Pawnee air-oil bear strut pressure

Larry Ruggiero

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Mar 5, 2018, 7:38:11 PM3/5/18

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Yes I know they’re problematic. Just returned our PA 25-235 from its annual, where one of ours was rebuilt (locked solid) and both serviced. Like I assume many of yours are, our Pawnee has no hopper and will never see gross weight again. So should the air side of the struts still be 575psi per the book? Noticed neither strut budged a bit during taxi and it landed pretty stiff. Plus the gear is now spread wide compared to “normal.” Called our IA and got a virtual shoulder shrug. Thoughts?

Larry Ruggiero, pilot/A&P
Carolina Soaring

Charles Longley

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Mar 5, 2018, 9:37:44 PM3/5/18

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OK I give up. What part are you talking about?

Charlie
Pilot/ A&P

Larry Ruggiero

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Mar 5, 2018, 9:41:18 PM3/5/18

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Landing gear struts instead of bungees.

Charles Longley

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Mar 5, 2018, 9:57:35 PM3/5/18

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Ahh who makes them? One of our Pawnees has bungees the other one has Cessna spring gear.

Charles Longley

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Mar 5, 2018, 10:04:26 PM3/5/18

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Never mind I found them as an option from Piper. I have no advice other then follow the POH for troubleshooting. Maybe set the pressure towards the lower end of the spectrum.

Roy B.

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Mar 6, 2018, 10:55:02 AM3/6/18

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On the subject of Pawnee landing gear - be very careful of the Hutch conversion 2 piece slab type gear that is fixed with 3 vertical bolts. If the centermost bolt fails (as it can from vibration over the years) the gear collapses, the prop strikes the ground, and you have a totaled plane from a situation that really can't be detected/inspected before the failure. We lost a towplane that way in a very light landing on grass when the bolt snapped.
The bungee system has some redundancy and the Cessna one piece gear slab is good - but the 2 piece Hutch gear is a problem.
ROY

Dan Daly

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Mar 6, 2018, 1:46:11 PM3/6/18

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The PA-25 SB 25/32/04 dated 01/03/2008 describes a Main Landing Gear Shock Absorption System modification adding a cable to restrict lateral movement of the landing gear leg should a piece of the Hydrasorb shock absorber crack and fail (which they do). We had a Pawnee mod'd (bungee gear system) and had the failure of one support on landing. The down wingtip didn't touch, and neither did the prop. Laviasa had a kit (KIT LA-K-005) with support fittings, a security cable, and longer bolts. Money well spent. I have a soft copy of the SB (2 pages text, 3 pages drawings) if anyone wants one. Also pics of the cable having done its job, a closeup of the installation, and a pic of an unluckier Pawnee without the mod kit.

For light reading, I attach a link to a Canadian Civil Aviation Safety Alert showing the fatigue cracking of the part. https://www.tc.gc.ca/eng/civilaviation/opssvs/managementservices-referencecentre-casa-2011-02-1344.htm

Dan

Larry Ruggiero

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Mar 6, 2018, 2:01:17 PM3/6/18

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Thanks Dan, I will look into this mod. Our gear’s pivot bolts have been replaced in the past few years, but I totally agree redundancy is good. At least one operator has shared with me a story of her experience with that bolt failing— scary. Right now I need to get its gear unsplayed and softened back up. The POH was written to accommodate a full-up gross weight ag plane, which ours will never be again. Unless greater wisdom appears here, I will start by reducing air pressure in modest increments and see what happens.

Larry

Waveguru

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Mar 6, 2018, 2:09:01 PM3/6/18

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If the gear is splayed, it means you need MORE pressure, not less.

Boggs

Larry Ruggiero

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Mar 6, 2018, 2:20:57 PM3/6/18

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Well having read through the above data, it's not applicable. Ours doesn't have the hydrasorb gear that also incorporates bungees. Ours is the 2 massive air-oil strut units Piper had on at least one series of Pawnees. I'll try posting a photo.

Larry

Larry Ruggiero

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Mar 6, 2018, 2:32:03 PM3/6/18

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More than the recommended 575psi? Knowing that these struts are back-asswards in function, maybe I shouldn't be surprised. The hydraulic side of it isn't compressible but the air is. Might it also mean some of the hydro has to come out as well? Since the IA and I had a big disagreement about its towhook, and since it was suggested I take our business elsewhere, I ain't going back. Second annual in a row where he left me with more crap to deal with than it had when dropped off, and all I get is shoulder shrugs and BS about it being an old airplane when I complain. Yet his business flourishes. Pisses me off...

Anyhow, wish I had looked more closely at it when he had it torn apart on the bench so I could wrap my head around its function. The service manual's really no help.

Larry

Charlie M. (UH & 002 owner/pilot)

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Mar 6, 2018, 4:27:54 PM3/6/18

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That may be worthwhile on this and other models (no, I'm not a A&P....).
I believe, due to other gear failures on a Cub and a Pawnee, the routine is to just replace some major gear bolts every few years.
Can't really check them every day, history has shown they wear out over time. When they wear out, broken bolt, then gear collapse follows right after.
On both of our normal towplanes, we have droop tips. This means we get a "wee bit more clearance" before a prop strike.
No, not perfect.
Yes, may be quite a bit cheaper.

curt...@mindspring.com

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Mar 7, 2018, 10:32:59 AM3/7/18

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Dan, thanks for sharing this information. I'd be very interested in the LAVIASA Service Bulletin kit information. LAVIASA has been very difficult to get ahold of. How can I get in touch?

And for those operating Piper PA-18 Supercubs, F. Atlee Dodge has an STC'd mail landing gear safety cable kit, which is very widely used by "off field" operators, e.g., in Alaska, viz: http://www.fadodge.com/safety-cables-for-mlg-std/

I've been of the opinion that the MLG bolts should be changed out, and attach points closely inspected based on number of landing cycles, rather than just hours, especially for tow operations.

Thanks. Curt

Dan Daly

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Mar 7, 2018, 10:41:01 AM3/7/18

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Laviasa is out of business. I'll send the SB etc. The drawings should allow you to re-create it; perhaps Johnson aircraft might be able to help. http://www.johnstonaircraft.com/

Dan

Dan Daly

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Mar 7, 2018, 11:01:07 AM3/7/18

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Sent to UH and Curt. Big (hi def scan, just under 8 MB) so if it doesn't get there let me know please.

I see Lavia Argentina have a website https://laviaargentina.com/ ; I used google translate and it seems to be active. "We have for immediate delivery all spare parts for your PA-25, as well as the necessary technical documentation for the operation or repair."

barrflyr

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Mar 7, 2021, 3:41:52 PM3/7/21

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barrflyr

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Mar 7, 2021, 3:44:34 PM3/7/21

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On Tuesday, March 6, 2018 at 12:46:11 PM UTC-6, Dan Daly wrote:

Dan
Please send the Laviasa PA-25 SB 25/32/04.
John

Dan Daly

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Mar 8, 2021, 8:28:59 PM3/8/21

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Love to, but "reply to author" which allows attachments is not available. If you'd like it, you'll have to send me an e-mail or your e-mail address.

Dan

youngbl...@gmail.com

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Mar 9, 2021, 8:24:22 AM3/9/21

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Larry, all you need to do is call Dan at Aerial Banners in Ft. Lauderdale, Florida. Dan is the most knowledgeable person around concerning Pawnee's, he operates about 60 of them and his rebuild shop is impressive. Tell him that I sent you, he will be the best contact available for Pawnee information. Bob

Tony

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Mar 10, 2021, 8:58:59 PM3/10/21

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Yes, but be sure ro speak with Dan - owner Bobby is a sociopath!

youngbl...@gmail.com

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Mar 11, 2021, 4:45:16 PM3/11/21

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And you are a bigger PSYCHO than Bobby

Dan Daly

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Apr 3, 2021, 2:55:22 PM4/3/21

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Did you get it? I think I could upload it to Dropbox if you still need it. Pity there wasn't a place for things like this on the SSA website.

Larry Ruggiero

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Apr 5, 2021, 2:11:19 PM4/5/21

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On Tuesday, March 9, 2021 at 8:24:22 AM UTC-5, youngbl...@gmail.com wrote:

Larry Ruggiero

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Apr 5, 2021, 2:23:07 PM4/5/21

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Thanks all. To close this out, I just finished overhauling its left strut with new O-rings and backup rings, and it’s fairly straightforward, although the fact that it’s now weeping 5606 out the bottom weep hole tells me that its days are numbered and we’ll probably convert to the hydrosorb/bungee struts after this season. Also the carb airbox wasn’t as worn as I thought and just needed new rubber bushings, which took awhile to get. Btw, the person referenced at Aerial Banners never returned my call.

Larry Ruggiero, A&P/IA
Carolina Soaring Association

youngbl...@gmail.com

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Apr 5, 2021, 3:49:13 PM4/5/21

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You should have called back! FWIW Dan at Aerial Banners is a great guy and has many parts for Pawnee's and is always willing to assist.

youngbl...@gmail.com

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Apr 5, 2021, 3:54:26 PM4/5/21

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I would convert that back to the hydrosorb/bungee configuration whenever you can. If you convert back you can alter the bungee cords used and go to two cords vs three for a much more docile landing bounce. I did this on all of my Pawnee's and it works well. not having 135 gallons of chemical makes a big difference. I might just have a \n old set of hydrosorbs in my stockpile. Bob

Larry Ruggiero

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Apr 5, 2021, 9:19:48 PM4/5/21

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Bob thanks, would be great to buy them used— they’re pricey new, assuming they’re available at Univair as advertised. Larry

youngbl...@gmail.com

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Apr 6, 2021, 5:36:53 PM4/6/21

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Larry, when you get ready let me know and I more than likely can help you out. Yes, they are pricey, way too pricey for what we need. Bob