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Gentle Curves - Lucas his Skywriter

Build blog - MB2017 - Skywriter

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Tim Ballinger13/02/2017 15:32:22
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796 forum posts
290 photos

Not looked at the wing design much yet but the webbing seems like a good thought. I copied your firewall jig last night; then built it upside down which would have produced left thrust ! Now re- done for another try.

Sun and wind today so I have managed to mow an airstrip on my field for the first time. Hand launching is quite limiting so pleased with that😊

Tim

McG 696913/02/2017 19:10:11
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3305 forum posts
1257 photos

Great progress, Lucas.

Allow me a question though > A few posts back, one of your pictures showed a gap between the trailing edge of your ribs and the flat cap stripping...

img_3667 (small).jpg

Now this more recent picture shows some 'underneath' strip filling up the rear gap.

As your ribs are supposed to be flat bottomed at the rear - ie. Naca 3414 - how does this comes, please???

Cheers

Chris

Lucas Hofman13/02/2017 20:34:28
668 forum posts
375 photos

Chris, you are a good observer. I recently found (after cutting and sanding all ribs for the upper wing that the bottom is not completely flat. I you look carefully you can see it on the profile drawing too:

naca3414.jpg

I had not noticed it before placing the ribs on the lower spar. When I pressed the tail of a rib down on the sheeting it jumped out of the spar. easiest was to put a 1/16'' strip under the aft lower sheeting, then everything fitted nice.

I think Peter Miller has adopted the airfoil slightly and flattened the bottom a bit. I may do that when sanding the rib pack of the lower wing - do not know yet.

Regards, Lucas

McG 696913/02/2017 21:19:11
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3305 forum posts
1257 photos

Hallo Lucas,

Thanks for answering, but I was just wondering - 'newbie's curiosity' - you know. angel

I thought you just had the Ballerina rib adapted to the Skywriter's dimensions.

But - IMHO -if you took the original 3414, I would stick to it for the lower wing as well...

Cheers

Chris

Lucas Hofman14/02/2017 07:01:53
668 forum posts
375 photos

Will probably do so. It is not a big thing to put a 1/16'' strip under the planking under the aft spar after all.

Lucas Hofman14/02/2017 07:13:27
668 forum posts
375 photos
Posted by Tim Ballinger on 13/02/2017 15:32:22:

Not looked at the wing design much yet but the webbing seems like a good thought. I copied your firewall jig last night; then built it upside down which would have produced left thrust ! Now re- done for another try.

Sun and wind today so I have managed to mow an airstrip on my field for the first time. Hand launching is quite limiting so pleased with that😊

Tim

Hi Tim,

Good that you caught that in time. I managed to glue the Ballerina firewall upside down, but happily spotted that while the glue was still rubbery - very embarrassing.

It sound privileged to have the possibility to mow a field on your own property!

Lucas (who will spend his lunchbreak on the ice flying the Ballerina - talk about privileged!)

Lucas Hofman14/02/2017 07:55:21
668 forum posts
375 photos

Lifted the lower forward sheeting last night and glued that to the ribs. The trailing edge pieced come in handy here. I remerbered from the Ballerina that the whole wing liftet from the board under this operation, so this time I put enough weight on the spars to keep everything down.

img_3673 (small).jpg

The nails press the front of the sheeting up to the ribs, so there is contact all the way. I glued with Superphatic after all was positioned and checked.

Cut the innen leading edge from 1/8'' sheet and the trailing edge from 1/4'' sheet. The inner leading edge needs camfering, which is a little fiddly. Better (but this I realised to late) to camfer before cutting, so you have more to hold while sanding.

Placing the trailing edge is easy:

img_3675 (small).jpg

The leading edge needs to wait until the glue on on sheeting is dry. That takes less then an hour. After that the sheeting gives a nice step to place the inner leading edge on:

img_3674 (small).jpg

Lucas

Denis Watkins14/02/2017 08:25:04
4544 forum posts
123 photos

At the beggining of the thread you wrote this Lucas

I am not sure if a lighter model is less robust either. Material that has no function adds loads to a structure on impact. Last winter I crashed an ARF that was completely made of laser cuttet light ply. It went down, not too fast in 20 cm of snow but looked like it has suffered an explosion inside. I am sure a decent balsa structure would have had less damage.

Explosion inside exactly, with the abrupt low speed stop, a shock wave richochettes up the model and snaps every thin former in its path.

I believe your beautiful structure lessens this possibility, and your considered building

Lucas Hofman15/02/2017 21:48:52
668 forum posts
375 photos

Thanks for the nice words Denis.

Not much progress tonight; one of the aileron servo's of the Ballerina started to twitch more when powering up than some my elderly fellow pilots. The model has now flown around 80 flight. Although the twitching disappeared after wiggling the surface a bit it did not give me a good feeling. Losing a favourite model because of a 6 USD servo failing would be painful, and downright awful if it has given ample warning that something was wrong.

So out with the Turnigy 9018MG's and in with 2 new Hitec 65HB. 11 gram both, and luckily exactly the same size as the old ones, so the servo mountings did not need fixing. The new servo's have less play on the bearing and on the gears too.

On Gentle Curves only glued in the blocks lining the cutout in the middle of the wing. And some blocks to put hinges in. I intend to make tape hinges (using the covering material), but if that goes sloppy I want to be able to fall back on tried and trusted furry hinges:

img_3677 (small).jpg

The next session will be a dusty one; sanding the upper side of the wing, including leading and trailing edge to be ready for the top sheeting.

Edited By Lucas Hofman on 15/02/2017 21:51:44

Edited By Lucas Hofman on 15/02/2017 21:52:10

Lucas Hofman17/02/2017 13:23:23
668 forum posts
375 photos

The dusty job:

img_3680 (small).jpg

The tape protects the ribs, or rather gives an indication when you are at the level of the ribs.

Ready to receive the top sheeting. The wing is stil quite flexible in torsion at this point, so I need it pinned down to ensure no warp is introduced. There i a certain beauty in a rib / spar framework; a pity halv of if will disappear under the sheeting:

img_3681 (small).jpg

john stones 117/02/2017 19:59:29
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11597 forum posts
1517 photos

Meaty bit of balsa around the wing cutout Lucas, gets picked up there yes

John

Lucas Hofman18/02/2017 21:10:22
668 forum posts
375 photos

Å good part of it will be cut away I think later John. I had not thought about that that is the logical lifting point.

Today some progress on sheeting. weighted both front and back of the wing to prevent torsion:

img_3687 (small).jpg

Tomorrow the center section and the cap strips!

john stones 118/02/2017 21:22:18
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11597 forum posts
1517 photos

What's in those bags Lucas ?

John

Edited By john stones 1 on 18/02/2017 21:23:31

Edited By john stones 1 on 18/02/2017 21:24:44

Lucas Hofman19/02/2017 12:26:57
668 forum posts
375 photos

Steel shot. I have a colleague in Houston who is very glad in his guns and fills his own ammunition. He buys this by the bucket and I received a kilogram. I packed it in 50 and 100 gram bags. Very nice, it forms itself after what youi place it on and does not only give pressure on one point (like steel bars do).

Lucas

Lucas Hofman20/02/2017 08:12:31
668 forum posts
375 photos

Top sheeting in place:

img_3689 (small).jpg

Trimming the sheeting and outer leading edge tonight. Maybe the trailing edge (inner part, near the cut-out) too.

Lucas

Edited By Lucas Hofman on 20/02/2017 08:17:42

Tim Ballinger20/02/2017 08:16:37
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796 forum posts
290 photos

Looking good.

McG 696920/02/2017 08:42:08
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3305 forum posts
1257 photos

Nice progress there, Lucas.

Very neat as usual.

Cheers

Chris

Lucas Hofman22/02/2017 07:41:57
668 forum posts
375 photos

Tip work last night. I try to make the spar support the tip, which should make it much more solid:

img_3690 (small).jpg

And filling in with wedges and gussets:

img_3693 (small).jpg

Edited By Lucas Hofman on 22/02/2017 07:55:53

Lucas Hofman26/02/2017 17:55:24
668 forum posts
375 photos

Many other things to do lately (not the least a reparation on a Ballerina), but the wings start to look the part now:

img_3699 (small).jpg

Lucas Hofman02/03/2017 11:18:08
668 forum posts
375 photos

Upper wing done (save some fine pre-covering fine sanding):

img_3703 (small).jpg

The whole wing feels quite light:

img_3704 (small).jpg

50 gram covering material, 20 gr. lugs to make mountpoint for the struts. About 260 gr in total I think. Anybody wanting to share the weight of their wing?

Lucas

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