homebuilt safety

On 16 May 2004 18:22:21 -0700, (Paul Lee)
wrote:

:This was inspite of the fact that the touchdown speed is 90+
:mph.

Oh, sweet Jesus, I hope you're kidding. What empty weight and CG
range are you running?

"Pete Schaefer" wrote in message news:Btqpc.53022$536.9082680@attbi_s03...
Landing speeds are a big driver for the amount of injury. I think that the
FAA has a lot of data on this. Can't think of a reference off-hand, but you
can search the NTSB site. But anyway, here's the math: KE = (1/2)mv^2. The
basic conclusion is that accidents occuring at lower landing speeds do less
damage. This was a driver for the design of the RV series aircraft. If you
want safety, get something with STOL capability, make sure there's nothing
in the cockpit that's going to smack you in the back of the head if you
screw up, then practice, practice, practice (with an instructor until you
feel confident).....then practice some more. Avoid low-level aerobatics
until you're a really ****-hot pilot.

You really need to forget about structural protection in a home-built. The
key is to prevent (by flight procedure, pilot skill and knowledge, and by
appropriate vehicle design) accidents from happening in the first place.

Is this because none of the ones available as designs currently have
any, or because you feel it's not feasible, or because....exactly why?
Race cars go faster on the ground than some homebuilts will _straight
down_ and, Dale Earnhardt aside, usually people go in the wall and
walk out (or get pulled out by the crash wagon crew).

I recall that the P-51's designer, Dutch Kindelberger, designed the
cockpit area as the toughest structure, so everything else would
crumple around the pilot and provide protection from the sudden
impact. Is this somehow no longer feasible?

Hey Jim-Ed:


"Jim-Ed Browne" wrote in message
om...
Is this because none of the ones available as designs currently have
any, or because you feel it's not feasible, or because....exactly why?

I've never looked at any airplane designs that have such features. There is
a huge price to pay in terms of weight, required power and such to provide
pilot protection. Drives up cost a ton, and makes operations more
expensive.

Keep in mind that crumple zones are only really for front impact, too.

Race cars go faster on the ground than some homebuilts will _straight
down_ and, Dale Earnhardt aside, usually people go in the wall and

They have requirements for driver protection. And they have huge budgets to
work with. I don't know about about NASCAR, but, to get the sign-off to
race, the CART guys have to slam a couple of chassis into a wall to show
that the tub holds together. Expensive, expensive, expensive.

I recall that the P-51's designer, Dutch Kindelberger, designed the
cockpit area as the toughest structure, so everything else would
crumple around the pilot and provide protection from the sudden
impact. Is this somehow no longer feasible?

Sure, it's feasible, but it's expensive. How many airframes do you want to
build for the purpose of destroying them to prove the design? Then there's
costs of test facilities. What's the cost in weight, performance, etc.? How
much is it going to cost to design, model, and test? If you see a couple of
zeros being added on to the total cost to build and get the FAA to sign it
off, then you're probably getting a realistic picture.

Even if you could afford to buy one, operation costs of a P-51 is probably
well beyond the average budget of the typical home-builder. Besides, the
P-51 was designed to go to war and get shot at, not for $100 hamburgers.

I guess the question I have is this: How much are you willing to spend to
get an airplane that protects you in case of a crash? If you've got
millions to spend, then you can probably get what you want. But on a $50k
home-built? Forget it. Maybe a certified commercial manufacturer would have
the resources to pursue safety features like this, but I would find it
surprising if people would be willing to fork out the extra bucks for it,
given that the costs would have to be recovered through the sale of a
relatively small number of airplanes.

There are probably much better approaches to achieving leaps in aviation
safety without doing anything about crashworthiness improvments. Think
about the safety improvements you'd get just by having a more reliable
powerplant and fuel delivery system. Think about potential improvements
from sophisticated engine health monitoring (condition-based
maintenance....catch and repair faults before they become
catastrophic...there are some really nice products out there right now)?
Then there are potential benefits for IFR/night flight using synthetic
vision to prevent spatial disorientation. These kinds of improvments might
cost thousands of dollars to the consumer, falling in the range of what is
affordable to the typical RV builder at least.

Anyway, just some things to think about. If you dig around for some of the
data on NASA's General Aviation Revitalization effort (no longer going on, I
think), you can find more comprehensive info on these topics.


Pete

P.S. Just to qualify my views - I'm not an airframe designer, but I do work
in aircraft development. I'm a flight controls engineer (meaning that I'm
one of the guys who's found ways to drive up the costs of an airplane
without driving the weight up) with Lockheed in Palmdale, CA. While I don't
work directly with these design/development trades, I am regularly exposed
to the issues and compromises that they bring up. So...knowledgable, but
not an expert.

On 19 May 2004 12:03:24 -0700, (Jim-Ed Browne)
wrote:

I recall that the P-51's designer, Dutch Kindelberger, designed the
cockpit area as the toughest structure, so everything else would
crumple around the pilot and provide protection from the sudden
impact. Is this somehow no longer feasible?

You do? References please. I've studied that fighter for years and
this is the first I've ever heard of Kindelberger designing the
cockpit like a modern car is designed.

Thanks, Corky Scott

I performed a fairly in-depth study of homebuilt accidents towards the end
of last year. The October issue of KITPLANES magazine will include an
article summarizing my results and conclusions.

During my analysis, I looked at the records of individual designs, thought
I didn't include the results in the article. Even though I performed my
analysis on a three-year period, the number of accidents of most particular
types is still fairly low that minor aberrations cause significant changes.

For instance, if there are 2000 examples of type "A" and 200 examples of
type "B", one or two extra crashes will affect the stats for Type "B" a lot
more than Type "A". If 20 Type "A" planes and 2 type "B" planes crash,
they both have the same accident rate. If both have two additional
accidents, Type "B"'s rate will now be almost *double* Type "A"'s. But
does that truly mean that "B" is twice as dangerous as "A"?

We also get into the aircraft type and aircraft operating mode issues. On
my first pass, I found one type of homebuilt with a significantly higher
accident rate than the rest. When I looked closer, I realized that this
was an amphibian...and a lot of the accidents were during water operations.

So I'm reluctant to point fingers are individual aircraft types. Here's a
list of the fleet accident rate (what percentage of a particular type
crashes in an average year) for ten major homebuilt kit companies. Note
that the statistics for companies with multiple types are grouped together
(e.g. the RV series is lumped under one, not listed individually). Only
aircraft listed as being licensed were included...many homebuilts of these
types are on the registration rolls but have the certification type column
blank.

The aircraft included are (in alphabetical order): Avid, Glasair, Glastar,
Kitfox, Lancair, Long EZ, RANS, T-18, Vans, Velocity. Note that this order
does NOT match that of the table below, nor does it include the amphibian
type I mention above.

Annual Accident Rate
% of Fleet
A 1.3%
B 1.2%
C 1.8%
D 4.9%
E 0.9%
F 1.0%
G 0.7%
H 2.4%
I 1.9%
J 2.9%


Ron Wanttaja

On Sat, 15 May 2004 19:34:27 +0000, Ron Wanttaja wrote:

I performed a fairly in-depth study of homebuilt accidents towards the end
of last year. The October issue of KITPLANES magazine will include an
article summarizing my results and conclusions.

Thanks, I'll look forward to the article.

AC

SNIP
I agree this sounds impossibly fraught. What I would like (ideally) would
be the results of something akin to the car-crash tests that show how the
test-dummies fared in various scenarios - e.g. side impacts etc... I saw a
documentary about car-safety a few years ago, that mentioned that the
technology of crumple-zones and reinforced passenger compartments was
originally developed for WWII naval aircraft. Don't homebuilt designers
think about features such as these? Or would they help in so few scenarios
that it's an irrelevance?



Again, I have read (but dont have the source handy) that one of the
biggest determinants of lethality in a small aircraft accident is based
on wether the aircraft contacts the ground in a near-level, controlled
attitude (or not). Crumple zones and side-impact airbags wont do much
when you hit upside down, in a spin, or screaming out of the sky with a
yard dart's downward trajectory. Preventing departure from controlled
flight is the key to survival. That is why you 1) ALWAYS fly the plane
first and 2) NEVER give up.

Dave

anonymous coward wrote:


I agree this sounds impossibly fraught. What I would like (ideally) would
be the results of something akin to the car-crash tests that show how the
test-dummies fared in various scenarios - e.g. side impacts etc... I saw a
documentary about car-safety a few years ago, that mentioned that the
technology of crumple-zones and reinforced passenger compartments was
originally developed for WWII naval aircraft. Don't homebuilt designers
think about features such as these? Or would they help in so few scenarios
that it's an irrelevance?


John Dyke did. The front page of my websitehas a 3D CAD rendering of
the cockpit with a pilot seated. Note the comparatively HUGE crumple
zone in front and to each side enjoyed by the pilot compared to most
designs. For most designs, trying to get this sort of crumple zone
would make the craft extremely safe...'cause it'd be so heavy that it'd
never fly!!

--
http://www.ernest.isa-geek.org/
"Ignorance is mankinds normal state,
alleviated by information and experience."
Veeduber

On Sat, 15 May 2004 15:09:43 +0100, anonymous coward
wrote:

I agree this sounds impossibly fraught. What I would like (ideally) would
be the results of something akin to the car-crash tests that show how the
test-dummies fared in various scenarios - e.g. side impacts etc... I saw a
documentary about car-safety a few years ago, that mentioned that the
technology of crumple-zones and reinforced passenger compartments was
originally developed for WWII naval aircraft

I'm pretty surprised to hear about this. My knowledge, such as it is,
about WWII fighters in general, and Navy fighters in particular is
that they were either designed with production/armament in mind or
aerodynamics (speed or maneuverability) in mind, but building
"crumple-zones" wasn't a priority, if they even knew of the concept in
1940.

This is especially true for the Navy fighters which had to do all the
things the non Navy fighters did, but in addition they had to crash
repeatedly on the carrier deck in what the Navy laughably calls
"landings". Needless to say, they were supposed to be in one piece
after every landing, which means that they ended up heavier in general
than the typical same size Army fighter.

It just happens that in a violent crash, the outer appendages will
tend to shed from the airplane. I've seen footage of an F6F botching
the landing and colliding with the island, after which the only thing
left intact was the cockpit, with the pilot still in it. But I doubt
that Grumman planned on guys hitting the island when they designed the
airplane, it's just that it shed all it's heavy pieces during the
oblique impact. The pilot was extremely lucky he did not hit head on:
he would have been the crumple zone.

Corky Scott

On Mon, 17 May 2004 13:29:04 -0400, charles.k.scott wrote:

On Sat, 15 May 2004 15:09:43 +0100, anonymous coward
wrote:

I agree this sounds impossibly fraught. What I would like (ideally) would
be the results of something akin to the car-crash tests that show how the
test-dummies fared in various scenarios - e.g. side impacts etc... I saw a
documentary about car-safety a few years ago, that mentioned that the
technology of crumple-zones and reinforced passenger compartments was
originally developed for WWII naval aircraft

I'm pretty surprised to hear about this. My knowledge, such as it is,
about WWII fighters in general, and Navy fighters in particular is
that they were either designed with production/armament in mind or
aerodynamics (speed or maneuverability) in mind, but building
"crumple-zones" wasn't a priority, if they even knew of the concept in
1940.

The argument, provided I'm not confabulating it, was that there was a
shortage of combat pilots so it was worthwhile building a 'plane that
let them live to crash again.

This is especially true for the Navy fighters which had to do all the
things the non Navy fighters did, but in addition they had to crash
repeatedly on the carrier deck in what the Navy laughably calls
"landings". Needless to say, they were supposed to be in one piece
after every landing, which means that they ended up heavier in general
than the typical same size Army fighter.

It just happens that in a violent crash, the outer appendages will tend
to shed from the airplane. I've seen footage of an F6F botching the
landing and colliding with the island, after which the only thing left
intact was the cockpit, with the pilot still in it. But I doubt that
Grumman planned on guys hitting the island when they designed the
airplane, it's just that it shed all it's heavy pieces during the
oblique impact. The pilot was extremely lucky he did not hit head on:
he would have been the crumple zone.

The footage I remember was of a prop-plane coming in to land very heavily.
The entire aircraft snapped in two behind the pilot compartment. Suffice
to say, Google can't find any link between "crumple-zone" and "aircraft
carrier" so it's possible my memory has gone cloudy.

AC