dynafoam seat cushions

[RansS9]

Anybody got experience with these cushions? In particular... required thickness to give adequate protection in case of an accident? I ask because I'm thinking of substituting our regular seat cushion (in a pitts) for one. Limited canopy height coupled with helmet means thinner is better; this can be at the expense of comfort (not a factor) but not safety (major factor especially given the recent report on the extra crash.)

Any opinions gratefully received TIM.

[Zulu Alpha]

I use one in an aerobatic aircraft. I only have room for a 1" thick one but I do sink into it so its probably half that thickness where I'm sitting.

They are quite delicate so do make a cloth cushion cover as they will rub away if not protected.

I have mine in a tight cushion cover which is attached to the seat pan with lots of velcro. I find this stops me sliding from side to side during aeros. This is much better than the old foam cushion.

Never tried the shock absorbing in anger though. There is some info on the aircraft spruce website
CONFOR FOAM SEAT CUSHION from Aircraft Spruce (http://www.aircraftspruce.com/catalog/cmpages/conForFoan.php)

ZA

[Pilot DAR]

I've had this foam in my seats for 15 years, and very much like it, with one major caution. If the aircraft will sit in temperatures colder than freezing, the foam will become rock hard. It softens once your butt warms it up, but the problem is that while it is stiff, if you kneel or stand on the seat, you will break the foam into co-located pieces, which then drift around within the covering. There really does not seem to be a way around this, other than to avoid placing a concentrated load on the cold seat (or only keeping the plane in a warm climate!)

Overall, a great idea though...

Pilot DAR

[Genghis the Engineer]

I've got some papers on design and use of them, which include graphs of thickness recommendations.

PM me a postal address and I'll see if I can dig them out and post you some photocopies.

But, from memory, 2-3" is about optimal for most light aircraft, and don't supplement them with other foams.

I can think of several people I know of who are still walking as a result of the stuff, and I'd certainly include dynafoam seats in my thinking about any aircraft build that I was planning.

G

[621andy]

The BGA highly recommend it be fitted in all gliders. Might even be 'law' in club gliders-sure someone will correct me.

Definitely a lifesaver though, or at least a back-saver.

But as someone else pointed out, ONLY use dynafoam- no other cushions.

[Fitter2]

There was a lot of work at Farnborough on this - the conclusion was that 3 inches is ideal, but less is a lot better than none to save your back. The foam was originally designed for comfort for wheelchair users, but US military studies showed that the deformation properties under stress of the firm type (actually 'extra-firm' in Dynafoam's rating system) reduced the maximum G on an ejecting pilot by well over 50% of the max stress. Enough to save you from a few years in a wheelchair needing the soft kind. The effect on heavy landings is the same, whereas soft foam actually increases the maximum accleration, as it compresses until you hit the seat which has by then stopped moving.

In practice, most modern glider cockpits only have room for one inch between the average pilot and the seat pan, but a half-inch layer of soft Dynafoam between your rear end and the firm layer deforms to add little thickness, improves comfort and adds a little more to the safety aspect.

As others have said, Dynafoam has been tested, proved to work, and is the stuff to go for.

I have PDFs of the study at Farnborough, and can e-mail them if anyone wants to PM me with an e-mail address.

I see they are available in UK here (http://www.afeonline.com/shop/index.php?manufacturers_id=16&osCsid=5b00680a7c34b609cfd9205e5f7a27eb)

[Rod1]

I use it in my MCR, but only had room for 12mm. It is incredibly good over a long run and has no downsides apart from cost.

Rod1

[RansS9]

Thanks for the informative replies. Your advice coupled with googled information (dynafoam + Dr Segal--he of the Farnborough research) results in:
--25mm(1inch) thick dynafoam pad heat cut to dimensions seat base
--covered in natural breathable material (cotton)
--actively secured so doesn't slip forward to impede control movements
--taken out after flight so the rodents don't eat it !
--protected from freezing temperatures so it doesnt fracture
--coupled with lumbar support (same material approx 10 1/2 * 4 inches of 1inch (25mm) thick dynafoam between back and parachute.)

Hopefully this may reduce the likelyhood of serious injury in an accident.
Now all I need to do is reduce the likelyhood of the accident which for me means WAY MORE LANDING PRACTICE !!

Thanks again TIM

[RansS9]

oopps forgot--it has to be "Extra Firm" grade Dynafoam.

TIM

[philjay]

This year some friends and I published our findings on safety cushions after a very lengthy period of experimentation.
The conclusion we reached was that a 2 layer combination of Confor C47 (1inch) with half inch of softer Confor C45 on top was very much more comfortable than Dynafoam alone and had better impact absorption. Dynafoam alone is OK but not comfortable. If you have the space in the cockpit then 2inches of C47 plus half inch of C45 is even better. Not just our findings, the USAF use it in ejection seats.
Phil

[Black Prince]

Following an incident involving a heavy landing resulting in serious back injuries to both occupants of an MT-03 Gyroplane, the AAIB has made two safety recommendations:

Safety Recommendation 2009-082
It is recommended that the Civil Aviation Authority amend the British Civil Airworthiness Requirements, Section T to make optimum use of energy absorbing materials in the construction of gyroplane seat structures, to reduce the possibility of spinal or other serious injuries to an occupant in a minor crash landing.
Safety Recommendation 2009-083
It is recommended that the Civil Aviation Authority promote the benefits of fitting energy absorbing seating foam to microlights and gyroplanes.

See AAIB September bulletin.

[chrisN]

If Confor is more comfortable than Dynafoam, it sounds as if one sinks into it at least a bit, whereas on Dynafoam it sounds as though one sits on it without much deformation at 1 g or only up to 2- or 3-g as in normal flight. Is that correct?

If this is true, how much Confor equates, when sat upon, to a 1-inch Dynafoam stiff pad plus a ½ inch Dynafoam “pudgee” (somewhat deformable) pad?

(The amount one can accommodate, with weight on seat, in a height –restricted cockpit, is limited by head-on-canopy syndrome.)

Chris N.

(PS – I am not getting into any comparison in energy-absorption effectiveness, just equivalence in thickness when sat upon. In fact, what would be nice for perhaps many users or potential users would be an equivalence table, somewhere on a website, if such exists.)

[philjay]

The research on the comfort of safety cushions made up of different combinations of Sunmate (branded Dynafoam in the UK) and Confor foams as well as Tempur is published in the paper entitled “Pressure measurements and comfort of foam safety cushions for confined seating” by Jackson, Emck, Hunston and Jarvis, published in June 2009 in the research journal Aviation Space & Environmental medicine: IngentaConnect Pressure Measurements and Comfort of Foam Safety Cushions for Con... (http://www.ingentaconnect.com/content/asma/asem/2009/00000080/00000006/art00011). The pressure mapping data showed that a cushion made up of a 0.5 inch top layer of Confor C45 on a 1 inch layer of Confor C47 would be comfortable for 85% of male pilots. It also showed that a cushion made up of 1 inch of Sunmate X-Firm (Dynafoam Extra- Firm, the standard Dynafoam sold in the UK) would be uncomfortable for 85% of pilots. The pressure mapping data shows the C45/C47 cushion adapting closely to the buttocks of the pilot. Sunmate X-Firm (Dynafoam Extra-Firm) did not do this. Self-evidently, you can only have low peak pressures if the torso weight is spread over a large area. The converse is true. In that respect, although the buttocks sink in a bit, as you put it, the glass transition temperature for Confor appears to enable the top surface of the foam to adapt well to the imposed “warm” weight.

Your question of how much Confor equates to 1 inch of Dynafoam when the foam is sat upon raises fundamental questions. Firstly the foams that we tested are all viscoelastic and absorb energy at high loading rates. Their compression at high loading velocities is significantly less than low rates. This is a key property. Pudgee is an extremely soft foam that appears to have low energy-absorbing properties. We are not aware of any tests on this material and we did not explore its properties. Secondly, your question requires the energy-absorbing properties of cushions made of the different viscoelastic foams to be compared. This needs to be undertaken for different impact rates and for different temperatures. We compared the different foams in an initially-uncompressed state in a paper entitled “A Simple Comparison of the Characteristics of Energy-Absorbing Foams for Use in Safety Cushions in Glider Cockpit Environments” by Jackson, Emck, Hunston, Jarvis and Firmin and published in April 2009 in Technical Soaring: Soaring Magazine Index for Technical Soaring organized by issue (http://soaringweb.org/Soaring_Index/Technical_Soaring/Technical_Soaring_issue.html#2009) . The relative order of the results is unlikely to be changed if the foams are tested pre-compressed, due to the relative stress-strain states of the foams in the pre-compressed and initially-uncompressed forms. Interestingly, an experiment undertaken by Segal, Anton, McKenzie and Gilkes in 1988 comparing soft furniture foam and a 0.5 ins layer of soft DLR90 on top of 1 ins firm DLR100 foam demonstrated this. Research by Hooper, Lim, Rahematpura, Goedken and Dakwar in 1994 at the American National Institution for Aviation Research at Wichita State University showed that the energy-absorbing properties improve when pre-compressed, which may seem counter-intuitive. In addition the research that we undertook and that was published in Technical Soaring corroborated the manufacturers’ claims regarding the percentage of energy absorbed – Confor absorbs around 97% of energy and Sunmate around 90%. This is extremely important because unabsorbed energy translates into a bounce – we have videos showing this. A bounce can ultimately generate an even higher deceleration than the initial impact in a crash. You cannot, as you propose, avoid comparing energy-absorbing characteristics. Thus, as you can see, there is no simple answer to your question.

With respect to cockpit space, this is at a premium in most modern gliders. The installation of energy-absorbing cushions often requires adjustments such as moving seat-back positions or removing existing seat cushions. Many glider pilots unrealistically think that they can just place a safety cushion in their existing cockpit and just “jump in and fly”. With respect to the Confor C45/C47 cushion, if, after trying to adjust the cockpit layout, there really is insufficient room, the top layer of C45 should be removed. Our research in Aviation Space & Environmental Medicine showed that Confor C47 was the second most comfortable viscoelastic foam. Furthermore, this single C47 layer has better energy-absorbing qualities than the equivalent 1 inch of Dynafoam Extra-Firm (Sunmate X-Firm).

As a final comment, the nearest that you will get to the equivalence tables that you requested are the results shown in our two papers.

Hope this helps. This subject is much more complicated than you might think. Good luck reading the research papers.
Phil

[MahirKaplan]

From the studies you have referenced, it shows that these foams are extremely effective at absorbing crash energy. So, why not use them underneath a seat as well, where the discomfort effects caused by them would not be important? I know aluminium honeycomb structures are used to absorb crash energy by deforming, but I'm fairly sure they dont absorb '90%+' of the energy as you describe these foams to be able to.

[Genghis the Engineer]

Because there are much lighter, cheaper ways of putting energy absorbing structure under a seat - the point of dynafoam is that it will conform to varying size and shape of pilot's backside.

G