Crashworthiness

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JimCovington

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No, I'm not. Out of the link I can't (or can't find) whether that happened during this occasion, but I know from another incident where a pretty big pilot was fine, ending upside-down. So for the moment I think that extending your head above the fuselage is a matter of bad seatbelt tension or bad aircraft design.
I agree. However - I was flying right seat just yesterday in a Seneca (moderate wing loading; higher than many homebuilts) when we hit a pocket that caused me to smack my head against the ceiling - and I always keep my belt very tight. I couldn't figure out after I hit my head how I'd managed to reach the ceiling (the belt was still tight) but I'm certain I did.

I've seen too many designs where there's some "rollover protection" included - but when you draw a straight line from the rollover structure to the engine, the pilot's head is above it - and that's *before* any crash damage!
 

autoreply

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I agree. However - I was flying right seat just yesterday in a Seneca (moderate wing loading; higher than many homebuilts) when we hit a pocket that caused me to smack my head against the ceiling - and I always keep my belt very tight. I couldn't figure out after I hit my head how I'd managed to reach the ceiling (the belt was still tight) but I'm certain I did.
I've seen a pilot doing it on landing as well (too sloppy belts), crushing his canopy.
Having experienced a couple of negative (inverted) flights, a 5-point harness (I've never flown with less than four in gliders) makes a lot of difference.
I've seen too many designs where there's some "rollover protection" included - but when you draw a straight line from the rollover structure to the engine, the pilot's head is above it - and that's *before* any crash damage!
Well, then we're back on the original question.

When hanging someone a drop of 4 to 6 feet will kill you (well, break your neck, and stopping your breathing) Assuming a plane that's 10 times your mass it has to drop only 1.9 feet to break your neck. That's an impact velocity of 6.7 m/s or 13kts (vertical) in a very positive scenario, helmet or not. I seriously doubt many crashes involve a plane turning inverted with such low speeds, especially considering the risk of breaking your neck (due to the extra weight of the helmet) at "ordinary" crashes. In fact, putting a Cessna 172 on it's spinner and flipping it forward is already enough to finish yourself.

Having said that I still suspect there's a rational reason pilots use helmets, but I still don't get why.

The advantages in other uses are fire protection (not applicable for the open helmets I've seen), it looks cool (applicable) protection when ejecting (no ejection seat in homebuilts and low enough speeds to eject safely naked) lower noise levels (applicable) and lower risk of sharp objects (applicable, but can be solved with a good cockpit design)

Am I missing something or is there no real reason to use helmets in homebuilts or Reno-racers?
 

Dana

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Flying ultralights and PPG's I wear a helmet because there's a very real possibility that my head could bounce on the ground or on structure in an otherwise survivable crash.

-Dana

I love my country, but I fear my government.
 

GESchwarz

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I tried out a 5 point harness in a Navy helicopter...I felt like I wasn't going anywhere.

Autoreply, regarding the helmet, I don't think you are missing anything. It's just a matter of choice. You will never know what sort of forces your head and neck will take in a crash. I think a good compromise is to choose a very light helmet. A very light helmet should protect you from most but not all impact hazards, and should be light enough on your neck in most but not all high g situations.
 

JimCovington

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Having said that I still suspect there's a rational reason pilots use helmets, but I still don't get why.
For me, it's not rational - it's habit.

I have a kayaking helmet, a hockey helmet, a skiing helmet, a rock climbing helmet, a motorcycle helmet, 2 biking helmets...

It might not be a good idea, but that's my reason.

I also have a 5-point harness in my plane, and I'm definitely glued to the seat when it's cranked.
 

Michealvalentinsmith

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I have a patent on an airbag design for PG pilots with a lot of research in this area and you guys have outlined the situation exceptionally well - far better than similar discussions elsewhere.

I don't know enough about the negative G forces on the pilot or the directions involved in aircraft crashes to extrapolate accurately - but 13 gs is not a difficult number to control. Most research indicates you need to get under 20gs to avoid major injury but the best paraglider airbags are reducing impacts from a freefall of 2 meters to as low as 8 gs.

A fixed structure like an aircraft should tolerate fixed systems - PGs use ram airbags primarily for portability - so something like car crumple zones might work. It's interesting to note though that cars use airbags in conjunction with crumple zones.

If such airbags were to be used, ram filled PG types would not be ideal as they lose as much as 50% of the available penetration thickness to compress the internal air adequately for impact resistance. Though this may not be the case with typical higher speed aircraft and significant internal pressures could be generated. The problem is they would be continuously deployed and in the way.

I think available car systems with detection devices and gas deployment using hypergolics could easily be adapted to aviation.

I do know one thing from my orthopedic experience. The human spine is exceptionally delicate fragile and doesn't recover well from insults.
 

Michealvalentinsmith

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For me, it's not rational - it's habit.

I have a kayaking helmet, a hockey helmet, a skiing helmet, a rock climbing helmet, a motorcycle helmet, 2 biking helmets...

It might not be a good idea, but that's my reason.

I also have a 5-point harness in my plane, and I'm definitely glued to the seat when it's cranked.
My sentiments exactly. PG pilots are more or less mandated to wear a helmet whereas airbags are optional. While the accident stats show far more injuries occur to the lumbar spine than head.

I suspect the same may be the case for the sports noted but since no adequate or practical protections systems exist for the most commonly injured regions, they figure you may as well protect the region you can. But I'm not convinced a spinal injury resulting in lifelong paralysis is better than a head injury and the head deserves a higher protection priority than the spine.

But practical and effective spinal protection systems do exists in paragliding and while head injuries (with much lower frequency) do occur, the practical thing to mandate would be the airbag first and the helmet next. But I've never been a fan of paternalistic legislation.

I recently got pulled up by the police and fined for not wearing a helmet while riding a bicycle on the beach. Turns out in theory the beach at the front of my house is a gazetted road so he had legal validity - but no cars are allowed in this region and it's clearly signed. Enforcing such laws seems to have more to do with perception than reality.
 

Hot Wings

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HANS device? Now that I know what they are called I had a chance to do a Google. I've considered a helmet for some time but decided the neck hazard outweighed the advantages. $600+ seems kind of spendy but I think I just may add helmet and HANS to the check list.

Not intending to cause any thread drift, but anyone have suggestions for the best kind of speakers to use with a helmet?
 

autoreply

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My sentiments exactly. PG pilots are more or less mandated to wear a helmet whereas airbags are optional. While the accident stats show far more injuries occur to the lumbar spine than head.

I suspect the same may be the case for the sports noted but since no adequate or practical protections systems exist for the most commonly injured regions, they figure you may as well protect the region you can. But I'm not convinced a spinal injury resulting in lifelong paralysis is better than a head injury and the head deserves a higher protection priority than the spine.
Similar to the Hans device I've been driving my motorcycle a couple of hours with the Leatt Brace which is a similar idea. Driving up the Stelvio requires quite a bit of looking over your shoulder which is sligtly irritating with the device. Otherwise you barely notice it and for risky sports it's a definite safety-device everybody should consider long before using a helmet.... well, in my opinion.

As for airbags, they're pretty usefull when the resultant structure isn't designed to crash properly (like most of the aircraft around us). If you don't have an aircraft around you (paraglider) it might be a very useful extra protection, maybe [video=youtube;TX_YIr5CkDM]http://www.youtube.com/watch?v=TX_YIr5CkDM[/video] some extra inspiration.

Funny to see that in most countries cycling with a helmet is very normal. Here nobody wears one, despite the 25 million bicycles (17 million habitants) that ride around.
 
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berridos

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madrid
Thinking about a benchlike seat with foam underneath for a little homebuild... at what weight should the butt-part brake apart from the back-part (vertical). The vertical part should avoid the cabin to implode and the lower part should brake apart to pass the energy to the foam.
 

autoreply

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Thinking about a benchlike seat with foam underneath for a little homebuild... at what weight should the butt-part brake apart from the back-part (vertical). The vertical part should avoid the cabin to implode and the lower part should brake apart to pass the energy to the foam.
It never should. When it breaks it accelerates you till you hit the bottom of your aircraft (or the tarmac) and then your back. I think various regulations state 16 to 20G's, but in a homebuilt (shorter crumple-zone) I'd bet at 40 or so, including safety factor.
Yes, that's 10.000 lbs of force..
 

JimCovington

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Similar to the Hans device I've been driving my motorcycle a couple of hours with the Leatt Brace which is a similar idea.
Very interesting - never seen it before. What's the main difference between that and a HANS? Can you turn your head as much as you'd like to in a plane?

One of the benefits of flying is looking out the side window - if I can't turn my head - why fly? :)
 

autoreply

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I've no idea what the differences are, though I'm told the Leatt brace is higher quality. The Hans device claims 45 degrees sideways motion and from experience I'd guess the Leat is the same or slightly more. Looking backwards (see the picture in the but last post) in hairpins became more difficult, but on a motorcycle you're turning your whole upper body already. I seriously doubt you have the ability to look sideways with it like I do here:


Having only a bit of experience on powered aircraft I can't tell for sure whether you need to be able to look back up to 135 degrees in a powered aircraft (very important in a gaggle of gliders), but I presume the 45/60 degrees isn't enough.
Trying however is the only way to find out, couldn't find anyone who did.
 
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RacerCFIIDave

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The HANS is the single biggest advance in motorsport safety of the last 20 years... I would not allow any of my drivers to get in anything faster than a Formula Ford without one...and wouldnt be happy about that!

The poured foam bead seat as mandatory in IRL is the answer to the spinal fracture problem... It sure works in Indycar and Indy Lights...

Dave
 

GESchwarz

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autoreply

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Dynafoam has been in use for a good 10 years and does so highly successfully.

It can be bought here (Austria, might have another supplier for the US where it's called Sunmate)

Here an interesting article about safety cockpits and especially dynafoam can be found.
 

GESchwarz

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Thanks for the contribution Autoreply! That's a good article.

Does anyone have any data on the effect of seat back angle in reducing spine injury? It makes common sense that the flatter you lay the safer your spine is.

My design has both occupants sitting with a seat back angle of 24 degrees. Under high vertical impact the seat pan swings forward and down in an arc in front of the wing spar, and the top of the seat slides down a track. This motion is against the resistance of an engineered foam block under the seat pan. When the seat goes down to full travel the seat back is laying down at about 45 degrees. My target travel for the seat is about 12". The foam under the seat would not begin to compress until reaching a load of around 6 or 7 g's and continue to compress up to 20 g's. So I have some drop testing in my future.

I am currently building the seats and will soon be building the mechanism to effect the motion I just described. The wing spar is below cockpit floor.

So I am still fishing for knowledge before I commit to making these parts.
 

autoreply

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Thanks for the contribution Autoreply! That's a good article.

Does anyone have any data on the effect of seat back angle in reducing spine injury? It makes common sense that the flatter you lay the safer your spine is.
Well, it's a small effect. Two things play a role.

"Buckling" is the major issue from my point of view. Support always helps with buckling. If you have a seatback angle, during a vertical crash you will have a force (sin of the seatback angle) that stabilizes your spline against the seat, thus raising the maximum acceleration that would "buckle" your spline. As for the vertical force on your spline, that barely decreases (cos), a seatback of 30 degrees still gives you 86% of the original force. So the effect of a big angle is small, but 20 degrees or so sounds like a good idea.

I have the idea that we often forget (or don't pay enough attention to) diving under the seat belts. Any 2, 3 or 4-point belt will give you the opportunity to dive under your hip belt and (with a bit of seatback angle) immidiately break your spline. The only way to prevent this is a 5-point harness. Cars can get away with 2/3 point belts because their crashes are (usually) purely horizontal. Obviously, a seat back angle will enlarge this problem considerably.
 
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