PSRU Oil Operating Temps

Discussion in 'General Auto Conversion Discussion' started by TXFlyGuy, Dec 14, 2019.

Help Support HomeBuiltAirplanes Forum by donating:

  1. Dec 16, 2019 #21

    wsimpso1

    wsimpso1

    wsimpso1

    Super Moderator Staff Member

    Joined:
    Oct 19, 2003
    Messages:
    6,163
    Likes Received:
    3,465
    Location:
    Saline Michigan
    Auto trans oils are excellent oils for operation of gears, bearings, and friction materials when designed and developed for them. Their use in manual transmissions has been common since the 1980's for fuel economy reasons. The gears and bearings are designed knowing that they will be using low viscosity oils. The bronze friction elements of the synchronizers are long gone, replaced with friction papers similar to that used in automatic trannys. They have other benefits - less oils need to be stocked at the dealer and the gearbox is much easier to operate cold. Since then the auto industry has gone to still lower viscosity auto trans oils in new trannies designed with those oils to further improve fuel economy.

    The gears used in axles usually have the input shaft offset below the axle centerline to lower the drive shaft in the car. This changes the gear set to a hypoid set, with some sliding between pinion teeth and ring teeth. Hypoid gear oils were then used for these axles, with a lot of attention paid to reducing wear in the gear teeth. The car companies and dealers simplified their systems for MANY years by carrying only the right oil for axles and then using that in manual transmissions too. My folks had a number of three-on-the-tree cars that were cranky to operate in the cold. That is until fuel economy became so important, then the industry started developing equipment that worked fine with lower vis oils...

    Billski
     
  2. Dec 17, 2019 #22

    Russell

    Russell

    Russell

    Active Member

    Joined:
    Nov 30, 2015
    Messages:
    31
    Likes Received:
    42
    Location:
    Ft Worth, Texas
    I pulled a couple of flight examples from my engine monitor for the Marcotte gear box. First example was during normal cruise when the OAT was 90F, gear temp was 188F. Second flight was during a race where we push the engine hard, OAT was 84F and gear temp was 198F.

    I found that if the oil level is lower than the manufactures suggested level, the temps are significantly lower. I think with high oil levels you are just converting horsepower to heat while grind up oil ???

    BTW we use Amsoil 75W-90 synthetic gear oil. The oil is circulated through an oil filter. I have a magnet in the line leading to the filter … I can easily check this magnet to look for iron particles. When new, I started changing gear oil at about 5 hours, now I go 50 hours.

    Russell Sherwood – Glasair/Subaru
     
  3. Dec 17, 2019 #23

    TXFlyGuy

    TXFlyGuy

    TXFlyGuy

    Well-Known Member

    Joined:
    Apr 26, 2012
    Messages:
    1,562
    Likes Received:
    456
    Location:
    Republic of Texas
    Russell - Thanks for the info, good advice.
     
  4. Dec 17, 2019 #24

    wsimpso1

    wsimpso1

    wsimpso1

    Super Moderator Staff Member

    Joined:
    Oct 19, 2003
    Messages:
    6,163
    Likes Received:
    3,465
    Location:
    Saline Michigan
    Interesting... It does sound like your gearbox losses are substantial, and with more oil, you are getting more losses. In the Marcotte, is the oil sprayed on the gear mesh and bearings or is it a bath/splash lube process, where the gears turn in the oil?

    I am also curious if you have ever found any degradation in the gear oil... Has the oil ever been sent out for spectroscopic analysis, and if so, what did they find?

    Billski
     
  5. Dec 17, 2019 #25

    Russell

    Russell

    Russell

    Active Member

    Joined:
    Nov 30, 2015
    Messages:
    31
    Likes Received:
    42
    Location:
    Ft Worth, Texas
    Billsky, the Marcotte has a bath type oil system. The gear loss question has come up before. I asked the manufacturer about this, he said that the box was run on a dyno three times and that each time they got a 1% loss. If I’m making 220 HP while racing, 2.2 would be converted to heat and noise. 2.2 HP equals about 1650 Watts. That is about what your wife’s hair drier makes.

    I do not have a lot of engine cooling air entering the cowl. There is a 2 inch by 1.5 inch hole just above the engine air filter (see photo). This air blows directly on the gear box. The only other cool air coming in is a NACA scoop for the oil cooler.
     

    Attached Files:

    wsimpso1 likes this.
  6. Dec 20, 2019 #26

    brucec995

    brucec995

    brucec995

    New Member

    Joined:
    Oct 18, 2016
    Messages:
    3
    Likes Received:
    0
    Location:
    South Eastern NSW, Australia.
    Hi Russell - do you have any pics of your radiator set up that you would like to post? Does it extend up into the fuselage?

    Bruce
     
  7. Dec 20, 2019 #27

    Russell

    Russell

    Russell

    Active Member

    Joined:
    Nov 30, 2015
    Messages:
    31
    Likes Received:
    42
    Location:
    Ft Worth, Texas
    Bruce, so as not to steal the “PSRU Oil Temps” subject, I answered your question under the subject titled “P-51 type radiator”
     
  8. Dec 22, 2019 #28

    TXFlyGuy

    TXFlyGuy

    TXFlyGuy

    Well-Known Member

    Joined:
    Apr 26, 2012
    Messages:
    1,562
    Likes Received:
    456
    Location:
    Republic of Texas
    I just heard from Neil Hintz (the manufacturer), literally minutes ago where he referenced our Viton seals. Neil said you can go much higher in temp, nearing 120ish (248F), but he in NOT comfortable with that even with the Viton seals.

    The temperature range of Viton® (FKM/FPM) is considered to be between -20°C and +205°C depending on the grade. It can take even higher or lower temperatures such as -30°C / -45°C and +230°C, but for short working periods.
     
    wsimpso1 likes this.
  9. Dec 23, 2019 #29

    Billrsv4

    Billrsv4

    Billrsv4

    Well-Known Member

    Joined:
    Sep 29, 2016
    Messages:
    125
    Likes Received:
    88
    Location:
    NW Oregon
    Bill ski, Russel,
    When running synthetic gear oils the temperature shouldn’t be a problem. They are capable of handling high pressure also. The thing I found out while talking to the Timken bearing engineers was they were concerned about oil viscosity in their larger bearings at prop rpm. The psru I’m working on has large diameter bearings, and they suggested an engine oil weight. So I’m plumbing for common engine and gearbox oil. The advantage is that the oil is full flow filtered and runs thru the cooler. The disadvantage is limited pressure capability. Synthetic engine oil for certain for the gears. Going with straight spur with minimal sliding also.
    T. O. Bill
     
  10. Dec 23, 2019 #30

    TXFlyGuy

    TXFlyGuy

    TXFlyGuy

    Well-Known Member

    Joined:
    Apr 26, 2012
    Messages:
    1,562
    Likes Received:
    456
    Location:
    Republic of Texas
    Like RS, we will run Amsoil 75W90. It surpassed both Mobil 1 and Valvoline in a blind comparison test.
     
  11. Jan 17, 2020 #31

    PMD

    PMD

    PMD

    Well-Known Member

    Joined:
    Apr 12, 2015
    Messages:
    99
    Likes Received:
    44
    Location:
    Martensville SK
    nothing that hasn't been covered, but just to confirm from a different source: I had a gearbox (on a very large vacuum pump) that came with 80/90 gear oil in each end. It ran so hot under even fairly light load that it would take out the factory supplied seals (around the 200/220 F range). Since we start that particular machine at sometimes fairly low ambient temps, and on a hunch (based on a fair bit of experience) I switched to 75W-90 full synth gear oil and the temp dropped dramatically into the 150F range removing the seal issue. It has over 8,000 hours now, and oil changes are something done on major maintenance times (as in a couple thousand hours). Point of this example: the oil itself can both be the source and/or solution to a problem.

    While I can agree that a properly vented gearbox is not likely to generate so much condensate to make frequent oil changes logical, I have lost a few hypoid gearsets due to water when once again OEM vent location was found to ingest road splash. Going to a better vent hose location ended any moisture accumulation completely (rear axle).

    I will say after decades of lubricant experience that if you NEED to change oil every 5 or 10 hours, you have a serious design problem. Even in engines (as pointed out, HUGE potential generators of acidic moisture) seldom is the pH out of range even on extended OEM change intervals. I can not even begin to imagine a gearbox that would require such short intervals. In fact: excessive changing risks more introduction of contaminants.

    As suggested elsewhere, oil analysis periods that begin as short, then extend until you can actually SEE some worthwhile (i.e. telling) results are a great idea for something experimental, but for PSRUs from a series manufacturer, that should have been done long before you put your money down.
     
    raymondbird and wsimpso1 like this.

Share This Page

Group Builder
arrow_white