DG Flugzeugbau

Safety Aspects for Glider Pilots

Dipl. Ing. Martin Sperber, representing the Air Transport section of The Technical Control Commission of Rheinland, ("TÜV  Rheinland") has studied safety questions for gliders intensively.  This has lead to results that are in part very surprising and should interest every Pilot.

1. Cushions:

 In almost all aircraft one finds various forms of seat- back- or leg-cushions in more or less good shape.  Almost no one knows that these cushions could be a great danger.

When the Martin Baker ejection seat for fighter planes was developed in the 50's, there were a number of  tests with dummies.  In the end, it was believed that they had an optimal concept and began delivery of the seat.  Not much later it happened that some military pilots had to use the seat.  The ejection seat was used three times and three times it worked as planed and three times it brought the pilot to the ground dead!

It turned out that in contrast to the dummies, the pilots sat on a rather uncomfortable survival pack containing a life jacket and inflatable boat, etc.  In order to make themselves more comfortable, they had put soft cushions of tooled leather on top of this.  That was all.

When the seat began to shoot out, the pilot remained unmoving for a few milliseconds while the cushion compressed.  That continued until the cushion was flat but the seat was now moving at a high velocity and rammed into the posterior of the pilot accelerating him abruptly.  This was too much for his spinal column......

The same thing happens with the use of a soft cushion in a glider.  The pilot is put into the position where he can continue unhindered in the original direction while the fuselage has already decelerated considerably.  This is particularly true of a hard "pancake" landing.  Also a horizontal movement is made possible by a cushion during a frontal crash.  This should not occur.  Even a back cushion is dangerous during a hard landing because of the semi-reclining position in a modern glider.  In this case, the upper body can continue its motion in the downward direction until it hits the glider seat which has by this time decelerated.

Therefore the best cushion is no cushion at all or is one made of energy absorbing foam.

Investigations in UK have showed that such a cushion of energy absorbing foam can reduce the impact for the pilot in the case of a crash and can save his health.

2.  Landing Gear:

 Flying too slowly resulting in a stall and "pancake" landing is a common accident.  This is usually caused by making the approach too slowly in a strong head-wind and encountering wind shear close to the ground.  In the next paragraph are some of the results of investigating crashes of this kind.

 A stall at 10 feet of altitude over an asphalt runway with the gear up can lead to severe injury or death.

The nature of the runway surface plays little role in this.  Even on grass, the impact is perhaps 2% less.  If, however, the gear is down and locked, there is usually no injury to the pilot in this situation.  Probably the main wheel and its support will be damaged.  The springs in the gear support structure will not sustain the impact of a hard "pancake" landing.  The energy is further absorbed by the bending of the gear support tubing.

There are still instructors who advise beginning cross-country pilots to land gear up on a plowed field or overgrown or forested land.  This prevents damage to the landing gear and the glider can be flown the next day.  But no one hears over the sounds of the crash the breaking of the pilot's vertebral column.  There is also the advantage that a wheelchair is cheaper than new landing gear!

Out of consideration to your spinal column, never land gear up under any circumstances!

In connection with this, some advice to the motor-glider pilots.  One often hears the complaint that the main wheel fork is to weak, and will bend during a hard landing.  There are pilots who have reinforced the fork by welding flat pieces of steel onto the forks.  It's better to leave them be.

The main gear fork is designed to be a break-away point and it's much cheaper than tearing the entire gear support mechanism out of the glider!  Keep a fork in reserve; then you can swear at the simple repair for 10 minutes and then go take off again!

3. The Headrest:

 The headrest is not primarily for the pilot's comfort.  They should not necessarily be used to rest your head against while flying.  That would be difficult to build because parachutes come in different thicknesses so the headrest position needs to be adjustable as it is in the DG-400.

Unfortunately, the adjustability does nothing for the actual purpose of the headrest.  In the case of a crash, the whole upper body including the head is accelerated forward.  Then it stops and springs backward to an over-extended position.  If you're lucky, this will only result in a whip-lash injury; if you're unlucky it could result in broken cervical vertebrae.  To prevent this, a headrest is necessary which can withstand 285 pounds force according to certification standards.  You can't achieve that kind of strength with an adjustable headrest.
 The headrest should be as wide as possible in case the crash is somewhat to one side in order to fully support the head.  Unfortunately a wide headrest makes it difficult to get at the baggage compartment.  In addition, a wide headrest reduces the visibility from the rear cockpit of a two seater.  As in many cases, a compromise must be taken.  But in any case the baggage compartment has to be covered sufficiently such that objects in it don't become projectiles hitting the pilot in the head or neck.

4. Airbag:

 Why shouldn't the safety-conscious manufacturer increase the safety of his gliders by building an airbag into an 80 mm instrument case and installing it in the instrument panel?  Because it would be ineffective.  In the first place, an airbag must be integrated into the entire glider as a system.  One cannot simply borrow something from the automobile industry as is.  In the second place, it's unnecessary because the distance from the pilot's face to the instrument panel is much larger in a glider than the distance to the steering wheel in an auto.  The head is held back much better with our shoulder harness than with an airbag.

5.  Ballistic Parachute:

 A system in which the whole glider comes down on a parachute has the disadvantage that the "landing" is rather hard and the pilot can be injured more seriously than if he jumped with a personal parachute.  Jumping with a parachute gives a good chance for an injury-free landing because the pilot has an excellent, built in  "sprung undercarriage":  his legs.

The pilot has to be sure he can safely exit the aircraft, of course.  At altitudes above 1000 feet, our NOAH (NOtAusstiegsHilfe) system can be life saving.  But at lower altitudes, the only useful system after a collision, for instance, is a parachute that lowers the whole aircraft to the ground.  The question then is whether it might be better to invest the construction changes and the weight in a super strong cockpit........

A rescue system in which only the pilot is separated from the glider by rocket assistance is hardly imaginable.  It would have to be some kind of smaller version of an ejection seat like in military aircraft.  Building such a system into a glider would be far too complex and costly.  Pulling pilots up out of the cockpit with the parachute would not work!

These were some of the conclusions presented at the Technical Control Commission of Rheinland, ("TÜV  Rheinland").

One year later we realized our new developed Consummate Safety Cockpit!

- friedel weber -
translated by David Noyes, Ohio, USA