homebuilt safety

Pete Schaefer wrote:
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.


Don't mean to tell you your business, but....bulls417!!

See my website for PICTURES of proof. Crumple zones are not only
feasible, reliable, and light, but they've been flying for over 40years.

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.


No extra cost or weight, and why would you get the FAA to sign off on a
homebuilt aircraft design? It won't cost any more to design, model and
test than any other homebuilt design. Why would you need to do
destructive testing? Do I have to break my wings to prove they will
hold me up in flight?

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.


My goal is to stay well under $20k. One builder lost his engine and
didn't make the airport. Buried his Delta in a barnyard silo after
passing it through a bale of hay. Walked away from it. If you can keep
the landing to an acute angle crumple zones WILL help.

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.


From the statistics, the fuel delivery reliability rest most directly
on the pump in the fuel truck back at the airport. There ain't any
hardware that can fix that fault. It's a software problem 8*)

As for the rest of that...now who's talking about spending big dollars?
Crashworthiness should be part of the primary structure. Not a heavy,
expensive afterthought.

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.



When I sit in my incomplete project, I can look around at all the steel
that has to bend before the outside gets to me, I can imagine all the
fiberglass that will have to give way, and even if I'm no safer than in
the aluminum can I trained in, I certainly feel that way. There are not
any electronics or flight systems that will ever make me feel safer than
several feet of protection between me and the hard stuff.


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

On Wed, 19 May 2004 19:46:43 +0000, Pete Schaefer wrote:

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.

Most paraglider pilots have a harness that includes some 'crushables' to
protect their backs if their canopies collapse at low-level. Recently the
tide has turned against rigid harnesses with carbon-fiber backplates.
These used to be popular on the grounds that they would reinforce the
backbone - now people believe that they are so rigid they can concentrate
the forces on small sections of the spine (typically the lower lumbar
vertebrae) and _increase_ the risk of spinal injuries. Now people prefer
airbags that let the air out gradually through the seams during an impact
(to prevent recoil). Alternatively some harnesses use foam to spread
impact forces over the whole area of the back. There's little consensus
about how well they work, but little doubt that they can provide an 'edge'.

This is just a longwinded way of saying 'I don't see why passive safety
should necessarily be heavy and expensive' It might be as little as 2" of
foam and a more ergonomically shaped seat.

To put it another way, I weigh 20kg less than average. I wonder how much
energy that weight of intelligently positioned crushable foam could
absorb? Or even a small fraction of that weight.

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

No reason why. Actually, I'd have thought it should be easier to design
passive protection into an aircraft because side and rear impacts are
probably less common.

I have heard something in the New-Scientist about weakened floors in
airliners that could crumple and save people's backs when planes crash
with too high a descent rate. I also heard that in one frontal collision
in an airliner, many lives were needlessly lost because many people's legs
swung forwards under the seat infront and fractured around the shins. This
meant that they couldn't leave the accident site, even though there was
time. Now, most airline seats have soft edges around the relevant parts of
the seats.

None of this directly applicable to GA.

AC

On Wed, 19 May 2004 20:03:57 -0400, DEATH wrote:



I hope I don't seem paranoid, but assuming I'm likely to be flying for 50
years, even accident rates down in the low percents seem quite alarming.


Assuming you plan on driving or even walking across a roadway in the same 50
years, accident rates are even more alarming.

Really?

"Ernest Christley" wrote in message
. com...
See my website for PICTURES of proof. Crumple zones are not only
feasible, reliable, and light, but they've been flying for over 40years.

There's a lot of stuff on your site. I didn't see anything about crumple
zones. Please provide pointers to what you're talking about. I kept flipping
through your pages, doing searches for "crumple"....no hits.

test than any other homebuilt design. Why would you need to do
destructive testing? Do I have to break my wings to prove they will
hold me up in flight?

As far as I know, crumple zones are not reusable. Isn't that the point of
them? How can you test the design if you don't do it destructively? Am I
missing something here? Or are you saying that analysis is sufficient? Or
are you confusing crumple zones with something else? I don't get your
analogy, either. You test a wing structure by putting it under load and
showing it holds; you test an energy dissipation feature like a crumple zone
by subjecting it to an impact and showing that it crumples by the amount
predicted.

the landing to an acute angle crumple zones WILL help.

I didn't see the crumple zone features of the Delta that you are refering
to.

Crashworthiness should be part of the primary structure. Not a heavy,
expensive afterthought.

ALL of the crashworthiness considerations I've ever seen have been the usual
"this is the max expected design load, so make it strong enough to withstand
XX times that". Often, there is additional strength in components that
protect the pilot. But that's different than crumple zones.

When I sit in my incomplete project, I can look around at all the steel

Fine. If that gives you a warm fuzzy, then good for you. Me? I'll place my
emphasis on accident prevention - both by design, training, and proper
preparation.

There are not any electronics or flight systems that will ever make me
feel safer than
several feet of protection between me and the hard stuff.

Not even an angle-of-attack sensor? Dang. Given that they are available, I
wouldn't consider building a new plane without one. But your Deltas don't
have enough elevon authority to reach CLmax, so that's probably not an issue
for you.

"anonymous coward" wrote in message
news
This is just a longwinded way of saying 'I don't see why passive safety
should necessarily be heavy and expensive' It might be as little as 2" of
foam and a more ergonomically shaped seat.

But that's not a feature of the basic airframe design, which is the subject
that we're addressing here. I would believe that crushable foam, as is used
in motorcycle & bicycle helmets can probably, under certain circumstances,
make the difference between a sore back and weeks in the hospital.
Likewise, seating position has a lot to do with what kind of injuries you're
likely to encounter.

To put it another way, I weigh 20kg less than average. I wonder how much
energy that weight of intelligently positioned crushable foam could
absorb? Or even a small fraction of that weight.

Probably quite a bit. But where would you put it? Are you talking about the
possibility of building a lightweight foam tub to put the pilot it? There
might be some possibilities there, but keep in mind that foam only really
helps you with compression loads.

On Wed, 19 May 2004 09:07:53 -0700, Richard Riley
wrote:

:On Wed, 19 May 2004 09:02:25 -0700, Ed Wischmeyer
wrote:
:
::It's easy for folks to only consider some emergencies when justifying their
::risk profiles. Of course, I've never done that :-)
::
::Ed Wischmeyer
:
:And you've never seen any emergencies, have you Ed? No blown tires,
:hung gear, drug wingtips, eaten valves, frozen control systems,
:clogged fuel filters. Aviation is like WestWord, where nothing can
ossibly go worng.

Ooops. Sorry, Ed, had a short brain fart there, and had you mixed up
with Cy Galley. Never mind.

On Thu, 20 May 2004 06:03:49 +0000, Pete Schaefer wrote:

"anonymous coward" wrote in message
news
This is just a longwinded way of saying 'I don't see why passive safety
should necessarily be heavy and expensive' It might be as little as 2" of
foam and a more ergonomically shaped seat.

But that's not a feature of the basic airframe design, which is the subject
that we're addressing here.

Does it really matter?

I would believe that crushable foam, as is used
in motorcycle & bicycle helmets can probably, under certain circumstances,
make the difference between a sore back and weeks in the hospital.
Likewise, seating position has a lot to do with what kind of injuries you're
likely to encounter.

To put it another way, I weigh 20kg less than average. I wonder how much
energy that weight of intelligently positioned crushable foam could
absorb? Or even a small fraction of that weight.

Probably quite a bit. But where would you put it? Are you talking about the
possibility of building a lightweight foam tub to put the pilot it?

That was one thing I had in mind. But all I can imagine this would
protect against would be loads on the spine if you hit the ground
horizontally and with a high rate of descent. Incidentally (and as you can
probably tell) I'm not an engineer, but I think I have enough engineer's
genes to realise that this wouldn't necessarily be simple. For example I'm
guessing you would need quite soft foam, otherwise it wouldn't deform
at all (loads spread over too large an area). Then you have the problem
that it's easy to put your foot through it, so you have to cover it with
something hard. And so on...

There might be some possibilities there, but keep in mind that foam only
really helps you with compression loads.

Another idea was putting a big chunk of foam at the front of the aircraft
to slow the deacceleration if you hit something frontways. Say you have to
land out, and hit a stone wall in the middle of the field (lots round
here). The pilot would pull against the harness straps (I think I'm right
in saying they would stretch to absorb some of the energy) but the
airframe may break. Perhaps a cubic foot of harder, crushable foam in the
nosecone could reduce peak loads on the airframe and spread them more
evenly, allowing it to remain intact?

I'd be interested to hear more about these gliders' reinforced cockpits.
Perhaps all this speculation has been despeculated already?

AC

"anonymous coward" wrote in message
news
But that's not a feature of the basic airframe design, which is the
subject
that we're addressing here.
Does it really matter?

I guess it's pertinent; it's all about risk mitigation. But pilot protection
(beyond accident prevention) starts with the airframe design. Having a
crushable foam seat bottom won't matter much if you end up with the engine
in your lap.

protect against would be loads on the spine if you hit the ground
horizontally and with a high rate of descent. Incidentally (and as you can

Yes, but a hard landing might be the most important design point. How many
ground loops begin with a pilot landing hard and losing control?

guessing you would need quite soft foam, otherwise it wouldn't deform

The foams they use for helmets are pretty hard. They won't deform until you
hit a threshhold. You don't want something that will compress under normal
loads.

Another idea was putting a big chunk of foam at the front of the aircraft
to slow the deacceleration if you hit something frontways. Say you have to

We could be talking about a lot of energy. Might require a lot of foam.

airframe may break. Perhaps a cubic foot of harder, crushable foam in the
nosecone could reduce peak loads on the airframe and spread them more

Where in the nose would you put it? I was thinking of maybe something behind
the instrument panel, maybe attached to the firewall. Speaking of fire....I
think I have an old bicycle helmet laying around. Maybe I'll put a match to
it. Anyway, I'm sure there's data available on foams currently in use.

I'd be interested to hear more about these gliders' reinforced cockpits.
Perhaps all this speculation has been despeculated already?

Perhaps. I would think that you'd have an easier time with composites in
building a really stout shell around the pilot. Just a couple more plys of
glass/carbon/kevlar/whatever..... It could give more protection than a metal
design. Composites seem to be easier to design with for energy-dissipation.
You can't tear them easily. The tubs that F-1 drivers sit in are all
carbon, with the outer structure designed to shred nicely if the car hits a
wall at high speed. I have a friend who used to work for Dan Gurney in
Anaheim, and he gave me an insiders tour. He showed me the chassis that they
had slammed. The inside of the tub looked new, but everything outside it
was just shredded. Airplanes don't give anywhere near that level of
protection.

On Thu, 20 May 2004 03:25:58 GMT, Ernest Christley
wrote:


Don't mean to tell you your business, but....bulls417!!

See my website for PICTURES of proof. Crumple zones are not only
feasible, reliable, and light, but they've been flying for over 40years.

Where on your website?

Corky Scott

Richard Riley wrote in message . ..
....
Any idea why the airplane ripped out it's gear? I know it was in a
storm, but did he catch the gear on something on touchdown? Excessive
sink rate? The gear should be able to take 3-4 G's without departing
the aircraft,

It didn't actually rip out. They hit the gear sideways in the storm.
Its not a fixed gear and the lower brace pivot pin sheared and of
course the whole thing folded up under the fuselage then. You can see
how it is contructed at http://www.abri.com/sq2000/rg06.jpg

Its similar to Infinity gear design http://www.infinityaerospace.com/infgear.htm

Stan has since then reinforced the pin mountings. And I am modifying mine
in a different way.