" In a single you have a huge mass of metal weighing hunderds of kilos that crashes first before the pilot crashes."
Unless it’s a pusher.
A landing into a 25 knot wind can be stall speed minus 25 knots.
With an airframe parachute deployed, it’ll be 25 knots, followed by dragging unless there’s a quick release.
A landing up a steep slope will give better g deceleration before you hit something solid.
Your average fleet sitting at your local airport are all built to crash standards from the 60’s. Because of grandfathering rules, the “old” designs are just upgraded and sold as new.
This is the 9g requirement.
FAR23 has a much higher g requirement if I remember correctly any newly built planes need to withstand 21g.
Would you want to sit in a seat of a 60’s design, or in a seat that is designed to crumple under 21g???
RobertL18C wrote:
In fact MEPs have a much higher fatality rate per accident
Low handling / stall speed has been part of the choice for a 182 in my mind.
Now, I’m looking to install Vortex Generators, partly in the same state of mind.
They claim a reduction in stall speed by 8 KCAS (clean config) and 3 KCAS (in full flaps). This means stall speeds would go from 54/49 (w/o VGs) to 46/46 (w VGs)… In theory.
The point is that in case of a very bad day, it may:
- remove some extra knots and thus extra kinetic energy
- mitigate the risk of loosing control because of a stall
That said, Airbags utility has been studied, and the results is that, if they can help in some situations, it’s not by much.
AIRBAG UTILITY STUDY
Thank you for that. It’s an interesting read – not just regarding crashworthiness.
On reflection I’m sure the aircraft designers of the 1940s were humane people who did their best given the state of knowledge of the time. That said, the requirements seem pretty vague to me, and arguably either 1) my definition of a minor crash condition differs considerably from theirs or 2) a number of aircraft were wrongly certified as they lacked basic measures such as shoulder restraints that might have prevented vulnerable body parts such as heads from coming into contact with relatively solid objects such as instrument panels even under relatively low decelerations such as 9G.
In practical terms my reading of this is that seatbelt attachments would have to withstand a 9G force, but can’t see a lot else that they would have objectively needed to demonstrate. Reading part 23 I get the impression that requirements are perhaps deliberately kept vague, but that the actual requirements are set by exegesis such as the following:. Compared to the meagre requirements set out in part 23 or part 3 it’s like night and day – it also becomes obvious why modern aircraft are so much more expensive.
I’m fond of all the aircraft I’ve flown, particularly my own, whose crashworthiness has been likened to that of an orange crate. Without wishing to denigrate the classic types it would be disappointing if nothing worthwhile has been learned about crashworthiness over the past 6 decades.
Actually, they did think about crash survival, even in the late 1940s:
EMERGENCY PROVISIONS
ยง 3.386 Protection. The fuselage shall be designed to give reasonable assurance that each occupant, if he makes proper use of belts or harness for which provisions are made in the design, will not suffer serious injury during minor crash conditions as a result of contact of any vulnerable part of his body with any penetrating or relatively solid object, although it is accepted that parts of the airplane may be damaged.
(a) The ultimate accelerations to which occupants are assumed to be subjected shall be as follows:
A Upward———————— 4.5g Forward———————- 9.0g Sideward———————- 1.5g
The 9g reqirement for our old mature airplanes is in 3.386(a) of FAA CAR Part 3
[ local copy ]
kwlf wrote:
I find it hard to believe they were designed with crashworthiness as a significant concern.
I would agree that (pun entirely intended) that the crashworthiness of many older designs is purely an accident.
For the old stuff many of us fly, forced landing safety is mostly a function of how slow it lands and not much else.
Clearly aircraft are not cars and have a much tighter weight budget, but I would be surprised if there are no ‘easy gains’ to be made.
Reading around on the internet there are some interesting ideas, such as beveling the bottom of the firewall so that if you hit nose-low, the aircraft is more likely to slide rather than dig in and your deceleration is slower. That’s not going to weigh a lot. You’re less likely to injure your feet if you have flat rather than tubular pedals. Spinal injuries in glider pilots have been reduced by correctly designed cushions. Paraglider pilots used to use composite back protectors, but it was found that they concentrated stresses and caused avoidable fractures. Simple padded harnesses gave more protection. Cubs have a mod that can prevent the spar from being thrust through your head should you crash. And so on.
kwlf wrote:
I very much doubt it was because passive safety was a solved problem in 1955.
Within the weight budgets that apply to light aircraft (equally then and now) armoring the cockpit is not as viable a concept as it is for an elephantine 2018-style car, which is one reason it wasn’t done then and isn’t now. Aircraft are not cars. Parachutes are a better solution, for some aircraft and some accidents. They wouldn’t work well on a car. Good seat belts remain a good idea for pilots, then and now: in my many decades old aircraft I wear either a four point or (usually) five point harness. The five point harness was installed at the factory in 1971. Not many people wear five point harnesses commuting to work in their car. Air bags don’t add much if you use the harness. Seats that absorb vertical acceleration may help a little, not something that’s effective on cars.
Its got nothing to do with new or old designs, but I do think some air frame designs are better than some other designs in specific kinds of collisions with objects on the ground, e.g. steel tubular structures as per Mooney sometimes absorb more energy when hitting an immovable object, strut braced high wings as per Cessna are better for flipping upside down after impact, two doors instead of a single door or sliding canopy generally provides easier egress.
Jacko, can you link to the certification criteria for 1950s designs such as the 150/172? All I can find is a document talking about luggage restraint criteria being increased from 4.5g to 9g at some point in the 1960s. Heck, there are still C172s around with no shoulder restraints, and could nobody have thought of making a way for doors not to jam closed on impact so you didn’t have to remember to open them whilst performing a forced landing? I find it hard to believe they were designed with crashworthiness as a significant concern.
Through my job I often meet people who have been in car crashes. The things that people get away with in modern cars are stupendous. They roll multiple times; they hit lorries coming out of 90 degree junctions on main roads (60mph before you start braking). They hit trees backwards at 70mph – quite how, I don’t know, but they do. And generally speaking they get away without any significant harm other than bruises where the seatbelts go, and airbag tattoos.
People in older cars seem to end up as inpatients even when the accidents were much less energetic. Last year I was surprised when two people told me how slow their accidents had been – 20-30mph. One was in a 1970s Ford Fiesta which apparently now counts as a classic car. The other was in a VW camper van of similar vintage. I believe the official statistics bear me out. This isn’t an ‘European economy sedan’ thing: American car accidents are 5-6 x less likely to kill you per mile these days, compared to the 1950s when our spamcans were designed.
My vote would be for the C172 being so safe primarily because of those glorious flaps which mean you can crash at jogging speed at a location of your choice. I very much doubt it was because passive safety was a solved problem in 1955.
