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Author Topic: Walt Mooney Cook-up 2020  (Read 44833 times)
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Pete Fardell
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« Reply #2700 on: June 24, 2020, 08:54:12 AM »

Thanks guys. Tim, If I do anything Eng/Oz related it would probably have to involve our Amy and a dark green Moth I think!  As to a Fillon cook-up, someone else can start that one (but I’d be in!)

Anyway, for this cook-up, after that favourable response I shall do as suggested and keep going till July 17th, updating the spreadsheets and adding pics to the finished models thread till then. After that, I’ll just let it go where it likes. (I neglected to fit a D/T though I’m afraid, so there’s no telling where it will go, or whether it will ever land.)
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Pete Fardell
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« Reply #2701 on: June 24, 2020, 09:15:20 AM »

DHC Beaver
I managed to get over to my field for 45 minutes this morning for more tests with the Beaver. Gorgeous weather and gorgeous Keil Kraft grass.
By way of baby step tweaks involving rudder, side-thrust and a few grams of nose-weight, I eventually got from lots of flights like THIS to one like THIS before I had to come home. I'm thinking maybe yet more right thrust might be the answer next time? If I want more right rudder though, it'll need some minor surgery as it's not hinged.



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Jack Plane
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« Reply #2702 on: June 24, 2020, 05:52:00 PM »

Always hinge.  Wink
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D/T
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« Reply #2703 on: June 24, 2020, 06:13:30 PM »

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If I want more right rudder though, it'll need some minor surgery as it's not hinged.

You could try a small Gurney flap on the rudder RHS, say 1/16"sq x 1", to see if that solves the trim, before surgery.

Don
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Pete Fardell
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« Reply #2704 on: June 24, 2020, 06:37:16 PM »

That’s a good idea- thanks. So far I’ve just forced the rudder over as far as I dare and pinned it (see pic). I thought I might run a knife along the hinge line next though, but not go right through. Should mean I can haul it over a bit more and re-pin.
By the way, am I correct in thinking rudder is a better fix than side thrust, given that the turn only really tightens after the initial power burst?
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OZPAF
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« Reply #2705 on: June 24, 2020, 08:30:23 PM »

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By the way, am I correct in thinking rudder is a better fix than side thrust, given that the turn only really tightens after the initial power burst?

Yes i think you are correct there. However I would suggest as an alternative to more rudder offset to use a gurney or a wedge on the left wing about 2/3 semi span. The model has a nice turn developing and more lift on the inside wing may be all it needs.

It looks a good potential flyer.

John
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OZPAF
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« Reply #2706 on: June 24, 2020, 08:32:20 PM »

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John - it will be worth waiting for!
Thanks Tim, you have more confidence than I have Smiley

John
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cvasecuk
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« Reply #2707 on: June 25, 2020, 03:00:20 AM »

Pete
You could always try an acetate trim tab on both fin and wing. Super trimming field!!
Ron
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Pete Fardell
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« Reply #2708 on: June 25, 2020, 03:40:52 AM »

Thanks both. I think I'll do what John suggests first and put a gurney on the inside wing. It's certainly what I'd do if it were an indoor model (which it might conceivably be if I ever take it to Nijmegen). It would be nice to keep the circle from getting too much wider as there are trees lurking on the edges of the field.
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billdennis747
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« Reply #2709 on: June 25, 2020, 04:42:13 AM »

Pete, why not fly it to the right, like absolutely every duration model?
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Pete Fardell
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« Reply #2710 on: June 25, 2020, 05:16:36 AM »

Pete, why not fly it to the right, like absolutely every duration model?
Only because it’s going left and would need a big shove of unhinged rudder to go the other way. My Comte goes right though.
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DHnut
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« Reply #2711 on: June 25, 2020, 06:36:40 AM »

Pete,
       From the video I would use a gurney flap on the port wing and a small amount of right thrust as a start and add a little left rudder if needed. The gurney flap will make the lift vector more in the vertical plane and give a better climb and reduce the horizontal element that is assisting the spiral to develop. I had this situation with the Luscombe Sedan in the early trimming stages.
Ricky
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LASTWOODSMAN
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« Reply #2712 on: June 25, 2020, 06:55:09 AM »

Which side of the wing does the Gurney flap get installed on?   Or are Gurney flaps always placed on one side all the time?    Sorry for the dumb question.

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Richard
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OH, I HAVE SLIPPED THE SURLY BONDS OF EARTH ... UP, UP THE LONG DELIRIOUS BURNING BLUE ... SUNWARD I'VE CLIMBED AND JOINED THE TUMBLING MIRTH OF SUN-SPLIT CLOUDS ...
Rich Moore
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« Reply #2713 on: June 25, 2020, 07:06:01 AM »

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what John suggests first and put a gurney on the inside wing
I vote for that.
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alfakilo
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« Reply #2714 on: June 25, 2020, 08:38:43 AM »

I think I understand the idea of a gurney flap, but I'm unsure of the practical details.

What is it made of? Size? Where is it placed on the wing? How is it attached? Is the placement intended to be permanent?
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Pete Fardell
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« Reply #2715 on: June 25, 2020, 09:26:30 AM »

The gurney strips on my indoor models,  and on others I’ve seen, are just short lengths of approx 1/16 square balsa stick stuck under the trailing edge of whichever wing you want to lift. Used wherever you might have added a downward bent trim tab I think.
You can also make them wedge shaped in cross section, positioned so that the air flows down the slopey side as it reaches the edge of the wing. Someone tell me if any of that’s wrong. On scale models they are much less noticeable than trim tabs, and don’t glint in the sun like acetate ones do!
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LASTWOODSMAN
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« Reply #2716 on: June 25, 2020, 10:13:14 AM »

     Hi Pete.  That  37"  Beaver flies with a stately magesty.  And what a pillow landing in that tall wheat!   Not even a cartwheel!  What a soft stop!    That is a very clear video study of aerodynamics, against that green background of trees,  as your Beaver is wavering and correcting its flight.   Smiley
      With your Beaver circling left in too tight of circles, and you want to raise the left wing, so the left wing is then called the "inward" wing.   Tell me if I have this right or not.   Raising the left wing will also widen the circle, which I think is what you are after.
        The circle could also be widened by adding a piece of clay weight to the right wing tip (but this clay ballast weight must weigh more than a balsa Gurney strip - is this a reason they use Gurney flaps instead?).  
     Pete I think you have explained it to me.   The Gurney flap (always at the rear of the wing?),  does the same as a trim tab.    If, for example,  I needed do the other way, to lower the right wing in this case, I would then put a trim tab on top of the right wing bent upwards, or put a Gurney strip on top of the right wing.   Does that sound right?   I have been wondering about this for a long time ... Undecided

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Richard
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OH, I HAVE SLIPPED THE SURLY BONDS OF EARTH ... UP, UP THE LONG DELIRIOUS BURNING BLUE ... SUNWARD I'VE CLIMBED AND JOINED THE TUMBLING MIRTH OF SUN-SPLIT CLOUDS ...
billdennis747
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« Reply #2717 on: June 25, 2020, 10:35:56 AM »

https://en.wikipedia.org/wiki/Gurney_flap
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alfakilo
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« Reply #2718 on: June 25, 2020, 11:18:31 AM »

OK, so using the above info and assuming a wing with a 4" chord, I get a flap that should be about 1/16" tall, so a 1/16" stringer works great. Now, how long is this flap? And is it attached flush with the trailing edge?

If no additional corrections are made, then it would seem this is a permanent fix.
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Pete Fardell
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« Reply #2719 on: June 25, 2020, 12:41:01 PM »

John (OZPAF) above suggests it should be about 2/3 semi span, but I think it’ll work however long. I’m only a beginner with using gurney strips though. There’s quite a lot of discussion of them on other threads too, which might help.
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cvasecuk
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« Reply #2720 on: June 25, 2020, 01:42:37 PM »

I think that John meant "at" 2/3 span. I would use a piece of 1/16" square about 3" long and then adjust its length as necessary.
Ron
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Pete Fardell
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« Reply #2721 on: June 25, 2020, 01:52:18 PM »

I think that John meant "at" 2/3 span. I would use a piece of 1/16" square about 3" long and then adjust its length as necessary.
Ron
That makes more sense. I thought it sounded a bit long!
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Jack Plane
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« Reply #2722 on: June 25, 2020, 05:57:52 PM »

I'm a fan of gurneys.  On, say, a 16-18" span model, mine would be about 1.5" long, positioned 2/3 to 3/4 of the way towards the tip... much where one would traditionally have mounted a trim-tab.

But if one overdoes the gurney then as the rubber runs down towards the end the model can roll straight (not enough airflow over the rudder) or continue rolling into a right turn... in both cases straight towards the wall!  So I've learnt to keep the gurney effect slight but add a bit of tip-weight to the opposite wing as well - the theory being that weight isn't speed-dependent as gurneys or tabs are.
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OZPAF
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« Reply #2723 on: June 25, 2020, 08:50:12 PM »

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I think that John meant "at" 2/3 span. I would use a piece of 1/16" square about 3" long and then adjust its length as necessary.

Yes Ron is correct - I meant at 2/3 semi span not 2/3 semi span long. Blast - another senior moment - sorry about that Cheesy Ron's suggested size sounds ok for a start.

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And is it attached flush with the trailing edge?
Yes.

I temporarily attach them with glue stick - but cement or even dope would work with thinners to remove it if necessary.

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If, for example,  I needed do the other way, to lower the right wing in this case, I would then put a trim tab on top of the right wing bent upwards, or put a Gurney strip on top of the right wing.   Does that sound right?   I have been wondering about this for a long time ... Undecided

I haven't tried that Richard but I feel that they would not be as effective on top of the wing due to the way they work in the TE vortex of the wing.


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But if one overdoes the gurney then as the rubber runs down towards the end the model can roll straight (not enough airflow over the rudder) or continue rolling into a right turn
  Interesting point Jack - but it is possible that they have less drag(which would tend to keep the turn going in the same direction) than the typical deflected flap and with the loss of rudder power produce the effect you mention.

Anyway it's easy to try so back to your local Keil Kraft field Pete. Smiley

John
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Pete Fardell
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« Reply #2724 on: June 26, 2020, 07:47:47 AM »

This forum is just brilliant for getting instant good advice. Thank you all!
I went back to the field this morning with a gurney strip under the left wing. Only other change was a slightly longer motor of the same width as before (4 strands of 3/16) just to give me a bit more winding range.
To start with the left wing was still dropping, but definitely better, but then with 1g of tip weight added to the right wing it did this: https://youtu.be/Qu4v8t9vOYw

 That flight was 900 turns. It was a nice safe circle for that field too with no tree scares. Pics show the gurney strip and tip weight. Also, a post flight celebratory shot with the picturesque horse-dung heap in the background. Thanks again for the great input!
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