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Dec 19, 2017, 05:13 PM
a quantum of science
Alex Guffler's Avatar
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Update: First Elevator build


...and here are the images of our first elevator build!
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Jan 17, 2018, 04:57 PM
a quantum of science
Alex Guffler's Avatar
Thread OP

Update


Hi everybody,
since it was Christmas, the project was paused for two weeks. But now, we have already begun working with full force again and I can give you a little update on the project progress. Meanwhile, the CAD surface design was finalized. There was lot of discussions going on in the team about many details. Right now, tooling design is in its final stage.

One of the major points was the making of the wing and fuselage molds. We decided to make all molds from aluminum, including redoing the already existing elevator molds. The plan is to recieve the machined molds back by beginning of march.

I plan to make several posts here as soon as I have enough time to prepare them properly. One will be about our core milling technique, which works excellent by now. Another will reveal the calculated aerodynamic performance (including polars!). Maybe i can also make a post on our mold design, which might be interesting to some people here.

I will attach some pics: We have built the first elevators from our carbon molds with the materials, that we recieved from GRM. The two elevators were built with 20 g/m² and 16 g/m² biax carbon and the core was milled from the PMI-like 30 kg/m³ foam from GRM. We used transfer tape and 27 g/m² glass fiber to close the skin at the seading edge. The elevators turn out at 5.2 and 5.4 g - and we did not attempt to save as much weight as possible! The surface quality is really nice, even for the 16 g/m² skinned piece.
We also made the core milling tools for the fin. We made a set of 3d printed fin molds to test the idea with the allen key insert. This will also be one post coming up soon!
Finally a new rendering with the airplane, a treat to motivate our team to keep things going!
Jan 17, 2018, 08:43 PM
Charles Martin
BavarianCharles's Avatar
Quote:
Originally Posted by Alex Guffler
Hi everybody ... Another will reveal the calculated aerodynamic performance (including polars!)
Looking forward to polars - for the entire aircraft, and not just the wing, right?

Servus, Charles

Jan 20, 2018, 06:07 AM
a quantum of science
Alex Guffler's Avatar
Thread OP

Airplane polars


OK, here are some calculated polars for our DLG. I calculated them with my version of tornado vortex in MATLAB. I could have used xflr5 as well, but there are some advantages of tornado:
- the viscous drag is not interpolated from airfoil polars, but calculated directly
- all points in the polars represent a trimmed, stable state of flight. So the elevator deflection is adapted to flight speed. Static margin is set to 9%.
- my version of tornado can handle small airfoil chords (small Re numbers) way better than xflr5.

The polars are airplane polars, so they include elevator and fin. Fuselage drag is not included. I think, for comparison with your projects, a calculation without fuselage drag is more helpful. All polars were calculated for a takeoff mass of about 250g.

You may notice the rather "speedy" design philosophy. We at AkaModell Munich discussed the basic design philosophy in the beginning of the project. Everybody was more in favor of a fast flying, high launching DLG than of a floater. Nevertheless, a possibly large range of good performance was one of the key objectives in aircraft design. One can see, that the 1° flap down configuration posesses an wider peak in the CL/CD to airspeed polar. It was possible to tune the configuration towards more peak performance, but exploiting only one flight state in a theoretic model might turn out far off reality.

Of course, this is theory and calculations only, we are looking forward to see the plane flying in late spring this year!
Jan 21, 2018, 06:21 PM
Drat and double drat!
Virtakuono's Avatar
I will probably be visiting munich in the fall, might i have a chance to see the plane myself?
Jan 22, 2018, 05:51 PM
a quantum of science
Alex Guffler's Avatar
Thread OP
Quote:
Originally Posted by Virtakuono
I will probably be visiting munich in the fall, might i have a chance to see the plane myself?
Depending on how much time you will spend there, yes you have a chance! Everybody passing Munich in the second half of 2018 can write us and hopefully we can arrange a meeting! Let's have a beer and talk about F3K!

We are also thinking of taking part in some nearby contests (southern Germany, maybe France...), just for fun. But first, our DLG must be ready!
Jan 22, 2018, 10:08 PM
Charles Martin
BavarianCharles's Avatar

Sink Rate(s)


Quote:
Originally Posted by Alex Guffler
OK, here are some calculated polars for our DLG.
Alex,

that's a very interesting Polar #3 (Sink Rate). It leads me to believe that the minimum sink rate is almost the same for all camber settings, albeit at different flight speeds. That could also mean that the wing will not need a lot of variation in camber for cruising and floating at low angles of attack.

Do you concur, or am I overlooking something?

I also plan to visit family and friends in Bayern during August or September. Would love to meet you in Munich for a Schneider Weisse!

Cheers, Charles
Jan 23, 2018, 07:17 AM
a quantum of science
Alex Guffler's Avatar
Thread OP
Quote:
Originally Posted by BavarianCharles
Alex,

that's a very interesting Polar #3 (Sink Rate). It leads me to believe that the minimum sink rate is almost the same for all camber settings, albeit at different flight speeds. That could also mean that the wing will not need a lot of variation in camber for cruising and floating at low angles of attack.

Do you concur, or am I overlooking something?

I also plan to visit family and friends in Bayern during August or September. Would love to meet you in Munich for a Schneider Weisse!

Cheers, Charles
Hi Charles,
That's what it seems to be like. The minimum sink rate is almost identical (10% range between 0°, 2°, 4°, 10°), however the sweet spot should be around 2° to 4° flaps. Of course, there is quite a range in airspeed, so the best flap setting rather depends on the current airspeed. If you set the flap wrong in relation to airspeed, sink rate will be increased. The least sink rate is about 0.28 m/s (calculation without fuselage).
Best regards, Alex
Mar 14, 2018, 04:16 PM
a quantum of science
Alex Guffler's Avatar
Thread OP
Hi everybody!
Our project is still going on with full power! In the last weeks, there was a lot of work to do and I had a little less time for writing here. Today I can give an update on our recent progress:
First up we gave a name to the project and the plane. It will be called “Ascender”.

Second, we completed all molds CAD and gave the wing and fuselage mold blocks to a friend nearby who will do us the big favor and mill the four wing and the two fuselage master molds. As far as I know, the next weekend milling of the wing molds will take place. It will take some time to finish the master molds, but my team mates have practiced a lot now!
We also milled the master mold for the fin and small part molds like canopy and wing spar joiner. One of our team members is also working on aluminum molds for the empennage! We are really looking forward to testing aluminum equipment.

As modern DLG’s feature directly molded flap spars we asked ourselves if it was not possible to build this type of mold also from composite. Usually, these molds featuring such “ribs” for the separation of aileron and wing are made from aluminum. So, we made a test piece with different groves featuring different drafting angles and then we demolded a test piece. Even the groves with only 5° draft angle and with of 2.5 mm came out fine. Nevertheless, we decided to go with 10° draft angle and an approximate 2.5 mm wide grove in the master mold. To avoid bubbles in the edges, we rounded the edges. You can see the geometry of the test piece in the drafting below. We are very happy to be able to build completely by carbon fiber surrounded ailerons in one step.

We also milled the last foam core milling molds. For the wings, it was quite some machining time! It was possible to fit the wing core into a 10 mm thick rohacell board. One board with standard size 1250 x 625 will give us 2 sets of wing cores and 4 sets of tails. Considering the price of rohacell, this is quite an effective use of material. And you get one spare set of tails for the event of damages 😉

We designed the aileron horn and made some 3d-printed test parts from carbon-fiber reinforced filament. They are really stiff and strong. The possibility of 3d-printed parts is attractive! The parts are printed with 0.03 mm layer height and they have a better quality than the laser sintered parts that I see at my job. However, a molded part is even better. By the way, it is a fork connection system. We liked the idea of having a quick installation of the wing without sacrificing much aerodynamic drag.

We already built a prototype of the fin from 3d-printed ABS molds. It is a great way to get some molded prototypes! We were not sure, if the idea to have a hexagonal insert for the fuselage will work. But it worked out fine. As weight (5,64g) and geometry were pleasant, we moved on and milled the fin mastermolds.

We have built some throwing pegs from a 3d-printed mold. 3d-printing molds is quite easy and I am sure we will keep experimenting with peg geometries. Everybody has a different hand size and different fingers and so we could make quite a range of customized pegs.

Finally, there is great news about further project sponsors! I will make extra posts on this topic to appreciate the support in an adequate way.

I attached a lot of photos from the last weeks. Enjoy!

Best regards, Alex
Last edited by Alex Guffler; Mar 15, 2018 at 05:26 PM.
Mar 15, 2018, 02:18 AM
In F3J size does matter!
roydor's Avatar
Alex,
I love following this thread!
Keep up the good work and keep posting updates of your work.
Thanks for sharing!
Mar 15, 2018, 03:28 AM
1 revolution and throw!
hello Alex,


could you share more info about the third last picture? yellow mold with roving with carbon sock around?
i assume it's the sparjoinder mold ?

i would think you could shed weight from the sparjoiner , sub 4gr should be possible i think with foam core and UD/roving tapered down towards the ends
Mar 15, 2018, 04:58 AM
In F3J size does matter!
roydor's Avatar
Joiner looks like untrimmed length, trimmed it should be half the length and half the weight.
Carbon sock is easy to use but usually comes out a bit heavier.
I made a 2 piece wing joiner that weighed 2.5 grams and was stronger than the wing (wing got stepped on while the model was upside down, broke but the joiner stayed intact)
Mar 15, 2018, 05:51 AM
1 revolution and throw!
Quote:
Originally Posted by roydor
Joiner looks like untrimmed length, trimmed it should be half the length and half the weight.
Carbon sock is easy to use but usually comes out a bit heavier.
I made a 2 piece wing joiner that weighed 2.5 grams and was stronger than the wing (wing got stepped on while the model was upside down, broke but the joiner stayed intact)
2 piece wing joiner ? how does it work?
Mar 15, 2018, 06:57 AM
In F3J size does matter!
roydor's Avatar
Quote:
Originally Posted by krikkens
2 piece wing joiner ? how does it work?
A joiner for a 2 piece wing... I guess a comma could have helped a lot in the original sentence
Mar 15, 2018, 12:32 PM
1 revolution and throw!
Quote:
Originally Posted by roydor
A joiner for a 2 piece wing... I guess a comma could have helped a lot in the original sentence
i assumed that but hoped i could learn something fancy here


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