I started learning to land my instructor pointed out that just
because the runway was long doesn't mean you have to float the entire
length. Next landing he explained to me there was a happy medium between
the light landing I had done before and the heavy one I had just done. I
decided to listen to him.

Dan, U.S. Air Force, retired
 




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