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Exian's composite planes

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Exian

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Joined
Jul 26, 2018
Messages
53
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BORDEAUX
I will talk about my composite planes in this dedicated thread.

First project : EXIA, completed and flying well for almost 2 years (70h)
- single seat, under french UL regulation
- wing span 8,2 m
- lenght 5,15 m
- empty weight 130 kg
- MTOW 210 kg
- engine AIXRO XF 40, wankel type, 35hp, consumption 9l/h at 70% power
- tanks in the wings 36l total (wet wings)
- glass sandwich skins with some carbon parts (spars), made in typical composite molds
- special equipements : ballistic parachute (GRS)

Current performance (to be improved with adapted prop that I built but cannot test due to flight bans with COVID19 in France...) :
- Stall speed 65km/h (tested)
- Cruise 180 km/h (real, tested in long cross country flights)
- Top speed 205 km/h

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Exian

Well-Known Member
Joined
Jul 26, 2018
Messages
53
Location
BORDEAUX
Second project : KYRIOS, under work, completion expected Summer 2021
- Electric Sailplane, single seat, under french UL regulation (new regulation, MTOW allowed up to 345kg and 70km/h stall)
- wing span 15 m
- lenght 6,6 m
- empty weight 220 kg ?
- MTOW 345 kg
- motor RET60, 25kW at 4500rpm 120 volts
- batteries in the wings 2x5kWh (50kg)
- Carbone fibre sandwich construction, made in "soft molds" (hotwired polystyrene covered with plastic foils)
- special equipements : ballistic parachute (GRS)

Best glide ratio expected around 45 at 100km/h

horizontal tail plane mold :
IMG_20180910_213252.jpg

Horizontal tailplane skin in mold with inner structure bonded :
IMG_20180925_192756.jpg

Horizontal tailplane closed with sanded dry micro
IMG_20181028_121031.jpg

Vertical tailplane before closing :
IMG_20190302_103700.jpg

Tail cone mold :
IMG_20190318_201640.jpg

Tail cone skin :
IMG_20190325_200201.jpg

Front fuselage skin (top) under vacuum, jonctionned with tail cone skin :
IMG_20190525_114917.jpg

Front fuselage skin (bottom) under vacuum, jonctionned with tail cone skin :
IMG_20190608_185205.jpg

Top, bottom and vertical tailplane jonctionned :
IMG_20190630_164013.jpg

Fuselage with sanded dry micro
IMG_20190723_210709.jpg
 

fly2kads

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HBA Supporter
Joined
Jan 2, 2010
Messages
1,777
Location
Justin, TX
Horizontal tailplane closed with sanded dry micro
View attachment 95444
Very cool projects, thank you for sharing! I hope you indulge our questions. I presume that the chordwise lines of micro seen here are filling discontinuities between the individual blocks of foam in your molds. How hard has it been to get a fair surface using this "soft mold" technique? It looks like it would save both cost and time, with a trade-off of some extra work to get the surfaces smooth.
 

Exian

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Joined
Jul 26, 2018
Messages
53
Location
BORDEAUX
How are the rod end bearings attached to the tubes?


BJC
I glue a piece of rounded Aluminium at the end of the carbon tube
Then I do manual winding of carbon roving around it : longitudinaly, and circularly to compact and hold together the firts layers.
The part with the pikes it a tooling that enables me to attach the longitudinal roving.
Of course I lay a thin layer of glass over the aluminium before doing the winding.

IMG_20200217_214628.jpg
Building notes, in french with horrible wrinting...
IMG_20200217_214102.jpg
Of course this takes longer than making the classic riveted end with a lathe, but I don't like the idea of the concentrated load of the rivets in the carbon tube.

Here the rovings transfer the load to the tube in shear on a broad area.
 

Exian

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Joined
Jul 26, 2018
Messages
53
Location
BORDEAUX
Very cool projects, thank you for sharing! I hope you indulge our questions. I presume that the chordwise lines of micro seen here are filling discontinuities between the individual blocks of foam in your molds. How hard has it been to get a fair surface using this "soft mold" technique? It looks like it would save both cost and time, with a trade-off of some extra work to get the surfaces smooth.
Yes, the mold surface is composed of several small hot-wired blocs to get close to an elliplitcal plan form in this case. Max deviation is 0,5 mm. Those blocs are cut and used direcly : no sanding to get a closer shape, not even removing the melted polystyrene trails, there is no need to waste time at this stage since small defects will be removed during the finishing process anyway.

Finished tailplane weights 3000gr (0,8m²), and there is only arround 100gr of dry micro remaining on it. Most of it is for shaping the tips that could not be done directly in the molds.
For the fuselage, there is arround 1,5kg remaining, but also to fill a "volontary depression" that is the consequence of using the same "compromised shape" for top and bottom fuselage shells.
Like someone else says "I am OK with that"

When using really dry micro in a uniform layer of 1.5 mm and really big sanding blocs (grit 40), sanding is quite fast and easy. Tail plane was one day of 8h, fuselage was 4 x 8h.

Really dry micro is really difficult to get to stick to the surface, so people tend to have it more wet (more difficult to sand). Also to have at least minimum sanding thickness every-where despite the manual and irregular work, people tend to put a really thick layer that will also take some time to sand.

But here is my real trick :IMG_20190712_111932.jpg
I am using 1 mm steel wire tensionned with weights to calibrate the thickness. I can press the dry micro like crazy (wetting the surface) so that it sticks well, then adding a good layer also pressed well without worrying about how much micro I use, and then remove the excess, being helped by those wires.
After the micro is hard, I fill the voids left by the wires.
The part is post cured after the micro is applied so that it sands really well (not softening with the friction of the sanding block, and not clogging the sanding paper).

Covering properly the surface with micro took me more time than sanding!
 

Foundationer

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Joined
Nov 29, 2016
Messages
233
Location
London
These are things of beauty! Well done! MOre pictures of construction please as it's all both inspirational and informative.
 

Right foot

New Member
HBA Supporter
Joined
Jun 26, 2019
Messages
1
Very beautiful!

I have some questions about Exia, maybe you have time to answer some of them.
  1. Did you add foam&glass inside of the wing skins & fuselage (is that what you meant by sandwich)?
  2. If you had to build the second time without existing molds, would you use the soft mold method as you used for the glider?
  3. How long would it take to do it from scratch with a design that’s similar to yours?
  4. What engine would you try the second time?
  5. Did you take any safety considerations into account when designing it?
 

Exian

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Joined
Jul 26, 2018
Messages
53
Location
BORDEAUX
Very beautiful!

I have some questions about Exia, maybe you have time to answer some of them.
  1. Did you add foam&glass inside of the wing skins & fuselage (is that what you meant by sandwich)?
  2. If you had to build the second time without existing molds, would you use the soft mold method as you used for the glider?
  3. How long would it take to do it from scratch with a design that’s similar to yours?
  4. What engine would you try the second time?
  5. Did you take any safety considerations into account when designing it?
No problem, all question are welcomed!

1. Yes, sandwich as glass (2x160gr/m²) / foam (4 to 5 mm) / glass 2x160gr/m².
Of course there are additional layers at strategic locations.

2. Yes, for a one of a kind, and the only plane in your life, soft mold built totaly manualy (templates, hot wire....)
If you plan to do other planes in your life (composite of course), invest in a CNC milling machine to mill your molds....
Exia is special case with full composite molds because I know that I wil build at least two other of it (one electric, and one with the same wankel but in 2 rotor version, 70hp)

3. Exia took me 5000h hours (I estimate 1000h per year during 5 years) with plug + mold + various waste of time because of bad luck!. Doing the same with soft molds would be something in the 2500h territory (1500h with the molds and experience)

4. In Europe, I would go for the industrial V twin conversion made by Vaxell :
35hp, 4 stroke, Electronic injection, strong looking reduction gear, full package without any adapation to be made.

5. Depends what you call safety. For Exia, I made two choices that I would call safety, despite the complexity it added :
- Ballistic parachute
- Tanks in the wing (no dangerous flammable liquid over my legs, but with the BRS I have dangerous explosive material there...!).
If you ask about crashworthiness, I did not do anything particular on Exia, but I am doing it better with Kyrios that has lot of reinforcement around the cockpit (safety cage), carbone kelvar fabric over everything around the pilot...

I hope it helps!
 

dave wolfe

Active Member
Joined
Dec 7, 2019
Messages
39
For the 'soft molds' , can you exlain what is placed between the raw foam mold and the skin layup? Plastic of some sort?
 

Exian

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Joined
Jul 26, 2018
Messages
53
Location
BORDEAUX
For the 'soft molds' , can you exlain what is placed between the raw foam mold and the skin layup? Plastic of some sort?
For fuselage mold (complexe shape) I create an air-tight / demoldable layer with two plies of 100gr/m² glass fabric and epoxy.

For molds like wings with long straight panels, people usually use a semi-rigid sheet of plastic (don't remember what type), and I even heard (on HBA) about very thin aluminium sheets (if not tight curvature at leading edge).

But I am not doing this because of two problems :
My wing panels are not straight (elliptical), so you cannot use a rigid sheets...
Instead, I use typical vacuum bag plastic that can stretch a little. To have it conforming to the mold, I put the whole mold in a vacuum bag and draw a slight vacuum (-0,1 bar). I use 100gr/m² glass fabric (dry) between the foam and the bag to drain air properly and keed +0,9 bar on the inner surface of the mold.

My other problem with the rigid sheet method, is that you need to put the whole mold + laid-up part under full vaccum for cure if the sheet was not glued on the foam to be sure that the part follows the shape of the mold. Then, the foam mold is compressed by -0,9 bar which is not negligible for its shape...

In my case, when I do the vaccum bag over the part (sealed on one face of the first -0,1 bar vacuum bag), the -0,9 bar does not apply to the foam mold that keeps a truer shape.
 

paraplane

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Joined
Jul 22, 2014
Messages
53
Location
California
EXIA is a beaut! Love the shaping of the vertical. Looks like the a number of the DeHavalid Type. I'd like to know how that Aixro engine has performed. Had there been any issues such as with seals, cooling, etc. What maintenance has been conducted on it? How many total hours of run time on the engine?
 

Vigilant1

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Thanks for the very helpful information, Exian.

Regarding:
4. In Europe, I would go for the industrial V twin conversion made by Vaxell :
35hp, 4 stroke, Electronic injection, strong looking reduction gear, full package without any adapation to be made.
For their three VW derived engines, they give the following specs (all at 8:1 compression ratio)
1600cc: 60 hp (continuous) at 3200 rpm
1914cc: 75 hp (continuous) at 3100 rpm
2275cc: 90 hp (continuous) at 3000 rpm

With or without fuel injection, these power outputs for a VW engine (2 valve pushrod) of the displacements shown are "incredible" (literally-- not credible). They are at least 10% higher than people actually get with these engines, especially at those (relatively low) RPMs. If they used the same "helpful" dyno to get the advertised power output for their V-2 engines, well, there could be some disappointment.
Just my opinion.
 

sming

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Joined
Apr 10, 2019
Messages
119
Well, they are a camshaft manufacturer for european brands, and started their aero activities by making a special camshaft for aero VW engines, so it's at least believable that they make a bit more HP... the "continuous" is probably more debatable ;)
 
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