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Thread: Some raven questions

  1. #31
    not real name 500 Club
    Join Date
    Mar 2009
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    Glen Innes NSW - previously The Banana Stip - aka Stoke International in Kent
    Posts
    847

    Some raven questions

    Henry,

    Well then that brings in the whole issue of effective dihedral of the wing.

    High roll forces come from a very stable wing - the more effective dihedral the higher the stability.

    With a swept wing effective dihedral is the sum of a lot of little bits

    1. actual dihedral

    2. sweep angle

    3. actual twist

    4. wing tips (not an issue on Ravens)

    If you want a nice easy to read paper on how all these fit together look at the B^2 website and these documents:

    http://www.b2streamlines.com/EffectiveDihedral.pdf

    http://www.rcsoaringdigest.com/OTW/o...veDihedral.pdf

    While they may be written for model flying wings but the same things apply to our bigger flying wings.

    For me my Eclipser cruises hands off just under 70mph at 4100rpm burning 11lph and I can throw it around without any real effort and I can fly through fairly fierce thermals for hours without an issue or getting worn out so I am leaving my tips/hangpoint alone because I have a happy point of stability and speed I like.

  2. #32
    Junior Member
    Join Date
    Dec 2006
    Location
    Deenethorpe
    Posts
    27

    Some raven questions

    Hi Kirk,
    I did speak to Chris earlier in the week, and he said that to reduce the roll heaviness, I could raise the tips, ie lengthen the tip rod. He also said that this would reduce slightly the trim speed. I havn't tried this yet, as I still havn't got the engine running to my satisfaction. I'm off for another fiddle this evening, so fingers crossed.

    A quick question, if you are only pulling 4100 rpm for 70 mph, what is your max rpm, ie at take off ?

    Cheers

    Ian

  3. #33
    not real name 500 Club
    Join Date
    Mar 2009
    Location
    Glen Innes NSW - previously The Banana Stip - aka Stoke International in Kent
    Posts
    847

    Some raven questions

    Ian,

    To be clear, I fly solo 95% of the time and therefore am not a gross weight no matter how many hamburgers I eat. 4100 for just under 70 is for a take off weight of around 340kg. When I go touring/camping I take everything but the kitchen sink and at MTOW of 415kg I need 4150-4200 for the same speed but seem to burn pretty much the same 11lph.

    As for take off I pull 5500-5600 as I leave the ground which is my max rpm. I never go wide open throttle in the air straight and level because I do not need to see that much speed in the raven so I never see the un-loaded max rpm the engine/prop can achieve but I guess it would be in the range of 5700-5800 which is the TADS max for 5 minutes on the raven.

    My prop is set exactly per the TADS and so far the eclipser has done pretty much exactly what I have wanted and delivered exactly what the book says it would.

  4. #34
    Senior Member
    Join Date
    Dec 2008
    Location
    Kaunas, Lietuva (Lithuania)
    Posts
    195

    Some raven questions

    Raven X 447

    I was playing in the air yesterday. Wind speed was about 10-12 knots. So, I'd head upwind direction and push bar until almost stop in the air (in reference of ground speed), sustain this for a while and pull bar increasing rpm at the same time to gain 75 mph speed as soon, as possible. Guys on the ground were amazed

  5. #35

    Some raven questions

    The joys of a joymachine eh Kestutis!

    Engine failures are really a doddle in them as they can dive to the ground so easily even if you pick a field directly below you!

  6. #36

    Some raven questions

    That's the only way you can get anywhere near the Vne for the check flight test Kestutis. It looks spectacular from the ground because, all of a sudden, you can see the TOP of the sail. The dive is quite radical. First time I saw a Raven (Gordon Faulkner(?) I think, at Weston Park, 1985), it arrived over the numbers at 500ft - then did that spectacular dive and landed on the runway.
    Dave

  7. #37

    Some raven questions

    Maybe with a Medway sail - the Southdowns would go to 100 quite happily just pulling the bar in. My Southdown Raven will continue to 110. The other one I have which is still an X but with a newer Medway sail will not go beyond 75 without accelerating via the method above (guess which I prefer)

    Mark Phillips taught me the rapid height loss... maybe 400 feet on the edge of the stall with just enough power to maintain height. Then power off and bar full in together and dive and pull out of it just above the ground whizzing along at 80 or so. Always stuns the passengers - I always would ask if they wanted a traditional boring approach like a normal aircraft or a roller-coaster approach. More women than men would opt for the rapid-height loss. I flew into the PFA rally one year at Cranfield and did one. People started running towards the end of the runway thinking I must of crashed once I dropped below their field of view ))))

  8. #38
    Senior Member
    Join Date
    Dec 2008
    Location
    Kaunas, Lietuva (Lithuania)
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    195

    Some raven questions

    Yep, done all that you all are talking about

    I always shock the "radio guy" reporting "final" in downwind postion ... and diving down to "numbers"

    Attached files

  9. #39

    Some raven questions

    Gwyn,

    I think you're right about the different sails. I'd not thought about that. I've had a Southdown, a Raven International (rigged for a Hornet), a Hornet, and old and new Medway, and it's much as you say.
    Dave

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