4500rpm propeller to negate the PSRU

Discussion in 'General Auto Conversion Discussion' started by pfarber, Jan 24, 2020.

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  1. Jan 26, 2020 #21

    BBerson

    BBerson

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    A totally new experimental engine should first be fully developed and tested on the ground. Like the Onan that was built first and then fitted to Burt's Quickie design.
    I don't know if the Boeing 777X tested yesterday was fitted with flight proven engines or not.
     
  2. Jan 27, 2020 #22

    pfarber

    pfarber

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    If that were the case then the EAA would have ended shorty after that memo was sent. The problem is most people think E/AB aircraft is a plane you assemble from a kit where you learn nothing more than to match drill and dimple.

    I have no delusions that its a weird idea, but its far from unique. No disrespect, but this forum is definitely not the place to look for forward thinkers. I'm sure there are many bright individuals here, but don't want to put up with forum quibbles and negativity.

    Since I have a motor picked, I will start on roughing out a motor mount to see what it will look like. Who knows, I may spend the $500 to get a prop made and see if it works or not.
     
  3. Jan 27, 2020 #23

    TFF

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    If you want to be an experimenter, do it. Don’t whine what no one sees eye to eye. Learn to make your own props and learn what you want to learn. Run the engine you want, but unless you come up with a true gold mine of an idea, don’t expect converts. It’s hard enough to do this with stuff that works off the bat.

    We as a group want you to show us. We as a collective are going to be doubting Thomas’, and proof is on you not us. Forward thinking? I think the group is, but it’s not a play group of yeses. When I was a kid, I could not believe everyone did not have a 3/4 P-51 with a Ranger V12. Sounds like the perfect idea. It’s not in practice. Everyone should have at least a T2 or VP1 that has a pilots license in addition to their good plane. The world does not work that way.

    I hope you are successful. I want to see the magic. I love the stuff. The pioneers never asked “will this work.” They made it work from multiple failures. That is why they are celebrated. Scratch the itch, but don’t ask to have someone else scratch for you.
     
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  4. Jan 27, 2020 #24

    lr27

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    Have any of you seen the Twin Lacey? Even uglier than the single engine Lacey, it had a big plank across the nose with a VW engine on each end. I imagine if someone figured out a low drag way to put two 1/2 VW's on a plane that normally only had one full VW, it would be much better at takeoffs and climbs, with no need for a reduction drive. Much larger disk area. The weight might not be any greater.
     
    Last edited: Jan 27, 2020
  5. Jan 27, 2020 #25

    BBerson

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  6. Jan 27, 2020 #26

    Dan Thomas

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    A LOT of that "negativity" is just us old guys that have been around homebuilts and aviation a long time and have watched people struggle and sometimes kill themselves trying to achieve something that could have been done a lot safer. There are always a group of guys that don't read the bloody history of aviation and seem determined to repeat all the same mistakes. Sure, there were early guys that had to design and build their own airplanes and convert engines for them, but they often copied existing aircraft designs and installed Model T engines or whatever, and thoroughly expected engine failures and weak performance. They didn't expect to put their families into a funky new design with a converted Jag engine and fly to Miami for the weekend. They were happy to get themselves off the ground and recognized the risks. That unfortunate history was just yesterday for them.

    There are forward thinkers here. Some of us old guys, including myself, have invented and built machinery as part of our careers. Some are professional engineers. Some, again including me, spent time as professional aviators and welcomed things like glass panels. We just hate to see someone end up frustrated and broke because he could have done things more sensibly. I once warned a guy that his (illegal) homebuilt was going to kill him, with its big CG problem and sharp leading edge. He ignored me, flew it and stalled and crashed on downwind. I was partly wrong: he survived.

    Edit: I had entirely forgotten that I designed and installed a Subaru 2.2 RAF conversion in a Stoddard-Hamlilton Glastar in the late '90s. Had to create a complex engine mount that reached around the engine to get at suitable pickup points, and make the shockmount sockets for those points. Had to get the thrust line exactly where S-H wanted it so I could use the cowling, and had to modify the lower cowl to clear the sump. Had to make mufflers (7 iterations of them over the test period, trying to get the awesome noise down to acceptable levels with the tiny mufflers that had to fit in there). Had to design and build a plenum to mount the radiator and get the cooling system to work well (it did, first time around). Had to design an electrical system with a means to keep at least one fuel pump operating for some time if the alternator quit; there was no place to mount a pump on the engine. Had to modify RAF's mixture valving design to get some spread to the control so that it didn't move from full rich to dead in a half-inch travel of the knob. Designed a cabin heating system based on the coolling system. And then I spent a lot of time tinkering with the whole thing to work the bugs out during testing. A LOT of time. It's not easy to create somthing that isn't imminently about to kill you.

    So when someone implies I'm just a negative thinker, I start to wonder if they have any experience at building or creating anything yet.
     
    Last edited: Jan 28, 2020
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  7. Jan 27, 2020 #27

    Himat

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    If 4500 prop rpm will fly an airplane. Certainly, some of the Cri-Cri builders may chime inn, but I think they run close to double that on some engine and propeller combos. That is, those with large model airplane engines.

    If a prop at 4500 will work on a BD4?
    Probably not that well. Prop diameter and rpm is part of the airplane design, not something added on afterwards. It is entirely possible to design a BD4 size airplane around an engine spinning the prop at 4500 rpm. Decent performance can be had too, but it will not look like a BD4.
     
  8. Jan 28, 2020 #28

    lr27

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    Would this BD-4 size airplane use a ducted fan? Otherwise I'd expect it to need more runway and climb more slowly. At least if it's a single.
     
  9. Jan 28, 2020 #29

    aeromomentum

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    Keep in mind that a faster turning prop of the same diameter has more drag for the same thrust so requires more power. With everything else being correct for the rpm and with the prop the same diameter if you go from 2240 rpm to 4500 rpm you will need 46% more power for the same thrust. Or from 2700 to 4500 rpm requires 30% more power for the same thrust. Smaller diameter props also require more power for the same thrust. So while it can be done you need a lot more power for the same performance.
     
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  10. Jan 28, 2020 #30

    BBerson

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    There isn't any reason to choose 4500 rpm for a V8.
    Something like 3500 or whatever Beachner or Wittman used for rpm would be a best place to start.
     
  11. Jan 28, 2020 #31

    pfarber

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    And this is exactly where auto engine shine. High HP high RPM.

    The only issue I see (its not really an issue, but I don't think it would be acceptable) is possible pitch change with power due to a low thrust line. Inverting the engine is not worth the effort for the result. Do we really need an E/AB version of the 737MAX??

    My idea was to lose the weight of the PSRU with a direct drive for a 4 or 6 cylinder engine. V8s make enough HP at 2000-3000 RPM that its not an issue, but they simply weigh to much. Its a valid idea for say a small 2 place... but when looking at my specific mission (high speed cross country) is really isn't a good fit.

    My fiance is a math teacher so after the honeymoon is over I hope she doesn't mind being my hot number crunching wife.
     
  12. Jan 28, 2020 #32

    pfarber

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    I always thought a ducted fan would work great on pushers like the Cozy or Long EZ. Add a belly deflector that automatically retracted when the nose gear unloads to protect the inlet.

    Sadly, I am just not a Long EZ sized pilot and a Cozy is out of my financial ability.
     
  13. Jan 28, 2020 #33

    pfarber

    pfarber

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    Nice resume. I'm sure we all have many projects that give us all unique insight to solving problems. I mean wisdom is the application on knowledge, and knowledge is mostly self taught through experience.

    The hard part communicating that wisdom. No one (me included) likes to have to explain the reasons why, in depth, something won't work. But just say 'lol no way' is not helpful.

    I also agree that there are 'idea people' and 'builders' but rarely 'idea people that can build'. You have to find the right mix of peers and then navigate through each one's idiosyncrasy's, build a rapport and respect, then do it all over again when the next one comes along.

    E/AB is a small community. Once screw up goes a long way. Your success is measured in how long it takes until your next screw up. Add on top of that the anonymity of the Internet and people get 'keyboard courage' they would never have in real life. Except me. I have no problem calling anyone out, online or in person.
     
  14. Jan 28, 2020 #34

    Lendo

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    Pfarber, Opinions are like assholes- eveyone has one - I love that expression :).

    However when listening to those with experience and knowledge, it shows true intelligence to sort the best advice for your application and it works.

    Nevertheless, any engine can work provided it meets your criteria for Installation (fit), Power, Weight and Longevity - sometimes a very difficult thing to achieve. Trade-offs are often a necessity - with their associated RISKS.
    George
     
  15. Jan 29, 2020 #35

    rv7charlie

    rv7charlie

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    It could save you a lot of grief (and money, and maybe danger) if you have a clear picture of the difference between forward thinking and wishful thinking. :)

    Seriously, what you want is something that has already been done to death. The science is well established, and the real world experiences are out there for you to read about. Consider Steve Wittman's V8 Tailwind. Wittman was obsessed with speed. If he could have cut down the prop a bit more on that V8, and turned it 4500 rpm instead of 3200, with the resulting significant increase in HP, and gotten a few mph more performance without killing climb performance, he'd a done it. (Sorry; it's southern thing.)

    For a this or that (or that) comparison, look at the Continental O200 engine. The Reno F1 guys run little short toothpicks at 4500 rpm. The VariEze & Quickie200 guys run slightly longer, toothpicks at 3200. *Zero* 'normal sized' planes turn them faster than around 2600, and run props that are *much* longer. If you plot runway requirements against max speed, you'll see the obvious inverse relationships. Do remember that the F1 planes are quite a bit faster than a BD4, and they always have that really looong runway available.

    Charlie
     
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  16. Jan 29, 2020 #36

    lr27

    lr27

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    BTW, just because I mentioned a ducted fan, doesn't mean I think it's a good idea.
     
  17. Jan 29, 2020 #37

    Dan Thomas

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    That there. Sometimes we old fellows run into scorn when we try to point out certain limiting factors based in physics. It seems to be a mark of recent generations, where truth is whatever you want it to be. They pick up that flawed philosophy in school, particularly as applied to social/moral/political issues, and then try to apply it to the world of physics, where it gets them into trouble.
     
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  18. Jan 29, 2020 #38

    aeromomentum

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    Just to keep things is perspective, our PSRU is 16.3 lbs and can be used on a 4 cylinder engine to about 225hp and on an 8 cylinder to about 400hp. Keep in mind the peak torque impulse is the limiting factor. With the mounting bits it is 25.7 lbs. It requires 8oz of oil. So 26.2 lbs wet. With a direct drive engine that uses the prop for the flywheel you can reduce the flywheel weight about 2 lbs but you need to add a prop flange and most likely a longer extension. So this would add about 6 lbs. So the weight savings is about 22lbs for direct drive. Our installed weight of our 112hp is about 200lbs. So 1.78 lbs/hp. A direct drive version would be 178lbs and 75hp @4000 rpm if optimized for that rpm. So about 2.37 lbs/hp. Now taking into account the reduced prop efficiency (-39%) the effective power (~46hp) to weight is now about 3.7 lbs/hp. About half that of the geared engine.

    Yes a direct drive automotive engine can be done. But the penalty is huge. At higher airspeeds the prop penalty is reduce some the actual engine power to weight is still poor. Keep in mind all fighters in WW2 had geared engines for a reason.

    With that being said, here is a design by Vance Jacqua from about 20 years ago based on the KIS TR1. I helped a little with this and actually proposed the use of a direct drive aluminum LS engine and did the calculations for the prop moments, etc. Vance also ran the numbers for a junkyard iron small block like in the drawing.

    JYDog.jpg
     
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  19. Jan 29, 2020 #39

    rv7charlie

    rv7charlie

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    I had the pleasure of meeting Vance at OSH many years ago. A *really* smart guy; a major vote for listening to aeromomentum just because, 'Guilt by Association'. :)
    Vance had a graph on his web site showing the penalties of using a smaller prop, and how much of the loss could be recovered by using a controllable prop in the smaller diameter (some, but nowhere near all). There was a lot of other great info on his site; it's a shame that his family let it lapse after he died, and for some reason it can't be found in the Wayback Machine.

    Charlie
     
  20. Jan 29, 2020 #40

    pfarber

    pfarber

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    EVERYONE thought the world was flat.
    EVERYONE thought the atom was the smallest particle.
    EVERYONE thought that the speed of sound could not be broken.

    So no, I don't care what EVERYONE thinks because we are where we are today because SOMEONE had an idea, and ran with it.

    This site is to explore and discuss ideas. If my ideas are not in your comfort zone, or if all anyone has to say is 'it didn't work before' then you're really not advancing the topic. EVERYONE knows that a house built on a poor foundation will fall. So lets discuss possibilities of making a solid foundation.

    I mean even 2 of the 3 piggies had their house blown down.. because no one else tried brick.
     

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