Would a roll cage plus a safety harness make a small GA aircraft accident more survivable? It seems to me that race cars (like Formula 1 and NASCAR) and small GA aircraft (like a Cessna 172 or Piper Cherokee) travel at generally the same speeds, roughly between 70 and 200 mph. Yet, if an accident happens, you appear to be more likely to die in a small plane than a race car.**

I figure this may have to do with some of the safety features of race cars versus the safety features of GA aircraft. The main features being the racing harness and the roll cage.  (And also, as Freeman pointed out in a comment, the HANS device and the helmet help quite a lot as well, especially in frontal impacts.)

I know roll cages weight about 80lbs and that they aren't cheap, and I know a safety harness can be difficult to put on and people might not like using them, and I know a HANS device can be cumbersome, as also a helmet can be. But forget all of that for a moment. I'm not asking about why we don't use them from an economic/utility perspective.  

What I really want to know is if putting these in a small airplane would be of any benefit to begin with. It's true that they are massively helpful in racing vehicles, but I wonder if the forces racing vehicles face during a crash are markedly different than what you would find in your typical GA crash (e.g., perhaps aircraft accidents happen at less predictable angles, or involve more torsion, etc.). And if perhaps those differences in forces make the use of a roll cage and a safety harness kind of pointless in a small plane because they can't actually help in that kind of accident.

So, would all of these racing safety devices actually make a GA crash more survivable, or does the nature of GA accidents make their use less effective than they are in a race car?

** Try as I might, I couldn't find hard stats on "deaths per accident" in either area.  So this is mostly an impression I've gained from reading a lot of NTSB reports and watching a lot of racing. The fact may be debatable, but shouldn't detract from the main question.
Short answer: Yes, a better harness would help in some cases, but will achieve little all by itself. A roll cage might help in a few cases, too, but would be much less effective per pound.

Your observation is correct: Race car drivers enjoy a lot more protection than GA pilots. This is a rather recent development; 30 years ago the chances of surviving a crash were equally low for both.

There are two factors which stand out in a GA crash:


Peak accelerations which will lead to internal lesions like the rupture of the coronary blood vessels, and
Physical injury by sharp objects entering the occupant's space, including flailing limbs being hurt by sharp objects in the cabin.


Both factors were also killers for race car drivers, and they were defused with improved design methods. A safety cage is not just a frame around the driver: Any structural failure must occur in such a way that the structure fails away from the driver. In addition, the whole car body is designed to crumple at roughly the same force over its length in order to use the available crumpling zone as well as possible. This allows to decelerate the safety cage at a constant rate, so that peak loads can be avoided. A third factor is a much better restraint system, of which the HANS device is only one aspect. Using five-point harnesses would already help to avoid "submarining", a process where the pelvis slides under the lower restraint, causing the harness to press against the intestines. The image below shows the regular pelvis location and body contours as a dashed outline and the displaced pelvis and spine as a solid line. The displaced body is the shaded area.



None of this was considered at the time when today's GA aircraft were developed and the regulations were set up. At that time the prevailing opinion was that nothing could be done in a crash, so all efforts focussed on avoiding crashes in the first place. Adding only parts of the whole protection packet will be of little help - only their combination can effectively protect the race car driver. Even the 5-point harness needs an adequate seat and properly located mounting points to be effective.

The US army has collected all research up to the early Eighties in a five volume work called the Army Aircraft Crash Survival Guide (pdf!). It's intention is to improve the crash survivability for helicopter occupants and Army aviators, and much can be transferred to General Aviation. If you look for hard stats, you will find at least lots of citations there. I remember in particular a study from the Fifties where statistics showed that J-3 pilots would mostly be killed in a crash, while the rear occupant would show only minor injuries. In the study, Pipers filled with test dummies were put on rails and crashed into an earth wall. Funny stuff.



A J-3 in Army livery. Then it was called O-59 or L-4.