Decalage angle

Discussion in 'Aircraft Design / Aerodynamics / New Technology' started by Eugene, May 29, 2017.

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  1. Jun 23, 2019 #1101

    AdvenJack

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    I am so thankful that Eugene started this thread and has continued it!
    All of you contributors of data are thanked most enthusiastically! As to Eugene's self depreciating humorous comments, he is obviously NOT a person suffering from psychological insecurity about an inadequate intellect. He's generously informative, comical, entertaining and mighty darn smart, thinks me! His 1 question to 5 experts, resulting in 7 new and conflicting answers is a perfect example. What a Great Thread!!!!!
     
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  2. Jun 23, 2019 #1102

    Eugene

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    IMG_2709.jpg

    Let's say we build little toy submarine, about 3 feet long and try to pool it under water straight and level using only rope to do it.

    - which one will be easier to pool?

    - which one will need biggest tail to stay level?

    - which tail will get cleanest flow and will be most efficient?

    My wife answered all this questions correctly and I am pretty sure that she doesn't have aeronautical degree.

    Are you guys trying to tell me that there is "real" designers out there and they don't know correct answer?????!!!!!

    My designer called me stupid many times and I used to agree, but I am not so sure anymore.
     
  3. Jun 23, 2019 #1103

    plncraze

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    In David Thurston's book Design for Safety he has an airplane (Patchen Explorer, IIRC) which has a high thrust line but the prop blows on the horizontal tail. Thurston is pleased he can manage pitch change with power by doing this and he doesn't care a bit about additive drag. His choice of configuration has other concerns besides the tail.
    Drag isn't a big deal to some folks. Get a copy of Pazmany's Light Airplane Design and find the section on center of gravity. He calculated horizontal and vertical centers. The horizontal is what you learn in pilot training. The see if your thrust line intersects this line or if you are forcing the airplane to fight this.
    You are in a situation where you are seeing inefficiency and it bothers you. It's not good or bad it's just your nature. Burt Rutan, Roy Lopresti and Mike Arnold (AR-5) all saw room for some improvement somewhere and acted on it.
     
  4. Jun 23, 2019 #1104

    Eugene

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    Burt Rutan, Roy LoPresti and Mike Arnold - I shouldn't have my name on the same page with them.

    I was looking for someone who has ready to go recipe for my situation. I understand now that there is no such person out there.

    I should move my airplane from experimental department in to research and development.
     
  5. Jun 23, 2019 #1105

    Hephaestus

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    I wouldn't say that there's no one. But not a lot of the big names in home building.

    Strojnick's son may have the theory and practice, not sure if janowski passed on the knowledge.

    Chuck Slusarczyk of CGS hawk fame may have some practical knowledge, and is a member on our forum.

    I wonder if an Oshkosh visit could let you bend the right person ear somehow ;)
     
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  6. Jun 23, 2019 #1106

    Eugene

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    Its hard to explain, but it is really not about drag or speed. Speed is only indicator. I have really no place to go and Oshkosh is only 100 ml away.

    At anything above 5000 RPM you are getting feel of some kind of tension, with your hand you feel that elevator is fighting for its life in turbulent air flow.

    It is situation were I really want to reduce RPM, turn around, go home and change or fix it somehow.

    fullsizeoutput_1746.jpeg
     
    Last edited: Jun 23, 2019
  7. Jun 24, 2019 #1107

    akwrencher

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    This right here I can identify with. If I was in your shoes I would feel exactly the same way. I'm OCD like that, can't stand when things don't work like they should, or at least how I think they should. Plus, I have a lot of stubborn Norwegian blood..... Keep at it though, I'm dying to know what the fix ends up being:)
     
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  8. Jun 24, 2019 #1108

    BBerson

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    The fix is to fly it at the reduced speed it was designed for.
    He already said he has nowhere to go.
    Sure, experimenting is fun. I did some things like root fairings and flush bolts to try to make my Cherokee fly faster. Nothing really worked because the designers had already tried everything.
     
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  9. Jun 24, 2019 #1109

    Eugene

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    Yes, experimenting is fun, but it’s only fun if there is hope for improvement. If there is a chance that when it’s all done you’ll feel satisfaction and you’ll see positive results. Otherwise you are going wrong direction, while everybody was trying to tell you not to go there, but you acted like you’re smarter than they are.

    One time in my life I found myself on German autobahn driving fiat bambino with 26 hp engine and big mattress strapped to the roof. I would pay a lot of money today for that picture. At certain speed front side of the mattress was flipping upright and acted like a giant speed break. If this would happen in this country with average American pick up truck, all you have to do is step on the gas pedal to keep up with traffic. But for that little two cylinder engine this was overwhelming !!! Only one single improvement possible was to get rid of mattress itself. Absolutely no another improvements on the list. Even with 10 times bigger engine that mattress will be ripped away and you would have to use BRS to save your life.

    As long as I have very smart and experienced people like Peter Garrison telling me that open engine represents 50% of total drag, I have an excuse for trying it out and prove to myself that is not the case. But at some point when I cross all items on the list with a big magic marker, there would be no excuse or satisfaction to keep on trying going against the wind with that big mattress on your roof.

    Maybe it does look that way at times, but I am not really that stubborn or stupid to keep doing the same thing over and over and hoping for different results.
     
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  10. Jun 24, 2019 #1110

    proppastie

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    instead of fiber glass shell cowl, might try light frames and sheet metal or even aircraft fabric cover....quick and dirty, do not even have to finish the fabric for a test. Use the bleeder cloth non-certified Dacron, you will not find anything cheaper... use contact cement, and shrink. Careful about stuff getting sucked into the prop though.
     
  11. Jun 24, 2019 #1111

    plncraze

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    Tuft testing is cheap!
     
  12. Jun 24, 2019 #1112

    Eugene

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  13. Jun 24, 2019 #1113

    plncraze

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    I was thinking of the tail since that is what bothers you.
     
  14. Jun 24, 2019 #1114

    Eugene

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  15. Jun 25, 2019 #1115

    Eugene

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    At this point it feels like I am against something bigger, something I still don't know or understand. Like I am playing around with small staff and don't see that big mattress on top of the roof.

    I know someone who learned to fly in Luscombe. He was telling me that in level flight if you stick your hand out of the window, speed was dropping by 5 MPH. Old-timers like that when they see how I moved muffler down, just like Peter Garrison , would definitely expect to see some improvement. But nothing at all.

    I think that maybe my big mattress is backside of my short and wide fuselage.
     
  16. Jun 25, 2019 #1116

    plncraze

    plncraze

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    In one of Jim Bede's design videos he suggested a smoke bomb to see where the air was flowing. If nothing else it would be a cool video!
     
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  17. Jun 25, 2019 #1117

    Eugene

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  18. Jun 25, 2019 #1118

    plncraze

    plncraze

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    Make sure you get lots of video!! And when you pull the first one scream "Heah! Watch this!"
     
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  19. Jun 26, 2019 #1119

    Eugene

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    Best placements for smoke generators???
     
  20. Jun 26, 2019 #1120

    BBerson

    BBerson

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    I would say above the wing and out in front of the wing. Should be in a cardboard tube or something to make the smoke eject in a streamline if possible.
     

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