Small aircraft crashworthiness

[turboplanner]

OK, I recall a book which included a chapter about how an engineer introduced flat rudder pedals and eliminated the broken bones that tubular foot pedals were causing, so maybe you could use a cricket box.

 

 

[Old Koreelah]

OK, I recall a book which included a chapter about how an engineer introduced flat rudder pedals and eliminated the broken bones that tubular foot pedals were causing, so maybe you could use a cricket box.

My rudder pedals don't cause me to lose sleep. They're ply laminates with little scope for injuring me. That CM steel fitting in front of the CJs is the problem. Let's hope the harness doesn't let go!

 

 

[Dafydd Llewellyn]

My rudder pedals don't cause me to lose sleep. They're ply laminates with little scope for injuring me. That CM steel fitting in front of the CJs is the problem. Let's hope the harness doesn't let go!

Look at automotive racing harnesses.

 

 

[Dafydd Llewellyn]

Quote: "In simple terms it is a seat which is effectively a box without hard items inside it. The top of the seat is designed to break/crumple/deform/distort so that your backside breaks through the 'lid' of the box and has room to travel into the box."

 

There are two questions that arise from this simple concept:

 

Firstly, how do you keep the safety harness tight whilst the seat is crushing? Simply putting a crushing element under the pilot's backside will normally allow the seat belt to slacken when the think crushes, which allows "submarining" - i.e. sliding forward under the belt.

 

Secondly, how do you prevent the control stick from injuring the pilot? AS OK says, a side-stick is a bit awkward on a single-seat (or tandem) layout.

 

My answer to the first question was to mount the stick pivot under the front seat cross-member, so the stick goes down with the seat. It requires some tricky design in the linkages, but the geometry takes the stick down and forward as the seat collapses. There may be a simpler way; the seat gets quite complex.

 

My answer to the second question is to put the lap-strap anchorages on the seat - and make sure the seat structure will not tear loose from its base pivots as it collapses. The shoulder harness anchors to the airframe in the usual way, which means it pulls tight as the seat goes down.

 

This approach seems likely to provide excellent occupant protection, but it's very labour-intensive to build - and not at all suitable for retrofit into an existing design.

 

 

[bexrbetter]

Let's hope the harness doesn't let go!

All car racing harnesses have to be approved and need to pass tests before getting that approval so look into those brands, there hundreds of race shops/online around.

 

Willans are one of the better and better known ones but there are cheaper alternatives that are still approved.

 

http://willans.com/

 

You have a look at what drivers walk away from in race cars through having proper harnesses, a good seat and a helmet.

 

And while I think of it, never mount you shoulder straps below shoulder height horizontal, some go over their shoulders and then over the back of the seat straight down to the floor, in this arrangement when you go forward in an impact, the straps compress your back .

 

 

[Dafydd Llewellyn]

Thank you, gentlemen. Looking at this thread, especially posts #4, #5 and #9 - and also that somebody found post #18 funny - and also the limited number of respondents - shows me that whilst there are a minority of people who do care about " secondary" safety considerations, and some serious thoughts there, the majority of people really aren't interested. This demonstrates yet again what Edsel Ford found out - safety is not a marketable commodity.

 

I wonder what % of the readers of this Forum would buy a somewhat more expensive aircraft, if it offered a higher level of safety? Not a sufficiently significant percentage, I suspect, to make it attractive to manufacturers to put out more than the most basic product; but to make manufacturers place some importance on styling.

 

So we get what we deserve - stylised garbage.

 

 

[Yenn]

We will pay for safety, but to get us to do that you have to make a big deal of it. make it look as if your safety device is really outstanding. The ballistic schute people are doing that, but my opinion is that it still has a lot of faults. One pilot popped his schute and came down in a dam. Due to the undercarriage not collapsing as it would have done on land he survived but is a quadraplegic.

 

The 5 point haness is very little more costly than the 4 point so it should be a no brainer.

 

One of the dangers we havn't mentioned here is in fuselage fuel tanks. My Corby has 40litres directly in front of the instrument panel. Just breaking a pipe will cover my legs with fuel and a serious crash would most likely break a pipe. The battery is directly beneath my legs, so in the event of a crash the first action is to shut off the master switch, next action is hope for the best!Fuel in the wings is much better, even if the wing is above your head in the top of a biplane.

 

 

[Dafydd Llewellyn]

Same situation in the Auster III I used to fly to work in, when I worked for H de H at Bankstown. You won't find that in many modern certificated aircraft - but it's still being done in some homebuilts.

 

Fuel system safety in an emergency landing situation is a major issue; in fact whether of not the fuel tanks rupture is probably one of the deciding factors in defining whether an accident is "survivable".

 

 

[metalman]

Thank you, gentlemen. Looking at this thread, especially posts #4, #5 and #9 - and also that somebody found post #18 funny - and also the limited number of respondents - shows me that whilst there are a minority of people who do care about " secondary" safety considerations, and some serious thoughts there, the majority of people really aren't interested. This demonstrates yet again what Edsel Ford found out - safety is not a marketable commodity.I wonder what % of the readers of this Forum would buy a somewhat more expensive aircraft, if it offered a higher level of safety? Not a sufficiently significant percentage, I suspect, to make it attractive to manufacturers to put out more than the most basic product; but to make manufacturers place some importance on styling.

 

So we get what we deserve - stylised garbage.

The latest version of the doctor killer seems to sell well, and popping the chute over the blue mountains was pure marketing genius( yeh I know I'm just being a smart as*e), personally I prefer the rag n tube types, they're strong ,fairly light, easy to repair and seem to handle a stack pretty well, vans 24000 ( with ,I think one of the highest completion ratios of any kit plane) smiling customers can't be wrong,,,,,,every aircraft is a compromise, from speed to comfort, and safety!

I will be looking at the fuselage on mine when I get to that stage ,I'm thinking some 4130 tube running from the bulkhead where the belts attach through to the panel ,I'll have to nut it out when I'm building that part but it has certainly been following the thread

 

 

[Guest Andys@coffs]

So in this thread I'm a lurker, I don't have technical expertise or relevant life experience to comment. Don't take my silence as lack of interest! I've read every post and am the better for it I think.

 

Safety was certainly a consideration of mine when choosing which trusty steed I would plonk down the ready's for. Since then the great debate about J engines has occurred....at the time though there wasn't much around about reliability and in general,it was thought the 6 was better than the 4......

 

Safety wasn't just another aspect it was a pretty important aspect. Reality is that most recreational pilots won't get enough hours or diversity in those hours to ever become the best there is, and as such anything that adds to our side is worth considering IMHO

 

Andy

 

 

[bexrbetter]

One of the dangers we havn't mentioned here is in fuselage fuel tanks. The battery is directly beneath my legs, so in the event of a crash the first action is to shut off the master switch, next action is hope for the best!F

Again refering to race cars, safety rubber bladder fuel tanks are widely available and reasonably priced, They are a must in some classes.

 

Could consider using a mercury switch that will kill everything if the plane goes inverted.

 

 

[kaz3g]

Same for me...I'm wedded to the Auster but I do think about the issues and survivability. Thank you for the thread.

 

I replaced the lap sash with a Hooker Harness but I wonder about the seats. I have the standard canvas buckets with a firm moulded sponge cushion on top. Should I put polystyrene inserts into the space below the canvas? I thought the canvas actually gave that progressive failure assurance?

 

I sit on one fuel tank (external belly tank) and the other is over my knees but not much I can do about that.

 

Kaz

 

 

[turboplanner]

I

 

Now you blokes have got me worried about that steel tube mounted just forward of my wedding tackle. I'd rather a side stick, but that's not so easy in a single-seater.My 4-point seat belt is old and getting hard to adjust. Anyone know where I can get a good 5-point harness from?

I would recommend a five point Simpson racing harness OK. Slightly heavier but when the belts drop on to your shoulders you feel safer, and I've been in about eight crashes which would border on fatal in a road car and the wide belts have never left any bleeding - plenty of bruising though. Easy to get in and out of, all points are released with one latch designed so it can easily be operated with heavy fire resistant gloves, so very easy to use.

 

 

[Geoff13]

I also am watching this thread will interest. Please do not take my lack of comment as lack of interest. I just feel with my expertise at this stage, I have very little to add to the conversation. I am currently looking for an aircraft and am in two minds. When it comes to accident survivability it seems that one make is a clear leader, in other threads it seems that same make is more likely to be involved in an accident due to reliability.

 

So does one buy a crash worthy aircraft that is likely to have reliability problems or a less crash worthy aircraft with less likelihood of the fan stopping.

 

This is not aimed at the motor in particular but there really are some very mixed messages out there at the moment.

 

Cheers Geoff13

 

 

[Happyflyer]

Geoff13, I agree with you about the mixed messages. Aviation is all about compromise. Lift and drag, power and weight, fuel capacity, range, speed etc etc etc. Crash worthiness is just another variable to consider. A helmet would probably be a very handy thing in a crash but who wants to wear one of those all of the time? Just remember the majority of accidents are in someway linked to the pilot so if we get that part right we may not need to use the crash worthiness.

 

Happyflyer

 

 

[turboplanner]

How important are safety considerations to you?

Dafydd, you might have widened the safety discussion with this question and I'm one of the guilty parties.

 

There's quite a large percentage of the community which just isn't interested in safety unless they are directly involved, so in the automotive and transport industries legislative motivation has been used with good support and very little objection.

 

In the various forms of motor racing, most people still seem to build to the minimum standard, but there is better acceptance of the higher costs.

 

Reading the above, I think the reaction on this thread is quite positive.

 

Going back to low wing open top fuselages, I think steel space frames have a lot to offer the home builder because if there are foot locations on top of the wing, the top tube can be quite high and still allow reasonable access, and you can design in some progressive crumple,and even some upper body protection, because the skins can be very light.

 

 

[Dafydd Llewellyn]

Yes - well, the thread was supposed to be about what car manufacturers term "secondary safety"; and the overall message on that is that there's considerable scope for improvement; and that it would be more widely applied by recreational aircraft manufacturers if:

 

(i) The means of qualifying an energy-absorbing seat were greatly simplified from those that apply to FAR 23.562;

 

(ii) The consumers indicated that it is a significant factor in their purchase decision.

 

Of course, overall safety is what the consumer looks for, to the extent that he considers it a priority, and that has to take into account all the various accident causes that are not simply pilot error. Engine reliability is a major aspect of that. But that's been hammered to death and I doubt there's any benefit to be gained by re-visiting it right now.

 

Going back to "crashworthiness" , it's obvious that is cannot readily be an "add-on", though there may be some things one can do to improve it in specific aircraft types. But to make a major improvement requires that it be designed in to the aircraft from the outset - and one does not see that in most recreational types. I hope this thread will give people some ideas as to what to look for in the detail design of the aircraft on their "short list".

 

 

[dlegg]

Yes - well, the thread was supposed to be about what car manufacturers term "secondary safety"; and the overall message on that is that there's considerable scope for improvement; and that it would be more widely applied by recreational aircraft manufacturers if:(i) The means of qualifying an energy-absorbing seat were greatly simplified from those that apply to FAR 23.562;

(ii) The consumers indicated that it is a significant factor in their purchase decision.

 

Of course, overall safety is what the consumer looks for, to the extent that he considers it a priority, and that has to take into account all the various accident causes that are not simply pilot error. Engine reliability is a major aspect of that. But that's been hammered to death and I doubt there's any benefit to be gained by re-visiting it right now.

 

Going back to "crashworthiness" , it's obvious that is cannot readily be an "add-on", though there may be some things one can do to improve it in specific aircraft types. But to make a major improvement requires that it be designed in to the aircraft from the outset - and one does not see that in most recreational types. I hope this thread will give people some ideas as to what to look for in the detail design of the aircraft on their "short list".

Daffyd, you make a very valid point in that in considering an aircraft purchase it must be designed from the outset with safety in mind. There aren't any homebuilts or LSA varieties that I have seen that really can claim this. New certified "safe" aircraft are simply priced too high for us recreational pilots. I.E new 172 is close to $500k, and just how robust and safe is it really? Granted, a lot safer than a RV, Zenith, Tecnam etc, but a high impact accident I think is a hard thing to survive regardless of aircraft design.

Clearly, operating a Drifter or Thruster carries a higher risk than a 172, protection wise that is. But the pilot must be aware of this and operate them accordingly.

 

Is there any recreational aircraft available, for a reasonable price, that has a higher crash worthiness inherently built in, that is readily available?

 

 

[M61A1]

A photo showing the structure of UH-60 pax seats, the structure is very light, yet is designed to compress under vertical/forward load. Note that he angled struts all facing the same direction, regardless of which direction the seat faces.

[Guest ozzie]

A few years back an Army Porter went in at Jaspers Brush on takeoff due to incorrect trim setting. The aircraft stalled and slammed into the ground right wing low. There were nine jumpers on board 3 killed i think. All were sitting on milk crates. Spinal injuries to the survivors were minimal. This was put down to the way the crates compressed under the load. Some studies were done by the NSW University. The results supported that theory.

 

 

[Guest ozzie]

Between a Drifter and a Thruster, i'd go the Thruster. Wings and tail boom and the engine and boom out front plus the structure around the pilot offer pretty good protection.

 

The Drifter, sitting out front is like going into a fight leading with your chin. Then the engine is going to smack you on the back of the head for good measure.

 

 

[reggie]

Yea sorry about the # 18 post funny, total accident. Scrolling on the ipad this sometimes happens. Not all perfect like some of you wankers.

 

 

[rgmwa]

So far I've also just been following this thread as an interested spectator, since I haven't had anything useful to contribute. However, I've been looking at the RV-12 cockpit more closely in the light of some of the comments here, and there are some points that may be of interest following on from the earlier RV incidents. Firstly, the RV-12 cockpit floor is ramped up under the thighs, and the standard foam seat bottoms are 6" thick, - more if you add the supplied bolster for those people who like to sit up a bit higher. Ideally, I guess the foam should be Temperfoam (and I'm thinking about getting some seat bases made using this material), but hopefully the depth of the seat should provide reasonable cushioning in a near vertical impact. The seat belts are a five-point harness and together with the ramp should stop the lower body sliding forward.

 

There is a hefty roll bar braced back to the top of the rear fuselage. The shoulder belts are attached to the upper fuselage just behind the rear window, so if the body folds up the shoulder belts would obviously lose their effectiveness. However, the bottom of the roll bar is also braced back to the cockpit sides with a short raking strut, and although the cockpit rail has the previously mentioned structural angle frame, the angle is reasonably well restrained against buckling by a 50mm wide secondary lipped rail and vertical fuselage stiffeners. Hopefully, the combination would be effective in preventing the fuselage from folding up in any reasonably survivable impact.

 

 

However, what has had me scratching my head well before any of this current discussion is the way the engine mount is connected to the firewall. Engine mount braces on other RV's, Cessna's and most other aircraft I've seen, typically connect at the outer edges of the firewall in line with main horizontal fuselage structural members. However on the 12, the two upper braces are about 250mm apart and are bolted to a pair of welded brackets riveted to the upper firewall and the instrument bay shelf, which in turn acts as a horizontal diaphragm to take the loads back to the cockpit rails. I thought this seemed like a somewhat flimsy arrangement (although more than 330 flying aircraft suggests that works OK), and considered adding some braces to the underside of the shelf to help transfer the loads to the side rails and also stiffen the shelf against buckling if the engine tried to force its way back into the cockpit in a head-on impact.

 

However, I'm hesitating because I haven't been able to decide if this apparently rather weak attachment method is part of a progressive crumple design that would be compromised if I tried to stiffen it. It's obviously a question for Van's although I doubt that they would want to discuss their design philosophy with me. Anyway, I mention it here only as I suspect that Van's have looked pretty closely at the safety of the cockpit structure in their more recent designs (RV10, 12 and 14) based on what they have learned from their older kits. You would hope so anyway, even though there will always be room for improvement.

 

rgmwa

 

 

[bexrbetter]

A few years back an Army Porter went in at Jaspers Brush on takeoff due to incorrect trim setting. The aircraft stalled and slammed into the ground right wing low. There were nine jumpers on board 3 killed i think. All were sitting on milk crates. Spinal injuries to the survivors were minimal. This was put down to the way the crates compressed under the load. Some studies were done by the NSW University. The results supported that theory.

Just to throw this one in, empty aluminium drink cans are awesome "crumplers", so good some years back a University competition for a bumper bar design for a crash test actually won over all the scientifically designed and built at great cost crumple designs. They bought a number of drinks and merely spiked a hole in them to drain them then taped them together. Apparently the tab opening gave way at 'X' pressure allowing the can to crumple after offering an initial air cushioning and worked a treat.

 

Might be worth looking at to put under your seats, weighs nothing.

 

 

[AVOCET]

Im trying to dig up photos of the avocet cockpit foam plugs ,

 

Of which i sculptured the seats for my wife & i . Then glassed over and into place

 

A 100 foam filled space under the seat with the aluminium control colum tube going through the foam to center stick .

 

In the prang the whole of the cockpit shatered under the impact and even the seat showed large areas of treeing and deformation , but conforming to my lower back shape & cussioned the impact and deforming the tube .

 

The turret and motor are high enough to be thrown clear in case of head on impact .

 

Like all things crashworthy , theres a certain amount of luck or good fortune in surving high end prangs !

 

Mike