# Crashworthiness

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#### Sockmonkey

##### Well-Known Member
Stacks of ping-pong balls in a matrix of that spray-foam insulation in a can.

#### Midniteoyl

##### Well-Known Member
Thank you very much that is a data point....So how do I measure the results without strain gauges and a scope.

##### Well-Known Member
If you find a good answer to this, let me know. I've got about 3" under my seat pan, and have wondered about the best material to put there. A honeycomb material of some sort (that's what is used to cushion equipment/loads dropped by parachute) seems to offer promise. It is very lightweight and seems to "progressively" crush with more and more load. I'd be concerned that typical 2 PCF XPS foam might be a bit stiff for getting maximum use of the whole 3" in a 10-25G drop (maybe use foam wedges or cones instead?). Viscoelastic foam would be terrific, but it is heavy and expensive.
If I had to do it right now, I'd go with 1/2" "soft" visco, 1" "firm" visco as padding on top of the seatpan (for comfort and impact absorption at moderate levels), engineer the seatpan to let go at about 10Gs (all harnesses remain fixed to occupants), then paper honeycomb for 2" under the seat with 1" of low-density XPS on top of that, under the seatpan. Strictly TLAR . . .
Aluminium foam. Does not spring back like many other foams. Honeycomb does neither.

Simply take pilot mass, critical G-load for the pilot and fail compressive strength for the medium under the seat and you're done. Having the seat remain intact under that load is essential. For crushing I'd aim at 15-20 G's.

Conforfoam is a great help too. Very confortable after 5 minutes and it doesn't spring back. Great addition to most airplanes.

#### SVSUSteve

##### Well-Known Member
Stacks of ping-pong balls in a matrix of that spray-foam insulation in a can.
Except the ping-pong balls probably aren't going to add much for the same reason as the soda can idea. In fact, it might actually reduce the energy absorption.

Given my choice, I would go with aluminum foam (which is the plan for the Praetorian) as suggested by Autoreply or with Rohacell foam wrapped in carbon fiber as tested to form attenuating keel beams in a previous research project.

#### Hot Wings

##### Grumpy Cynic
HBA Supporter
Log Member
-up to 3h record time...
Nice little unit for a "reasonable" price, but limited in the "G" range. A quick search turned up this little IC H3LIS331DL that would be very easy to add to a little Arduino to record and log up to 400 "G" for about $30 in parts. #### henryk ##### Well-Known Member Nice little unit for a "reasonable" price, but limited in the "G" range. A quick search turned up this little IC H3LIS331DL that would be very easy to add to a little Arduino to record and log up to 400 "G" for about$30 in parts.
=50 "G" is anoth to as!

#### SVSUSteve

##### Well-Known Member
If anyone is interested in the JAARS seats, this is the technical reference for the original design. I used to have a copy of the paper but no longer do. If anyone has a copy, I would appreciate if you could share it. An Energy-Absorbing Seat Design for Light Aircraft

#### BJC

##### Well-Known Member
HBA Supporter
The only drawback is that they continue to refer to the FAA regulations which are not realistic in terms of human survivability (the aircraft's design being the limiting factor). Otherwise, it's a very good starting point.
If I crash again, I hope to be in a Grumman Ag Cat, with nothing in the hopper, totally out of gasoline, on the parking lot outside of the Emergency Room at the hospital, just as a crew of EMT's is walking back to their vehicle.

BJC

#### SVSUSteve

##### Well-Known Member
If I crash again, I hope to be in a Grumman Ag Cat, with nothing in the hopper, totally out of gasoline, on the parking lot outside of the Emergency Room at the hospital, just as a crew of EMT's is walking back to their vehicle.

BJC
In theory at least, having the hopper full of water or slurry would actually probably increase the attentuation.

#### proppastie

##### Well-Known Member
Log Member
In theory at least, having the hopper full of water or slurry would actually probably increase the attentuation.
"attenuation (plural attenuations). A gradual diminishing in the strength of something. (physics) A reduction in the level of some property", so more mass means less G on pilot at crash?

#### NoStealth

##### Well-Known Member
There are other helicopter-plane seat patents-papers to limit G to 25-30? to reduce spinal compression in survivable crashes. Remember that spinal G tolerance decreases with age.

Stroke distance and energy absorption are key. Some of the factors include weight, age, seat position vertical to reclined, aircraft and seat springback, bottoming out without sufficient air crush space for foams. I doubt TLAR will survive the test.

Some compost sim and scale testing:
http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19990036755.pdf

Lumbar load attenuation for rotorcraft occupants using a design methodology for the seat impact energy-absorbing system : Open Engineering

"sensor fusion" has been around for some time. Some phones have had these for many years, there may already be a G app.
There are a number low cost vendor sensors e.g. STM, Freescale..

#### Sockmonkey

##### Well-Known Member
Except the ping-pong balls probably aren't going to add much for the same reason as the soda can idea. In fact, it might actually reduce the energy absorption.
The balls are just to create the honeycomb in a cheap and easy way rather than contribute much structurally.

#### SVSUSteve

##### Well-Known Member
The balls are just to create the honeycomb in a cheap and easy way rather than contribute much structurally.
Eh....you'd be better off with just a block of composite foam like Rohacell wrapped in carbon fiber/graphite.

Even off the shelf honeycomb in the thicknesses we normally see in designs (1/8" to 3/8") in and of itself doesn't have that great of attenuating properties. It's good for reducing weight but not much else unless you're going for a pretty substantial thickness.

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#### SVSUSteve

##### Well-Known Member
PropPastie said:
so more mass means less G on pilot at crash?
Ever seen those water-filled barrels in front of freeway overpasses? Rupture and blow the water out of one and you've expelled more energy before you hit a non-yielding object like a Jersey barrier or the bridge abutments than you would destroying the barrel itself. Same principle although it in theory would impart more load on the fuselage at initial contact in an aircraft crash.

#### BJC

##### Well-Known Member
HBA Supporter
Ever seen those water-filled barrels in front of freeway overpasses? Rupture and blow the water out of one and you've expelled more energy before you hit a non-yielding object like a Jersey barrier or the bridge abutments than you would destroying the barrel itself. Same principle although it in theory would impart more load on the fuselage at initial contact in an aircraft crash.
True, but in that case, the water is stationary. Energy from the car is transferred, somewhat "softly" to the water. In a hopper in an ag airplane, it is moving with the airplane and has, due to its mass, considerable kinetic energy.

BJC

#### SVSUSteve

##### Well-Known Member
True, but in that case, the water is stationary. Energy from the car is transferred, somewhat "softly" to the water. In a hopper in an ag airplane, it is moving with the airplane and has, due to its mass, considerable kinetic energy.

BJC
True but then the same applies to any mass you're carrying for energy attenuation purpose like under-seat stroking materials albeit to a much lower degree. It's why the cropdusters are designed the way they are because people- far more intelligent than myself, Autoreply, Billski, yourself or anyone else on this forum- realized that having any required mass out front is the best course of action for survivability and if you design the tank to burst, the action helps to safely decelerate the objects behind it. While it does increase the initial kinetic load, it does not seem to have a deleterious effect on survivability in comparison to most GA aircraft which crash at far lower kinetic energy levels. Part of it is due to making the mass work for you rather than against you.

#### cluttonfred

##### Well-Known Member
HBA Supporter
True but then the same applies to any mass you're carrying for energy attenuation purpose like under-seat stroking materials albeit to a much lower degree. It's why the cropdusters are designed the way they are because people- far more intelligent than myself, Autoreply, Billski, yourself or anyone else on this forum- realized that having any required mass out front is the best course of action for survivability and if you design the tank to burst, the action helps to safely decelerate the objects behind it. While it does increase the initial kinetic load, it does not seem to have a deleterious effect on survivability in comparison to most GA aircraft which crash at far lower kinetic energy levels. Part of it is due to making the mass work for you rather than against you.
And if you want to read about how the design process went creating the Texas A&M Ag-1, pretty much the granddaddy of all modern agricultural aircraft, read From the Ground Up by the late, great Fred Weick (who also came up with the NACA cowling and the Ercoupe) or if you're at the Smithsonian, you could read the original interview transcripts on which the book was based.

From Aerofiles.com...

Texas

Texas A&M College Aircraft Research Center.
Texas Ag-1 [N222]

Ag-1 aka Weick Ag-1, -2, -3 1950 = Agricultural plane. 1pOlwM; 225hp Continental E-225; span: 39'0" length: 29'8" load: 1200# v: 115/100/45 range: 400; ff: 1/x/50 (p: Ted von Rosenberg). Hugh DeHaven, Fred Weick. Might be considered as the mother of all modern ag sprayers in the world. POP: 1 [N222]. There followed Ag-2 with 450hp P&W R-985 in 1956, redesigned by George Wing at Transland Company (qv), and the 1958, Wieck-designed Ag-3, which became the prototype Piper Pawnee.