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I find it interesting that if G100UL is a minimum of 20% xylene (per the SDS) then it would seem it will NOT meet the Military Services "Determination of Volatility" requirement described on page 13: "...at 275F not less than 90% shall have boiled off" since xylene's boiling point is 281 F. This is also true for the other constituents in the mix that are highlighted in yellow: while they wouldn't fail the 90% criteria, they would remain behind. Granted, this may no longer be a pertinent or required test. It's just way different than what would happen with 100LL.

Thanks for asking and clarifying. The main variable is the fuel's volatility. When exposed to free air at a given temperature, the components of the fuel are evaporating at rates related to their boiling point. Each of the ingredients has a different boiling point, and at a given room temperature, will evaporate at different rates. That's what I saw in 100LL vs G100UL. G100UL appears to have some components with a high boiling point that are left behind compared to 100LL. I found an old comparison of G100UL vs 100LL SDS that I overlaid boiling points onto. A significant portion of G100UL is higher boiling point materials. The most volatile (easily evaporated) is the alkylate/distillate. See attachment below. In the case of the bladder or MIL-6000 hose test, there is a barrier (rubber) between the fuel and air. A given barrier will let stuff through over time, but usually this happens very slowly. If that's not the case, this means the material is very permeable, or that something in the material is changing to allow some components of the fuel to pass through it. In the case of 100LL or 100R, I'm not seeing that occurring with nitrile rubbers and it seems correlated to the amount of swelling of a material. If the material is swelling, it is essentially absorbing the fuel, and that means it can likely pass through the material (aka barrier). The MIL-6000 hoses do not appear to have a vapor barrier and rely on the compatibility of the fuel to prevent permeation. Bladders have a vapor barrier built into the sandwich which is there to further prevent permeation. My research says there is a nylon coated material in the middle that acts as this vapor barrier. From Eagle Fuel Cells "A cross section of a fuel cell wall construction consists of a fuel resistant polymer (typically liquefied nylon, Neoprene, Buna-N / Nitrile or Urethane) laminated to a fabric substrate (typically polyester or nylon) which provides structural support and puncture resistance." From Piper Flyer "FFC’s bladders consist of a four-layer construction. The layers (from inner to outer) are a nitrile layer that retards permeability; a transparent fuel vapor barrier that’s bonded to a nylon fabric layer; and an outer layer of nitrile rubber formulated to resist ozone attacks." From FFC "Fuel cell fabric has an integral fuel vapor barrier, eliminating seepage problems and making them stronger, longer lasting and more resistant to porosity." Couple excerpts from a new favorite book "Aviation Fuels and their effects on engine performance", circa 1951 Hope this helps. Michael

You'd have to as George Or, perhaps the FAA doesn't think helicopters glide as well as stuck-wings

So when was this done? I needed to fly into PV for a cousins funeral a couple of weeks ago and their runway is closed for seemingly a while! I was born in Paul’s Valley and looked forward to flying into it. I’m also wanting to replace my legacy ap in my J with an AeroCruze someday. i wonder what they are doing with the airport closed?

What makes helicopter so different that the blanket STC doesn't apply to them?

Do you ride race horses for a living? Or maybe you pack really light...

In November of 2025 I was billed $225 in labor and $725 in parts per mag to overhaul. Probably some mark-up in there too from the shop that sent them out. I had tried to buy another mag to just swap one out and speed up the annual. Had one due for inspection but 200 hours or so left on the other. Couldn't find one for sale in stock anywhere, talked to QAA who said they'd build and sell me one for $1,800 or so, but after two months of waiting I canceled the order and just had the shop send both mags out for overhaul.

No, they were in good shape. The slight pool of oil on the bottom of the cylinder was the only indication.

I have a 337 for my glareshield with LED light strip controlled by a PWM dimmer. But my incandescent lights still use the original rheostat-resistor-transistor for dimming control. I'd be happy if the original dimmer worked as it did when new, but it's 47 years old and I'm sure they are almost worn out. My M20J seems to be in a grey area. My dimmer uses the 200-ohm resistor although the drawing indicates it should be the later 50-ohm design. That's why I want to confirm that my installed rheo-resistor is paired with the proper transistor, but it wouldn't surprise me if they mismatched the components. I will look under the glareshield the next time I get to the hanger to search and confirm the transistor and its location. I never heard about PWM dimmers creating radio noise, but my King radios seem noisy, and maybe the PWM is contributing to the noise. I will keep that in mind the next time I fly. But less radio noise would also be a good reason to maintain the original dimmer setup. I found out that Mooney produced a Mooney Transistor Mod Kit 919003-907 to change the transistor from the RCA 2N2016 to the Delco 2N3079 involving rewiring the rheostat and changing the resistor and replacing the RCA with the Delco transistor. The best that my research could find is this partially obscured instruction sheet and a picture of the parts included in the kit (see attached). Unfortunately, I can see it is a 3-page instruction, but I only have this image of page 1. Is there a resource where we could find the complete 3-page instruction sheets for the Mod Kit 919003-907? I am hoping that if I have the RCA 2N2016 transistors that I can test them to ensure they are still working as intended. Otherwise, I may need to source new-old-stock for the 2N2016. And if the 2N2016 is out then I'd have to look at upgrading. Did Mooney ever specify a silicone-based replacement transistor?

So without going through all the college level theory of operation I will "attempt" to explain simply. So when we say "high side" or "low side" that is where the transistor is in relation to supply voltage and common (chassis ground in our case). Aircraft, "most" automobiles, boats generally use high side as our grounding system is the chassis and is actually safer. Our radios (ie light in KX170B or other instruments) are internally connected to chassis ground while the input expects voltage. There are some exceptions where I have seen both ends of the light brought out to the connector. I am going to say my disclaimer, I am going by the schematics I have SCI-800269L Rev F 10/1/82 and Maintenance Manual #106 1968-1984. Also Mooney has changed this circuit a few times, don't think they had an electrical engineer that understood transistors. For the Vintage I can understand that as they were still "new" in usage which is why, I would reckon pre '75 didn't have dimmer circuits. A little note on Germanium transistors: part of the issues with these circuits are as Germanium ages it breaks down causing leakage on top of their higher leakage than silicon, essentially the transistor does not operate as designed. Use the silicon versions of all transistors. I have never seen, in a textbook or otherwise, a NPN BJT situated like this (first design). High side and emitter to supply voltage (improper emitter follower aka common collector). Highly inefficient (voltage loss at Vemitter, Vce, rheostat; both transistor and rheo get hot), can’t saturate (Vb must be > Ve). Due to the voltage loss from the orientation there is very limited dimming range and not smooth, just flat out wrong. If using an NPN in a high side situation, usually a PNP is used, a proper emitter follower is constructed, collector to 12V, emitter to load. Still inefficient power dissipation but less voltage loss. The PNP is better in this instance as it dissipates more power while bright than while dim (we like it dim, well I do) while NPN is opposite. The second circuit they used caught a problem with the first, No base pull down resistor in the first. If the base is left floating it may/will remain on. They still had an improper emitter follower. With the J’s (24-0071 and on and an SB for SOME prior C, E, F) they changed to a strange configuration of a Darlington pair. Using One Rheo, the strange part is the output of one transistor feeds a load and not just the base of the other transistor. I surmise to split current load to use the same NPN as prior. Why they didn’t use a BJT to drive a MOSFET from the beginning, much less power dissipation, larger smoother range. like I said I guess they were not up to speed with proper transistor function, money maybe a few more parts. Mine in an F was stuffed in the center by the firewall. Somebody completely F’ed up wiring and such. I have seen them in a box with the dimmers in the console. They usually have unabtanium little fuses. I am in the midst of rectifying (HAHA I had to) the issues with a proper BJT/MOSFET design on mine. I think I need to get field approval. On PWM if you go that route, Be very careful with these even the PMA MaxDim. While they are very efficient and how dimmers are now, especially for LEDs (they only option). They commonly introduce noise into the system as our systems/radios (ex170B) are not designed for it. I have seen lots of noisy systems particularly interference on 170B radios from PWM dimmers. So in summary for you, ensure the resistor is there base to ground, Mooney had these at the Rheostat. You can check the transistor out of circuit with DMM if you know how but I would just replace them with current silicon 2N3055 w/heatsinks. The 2N2016 should have had heatsinks anyway. ensure proper wiring in the connectors.

Jee, are they really up to 2k just to oh a mag? That does seem excessive.

Interested. I'll see if I can figure out how to PM you.

@BrianW I have an 1970 F model and they are just under the glareshield on the pilot's side. I know it's not a J, but since you are having trouble finding them...it is someplace else to look

no, i'll have to install that at the same time. it's really not the mag that bothers me, it's the price, 2k right now, maybe 3k next time and if i'm lucky probably 4k the next inspection

Yes

From the 1 plane still using it

I have a new Aerocruze 100 autopilot that I was days away from beginning install on when Dynon announced their autopilot approval. It comes with all parts and documentation. It comes with a modification drawing ready for DER signature if someone wants to install prior to dynon receiving new revised stc approval (see letter from Duncan below). Modifications have been made to the kit parts per the provided modification drawing to allow it to fit in a short body. It will come with full ownership/stc transfer to new owner which I have already coordinated with and agreed with Duncan to help facilitate. If you want to wait for the STC revision for install, Duncan expects new parts kits to be provided free of charge. (see letter from Duncan below) looking for $5000obo Notice from Duncan: AeroCruze 100 Autopilot for Mooney Aircraft Update as of February 2026: Approximately Mid-Summer 2026 Bendix/King (Honeywell) ODA will be reviewing "Revised Drawings and Revised Installation Instructions" with the intent to include as additional FAA approved data for the current STC. This additional data, is considered a Minor STC Revision, and once approved (sometime late summer 2026), Bendix/King (Honeywell) will be working with their supplier's to fabricate "Redesigned Parts" and "Additional Parts" [i.e. added pitch servo push-rod of shorter length {for short body Mooney} and multiple pitch servo to fuselage mounting brackets {for medium body Mooney}] which are additional unique parts not currently in the STC Kits. Mooney owners who have bought the current STC Kits, but not yet installed - should be able to obtain these Additional Parts; we are assuming free of charge (when these newly designed & fabricated parts are available).

I think that it is pretty well agreed that the weight compressing the discs is a major factor in how long they last, as evidenced by the fact that the heavier late model planes require more frequent disc replacement. If that is true, keeping the weight off the discs, as these Puck Savers do, would almost certainly be helpful in extending the life of the discs. It would seem that the only questions would be how much their life is extended, and whether it is worth the extra time and effort necessary to put the Puck Savers in place each time you put the plane in the hangar. It seems that a lot of plane owners think they are going to be flying again in a few days, so they may reason that it isn't worth the x extra minutes it takes to hook up the Battery Minder, jack up three Puck Savers, put plugs in the air intakes, hook up the engine desiccator, etc.

Do you already have two batteries or dual chargers or whatever they required as backup? I really liked my sf, and I plan to get one on my 252, but I think I also like having a mag…

man, my mag is due this annual, looking at the price i'm seriously thinking of replacing with a second surefly. pay a little more now and never have to do it again

Why?

Owned 16 planes, 6 Mooneys, useful load has never entered my mind.

Ok, that sounds interesting and actually fun

I looked under the copilot panel at the dimmer switches and did not see the transistors there. I only saw the wires from the dimmer potentiometers going to the black wire harness connector. On the other side of the copilot panel, below the circuit breaker panel, I saw the 4 mini fuses but did not see any transistors around them. Where are these transistors typically located? My plane is a 1979 M20J. I just want to confirm whether I have RCA or Delco transistors. Thanks.

Pictures or your lying....LOL