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Outdoor Free Flight Forum => Towline Gliders => Topic started by: Jasco on July 30, 2017, 03:45:09 PM



Title: Kiel Kraft Dolphin: Banana Twist
Post by: Jasco on July 30, 2017, 03:45:09 PM
Hello one and all. I've been lurking around whilst I returned to the hobby of stick and tissue flying after about 15 years pursuing other interests and raising a family.
I returned to the hobby by building a KK Sportster all-sheet model using an old Sleek Streek prop I still had in an old box of supplies. And a strangely warped little project it turned out to be. To the designers credit, it still flies very nicely.

Anyhow, after I built a Gullow's Me109, (dead straight...i remembered how to build fuses with formers) I returned to pure plans-building with the Kiel Kraft Dolphin, which I shall attempt to document here. I admit I was inspired by javman's post on the design elsewhere on this forum. I hope my plane turns out as nice.


Title: Re: Kiel Kraft Dolphin: Banana Twist
Post by: Jasco on July 30, 2017, 04:55:23 PM
Let's see if this picture upload works!
I like to start with the wings. My enthusiasm for a new project is needed to make all the templates, etc. Fortunately, this plane didn't need laminated wingtips, but there are a lot of ribs. I cut my pattern out of 1/16 ply and faced it with 150 grit sandpaper. That made cutting the ribs out with a new #11 Exell blade a breeze. Notches for the spars were accurately cut at this time, too


Title: Re: Kiel Kraft Dolphin: Banana Twist
Post by: Jasco on July 30, 2017, 06:03:41 PM
As you can see, there is significant undercamber to this airfoil section. I love the slow, floaty glide they produce, but building requires some care. I shimmed the 1/4 x 3/32" trailing edge stock up enough to make a smooth transition with the rib on the underside, and notched the stock for each rib. This was sort of problematic because I just marked the position of each rib on the stock with a good old #2 Ticonderoga, then took it to the cutting pad for notching. Failing eyesight, lack of practice, and possibly the ingestion of an inebriate meant the notches didn't come out exactly where they should have. Nevertheless, the center came out twist-free and reasonably symmetrical.
The outer panels required only two of 4 or 5 sizes, so the rib patterns were made of 1/16" chipboard. The tip blocks were built up from 3/32" scrap stock.


Title: Re: Kiel Kraft Dolphin: Banana Twist
Post by: Jasco on July 30, 2017, 06:15:58 PM
Another problem I encountered was that the bottom spar didn't sit on the lowest point of the rib, so the spar was pinned down first with a straightedge to ensure alignment, then the ribs were fitted on it. Once the leading and trailing edges were glued in, along with the top spar, gussets, and wingtips on the outer panels, the assembly was removed from the board, inverted, and the bottom spar was pushed fully home into the notches and glued.


Title: Re: Kiel Kraft Dolphin: Banana Twist
Post by: MKelly on July 30, 2017, 06:57:09 PM
That's some really clean balsa work!  Interesting subject, don't think I've seen this plane before.


Title: Re: Kiel Kraft Dolphin: Banana Twist
Post by: Jasco on July 30, 2017, 07:25:43 PM
During my absence from flying models I built a lot of scale models from paper when I discovered the Excel brand of hobby blade. Far sharper than xacto.
It is a crazy looking plane, ain't it?


Title: Re: Kiel Kraft Dolphin: Banana Twist
Post by: javmon on August 03, 2017, 02:52:21 AM
Jasco,

You won't be disappointed with the Dolphin. Built with light enough wood and towed up using button thread, she'll cover a lot of real estate. Her glide seemed to go forever. She also lends herself to all kinds of cool color schemes. Best of luck. I'll keep following your build and hopefully some pictures of her in flight. Happy building, Javmon.


Title: Re: Kiel Kraft Dolphin: Banana Twist
Post by: faif2d on August 03, 2017, 10:57:53 AM
It is very nice to see someone else raving about Excel over Xacto.  I can still remember the first time I used one of their blades!  It was at least as sharp as a scalpel blade but stronger. I still tend to use Feather scalpel blades to cut ribs and whatnaught but do not know why.


Title: Re: Kiel Kraft Dolphin: Banana Twist
Post by: Jasco on August 03, 2017, 07:37:55 PM
Thank you all for the kind words. I don't know how fancy I'll get with decorating on this one. It's been a long time since I covered a plane but I remember the success of such an endeavor rested heavily on practice. And my recent projects have been surprisingly difficult to get symmetrical and square so I anticipate crash damage. (I've never towed or hi-start launched a glider in my life!)
On to the build.
I built the usual identical sides, taking care to follow the graceful top and bottom curves. This design features a square former located under the wing mount area, so I built that and carefully squared it to one of the sides.
Unfortunately, I failed to notice that the gracefully curved bottom was going to be a real pita to turn into a box. At least one that was straight. Or square. Pick one.
My solution was to make a jig as pictured from hardware store shelf brackets, magnets, and a small steel sheet. I originally made a magnetic  board to do all of my building on, and started (or tried to) the fuse using magnets to hold the sticks down like I've seen elsewhere. But my parsimony doomed the effort; I refused to pay even the reasonable price asked for the required number of specialty magnets, substituting craft-store fridge magnets instead. As the website I consulted predicted, they weren't good enough.
But the fuse jig seemed like a good idea and worked well enough, but I just eyeballed the crosspieces. I got impatient with the amount of time it was taking me to get the fuselage done compared to the wing that I think I rushed too much
This really was an inferior solution. I could have easily made a former from chipboard and balsa scraps to support the bottom longerons and keep them square and parallel. But I was sick of monkeying with it, so expedience was in order.


Title: Re: Kiel Kraft Dolphin: Banana Twist
Post by: Jasco on August 03, 2017, 11:28:32 PM
I would like to share my thoughts on some of the materials I am using.
The plans were downloaded from Aerofred.com and printed full size at the local Office Max.
I know gliders are supposed to be light, but I was too anxious to start building to wait for balsa stock to come in the mail, so I raided the rarely-restocked balsa supply of a local brick-and-mortar hobby shop ("Drones-R-Us"). I took all of the 3/32" sheet they had!
I wanted to try some of the newer products and techniques I'd seen on the internet on this plane. My wife has grown quite sensitive to the smell of anything potent. Hydrocarbons and other VOCs rank high on the list of things that trigger her migraines, so water-based products were preferred.
That being said, I built the wing with Zap-a-Gap. I never used it much in construction before. I just couldn't get the hang of it. This attempt was more successful. Instead of expecting miracles, I used it like any other glue: using small amounts, ensuring proper fitment of parts, adequate clamping and drying time. Worked great. I still don't like the stuff!
Sometime during wing construction I became aware of Deluxe Products "Super 'Phatic" glue. Claimed to be a water-based equivalent to cyanoacrylate glues, so I ordered a couple of bottles. I really like this stuff. Acts like a cross between Titebond and Ambroid. Dries fast, but you don't have to worry about getting it on your skin. You can wick it into cracks. It dries crystal clear, so you can see how lousy your parts fit, and has moderate gap-filling properties for the lazy man's solution to poor fit.
I also ordered a bottle of Eze Dope; a water-based dope also by Deluxe Products. I dont know if I'm going to use that or just Krylon. I've never used either on a tissue covered model, but I used Krylon a lot in card modelling. All I know is I can't use that jar of nitrate dope I've had sealed in the basement for 20 years, no matter how good it smells!


Title: Re: Kiel Kraft Dolphin: Banana Twist
Post by: OZPAF on August 04, 2017, 03:17:32 AM
Good to see you enjoying this build. Nice work.

John


Title: Re: Kiel Kraft Dolphin: Banana Twist
Post by: Jack Plane on August 04, 2017, 12:01:50 PM
I can still just see the long scar tissue on my left thumb when the horrible Stanley knife I was using to carve my Dolphin's nose-cone slipped... exactly forty years ago!   :o

Clean-looking build, look forward to seeing more.


Title: Re: Kiel Kraft Dolphin: Banana Twist
Post by: Jasco on August 06, 2017, 09:46:32 AM
     My earliest memories of my Dad are that of him sitting at a little desk pulling the pin sealing the tube of balsa cement out with his lips while he applied the glue to the parts. And my first "X-acto-dent" was early in life, bloody, and burned into memory!
     My point is that this won't be my first trip to the grassy field...but my imagination failed me entirely when boxing up this undercambered fuselage.
     I needed to put in at least one spacer between the bottom of the fuselage and the building board somewhere amidships, but didn't think of it. So in frustration, I eyeballed each one in.  And with nothing to positively register the crossmembers, I got them at cockamamie angles as shewn in the photos.  :P


Title: Re: Kiel Kraft Dolphin: Banana Twist
Post by: Jasco on August 06, 2017, 10:22:06 AM
There's nothing to do but learn and forge ahead, so I fitted the keel piece that holds the towhooks and beat some soft steel wire I had into the hooks themselves.
     You may be able to see in the pictures where I misinterpreted the plan as to the position of the central square former...the very first thing I glued when gluing the sides together!
     I had the choice of making a new keel or putting in another crossmember. I put in the crossmember and reinforced/filled in so the covering would have support. As pictured earlier, I installed some corner gussets at the front of the box. In hindsight they were completely unnecessary since the solid balsa noseblock is glued directly to the front of the stick box where the only way to twist the nose is to twist it off! I was thinking in terms of what would be needed for a rubber powered model. Did I mention I've never built a stick and tissue glider?
     A few items remain to do: hold down dowels for the wing and stab, and the cardstock cover over the towhook area.


Title: Re: Kiel Kraft Dolphin: Banana Twist
Post by: flydean1 on August 06, 2017, 12:49:51 PM
Source for the Excell blades???


Title: Re: Kiel Kraft Dolphin: Banana Twist
Post by: billdennis747 on August 06, 2017, 02:44:38 PM
I like my Dolphin - looks elegant in the air - but an autorudder is very advisable


Title: Re: Kiel Kraft Dolphin: Banana Twist
Post by: Jasco on August 06, 2017, 07:43:36 PM
     I think I bought a pack of 100 blades directly from http://shop.excelblades.com
     I built many card models with the first half of that pack, and paper is a lot tougher on knife blades than wood. They seem to last forever when cutting balsa.
     A little pricey, but you really get what you pay for. The tiny points are much stronger than X-acto, too.
     I supplemented my #11 blade with a couple of cutters I made out of double-edged razor blades and popsicle sticks. Nothing better for precision notching. Sadly, they don't last forever and seem to get too dull to use when you only have 4 ribs to go.
     Any direction anyone could give on crafting an auto rudder would be helpful. Sounds like it might be kind of complicated for a sport glider, and I need something in the air soon!


Title: Re: Kiel Kraft Dolphin: Banana Twist
Post by: billdennis747 on August 07, 2017, 09:14:35 AM
Sounds like it might be kind of complicated for a sport glider, and I need something in the air soon!
Without an autorudder, you can either a) trim it for a turn and then chase it all over the sky to avoid it crashing on the line or b) trim it straight so it will tow, and then watch it fly away. There are lots of simple solutions, taking about 30 minutes. One of the simplest is shown on the Keil Kraft Caprice here in the plans gallery. It´s worth doing.


Title: Re: Kiel Kraft Dolphin: Banana Twist
Post by: ZK-AUD on August 08, 2017, 03:57:31 AM
not really my field of expertise but I think you can mount the tow hook well to one side and put on rudder to counter the imbalance.  this becomes your turn when you release


Title: Re: Kiel Kraft Dolphin: Banana Twist
Post by: PeeTee on August 08, 2017, 06:01:21 AM
Offset tow hook it's called!!

Peter


Title: Re: Kiel Kraft Dolphin: Banana Twist
Post by: Hepcat on August 08, 2017, 07:59:32 AM
Many have used offset tow hooks successfully and I will leave them to explain their methods.  I tried them in my early years of flying gliders and thought them not very effective at at times very dangerous.  Flying in light winds and at low angles of climb was possible but as the model got higher overhead the tow line would not be just pulling forwards but would be pulling downwards, trying to roll the model and any increase in wind would increase the lift and would try to roll the model even more.  Early auto-rudders often had a vertical arm pivored near the top of the fuselage and extending out of the bottom near the tow hook and tensioned backwards with a rubber band.  A line went from the arm to the rudder so when the arm was back the rudder was turned and when the tow ring was on the hook it held the arm forward and the rudder straight.  Again some flyers said they could very the amount of rudder used on the climb by varying the pull on the tow line.  I could not do that and I settled for an autorudder that remained in one position whilst the tow line was attached and flicked over to a new position when the tow line fell away.
If you don't understand I will do a sketch if somebody (like Jom Mosely) doesn't beat me to it with a photograph.
John


Title: Re: Kiel Kraft Dolphin: Banana Twist
Post by: Jasco on August 08, 2017, 09:33:20 AM
Photographs of a simple autorudder would be great.  Unless I can figure out something to easily retrofit, I'll take my lumps with learning how to tow without it.  And although I can always dream, I've never had an airplane fly away. They get caught in trees, fly into soccer goals, land out in the street...I even had one get smashed by a softball...but never has one flown away.  :'(


Title: Re: Kiel Kraft Dolphin: Banana Twist
Post by: Pit on August 08, 2017, 10:44:21 AM
Here is one.


Title: Re: Kiel Kraft Dolphin: Banana Twist
Post by: applehoney on August 08, 2017, 02:00:38 PM
I'm with Pete regarding the use of the rudder activated by the towline pulling a pin as it drops away.   Only minor difference is that instead of  a string/band system I use a thin monofilament with gentle stretch to supply tension.

John, I wouldn't dream of trying to upstage the Master!  I agree, offset hooks could be a pain; however I did use the pivoted arm system on the original "Walkin' Shoes" back in the 50's and I cannot recall any problems with it though I suspect linkage tension was very light and the rudder only activated upon towline release


Title: Re: Kiel Kraft Dolphin: Banana Twist
Post by: Jasco on August 10, 2017, 08:28:47 PM
I can't resist mocking it up.

Covering will be next. I'm trying Eze-Dope water based dope.
I used to do pretty OK tissue work, but I depended on good old nitrate dope and laquer thinner. In fact, it wasn't until I learned how to thin bulk nitrate instead of using whatever hobby-shop butyrate I could get my hands on that I did a decent covering job. That, and finally abandoning the crappy tissue provided in kits!


Title: Re: Kiel Kraft Dolphin: Banana Twist
Post by: Jasco on August 10, 2017, 10:01:48 PM
All the pictures didn't upload. ;D


Title: Re: Kiel Kraft Dolphin: Banana Twist
Post by: Jack Plane on August 11, 2017, 03:23:14 AM
Looking very reminiscent!

How do you train your cat(s) not to touch?  :o


Title: Re: Kiel Kraft Dolphin: Banana Twist
Post by: OZPAF on August 11, 2017, 03:45:03 AM
Nice work Jasco.

John


Title: Re: Kiel Kraft Dolphin: Banana Twist
Post by: Jasco on August 11, 2017, 01:00:57 PM
Jack Plane, I went through all my photos trying to figure out how you knew I had cats!
Projects sit out in the family room on my tv tray all the time.  I don't know why the (2) cats don't bother them, although I did catch them in the garage a couple days ago taking an unwanted interest in the Dolphin fuselage.  More dangerous are the 4 dogs...specifically their tails. 
They also have shown a tendency to chase down airplanes at the field.  No damage yet, but I'll leave the dogs at home for test flying!


Title: Re: Kiel Kraft Dolphin: Banana Twist
Post by: Jasco on August 20, 2017, 08:07:13 AM
Summer vacation is over and time to return to the Dolphin. I hoped to have this plane done for summer evening flying and I may still accomplish that!
     As I mentioned several times I used Deluxe Products "Super 'Phatic" glue for the majority of construction and I'm a convert. Not as fast drying as cyanoacrylate, but if you are familiar with the use of Titebond, etc you will not be surprised. The advantage is in the amount of glue required is very small especially for tight fitting joints. Both my joinery  and glue application need serious work, but I was very pleased with the stuff.
     Also mentioned was the use of "Eze Dope" water based dope for covering. That has been an experience worth documenting.
     Before I go any further, I encourage anyone trying this product to watch the instructional video on YouTube. Do it the way they say, and it works...for the most part.
     I haven't done a lot of wet covering, but that's what DP recommends, so a coat of 70% water, 30% dope was applied to the framework, Japanese tissue was sprayed with a 5% solution, applied to the framework, and more thin dope flowed through to the structure. A very familiar process. I found I tended to UNDER wet the tissue, but when I  got it wet enough, the dope tended to pool on the surface. As it turned out, the pooling didnt cause a problem. Getting the tissue to stick WAS a problem, requiring that I constantly rub the tissue down around the edges. My paranoia payed off, and enough water finally evaporated that it started getting sticky and I was confident to leave it alone to dry.
     The results were encouraging, so the same process was used for the top side of the stab. The tissue I'm using is some old Japanese tissue I had laying around since the pre-internet days; it was probably ordered from Peck-polymers.
     You can see in the photos how frighteningly wet the tissue needed to be to give me enough time to position it, but it went around the compound curves beautifully!  I applied 2 coats of 70/30 dope with some little foam brushes found at Michael's and the stab was complete.  I think it looks pretty good!



Title: Re: Kiel Kraft Dolphin: Banana Twist
Post by: mick66 on August 20, 2017, 08:33:20 AM
Nice job

I always wanted the KK Conquest as a kid but the model shop owner (Chippies in Sunderland) would never get it in.  Too many other kits to sell in stock already I guess. 

Look forward to seeing it finished.

Mike


Title: Re: Kiel Kraft Dolphin: Banana Twist
Post by: Jasco on August 20, 2017, 11:23:28 AM
     The only FF kits my local hobby shop stocked was Guillow's scale models and sleek-streeks. If i wanted to see the models I had no hope of ever paying for, I rode my bike about 5 miles to a neighboring shop. Still, I never heard of Keil Kraft or Frog designs until just recently. Now I'm hooked. ;D


Title: Re: Kiel Kraft Dolphin: Banana Twist
Post by: Wind-it-up on August 30, 2017, 07:26:38 AM
Can't wait to see how this comes out!  I love this design.

Chuck


Title: Re: Kiel Kraft Dolphin: Banana Twist
Post by: Jasco on August 30, 2017, 08:13:01 AM
I'm still working on covering and will post progress this weekend in all likelihood.
But a hint on how it's coming out is in the subject of this topic! ::)


Title: Re: Kiel Kraft Dolphin: Banana Twist
Post by: Jasco on September 27, 2019, 04:48:43 PM
I see my last post on this topic was over two years ago.  Sometimes things like that happen! 
I finished covering the dolphin and there it hung from my ceiling waiting for a hunk of nose weight and a windscreen.  Well, I finally overcame all obstacles and got it out to the field yesterday!  The weather was far from ideal. I had wasted several perfect mornings to fly in the last month and the forecast in the Midwest is for rain and more rain, so the pressure was on if I wanted to fly it this year. So I ignored the gusty wind and gave it a shot.
I decided to try a bungee launch since my attempts at towing with a towline were comical and mercifully unrecorded.
https://youtu.be/PhDE6O6Uq-c



Title: Re: Kiel Kraft Dolphin: Banana Twist
Post by: Jack Plane on September 28, 2019, 01:09:18 AM
Yay!

I'm sure someone will be along shortly to advise on flight trimming (more nose-weight? check tailplane incidence? launch angle?) but that looks like a most successful maiden session... i.e. if you need toothpicks you'll have to buy them from a store!

BTW, its always worth bringing some sellotape and a bit of modelling clay to the park.

Jon


Title: Re: Kiel Kraft Dolphin: Banana Twist
Post by: TheLurker on September 28, 2019, 02:32:51 AM
Quote from: Jack Plane
...that looks like a most successful maiden session
+1
I count that a success.  Congrats.  Now just a matter of trimming, but maybe wait for a calmer day eh? :)

BTW how far away are those trees?  They looked worryingly close to me.


Title: Re: Kiel Kraft Dolphin: Banana Twist
Post by: FreeFlightModeller on September 28, 2019, 03:42:03 AM
That's showing great promise .... especially on so short a bungee line!

By coincidence, a video came up on Facebook from exactly 5 years ago. It's of me flying at Old Warden, taken by Monz. I forget the length that was used here, but it "smooths out the phases of launch" more, giving the model more chance to settle.

I have a feeling that the link may only work for friends of Monz

EDIT: Link deleted .... it wouldn't work for me either!

I do understand that your model might be lost in that field on this length of line!


Title: Re: Kiel Kraft Dolphin: Banana Twist
Post by: billdennis747 on September 28, 2019, 04:43:37 AM
I too have a Dolphin, enlarged to 36" and it goes well from a bungee, but yes - yours looks more like a catapult! I think mine is something like 25' of 1/8 rubber and 75' of line. The model just kites up in leisurely fashion.
Can you give details of your anti-tree device?


Title: Re: Kiel Kraft Dolphin: Banana Twist
Post by: Jasco on September 28, 2019, 08:53:46 AM
My word!  :D I hoped to get some feedback, but this is great!
Billdennis747 referred to my "catapault". I saw some suggested lengths for the various components somewhere on the internet, but found no videos of such light models being launched. The histart videos I found looked like those planes were really being ripped into the air, and I knew the field wasn't big enough for that.  But next time out I'll use more rubber and more line. The launch should be a more gentle affair.
One question I have is how much do you stretch the rubber? 50%? Just as far as you dare? Do you have to "feel" for it based on wind conditions?

The yellow object near the end of my bungee is chock-full of modeling supplies. Clay for noseweight, tape for repairs, a knife to lose in the grass...but none of this registered as my little Dolphin stalled around the sky.  One of the reasons I do this is that it kinda makes me feel like I was 10 years old again...sometimes I'm about as insightful as a 10 year old! ;D
To wit: launching directly into the trees! They aren't as close as they look and the direction the wind was blowing made it unlikely the plane would fly over there. I have a video of my RTF P1B flying from about the same spot. The barn swallows come out of the trees to check it out. If the huge open area of the field suitable for free flight wasn't mined with soccer goals, I may have moved further out.

There were some other factors that cut the session short. The wind was getting stronger, the airplane was getting wet, and the mowers were getting closer, so I called it a glorious success and took the plane home in one piece.


Title: Re: Kiel Kraft Dolphin: Banana Twist
Post by: billdennis747 on September 28, 2019, 09:26:27 AM
The Peterborough club rules use 7.5mm 1/8 rubber and 22.5m line. As I said, let the model kite up rather than giving it a good twang, then it will be less likely to go off sideways. If you stretch too far it doesn't get much higher and is more stressful. An auto rudder helps but you may get away with it with a wide turn


Title: Re: Kiel Kraft Dolphin: Banana Twist
Post by: Jack Plane on September 28, 2019, 09:36:56 AM
Jasco - I've just given you a Kudos point for being able to feel like a ten year old again!  ;D


Title: Re: Kiel Kraft Dolphin: Banana Twist
Post by: Jasco on September 28, 2019, 12:06:15 PM
Thanks for the kudo! I tried this plane about 2 weeks ago with a spool of thread as a towline. As I ran downhill, I started over-running my feet and ended up going down. I got grass stains on my pants and ended up on my knees looking around for my plane which was descending the last few feet to the turf. Fortunately, my wife was busy containing our pack of dogs so my antics didnt get video'ed.
I wish the rain and wind would let up.... :-\