Terrafugia wants to make their roadable airplane meet the 571.208 passive restraint requirement. Basically they need to hit the wall at 35 mph and get under 1000 HIC.
Here is the problem: Mass ratio.
Let me explain: Basic mechanics of the crash is two masses coming together and joining.
If you assume 35 mph for both the low weight Terrafugia (lowM) and the Higher weight vehicle that hits the Terrafugia (highM), the mass ratio results in an "equivalent barrier crash" of the following speeds depending on the mass ratio.
Ratio __ lowM __ HighM
1:1_____ 35______ 35
1:2 ____ 55 ______15
1:3 _____60 ______10
1:4 ____ 62 _______8
1:5 _____64 ______ 6
1:10 ____67 ______3
1:100 69.6 0.4
If the Terrafugia hits a vehicle of equal weight, the crash test and airbags are valid. Clearly as the weight ratio increases the airbags become unable to save the life of the occupant. Since 99% of all vehicle are at least more than 2 time the weight of the Terrifugia, the system will only be good again motorcycles. Even a Smart car at 2000 lbs would give a 50 mph barrier crash and result in near death.
In order for the Terrafugia's safety equipment to have meaning against a Buick or Camery, which is around 1:3 in ration, the Terrafugia MUST be able to be near a 60 mph test and below 1000 HIC (Acceleration^2.5 x period of 0.036 seconds).
The Terrafuia's crash protection is USELESS if it only is based on 35 mph and near 1000 HIC.
This requires at least 3.8-4 times MORE stroke than a 35 mph test provides.
Bottom line is the Terrafugia has WASTED $5 million because the CEO (Phd from MIT) missed this issue, or at least has been duped into the false dogma of the NTHSA.
That said, then what is needed? Clearly a vehicle with a 70 mph barrier test below 1000 HIC. (1000 HIC is about 60 G's if you back out the numbers...).
Said in terms of stoke, if 35 mph requires 1 ft to get 1000 HIC, you need 4 feet of stroke, or 4 times the protection.
In a car with 3 ft of nose and 1 ft of interior bag space to stroke, current airbag inflation issues make it so that 2-3 ft of stroke is used in order to get the bag out and get 1 ft of stroke in the airbag. Belts cannot stretch 4 ft, nor can a person lean over 4 ft. Therefore the additional 3 ft of stroke must come from the vehicle. Current car engine layouts WON'T work. BTW, I made this presentation to Autoliv who has 40% of the airbag market. Basically the old bags MUST be replaced in part by new technology to achieve the needed stroke.
Holden
Here is the problem: Mass ratio.
Let me explain: Basic mechanics of the crash is two masses coming together and joining.
If you assume 35 mph for both the low weight Terrafugia (lowM) and the Higher weight vehicle that hits the Terrafugia (highM), the mass ratio results in an "equivalent barrier crash" of the following speeds depending on the mass ratio.
Ratio __ lowM __ HighM
1:1_____ 35______ 35
1:2 ____ 55 ______15
1:3 _____60 ______10
1:4 ____ 62 _______8
1:5 _____64 ______ 6
1:10 ____67 ______3
1:100 69.6 0.4
If the Terrafugia hits a vehicle of equal weight, the crash test and airbags are valid. Clearly as the weight ratio increases the airbags become unable to save the life of the occupant. Since 99% of all vehicle are at least more than 2 time the weight of the Terrifugia, the system will only be good again motorcycles. Even a Smart car at 2000 lbs would give a 50 mph barrier crash and result in near death.
In order for the Terrafugia's safety equipment to have meaning against a Buick or Camery, which is around 1:3 in ration, the Terrafugia MUST be able to be near a 60 mph test and below 1000 HIC (Acceleration^2.5 x period of 0.036 seconds).
The Terrafuia's crash protection is USELESS if it only is based on 35 mph and near 1000 HIC.
This requires at least 3.8-4 times MORE stroke than a 35 mph test provides.
Bottom line is the Terrafugia has WASTED $5 million because the CEO (Phd from MIT) missed this issue, or at least has been duped into the false dogma of the NTHSA.
That said, then what is needed? Clearly a vehicle with a 70 mph barrier test below 1000 HIC. (1000 HIC is about 60 G's if you back out the numbers...).
Said in terms of stoke, if 35 mph requires 1 ft to get 1000 HIC, you need 4 feet of stroke, or 4 times the protection.
In a car with 3 ft of nose and 1 ft of interior bag space to stroke, current airbag inflation issues make it so that 2-3 ft of stroke is used in order to get the bag out and get 1 ft of stroke in the airbag. Belts cannot stretch 4 ft, nor can a person lean over 4 ft. Therefore the additional 3 ft of stroke must come from the vehicle. Current car engine layouts WON'T work. BTW, I made this presentation to Autoliv who has 40% of the airbag market. Basically the old bags MUST be replaced in part by new technology to achieve the needed stroke.
Holden
