Decalage angle

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

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  1. Jun 5, 2019 #1001

    Eugene

    Eugene

    Eugene

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    I don't think this airplane will fly any better with different name.

    IMG_0544.jpeg

    Looking at this picture I am thinking to send my Skyboy for MRI from top down. May be for only 10 images with dimensions. Everybody call this airplane fat and short, but nobody knows how bad that is.
     
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  2. Jun 7, 2019 #1002

    Eugene

    Eugene

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    6F9664FD-1DEA-4F80-8545-82D1041F1377.jpeg 7FD9AB6E-7E92-489F-B250-272AA115E19A.jpeg 5A90ED67-F4D8-4404-9613-A15703F7760A.jpeg MRI results. Only two slices for now
     
  3. Jun 9, 2019 #1003

    Doggzilla

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    Maybe it is just an illusion, but does that rear blue area on the bottom fuselage behind the landing gear flair outwards and is angled upwards with the tail boom?

    If it was level it wouldn't be so bad, but if it's protruding and angled upwards it's definitely going to create some low pressure and drag as the air flows over it.

    Especially since the belly is already angled like an airfoil.
     
  4. Jun 9, 2019 #1004

    Eugene

    Eugene

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    IMG_0917.jpeg

    Yes, this is definitely problem area and air separation is getting sucked in to the prop reducing its efficiency. Russians telling me that rear cowling needs to be changed first. They think, that it's much more important than engine cowling. Rear cowling should be longer than prop to eliminate possibility for bottom air to get in to the prop.
     
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  5. Jun 9, 2019 #1005

    Eugene

    Eugene

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    I was talking to russians who designed and build airplane on picture below.

    Image 6-8-19 at 22.10.jpg

    It is tandem but with 80 cm (30") wide cabin. They tried to do everything right. But after 120 km/hr prop starting to make a lot of noise and aircraft not going faster then 150 km/hr (93 MPH). Air separation from fuselage in combination with wings blockage almost taking lower part of your propeller out of operation.

    This is how pusher must look like (below), with clean airflow in to the prop

    Screen Shot 2019-06-08 at 06.33.14.png

    Balancing drag apparently not very big factor, but prop efficiency is.
     
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  6. Jun 9, 2019 #1006

    BBerson

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    What is that low wing seaplane called? Looks like a Molt Taylor "Coot" with " float wings" on the root of the wing.
     
  7. Jun 9, 2019 #1007

    proppastie

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    You seem to be saying you are stuck with what you have as regards the Skyboy?.......
     
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  8. Jun 9, 2019 #1008

    plncraze

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    Amphibian is a Skyshark IIRC
     
  9. Jun 9, 2019 #1009

    BBerson

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    I searched for Skyshark seaplane and didn't find anything.
     
  10. Jun 9, 2019 #1010

    BJC

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  11. Jun 9, 2019 #1011

    BBerson

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  12. Jun 9, 2019 #1012

    plncraze

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    When Alex Strojnik was still alive and building planes he pushed (pun intended) for pusher configs but once I saw a comment that he did not get the performance he expected from his S-4 and that he thought it was due to poor inflow to the prop due to everything in front of the prop. Pusher props have a bad history overall due to the things that can go wrong or add weight. If a pusher prop is too close to something the wake and inflow to the prop gets crazy and if you move the prop downstream you have issues with the additional parts.
     
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  13. Jun 10, 2019 #1013

    Eugene

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    Main reason why I started this, is to find an explanation. I think I finally got it all together in to my head. Not understanding my aircraft behavior was making me crazy.

    It was very strange feeling in flight: 75 MPH = airplane perfectly relaxed, but at 85 MPH = you entering some kind of uncomfortable zone with much more prop noise, elevator vibrations that you feel in your hand. As soon as you entered in to this uncomfortable zone any more power advancements almost not resulting in to any speed gaining at all.

    Fact that I am terrible test pilot doesn't help. At work if I don't understand something, all I need to do is dial 1-800-tech-support and I get to talk to someone 10 times smarter. So far I was able to find problem and fix or order correct part. So, with Skyboy questions I did same thing = dial EAA tech support..............

    So, this aircraft has build-in limitation by design. I understand, that most of my improvements will have minimal impact, if anything at all. But this platform will let me try and do all this things I want to do with price of motorcycle. I can be "one of them" , I can fly to Oshkosh every year, I can fly and experiment and be active EAA member.

    I will be doing all that at only 85 MPH vs 100-120 MPH like everybody else with 100 HP engines in LSA community. So what?!
    This is price I will pay for helicopter-like visibility and my cockpit will not smell like engine compartment.

    Main thing that I understand what is going on and my aircraft will not brake apart in flight.

    I don't see any alternative for $20-30K. Some day when I grow up and nothing else to do with time and money, I will build something cool and fast! But until that happens - I will play with my Skyboy.

    IMG_6317.JPG
     
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  14. Jun 10, 2019 #1014

    Doggzilla

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    That explains a lot actually.

    The flow around the engine widens as speed increases and is causing interference drag with the top of the wing. This also would make flow uneven and cause vibrations. And also change pitch and drag.

    The designers clearly knew this because they added a "spine" above the wing that moved some of the drag and high pressure in front of the wing instead of in front of the engine. As the front of the engine is aligned with the low pressure section of the wing and any high pressure at the front of the engine would affect the wing. The spine moves some of the high pressure forward and away from the center of the wing.

    This is probably why so many other similar aircraft have long cowlings, so that they move the high pressure leading edge forward and away from the low pressure on the top of the wing.
     
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  15. Jun 10, 2019 #1015

    rotax618

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    82E119AF-29FF-420F-B467-0F16769D0581.jpeg My Boorabee aircraft exhibited an oscillation in the yaw plane, lots of prop noise and a limited airspeed of around 75kts. After fitting VGs to the fuselage sides just before the widest point, the oscillation stopped, I had to decrease the pitch of the prop and the top speed went to well over 90kts. The plan sectional view of the boorabee fuse has the widest point around 2/3 back, similar to Strojnic’s designs, you can see the lexan VGs down the side of this Jabiru powered Boorabee
     
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  16. Jun 10, 2019 #1016

    Eugene

    Eugene

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    Yes, maybe I can try larger size VGs on my airplane. Anybody know dimensions for ones on this picture and installation angle? Screen Shot 2019-06-10 at 06.22.29.png
     
  17. Jun 10, 2019 #1017

    Hephaestus

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    NASA has a few articles on them.

    [​IMG]
    I keep wondering why people use the strake style instead of these ones...
     
  18. Jun 10, 2019 #1018

    Doggzilla

    Doggzilla

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    Since you work in HVAC you could just take a strip of sheet metal and cut and bend out your own in one large piece instead of having to individually attach each one.

    In fact, you dont even have to cut. You can just fold the sheet like origami.
     
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  19. Jun 10, 2019 #1019

    Eugene

    Eugene

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    Yes, I can make anything as long as I know dimensions and the angles to follow.
     
  20. Jun 10, 2019 #1020

    rotax618

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    F93A4FFA-9FDD-48FD-B889-1F85DC397DB4.jpeg I carried out the experiments with VGs nearly 30years ago at a time vortex generators were still a “black art” especially in the sport aircraft realm. Being a pusher aircraft, anything forward of the prop has to be attached well or it could be catastrophic. I made the VGs from Lexan figuring that if they were to go through the prop they may not cause a blade to depart, during the experiments they were attached using double sided foam tape with a single pop rivet. I made a series of different sizes, all had the fin at 30-45deg to the airflow. The VG placement and number was LAR (looks about right), some of the Boorabee builders have done their own interpretation and claim a slight improvement, all Boorabees have required VGs to get clean air into the prop and to prevent the airflow around the rear of the pod from alternately stalling one side then the other causing the slight phugoid oscillation in the yaw plane.
    You can see the different arrangement of alloy VGs on this Boorabee.
     
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