Successful Auto Conversion Trials, Tribulations and Tips

Discussion in 'General Auto Conversion Discussion' started by rv6ejguy, Aug 27, 2019.

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  1. Aug 29, 2019 #21

    rv6ejguy

    rv6ejguy

    rv6ejguy

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    Here is a page on my RV6A which has lots of photos and details some of the flight testing with the new rad setup: http://www.sdsefi.com/rv17.htm
     
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  2. Aug 29, 2019 #22

    pfarber

    pfarber

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    There are also some guidelines that seem to be rediscovered every new attempt at liquid cooling:

    You must reject boundary air from the fuselage. The inlet should be an inch or more off the surface.
    The opening should should be roughly 1/4th to 1/3rd the radiator area.
    The plenum should not diverge significantly... less than 20deg or less is optimum
    The radiator should pass maximum airflow
    Single pass/single row radiators offer optimum cooling delta compared to multipass/multi row
    Outlets should be short and straight to eliminate back pressure.

    Even at idle the prop is creating a wind velocity that is more then enough to cool an engine. The trick is to harness that airflow and use it to the full advantage.

    Belly radiators are easiest as they allow for most of the above to be met with minimal issues. You can use most of the empty fuselage to play with intake/exhaust/plenums etc.

    But the most compact is going to be mounting the radiator below the engine in the cowl. There are trade offs, but I like the idea of a compact power unit all bolted up to the same mount.

    One idea that I like is having a slanted radiator, with the fins still perpendicular to airflow. Once you tilt the radiator, or mount it horizontally, the air as to either turn (lose airspeed) or hit the fins a high angle, also slowing it down. If the radiator could be designed to lay flat (or at a small angle) and the fins angled to allow the air to pass, THAT would be the bomb, yo.
     
    Last edited: Aug 29, 2019
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  3. Aug 30, 2019 #23

    Russell

    Russell

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    This photo gives you a fair idea of that my radiator looks like.
    Russell Sherwood
     

    Attached Files:

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  4. Aug 30, 2019 #24

    wsimpso1

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    Tremendous amount of well thought out design and then testing to show that the design really works.

    That those rubber bushings gave 25 lb-ft/ degree is lower than I might have expected too. Good work. Are those bushings typical of what we find in Marcotte and AutoFlight PSRU's? Between those spring rates, the BIG Inertia of the prop, and the increased Inertia on the engine side, well, it should drive down the first mode nicely. Again, really good work on the topic.

    I do have to shake your hand someday!

    Billski
     
  5. Aug 30, 2019 #25

    BoKu

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    Very tidy indeed! I imagine you considered bulging out the belly pan to run the coolant lines between it and the wing carrythrough skin, but what you've done instead looks a lot easier to service and maintain.
     
  6. Aug 30, 2019 #26

    rv6ejguy

    rv6ejguy

    rv6ejguy

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    These bushings are typical on the Marcotte M-300 PSRU. I believe Autoflight uses a Lovejoy coupler for TV attenuation.

    You'll probably enjoy this page more: http://www.sdsefi.com/rv16.htm
     
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  7. Aug 30, 2019 #27

    wsimpso1

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    Really well thought through, evaluated, and tested.

    So now that confifuration of psru, engine, turbocharger, and cooling system is worked out and proven successful. Ross, please what appear to be your areas and volumes per unit horsepower (or other pertinent figures of merit) of your radiator, oil cooler and intercooler, and their inlet/outlet sizes. Similar data on Russel's installation would be really helpful too.

    Billski
     
  8. Aug 30, 2019 #28

    rv6ejguy

    rv6ejguy

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  9. Aug 30, 2019 #29

    pfarber

    pfarber

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    Great tip:

    Rad tanks are not exposed to the airstream, only the core matrix.

    This?
    total passes 15

    That's 15 reversals of the coolant? Did you try fewer passes but realized this is the optimum? Most books would say the lower delta T you get (from the long dwell time) the less efficient your cooling air becomes.

    It obviously works.. just wondering why.
     
  10. Aug 31, 2019 #30

    Russell

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    I went to Ross’s post 52, then I looked at a few other of his cooling posts. My findings are usually very much in line with Ross.

    I made a removable slip-on scoop inlet to reduce the original inlet opening. The small one easily slips over the original and cuts the inlet area from about 33 to 23 square inches. The small one is used when OAT is <80F. Sometimes we use it in the summer if we want to go fast or have a longer flight. I usually remove it in the summer because if we have a long taxi with a high x-wind the prop blast tends to get blown to the side and the small inlet catches less air. Inflight the small still lets in more air than necessary.

    The radiator core is 240 sq inch and 2.75 inch thick. It is a two row with 14 fins per inch.

    The aft door can open from about 10 to 60 sq in. During flight the door is generally set around 15 to 25 sq in. Don’t hold me to exact measurements of the inlet/outlet openings, it’s hard to measure curved areas … if you ask me in a year I will likely give a different answer.
     
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  11. Aug 31, 2019 #31

    Russell

    Russell

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    Forgot to mention that my radiator is a single pass.
     
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  12. Sep 2, 2019 #32

    pfarber

    pfarber

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    Thank you!

    I understand the process used to create the meredith effect and its benefits Reducing the parasitic drag of the radiator with proper ducts seems to be something that should be touted as a benefit of water cooling. I wonder if you could 'package' the radiator and scoop into a kit? Making the molds are the big time sink... glassing is nothing.

    Looking at variable intakes it seems there should be an easy and aerodynamically friendly way to vary inlet opening... maybe a simple ramp device that opens into the inlet. I'll add that to the notebook of things to look into.
     
  13. Sep 2, 2019 #33

    rv6ejguy

    rv6ejguy

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    A pass is a tube. Coolant only flows in one direction on my rad. I built a test rig to evaluate various rads for temperature and pressure drop before settling on the rad I used.
     
  14. Sep 2, 2019 #34

    rv6ejguy

    rv6ejguy

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    A clean sheet design could submerge the rad into the fuselage and have an even better duct shape than what I could do on the RV. The duct is vitally important to effectiveness and lowering drag on liquid cooled installations. Most people don't bother and have either higher drag and/or poor cooling.

    In my case, the rad duct took over 200 hours to design and build- no molds. Unfortunately no way to make a duct kit to fit multiple aircraft designs. Lots of airplanes, like the RV are not flat on the bottom. Rad size is determined by installed hp, and generally best ROC speed so you'd need several different designs. What is the demand for such a kit?

    Variable inlets have been tried way back to the prototype P51 and usually abandoned. Not a good way to go. Throttling the exit works better which is why you see almost every liquid and air cooled engine installation doing it this way.
     
  15. Sep 3, 2019 #35

    pfarber

    pfarber

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    I see, I understood it to be a splitting of the tank to reverse the flow back through the radiator.

    Did you try honycomb core or was it always tube and fin?

    Also, are you saying that each engine would need a new duct geometry based on radiator size? Heat output? I didn't think that the effect was that specific for each application. So a duct system could not be designed that, say, covers a radiator from 150-200sq in? To see any benefit you need a 150sq/in duct and a 200sq/in duct?

    Thanks again for your answers!
     
    Last edited: Sep 3, 2019
  16. Sep 3, 2019 #36

    rv7charlie

    rv7charlie

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    You're right, common use of terminology is for 'pass' to mean direction through the core; '2 pass' commonly means that water enters on one end, flows through 1/2 the core volume the length of the core, then back through the other half of the core volume. A VW Rabbit style rad is a common example. It has the convenience of in/out being on the same end of the rad. However, most agree that it's not particularly efficient, because the temperature delta between water & air is much lower on the return path. (Front-back '2 pass' tend to be more efficient.)

    Not to speak for Ross, but a 'one size fits all' approach could only work if the core is sized for the highest HP engine, and the duct (diffuser) has a large inlet/outlet, for a slow a/c. Now, all other cases will be over-cooled and have greater drag than required. And you still have the problem of fitting it to various airframes. That would work for say, an RV-7/9 (and maybe, the -6), but all bets are off after that. Drag would likely be horrendous, on the vast majority of installations.

    Charlie
     
  17. Sep 4, 2019 #37

    pfarber

    pfarber

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    Most E/ABs use 150-180-200hp. So using the 1sq/in/hp rule you need 10x15x1, 10x18x1 and 10x20x1.

    So your belly scoop would not vary in width or length, only height, inlet and (variable) outlet.

    If you design the 'housing' for the 10x20 radiator, you would then use inserts to fill the unneeded area for the smaller radiators.

    For example, the rule is that 30% opening for the inlet. 30% is 45sq/in, 54sq/in and 60sq/in. Since the bottom 'half' of the scoop/housing is constant, you can screw in an insert to reduce the intake plenum and ducting to the proper volume.

    Then for installs all you need is one template for the fuselage hole and the proper insert. If the owner ever upgrades, a new insert and radiator core.

    I'll start the go-fund-me now.
     
  18. Sep 4, 2019 #38

    rv7charlie

    rv7charlie

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    I'd wish you luck, but in this case, it's a zero sum game; all downside for the funders. You *might* get away with your plan for a sub-100mph high drag something where cooling drag is a relatively small percentage of total drag.

    Suggest you build yourself a prototype, to explore what it would take to make the idea functional. Then do some efficiency calcs, for the various sizes.
     
  19. Sep 4, 2019 #39

    pfarber

    pfarber

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    Well I found some info.. generally the diffuser is the money maker:

    http://www.arpnjournals.org/jeas/research_papers/rp_2016/jeas_0416_3979.pdf

    Therefore, the traditional compromise-dimensioning advices a value of the semi-angle opening of the duct of about 7°, that is the value usually used in the wind-tunnel diffuser.
    However, with modern polished RP (Reinforced Plastic) construction and anti-friction paints it is possible to reduce this angle down to about 2°

    A fully deployed streamline diffuser is long 3 times the height of the radiator divided by two (YB).

    The other factor is that the duct is rarely rectilinear and cylindrical, but often has S-shapes and ovoidal sections, that further reduce efficiency in “critical” ducts. - This means make it straight into the radiator.

    "The Meredith duct should be embedded in the fuselage or in the wing to avoid excessive external drag. Only the air intake is positioned outside. The optimized intake is positioned in the lower part of the aircraft at about 2/3 of the wing chord, where the pressure reaches its maximum."
     
  20. Sep 4, 2019 #40

    pfarber

    pfarber

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    Sarcasm is lost on some people. Just talking out loud. If you're just gonna nay-say then I'd be nice if you said nothing. I mean really.. what is the purpose of your post?

    Build a prototype? DUH. I have an airplane to finish. Of course there will be a prototype, then it will be tested, refined, then flown. Sell it? The last thing I want to do is deal with nay-sayers claiming it doesn't work, when it clearly does and will.

    Some peoples kids....
     

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