F-18 v4 NASA High Alpha Research Vehicle

Discussion in 'Scratchbuilding!' started by Slaintemaith, Aug 9, 2016.

  1. Slaintemaith

    Slaintemaith Cadet

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    F-18.jpg After its first flight!
     
    Last edited: Aug 9, 2016
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  2. pileit1

    pileit1 Ace Pilot

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    Looks good Slain. Let us know how the maiden goes.
     
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  3. Slaintemaith

    Slaintemaith Cadet

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    Flew it just before dark.
    WAY too pitchy. Went straight into high alpha on takeoff, which you'll see in the video. Seems like it's tail-heavy, which it shouldn't be since the CoG is right on the money where the plans say it should be.
    Unless, of course, the plans LIE!

    Here's a video of the flight.
     

    Attached Files:

    Last edited: Aug 9, 2016
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  4. BadAxeFlyer

    BadAxeFlyer Ace Pilot

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    Holy Cow you are a brave man flying amongst all those wires and trees. :eek:
     
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  5. sirskyhi

    sirskyhi Ace Pilot

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    Just curious, what did you have your throws set at?
     
  6. Slaintemaith

    Slaintemaith Cadet

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    Nevermind the soccer goals on the ground. The trees and wires are farther away than they look.

    The throws were maxed. But it was "twitchy" like tail heavy.
     
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  7. Dial in 30 to 50% expo and move the battery forward until you find the happy spot. With those drooped leading edges they get really floaty, I personally don't like them.
     
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  8. F1wanabe

    F1wanabe Top Gun

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    Nice plane, Slaintemaith! You're right, it did look a little tail heavy didn't it? The cg on the plan is perfect for all around flying and I went back even more when using flaps without the pitching. The le flaps really open up the cg envelope. One thing that I noticed when you came in for landing was that the nose dropped abruptly as you cut power. Is it possible your motor's thrust angle is out of alignment with the wing? If the prop nut is above the wing that would pitch the nose up under power and let it drop when power was off. Can't quite tell from the picture.
    [​IMG]
    Can you take a close up picture of the prop nut from the side?
    But, you flew it and got it down well! What I found with the f18 is it flies really stable hands off and the more I kept off the controls the smoother it flew. Just minor inputs required. Raising expos would do the same thing as Wildthing noted.

    www.frcfoamies.com
    www.youtube.com/user/gstrysky
     
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  9. Slaintemaith

    Slaintemaith Cadet

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    I think I had the opposite issue, as I was clicking in up elevator trim, since the nose kept wanting to drop even while powered.
     
  10. Slaintemaith

    Slaintemaith Cadet

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    ...if anything, it's vectored down--but it's pretty solidly centered.
     
  11. Flybyknight22

    Flybyknight22 Top Gun

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    Nice flight Slaintemaith,

    Your F-18 v4 looks great!

    Na, plans ain't lying out right at all :)

    I have found that the marked CG on these plans are a ball park "spectrum" starting point.

    In fact the new V5 planes show a CG spectrum of sorts in the PDFs.

    The new Ebook offered by RCPowers covers these and other factors quite well.

    Everybody builds a little different. Some build heavy others build light.

    Some use foam Tac, some hot glue, some epoxy and others a combo of all the above with different types of foam and different size batteries etc.

    All those factors have an affect and can change the CG a little bit and it's always generally a safe bet to maiden a little nose heavy to start and then adjust until you find the sweet spot.

    Sometimes the sweet spot in CG is as marked other times it is not.

    Placing a perfect CG mark on a set of plans for a custom scratch built plane that everyone builds a little different than the others I think is virtually impossible but the starting point is close and sometimes right on the money.

    I have the V4 also and love the plane. I fly mine a little nose heavy, just a "smidge" forward of stock CG.
     
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  12. Slaintemaith

    Slaintemaith Cadet

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    Such is the plan--moving that battery far more forward, and scooching it back to find the sweet spot.
    Of course it's been raining off and on all day, so there'll be no flying tonight.
    Maybe tomorrow!

    I've also put in some expo just to tame it down...
    I see all the other videos of Maiden flights with the plane totally dialed in... I'm a bit envious.

    On the other hand, mine looks cooler... (=
     
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  13. Slaintemaith

    Slaintemaith Cadet

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    Nope. Flew it again today and it seems like the C/G markers LIE! I flew with the battery as far forward as the wires would allow and it seems like she needs some weight in the nose even still. (Although she wasn't as twitchy as she was on the first flight.)
    Good thing I've got some lead weights lying around at home...
     
  14. F1wanabe

    F1wanabe Top Gun

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    Slaitemaith, the cg marks are good. Have you transfered them onto your plane well? As you said, many others have perfect maidens with the cg set exactly on the marks and mine was beautiful. One of the best maidens I've had.

    If you have cg on the marks and it feels like you need a ton of weight on the nose, I'd look elsewhere.


    www.frcfoamies.com
    www.youtube.com/user/gstrysky
     
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  15. Flybyknight22

    Flybyknight22 Top Gun

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    Slaintemaith,

    The CG marked on the PDF plans for your beautiful F-18 are purty dang tight Bro.

    What size battery are you using?

    2200mah, 1800mah, 1600mah or 1300mah?

    Shooting in the dark here a little but a smaller battery obviously would make it lighter up front.

    Can you take a pic showing where you have the CG marked?
     
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  16. Flybyknight22

    Flybyknight22 Top Gun

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    Wow! What a beautiful plane!
     
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  17. Slaintemaith

    Slaintemaith Cadet

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    I just had to get it dialed in. It flies dreamily now--but I did have to put the battery as far toward the nose as I could. *Shrugs* Results are all I care about.
     
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  18. Flybyknight22

    Flybyknight22 Top Gun

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    Sounds like you got it, way to go!
     
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  19. Slaintemaith

    Slaintemaith Cadet

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    Got to basically hover it today in the wind with the flaps down.

     
    Last edited: Aug 12, 2016
  20. pileit1

    pileit1 Ace Pilot

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    Looks like she's flying pretty good now Slain. Could you possibly post a pic showing the location of the
    cg per the plan and where it is located now?
     
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