Balsa DLG

[danskis]

Thomas - thanks for sharing over here on this forum otherwise I might not have seen this otherwise. What a great project and fantastic plane. I too have been bitten by the DLG bug - partly because I live in the same city as a former world champion and there are plenty of guys flying DLGs here. I'll have to start the thread from the beginning and read through it. That said I'm a little surprised that a flat elevator was not as good as the airfoiled one. I believe my Vortex has a flat elevator - its supposed to be a pretty good plane.

I'd be interested in finding out about a kit. You can email me at danskis@live.com

Dan

@ThomasMartino

 

[danskis]

Thomas - I just read through this and had a thought - BTW I'm very much a beginner. What about using a carbon fiber tube or rod for the leading edge of the stabilizer. Thats what the Yellow Jacket I'm building now uses.

 

[ThomasMartino]

Hi Danskis! Thanks for your interest in my project. My first DLG had a flat plate stabilizer and it worked great. The performance difference between the flat plate tail and the HT12 airfoil tail on this plane was small, but I did feel a difference. In flight it felt like the built up tail with airfoil provided better pitch authority and was less likely to flutter during hard launches. The weather conditions were not very good during testing, so I based these assumptions purely off my impressions rather than any data collected from the flights.

Regarding the construction of the built up tail; carbon fiber tubes or strips might be a good idea. The curved leading edge will make it challenging to incorporate them. The tail is the area I plan on redesigning the most for the next prototype. I want it to be stronger, lighter, and easier to build. That’s a tall order but I learned a lot from the first prototype and I think I can pull it off.

Im still waiting on the tail booms to arrive. Shipping from the UK to the US is slow right now (rightfully so). Once those get here I can dive into V2 of the Disco DLG. In the meantime I’m catching up on my other build and brainstorming ideas for the pod construction and wing mount. The wing was glued directly to the fuselage on the prototype. That worked fine for me since it was simple and lightweight, but the wing needs to be removable on the next version.

 

[hsquier]

Hi,
May I share the web site that "helped me immensely" for my molded DLG project (don't take it bad I know you're a master of building skills - you perhaps already know him/what he shows) :

http://kousaku.biz/RC/

He shows his way for pod mounting.

 

[ThomasMartino]

A great resource. Thanks!

 

[hsquier]

The next version of the plane will be slightly longer. The tail booms I ordered are half the weight of my scratch built prototype. This means I can lengthen the tail and shrink the stabilizers to save weight and reduce drag. It should be a win-win.

This has been one of my questions. And I was until now too lazy to calculate the answer - I had some time and your MIT article gave me the opportunity to do it.

Based on the shape of my Molded DLG :

I was at first surprised to have a Vh on the lower end (0,44) :

As my DLG was a blend of known best sellers the Vh was logically found in the same range.

I calculate the moment of boom + vertical and horizontal stabilizer 7 cm forward and 7 cm aft the actual location with the same Vh (at 0,44).
It's naturally an approximation with the hypothesis on a linear relation between stabiliser surface and weight (I think it's not true, the bigger it is the lighter proportionally it is).

I found the results very interesting :

Logically when stab moves forward, Surface and weight raise and vice versa.
With the same Vh, narrower stabilizer shows a better moment.

But translated in lead weight in nose (at 29 cm of CG) the results can be considered as equivalent :
Stab 7 cm forward : remove 0,85 gr of nose lead.
Stab 7 cm aft : Add 0,45 gr of lead in the nose.

!!!

 

[hsquier]

Im still waiting on the tail booms to arrive. Shipping from the UK to the US is slow right now (rightfully so).

hyperflight.co.uk ?
May I share a tip I found on french RC web site :

Carbon fishing rod for carp.

Cons :
- Surely less HiTech than the german "R&G composite" specific ones
- Surely a little heavier (1 mm thickness vs 0,3 or 0,5), but you can sand it down (my boom was 44 gr raw and 34 gr after sanding (but I sand it a little too much)).

Pro :
- Unbeatable easy access (local sport shop).
- Cheap, you have 2 booms one for a 1,5 and one for a 1,0 m DLG ( big and medium rod).
- Up to me the ratio scratch build hobby / quality is good.

 

[ThomasMartino]

Yep, I purchased them from hyperflight. They arrived yesterday. I ordered two different kinds. One is 12 grams and the other is 14 grams. Super light!! I can’t wait to try them out. My scratch built boom was 30 grams so the weight savings are pretty significant. They are not as stiff as my boom, and also surely not as stiff as the fishing rods. I think that is okay though. A little bit of flex might come in handy for absorbing the impact of unplanned landings.

I will do some more research on carbon fishing rods.

 

[hsquier]

Oh ... 12 gr !!! Ok you can't beat. Thank for feedback. I will consider it for next project, I now know it's finally clearly worth money.

PS : I have the medium part left : outside diam 10,9 mm / 8,3 mm - 900 mm lenght - 0,6 mm thickness : 19,1 gr.

 

[ThomasMartino]

I am going to try a low wing mount this time. Here is the fuselage pod master pattern. Notice the contour to match the top profile of the AG46 airfoil.

 

[ThomasMartino]

Here it is framed up and ready to make the first half of the mold. The mounds of clay create returns for the two mold halves to key together.

And here is the finished mold.... it’s useless but it was a good learning experience.

I used polyester tooling gel coat and resin. When it’s cold in my shop I can get away with making thick parts. When it’s warm I need to be more careful to prevent a serious exotherm. It was warm in my shop yesterday so I should have made the mold slowly. One layer at a time with plenty of time for the resin to cure between layers. Instead of doing that I did the entire layup all at once. Within a few minutes the part was too hot to touch. The mold release wax was melting out and the hot glue used to hold the frame on had liquified! The mold surface cracked pretty badly and is slightly warped. Lesson learned. I will be more patient on my next attempt.

 

[hsquier]

At this game I've not reach the "mold level". Congratulation !

I'm seriously thinking about it. this especially since I broke my DLG last WE.
It hit the ground on the wing after a 45° side dive induced by a reception failure.

Logically the wing broke.

Like all human being I suffer from paradoxical behavior.
But some times pushed to it's limit.
I can spend significant money for expensive UD carbon fabric or significant time in fine tuning useless details AND ...

... Use ultra scrappy methods for vital organs.

This is my faulty cheap and unsecured battery plug (receptor side).
Believe it or not, before the flight I had on and offs when plugged the battery and it didn't dissuade me to bring her in the air .

 

[ThomasMartino]

Oh no!!! That’s awful! My red DLG suffered last weekend too. The stabilizer ripped right off during a hard launch. I will never make plywood V mounts again. Carbon fiber from here on out. Do you think your wing can be fixed?

 

[Matthewdupreez]

Today I’m working on the wings. The wingspan is 60”. The planform shape is a slightly modified ellipse. The root airfoil is AG45 and it blends to AG47 at the tip. View attachment 192519 View attachment 192520 View attachment 192521

cccclllllaaaammmmpppsssss ggaaallooorree

 

[danskis]

I learned that lesson too with my "store bought" DLG - a used all CF Vortex. I don't hesitate to not throw it if there is any sort of irregularity. I simply can't afford too many of those mistakes.

 

[Piotrsko]

When you're mixing your mold resin, slow it down by adding less oxidizer/catalyst, not much more than 10% less. You aren't needing full structural strength for a mold and an extra bit of cure time is faster than having to rebuild the new mold. There used to be buyable cure inhibiters at the autoparts body places, but I havent seen them In years since they are really toxic.

I really prefer plaster of paris or a $9 usd 40# box of drywall spackle.

 

[ThomasMartino]

When you're mixing your mold resin, slow it down by adding less oxidizer/catalyst, not much more than 10% less. You aren't needing full structural strength for a mold and an extra bit of cure time is faster than having to rebuild the new mold. There used to be buyable cure inhibiters at the autoparts body places, but I havent seen them In years since they are really toxic.

I really prefer plaster of paris or a $9 usd 40# box of drywall spackle.

Thanks. I used less than the recommended 2% this time and it’s working fine. Letting each layer cure first is still a must. A half inch thick layup would still get hot otherwise.

When you make a plaster mold do you start with a layer of gel coat? Or is it just plaster?

 

[hsquier]

I'm on a new DLG project (I discovered with huge envy the new DLG "Yoda" of Vladimir's model).
It won't be multi dihedral but I will be inspired by the very impressed servo mounting system.

About that may I ask you what servo you (and you all) use +/- feedback ?

For my first full size DLG I didn't knew where it would go and used the (too) cheap "Power HD 1600" servos.
The airframe result was beyond expectancy and the Power HD 1600 became thereby undersized. Clearly not in power but in precision : When you have a very nice wing you feel a little disappointed when the ailerons don'y come back on pitch neutral.

Although I won't put 40$ KST. Easy to find low and high end servos but I didn't find medium range servo.

What are your alternative ? I consider the Protronik 7350. Have some ideas ?

 

[ThomasMartino]

I'm on a new DLG project (I discovered with huge envy the new DLG "Yoda" of Vladimir's model).
It won't be multi dihedral but I will be inspired by the very impressed servo mounting system.

About that may I ask you what servo you (and you all) use +/- feedback ?

For my first full size DLG I didn't knew where it would go and used the (too) cheap "Power HD 1600" servos.
The airframe result was beyond expectancy and the Power HD 1600 became thereby undersized. Clearly not in power but in precision : When you have a very nice wing you feel a little disappointed when the ailerons don'y come back on pitch neutral.

Although I won't put 40$ KST. Easy to find low and high end servos but I didn't find medium range servo.

What are your alternative ? I consider the Protronik 7350. Have some ideas ?

View attachment 195313 View attachment 195316 View attachment 195318

The Turnigy D56MG servos you posted a picture of are the ones I’m considering. They have very impressive specs considering the price. I doubt they will center as well as KSTs though. Armsoar had KSTs on sale last month and I almost bought some, but they were still too pricey. Bluebird makes some nice mid priced servos.

 

[Piotrsko]

When you make a plaster mold do you start with a layer of gel coat? Or is it just plaster?

just plaster, my stuff is cast and dirty, done quickly with no finesse.
Actually dampen the model down if it's water resistant, and use clingwrap stolen from the kitchen drawer which will heat shrink some. When I get caught, paste wax for the wood floors and don't wipe it off, or if I'm really in trouble, cooking spray. You COULD use extra thick jello (aka Boeing spraylat green skin) but that's a pain to remove. I'm too cheap to buy a actual mold release.