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Author Topic: Kiel Kraft Dolphin: Banana Twist  (Read 3881 times)
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OZPAF
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« Reply #50 on: June 22, 2020, 03:20:26 AM »

It is showing it's potential in those flights Jasco. It is climbing too fast in my humble opinion and that most likely means that the rubber is too powerful and or it is being stretched too far, or that the tow hook is not far aft as the angle of the model is quite low. This will cause eh model to overshoot the line and fly off in a climbing position and stall.

As bill mentioned earlier - the model should climb like a kite and thus if you are using a similar setup to that used by the Peterborough rules. then actually the most likely problem is a hook too far forward. Try moving it back as 1/4'' or so by packing balsa in the hook and see what happens.

John


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Jasco
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« Reply #51 on: June 23, 2020, 03:14:07 PM »

     OZPAF you are the first to suggest I move the hook back...I think your reasoning is sound and I'll give it a try.  Several people have compared the towing experience to flying a kite and this is definitely not that!

     I now have 4 aircraft awaiting repair. 5 if you count the one with the broken motor. I wish I had built some of those cat-a-jets during the winter. Grin

     
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billdennis747
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« Reply #52 on: June 23, 2020, 04:13:10 PM »

    Several people have compared the towing experience to flying a kite and this is definitely not that    
That's because your line is too short compared to the rubber, as stated earlier, and that's why it's acting as a catapult.
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OZPAF
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« Reply #53 on: June 23, 2020, 07:53:41 PM »

Jasco, here are the Peterborough model Club high start specifications which have proved to be very successful.

Hi-Start Glider

Model Span 36 inches tip to tip (NOT flat span)
Hi Start 7.5m of 1/8” rubber Plus 22.5m of line


Note the lengths and ratio of the line length to the rubber - this is critical as Bill has mentioned.

I would try a high start like this before modifying the hook position. The problem lies basically in the rubber/ line length which needs to be matched to the size of the rubber. The line itself should be very light (just strong enough) for best performance- something like 10lb breaking strain fishing line.

I hand towed a 30" model on cotton sewing thread and this was common for small hand tow gliders.

These gliders are not designed to fly fast and thus a catapult approach does not work.

Good luck with it.

John
« Last Edit: June 23, 2020, 08:57:44 PM by OZPAF » Logged
Jasco
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« Reply #54 on: June 24, 2020, 12:33:19 PM »

     Thanks for the feedback on flying.  I did increase the length of the line from the first time out last fall, but the ratio of rubber-to-line length is a criteria to consider as well, eh?.  I see...I will increase it some more and follow OZPAF's "Peterborough" set up.

    My tow line should be:  (22.5m*9/5)+32= 72 1/2 freedom units of line!  Grin(just kidding) Actually, it works out to be 73.8 ft, so I woulda been OK!
I'm using 6lb monofilament fishing line and 1/8" rubber.  I did not actually measure it. Looks like about 10 feet of rubber. So I guess I don't have enough of that either.

     I'm afraid when flying day comes I get a little flustered and frequently forget some of the advice I've been  given so forgive me if you guys end up repeating yourselves. Roll Eyes

     I also obtained a digital gram scale for the first time in my life and I'm running around weighing everything.  The Dolphin weighs 43 grams without a vertical stabilizer or wing hold-down bands.  Is that good or bad?  Somewhere I got the idea this plane should weigh 38 grams.   Huh
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Jasco
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« Reply #55 on: June 24, 2020, 01:02:33 PM »

I went back and re-read this thread.  I have been told at least 3 times what length line and rubber to use. Tongue
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Jasco
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« Reply #56 on: June 24, 2020, 04:34:22 PM »

And I mispelt Keil Kraft in the title.
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OZPAF
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« Reply #57 on: June 24, 2020, 08:13:02 PM »

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Looks like about 10 feet of rubber. So I guess I don't have enough of that either.
Yes that is too short.

Consider pulling the line back say 5 paces - 5 yards or 15' - you have stretched the rubber 1.5x it's resting length. This as you have seen will be too much power for the model.

Now consider using say 7.5m of rubber - ie around 25'. Pulling the line back 15' will only stretch the rubber 0.6x it's resting length. The power or actual force on the model is proportional to the stretch and thus you have achieved a slower climb and if you have the 75' line as well it will climb longer and higher.

How much stretch would be enough in practice will need to be determined - probably close to what I have said. However the model should kite up on a cotton line which is one indication.

As you can see for a given model - the size and length of the rubber is critical. The only way to use a shorter length of rubber is to use a thinner batch - but this would mean lower launches as the length of the combined rubber/line would be less.

We are all keen to see you have a good flight with your Dolphin so hope this helps.

John
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« Reply #58 on: June 25, 2020, 06:01:02 PM »

Jasco

Trying to remember things is a hopeless task.  Get yourself a small pocket notebook and write down what you need to do there, then you've got something to refer to at the field!
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« Reply #59 on: June 29, 2020, 08:49:14 AM »

     Over the weekend I repaired the Dolphin (didn't fly it) but did fly an HLG a little with 4 loops of 1/16" about 6" long as a catapult.  I used 1/16" because I -ahem- lost my box of 1/8". At any rate, the plane flew much better and longer when I used just 2 of the loops than it did when I used all 4 loops. I'm obviously experiencing the same thing with the Dolphin.  Just one of those object lessons that I have to experience before it really sinks in.

     I hope to get to the field this week for more flying.  I WILL have a regulation length bungee. Grin
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OZPAF
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« Reply #60 on: July 01, 2020, 04:38:49 AM »

Good luck with it.

John
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« Reply #61 on: July 03, 2020, 07:05:48 PM »

Another trip out to the field. 
https://youtu.be/4zIQ6Mv2fII

I'm not 100% convinced I'm launching it correctly, or that I have it trimmed right.  Seems to turn pretty tight, eh?

There was no wind again, but it lost a lot of altitude right after the tow release when I faced west. I thought whatever air movement there was was the opposite way, so I started launching toward the east and it stayed up in the air when the ring came off.  There were many unrecorded flights because of phone probs, but they were very consistent albeit short. I had to bend the towhook on the plane down a little to facilitate the ring coming off.

The advice about the bungee length was right on the button.  Maybe I should try about 5-10 more feet of rubber stretched a little further for a longer tow? 

13 paces seemed to give the best results.  15 paces and it would stall at the top.

Things to change: I currently tie the rubber to big nail and jab it in the dirt, but the rubber gets caught in the clover. I think if I make the anchor point about a foot off the ground, I'd be able to adjust my launch direction easier. And maybe give it one more foot of altitude.

I'm really digging gliders...maybe a 48" Dolphin with 2-channels! (R/C? On a free flight? Sacrilege! ) Grin
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« Reply #62 on: July 03, 2020, 08:15:51 PM »

My suggestions:
Open up the turn a little.
Move the tow hook to the left longeron to help counteract the turn under tow.
Launch with the nose higher to keep the speed down.
Use thinner rubber for a slower climb.

FWIW I can launch my F1H size glider (220 grams, 279 sq in total) with 150 feet of line and 25 grams of 1/16th rubber. I prefer 3/32 rubber but the folks I fly with have lighter gliders and prefer 1/16. Admittedly, I pace off the 1/16 rubber 7 times its slack length.
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« Reply #63 on: July 03, 2020, 08:29:01 PM »

Hi Jasco!   I really enjoyed your Dolphin glider flights!   Shocked  Thanks for posting.    It looks really good in the air.   Plus +1  on your [ADD Kudos] button on the left.   Cool

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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 ...
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« Reply #64 on: July 03, 2020, 08:36:33 PM »

Good on you Jasco! You are definitely getting on top of this launching method.

As well as David's good tips I would suggest skewing the wing slightly - moving the left tip forward a bit. Try it in very small steps - you shouldn't need much . This is a crude way of adding wash in on the left wing and it will help to straighten the climb and also open the glide turn - keeping the left wing up. If it works then you can add something like a Gurney flap to the left wing around 2/3 of the  semi span from the root.

David's tip re launching more nose up is very important as well - the stall you mentioned is caused again by the model flying too fast up the line and over running it. the angle at launch to the rubber could be as high as 30- 40 deg or even more. Think of a kite on a string.

Good luck and I enjoyed your nice video in that pleasant warm looking area Smiley

John


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« Reply #65 on: July 04, 2020, 03:05:02 AM »

Nice flights.  All you need now is for it to catch a thermal.

Quote from: Jasco
Things to change: I currently tie the rubber to big nail and jab it in the dirt, but the rubber gets caught in the clover.

You can buy "Dog Anchors"* fairly cheaply in pet shops.  The one I use, see pic., cost about five quid. They have a swivel which makes it easy to alter your launch direction if you need to and provides an easy way to swap out lines with different rubber x-section.  The screw fixing also means that it won't come out of the ground until you want it to.

As for the line getting snagged in the vegetation.  The simplest fix for that is to walk back to the anchor point, lift the line and run it out through the palm of your hand as you walk back out more or less on the wind line. If the wind direction is fairly constant that'll solve most snagging probs.

Cheers,
Lurk

*There's probably a proper name for these, but it's as good a name as any. Smiley
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billdennis747
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« Reply #66 on: July 04, 2020, 08:33:57 AM »

The best thing about this activity is that it's the only FF that comes towards you, so you can appreciate the shape of the model.
It's much better but not quite right. I would go back to basics - is the cg in the right place, then trim the glide with tail incidence, using hand glides. Then leave it alone and concentrate on finding the right hook to use. Yes, angle it up slightly but I still think you could reduce the rubber/line ratio and stretch it a bit more.
I enlarged my Dolphin to 36" and used an autorudder - well worth it.
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Jasco
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« Reply #67 on: July 04, 2020, 11:11:00 AM »

Dog anchors!  Now why didn't I think of that?  I have several in the garage!

It looks like I often start to drop my hand away from the plane before I let go, lowering the launch angle. I saw on the one fairly good flight I recorded, I did not do that. Maybe that's why the flight was so good!  And I see the reference again to kite flying, OZPAF. I'll keep trying.

I tried what I understand a "gurney flap" to be on the left wing. And the right wing. It seemed to have no effect.   I think most of the turn is being induced by the stab tilt inadvertently built into the thing. Hence "Banana Twist". I already have some of the twist shimmed out...maybe I should check that shim.

DavidOWade, the towhook cannot be moved...but I can probably bend it over 1/4" or so...is that what you mean?

I have advice and encouragement coming from Australia, England,(I assume), Canada, the US....this is what the internet is for.
Thank you every one!

It was hot and still that morning. Dew on the grass and everything associated with free flight was perfect.  I distinctly saw some wing waggling and nose rising as the morning heated up, so there were thermals to be had.  I have never actually caught one.
I called it quits because it got too hot and my glasses were smeared up with sweat. I guess I should pack a little cooler to take to the center of the field. The field, BTW, was a cornfield until about 3 years ago. Soccer fields are not ideal for FF, but better than corn.

I don't understand the kudo system. I mean, I understand what a kudo is, but what are the criteria for awarding these coveted things?
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« Reply #68 on: July 04, 2020, 06:12:12 PM »

For the heck of it, see if you can find plans for the Jasco Trooper on OuterZone. You will see what I mean about having the towhook on the same side of the fuselage as the turn. Can you just add a makeshift towhook on the left side?

As far a the kudo system goes, they are quite inexpensive, generally free, and often propagate once released into the wild.
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« Reply #69 on: July 05, 2020, 03:58:02 AM »

Quote from: Jasco
kudos ... what are the criteria...
Entirely subjective.  Think that someone has done something worthy of praise or recognition?  Click the  "Add Kudos" button on her or his post.  It's not dissimilar to the "like" buttons on the various anti-social applications but isn't tied to a particular post.

As for tow hook disposition, the Walthew MKII (HPA Gallery & Outerzone) also has the tow hooks set to one side of the fuselage and should be trimmed to circle to that side.
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« Reply #70 on: July 07, 2020, 11:07:36 AM »

     Had the Dolphin out for some "Golden Hour" flying Sunday night. 

     I took out the 1/32" shim under the T.E. of the wing and replaced it with a 1/64" shim and shimmed out the stab tilt to try and get the plane to "kite" up.  The one flight I video'ed missed the tow release, but the plane stalled at the top, yet didn't take that long to recover, but glided to the ground dead straight ahead with no turn. I decided I needed that turn, so I let the stab tilt to the right again. On the next launch I learned that there are a finite number of times you can wingover into the ground without breaking.  I had just glued the fin into it's slot, too.  I guess the added mass was too much for the longerons. 

     I will repair it, but I won't be able to make it strong enough to withstand any more mishaps.  I'll have to build another fuse...... I'm such a procrastinator!

     See the Keil Kraft Sportster with similar tailcone problems.

    We went to the field in the forest preserve where we walk the dogs which is nice, but ringed with trees.  The Dolphin would have been in trouble if I actually got it to fly.  In the end, I broke the tail off a hand-chuck glider and lost my rubber powered  P1B Sky Voyager about 35 feet up in a tree.  Of course, it has been beautiful flying weather here, so there has been no wind to blow it down. Roll Eyes  If it ever comes down.
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OZPAF
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« Reply #71 on: Today at 08:37:05 PM »

That's a bit of bad luck Jasco. Just a temporary lull in your return to childhood Smiley

If you do build another fuselage - although that one looks quite repairable, I would suggest adding a adjustable hook so that you can move it forwards, backwards to trim the climb.

This I think is the main problem apart from too much power in achieving a good climb.

John
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