Stuck in grass

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gcampbe2
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Stuck in grass

Post by gcampbe2 »

I had my first experience parking my DA40NG on grass last weekend, and an experience it was! The ground was not soggy, though it had rained a couple of days before, so the turf was also not rock hard. What I found was that as soon as I departed the asphalt taxiway onto the grass I needed a good 70% power just to keep inching the plane forward. Trying to subsequently move the plane by hand required three men giving 100% (me pulling on the tow bar, and one guy pushing on each wing).

I could see clearly that the issue was the tires trenching into the grass several inches. During my time trying to get my plane positioned a couple of other planes came and moved around on the grass adjacent to me with no issue whatsoever.

The culprit, I believe, were my Beringer wheels, and the associated 110 PSI inflation pressure. My theory is that my tires were both rock hard at 110 PSI, and also had a much reduced area in contact with the sod, resulting in the aircraft weight being concentrated onto a small area, and hence my beautiful trenches in the sod and extreme resistance while moving the aircraft.

A couple of questions:

1) Does this align with the experience of other pilots with Beringer wheels?
2) This experience makes me think that soft field landings and takeoffs would be very difficult with Beringer wheels, and my ground roll would be way above POH numbers. Anyone with experience doing grass fields with Beringer wheels? On the plus side I bet I would beat the pants of the landing ground roll numbers :P
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chili4way
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Re: Stuck in grass

Post by chili4way »

A couple of thoughts:
  • that 110 psi pressure seems to be high, almost bicycle high. what does the label on the wheel faring specify? I don't have the Berringer brakes and wheels, and my DA40NG is 48 psi for the mains. it seems odd that the psi would be double.
  • when I took my plane to Oshkosh in 2019, I was advised to get a piece of plywood or perhaps a thick plastic cutting board to distribute the airplane weight over a larger area of ground. It helped.
A relatively high power setting to taxi on grass isn't unusual, and it's better to keep the plane rolling than stop and try to get moving again.
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chili4way
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Re: Stuck in grass

Post by chili4way »

See photo below taken from a friend's 2022 DA40NG with Berringer wheels & brakes. Looks like you're over-inflated. What instruction did you get from your distributor (or ferry pilot) about tire inflation (if any)?

IMG_2143.jpg
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gcampbe2
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Re: Stuck in grass

Post by gcampbe2 »

Thanks Paul. Interesting that they would be so different. Mine are definitely placarded for much higher (110 PSI if memory serves). I'll be out at the plane tomorrow, and will take photos and post them.

Definitely my tires look much more inflated than your friends, with less rubber in contact with the ground, as one would expect at a higher pressure.
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gcampbe2
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Re: Stuck in grass

Post by gcampbe2 »

Here are the photos of the rear and front tire placards (112 and 88 PSI respectively).

Rear:
beringer_rear.jpeg
Front:
beringer_front.jpeg
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chili4way
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Re: Stuck in grass

Post by chili4way »

I've sent a ticket about the discrepancy to Diamond Canada support. From what I've found, it may be a matter of which tubeless tire is paired with the Beringer wheels. There appear to be two "plys" available 6-ply and 10-ply, and that could be the difference.

Nose (5.00x5)
  • Flight Special II / 505T61-1 / 6-ply
  • Flight Eagle LT / 505T08-1 / 10-ply ← you appear to have these
Mains (15x6.00-6 or 6.00-6)
  • Aircraft Rib / 461B-2297-TL / 8-ply / 6.00-6
  • Flight Custom II / 156E06-1 / 10-ply / 15X6.0-6 ← you might have these
  • Flight Eagle LT DDT / 156E06B1 / 10-ply / 15X6.0-6
The pressures placarded on your plane are within the same range as Cirrus aircraft with the same Beringer wheels and (at least) your nose tire. A Cirrus training source offered this about their Beringer wheels/tires: "The nose wheel should be 40 to 90 PSI and the mains should be 62 to 112 PSI."

We'll see what Diamond says... and I'll try to find out which tires are installed on my friend's plane.
Here's a handy Goodyear tire size reference.
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Re: Stuck in grass

Post by gcampbe2 »

Wow - thanks for digging up all that information Paul! The different plys do explain the discrepancy in inflation pressures.

Of course, I go back and wonder: With the 10-ply mains inflated at 112 PSI, what would happen landing on a grass strip? The amount of weight on the mains would be relatively low on initial touchdown because the wings would still be generating lift. But, as the nose wheel touched down, reducing the AoA, the weight transferred through the mains would rapidly increase, and with it (I assume) a similar trenching effect to the one I experienced. I think perhaps the wise approach, if one knew in advance that they would be doing soft field landings, would be to decrease the pressure to the minimal allowed (looks like 62 PSI for the mains based on what you found).

I, for one, would be very nervous about conducting a soft-field landing with the tires at 112 PSI, unless I knew the turf was bone dry and rock hard. For takeoff the POH states to add 45% to the ground roll for grass longer than 2", and another 15% if the grass is wet. My gut tells me those numbers are for the standard tires inflated to 48 PSI. I think the distances would be significantly longer at 62 PSI, and even worse at 112 PSI.
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Re: Stuck in grass

Post by chili4way »

Greg, I have no experience with a grass landing, only with grass taxiing and parking. Another DANizen may be able to provide an experience-based perspective.

I think it's a balance between minimizing the rolling friction due to tire deformation (which would favor inflation toward the higher end of the allowable range) and the mud-sink factor related to the amount of surface area distributing the weight of the airplane on the ground (which would favor inflation toward the lower end of the range).

As an aside, I noticed you have wheel fairings ("pants") on your mains, but not on the nose. Any reason why?
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Re: Stuck in grass

Post by alanhawse »

The relative placement of the hole in the fairing and the valve stem is super frustrating to get an air hose/gauge onto it … I tried several different angled valves… and I have something which is only adequate at this point

If anyone knew what the perfect solution was I would sure like to know
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Re: Stuck in grass

Post by Davestation »

Beringer lists 112psi as the MAX pressure for the 15x6-6 tires in their CMM, however in their installation manuals they merely say to follow the aircraft manufacturers' instructions. The ICA for the DA40 as an example:
Beringer.png
Indeed there are different tubeless tire options. I believe the kits normally come with Michelins but those have been out of stock and lately they've been using Goodyear, so the ply rating will likely vary as well from plane to plane. I'm not sure which is standard for the DA40 specifically but I believe all the Michelin tires that are rated for tube and tubeless (Air/Pilot) are 6ply whereas the standard Goodyear tubeless (FCII) is 10ply.

That said, I wouldn't think you'd inflate them higher just because they have more plies. As stated above, Beringer doesn't speculate different pressures based on which tire is used, they just say to refer to Diamond, who otherwise uses a 6ply tubed tire.
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