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Author Topic: E-36 Pulsar  (Read 1434 times)
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USch
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« on: June 11, 2017, 12:59:06 PM »

It is quite some time I would like to build a structure as used now in all duration FF classes, carbon D-box, carbon TE, balsa ribs with cap strips. Problem was for which class? Not to big a model, so it can be build fast and in any place, not to many complications and gimmicks, a model suited to be test flown without going to a big field (80km away from my home). Coupe d'Hiver was out of question because you need a lot of space for the 40+ second motor run.

Last year I had build a E-36 Pearl 202 just to "taste" the class and as an old F1C flyer liked it. Before beginning I defined some points to be included (hopefully) in the new model:
   - d-box structure
   - use of a "decent" airfoil, not the usual Lucky Lindy style
   - a clean fuselage without anything sticking out, if possible
   - use of a new, superlight motor COBRA 2203-2800KV, only 19g
   - making my own propeller
   - making 2 wings, one with traditional dihedral (about 10% of WS, the other with 5% dihedral and tip plates

That's it!
For the wing section I opted for the Midic 309 taken from Tapio L. suggestion.
First thing to start with was making the plug and mould for the D-box. In good old tradition the plug was made of balsa sheets, the once which will stay forever in the balsa box because to hard and heavy for any model. Only the templates are milled from fiberglass. To help laminating the d-box I opened the V by 5° so to have better access to introduce the cloth. Thanks to CAD this is any easy task. The mould itself is made of simple glass cloth to about 2mm thickness. The laminations I tried up to now are
carbon cloth 90g/m2 and 25g/m2 outside
and
carbon cloth 90g/m2 and Modelspan 12g outside

With both laminations the final weight for the raw d-box (500mm long, 38mm large) is around 8g, a little bit to heavy for an model of this size. But being the first one's I dont care  Wink
Here the first pic's

Urs
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E-36 Pulsar
E-36 Pulsar
E-36 Pulsar
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Konrad
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« Reply #1 on: June 11, 2017, 01:12:24 PM »

I'll be following along with this build.

What I've learned is that it takes pulling a few parts out of any mold to get the weight and quality we want. I never get this right the first time.
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USch
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« Reply #2 on: June 11, 2017, 01:29:55 PM »

Right Konrad !!!
And that is the big difference to pure balsa bashing. You can go forever trying to do the thing better. No fear to use just this only one, good sheet of balsa for a certain job. A certain cloth remains the same weight even if you have to order some more  Grin

Next step was to order the rib set for 2 wings, laser cut, I'm getting lazy, and the preparation of the main spar. The very first spar set is made of
top and bottom runners 2x0,4mm carbon from root to tip, way to strong and heavy!
The second set is 2x0,4mm top main panel, 2x0,13 (actually cap strip format) bottom main and top and bottom tip. Infill 2mm balsa with vertical grain. This saves already more than 2g on the wing.
Wing warps, another argument. Not willing to prepare 4 building boards with the warps included, I will try to mount the wing half's offsetting them by, for now, 0,8mm difference to give the desired wash-in on the right panel. My laziness is also the reason for choosing a rectangular plan form for the wing.

Urs
Attached files Thumbnail(s):
Re: E-36 Pulsar
Re: E-36 Pulsar
Re: E-36 Pulsar
Re: E-36 Pulsar
Re: E-36 Pulsar
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USch
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« Reply #3 on: June 11, 2017, 01:38:15 PM »

A few more pic's about my wing-building.
My way to keep straight and vertical the ribs during gluing and the first near finished wing, only half covered and waiting for a further supply of 5 my mylar  Sad

Urs
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« Reply #4 on: June 11, 2017, 01:48:58 PM »

Urs,
I think 1 layer 90 gram/sqr/M is enough for E36/F1S.
What is the weight of the wing without covering?


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USch
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« Reply #5 on: June 11, 2017, 03:27:47 PM »

Weight of the uncovered wing is 34g, at least 8g to much, but it's the first one.
The 90g/m2 cloth is to much anyway. And it is a open weave cloth so it will never get airtight without tons of resin. That's the reason for using either glass or paper outside. Now I ordered some unidirectional layup with 2 layers +/-45° of 19g/m2, maybe even that will need a "closure" layer on the outside, but at least it is only 40g.
Like to fiddle around  Grin

Urs
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« Reply #6 on: June 11, 2017, 05:42:47 PM »

Urs,
Your workmanship is very nice plus your work bench is much neater than mine.

I think an uncovered wind weight of 26 grams is only needed for a model with relatively low power, and I would consider your 2203 motor low power. For a stronger motor such as a 2205 from a quad racer more weight is OK.

When you get to a finished process can I buy two sets of d-box shells from you?

Dick

 
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USch
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« Reply #7 on: June 12, 2017, 11:45:05 AM »

Just to put the record straight....
My work place is so cluttered that, if I would take the pictures on it, I would need to write a text book to explain what I wanted to show  Wink Grin
So better move to another, cleaner table.

Motors, on the Pearl I started with a Maytech 2205-2300KV, a Graupner Speed Cam prop 6"x6", the Nanotech 350mAh LiPo's and a YGE 12A controller.
Together with the COBRA's 2203-2800 I got also the COBRA 2204-2850 which I use actually. Height in 10 seconds is around 120m, nothing special, judging from what I read from Tapio L. and Airplay stating 180m. The bottleneck could be the controller. But to my experience an overpowered controller is cutting completely alimentation of the motor or at least starts with a rattle. Nothing similar happens, but for the sake of knowledge I will fit a 18A controller and see what's happen.

The Cobra 2203 is given for about 120W with a Graupner 7,4x4 folder. 120W is a good figure, but I could not try it yet. To many things to do, to little time....

Dick, no problem to send some d-boxes over the big pond, just leave me time to refine my techniques. I will PM you as soon as possible.

Urs
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USch
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« Reply #8 on: July 05, 2017, 11:28:45 AM »

No, I am not sleeping, but progress is slow. In the meantime I made more D-boxes with the new unidirectional carbon weave and the final weight is around 5,5g per wing half. But of course I already started the wing with the heavier D-boxes and will finish them for a first "proof of concept" model.

Here some mass production of fins and a first front end with carbon tube and pylon. The part in front of the wing will be shortened as soon as I finish the rear part so to put everything in place and cut the front to find the approximate position of the CG.

Urs
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Re: E-36 Pulsar
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« Reply #9 on: July 05, 2017, 09:08:28 PM »

Interesting project Urs. Are you sure you will be able to keep this in your small flying field Smiley

John
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USch
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« Reply #10 on: July 06, 2017, 09:58:00 AM »

Are you sure you will be able to keep this in your small flying field Smiley

Well, here the new electronic devices come's in handy. Indeed, after some 30 years of absence from the FF activity, having now at hand electronic timers and RDT is like heaven  Grin 
I just keep constantly the 10 sec motor and the 2 minutes DT time and if anything goes wrong... one blip to stop the motor, another blip and DT, marvellous. Speed's up trimming a lot and saves models, can't ask for more  Tongue Tongue Tongue Tongue Grin

Urs
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« Reply #11 on: July 06, 2017, 10:16:27 AM »

Are you sure you will be able to keep this in your small flying field Smiley

Well, here the new electronic devices come's in handy. Indeed, after some 30 years of absence from the FF activity, having now at hand electronic timers and RDT is like heaven  Grin  
I just keep constantly the 10 sec motor and the 2 minutes DT time and if anything goes wrong... one blip to stop the motor, another blip and DT, marvellous. Speed's up trimming a lot and saves models, can't ask for more  Tongue Tongue Tongue Tongue Grin

Urs


There is nothing to add.  Smiley


Heinz
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USch
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« Reply #12 on: August 13, 2017, 08:10:14 AM »

Back again.
The long absence is due a radical modification of the initial goal of just building a new E36. At one time I realized that I did not have (yet) the sensibility to dimensioning all this carbon stuff which goes into a wing like that. Of course I could have asked one of the Ukraine masters, but I dont have one in the neighbourhood  Grin. And discovering personally new things is not bad at all.

Here a short run-down on the 4  wings build up to now (#3 and 4 only left wing half's).

#1
D-box extends to 30% of the wing cord and is build with a 25g/m2 glass cloth on the outside and a 90g/m2 carbon cloth on 45°.
Spar is a 2x0,4mm carbon strip top and bottom with 2mm balsa spar web in between. Cap strip 1x0,12 and 2x0,12mm on all ribs. Full balsa fill between rib 1 and 2.
Weight of left wing 17g.

#2
D-box still 30% of cord, but with Modelspan 12g/m2 outside and the 90g/m2 underneath. Spar is 2x0,4mm on top of the main panel, tips and main underside is all 2x0,12mm. Cap strips on all ribs as in #1. Between rib 1 and 2 sheeting with 1mm balsa.
Weight of left wing 16,02g.

A little bit disappointing to gain only 0,98g. At this point I decided to go ahead and build some more (left) wings to see where's the potential to reduce weight even more. In the meantime I had got a new material, a mesh of UD carbon, laid down at 45° and superimposed at 90°, like a cloth laid on the bias. Weight of the mesh is 48g/m2. I did 2 sample boxes with 2 and 1 layer. Net result was a raw D-box with 5,5 and 3,4g weight, quite an achievement against the 7-8g of #1 and 2.

#3
D-box 25% of wing cord and the double layer D-box. Between rib 1 and 2 the D-box extends behind and has a fill up with vertical balsa to retain the bush for the wing hold-down screw. The bush has a very large disc to go over the main spar and transmit the forces to the fuselage-pylon. No carbon strip to hold the ribblets on the LE. Spar as on #2 but a little softer wood. Rib caps on the top is one rib full length alternated with only a short piece at the trailing edge. Bad idea= the weight gain is so small and the ribs remains so weak that it isn't worthwhile. TE is 3x0,7/0,5mm as on #1 and 2.
Weight of left wing 12,77g, getting closer   Tongue

#4
D-box 25% and single layer of carbon. Now this is a very thin D-box, it feels more like a paper rather than a carbon thing. But it is still extremely stiff. Would benefit from a lot more ribblets to avoid buckling. Spar is as per #2. Rib caps only on the intermediate ribs and none on the dihedral and tip ribs. TE is 1,6x0,6/0,4.
Weight of left wing 10,48g.

If I find the drive to build some more I will do it with the 1 layer D-box, double the ribblets now at 15mm distance and go to 8mm, add a 1x0,4mm strip on the LE, I am afraid the #4 wing LE will get damaged as soon it hits something on the landing. 13 more ribblets weigh only 0,3g! TE with 1,6x0,6/0,4 is more than strong enough for the job.

Now I have still to finish the #1 model to see if and how it fly's. Not being happy with the general lay-out I decided to redo also the tailplane and go to a 25% tpl to advance the CG to about 70-75%. The first 2 tpl where 30% which would have asked for a more rear CG in the region of 80-85%.

Urs
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Re: E-36 Pulsar
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« Reply #13 on: August 15, 2017, 02:00:19 AM »

Very successful experimentation there Urs. Interesting stuff!

John
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« Reply #14 on: August 16, 2017, 10:19:36 AM »

Hi Urs,
nice work! thanks for documenting this. It will help me with my own efforts. I have a few questions for you.

When you make a D-box do you simply lay the carbon cloth in the female mold and then press this over the male mold?

I assume you clamp it down to get a nice even result?

How do you ensure you get most of the resin out of the cloth?

Do you use epoxy to attach the box to the riblets?

Thanks for the info.
Bernard


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« Reply #15 on: August 16, 2017, 12:40:13 PM »

Bernard,
you put your finger right in one of the most delicate question  Cheesy

I can only describe MY approach, as there are many different solutions and how to do's, depending how much work you want to put into, what machining facility's you have at hand, what you have already in your workshop and so on.

As I wrote in one of the first reply's I choose to make a one piece mould. To work better inside the mould I did graphically "open" the shape by 5°. This could have been even more, say 10°, but that is the learning curve which teaches the trick's.
To press the layers I use exclusively vacuum, I did also a silicone male form but it did not work for me, trouble was not enough pressure on the whole surface and cloth sliding. Probably in combination with the silicone plug you need a 2 piece mould, just a guess. 2 piece moulds will have other problems as a flash on the parting line right on the LE radius.

For the lay-up I used two different methods, with the carbon cloth I staggered on the table (actually on a heavy, thick cartoon to not spoil the table)
1. micro perforated plastic
2. peel-ply 65g/m2
3. carbon cloth
4. light glass or light Modelspan
Then I flooded liberally with epoxy till the resin is impregnating all layers.
To transfer it to the mould I slide a 3mm wire between the cartoon and the micro perforated plastic in the middle of the rectangular wetted piece, place the mould with the open end over it and lift the wire till it touches the LE radius. In this way you do not move the weave. Inside the mould the perforating plastic is now the outside layer. On top of this goes a woven-non woven absorbing felt, about 3-4mm thick. And then you make the bag around it and pull out the air to about -0,9 bar.
The pressure from the vacuum compresses the carbon cloth and the excessive resin passes through the perforated plastic and soaks the felt.
The laminations from the carbon mesh I did without the peel-ply.
Then I place the mould in an oven at about 45-50°C for 24 hours. Afterwards you will have to take of the bag, the felt, the perforated plastic and eventually the peel-ply. The peel-ply is a somewhat delicate operation, always bend it over by 180° and pull slowly to not bend the composite to much and damage it.
Working on hard, non absorbing surfaces where I can apply full vacuum I never pick up excess resin (plotting) before closing the bag. The pressure will do that job quite well.
The riblets are given a slight coat of sanding sealer on the circumference to avoid excessive absorption of resin. Then a thin layer of resin is given to all riblets and the spar. The bone (spar with riblets) are placed in the carbon box and held firmly on the jig to take the right shape. BTW, old Coupe motors do an excellent job here.

Hopefully you can understand a bit of the process, otherwise just ask!

Urs
 
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USch
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« Reply #16 on: August 19, 2017, 02:09:48 PM »

First outing with the Pulsar this morning.
The battery is still outside the fuselage , this will be tackled later when I know where to place the CG.
The climb was sorted out quite easy, a bit of down and left, a bit of right rudder tab and it got on the rails. Not so much glide, strange, but CG at 72% seems to far back with a poor recovery from a bad transition. Now I either move the CG ahead or I change stab to the 30% one, still pondering  Huh

But happy to see the new baby up in the blue sky  Grin

Urs
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« Reply #17 on: August 20, 2017, 10:40:29 AM »

Thanks Urs you response was helpful. Model looks good.
BG
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« Reply #18 on: September 02, 2017, 07:38:29 PM »

No trouble Bernard, just ask about the dark points  Smiley

I did not have much time to go out and do some flying, but did some homework on battery's. I had ordered from HK the Nano-Tech 350mAh cells. But as it happened I ordered the wrong pieces and got 6 single cell's instead of 6 2 cell packs. They were fitted with the BEC cable-connectors as in the first picture.

I thought that this was the ideal moment to measure the internal resistance of each cell and match them accordingly. Because the internal resistance is the single most important factor in a power class like E-36/F1S. The lower the resistance, the more power a given propeller-motor-esc will provide as net-output (and the less the cell's will heat up). C-rates given by battery manufacturer is actually a derivate from the resistance, but it is just to easy printing a number on a label, so dont trust the label, measure yourself.

Just to have a reference my 2 cell packs of 300mAh Nano-Tech cell's have around 80-90mOhm (mO), that means each cell has about half of that value. After the first charge-discharge cycle of the 350mAh cell I had numbers reaching from 120-220mO, 3 to 5 times the value of the smaller 300mAh cells, very disappointing to say the least. So I cycled each cell 3 times hoping in a run-in effect. But actually the resistance increased on each cycle!!! At a certain point I realised that this value had to do with another element, not the cell itself. So I took 2 cells, soldered them together as usual and fitted the 2mm connectors I usually use on this type of model up to 25A. This gave me the opportunity to fit smaller balancer leads and connectors instead of the clumsy connectors you find on commercial battery packs.

And woooow..... on the next cycle the resistance went down to 28-32mO/cell. Now that's an improvement against the 300mAh cell's, but at the expenses of an 10g increase in overall weight.

Moral of a long story, fit your system with the best connectors and change them as soon as they slide in and out to easy.

Urs
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« Reply #19 on: September 03, 2017, 10:07:48 AM »

Urs, What connectors are you using in the second photo?  Thanks!
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« Reply #20 on: September 03, 2017, 02:15:59 PM »

Derek, I use the MC 2mm connectors from Multi Contact as in the picture. You have to cut them in half to form a male and a female connector to be soldered to your cable. There's a reason why I write down the manufacturer's name. Nowadays there are a lot of clones of all types of connectors on the market and they can hardly be distinguished. Few of us have the knowledge, the equipment and the time to measure details like the resistance of connectors, we all like to build and fly models. So the only thing is trusting somebody else who does the work for you. Many clones are quite ok for the fist few connections, both loose soon the contact force needed for 20A.

I still like the separated plugs to connect the battery. Today the XT30 with a housing for both contacts, should have about the same properties, lesser than 0,8mOhm, as the MC2  one. Your choice  Wink

For the balancer lead I use the Molex connectors with 1mm pin spacing. Actually they are left-overs from long gone servo leads.

Urs
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« Reply #21 on: September 06, 2017, 12:56:04 AM »

Thank you Urs. Very helpful information!
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« Reply #22 on: September 06, 2017, 03:44:20 AM »

For 2mm bullets, I use connectors from HobbyKing. I used to buy ones with plastic housing, but discarded that, soldered the pins to the wires and then protected with plastic shrink wrap. Cannot find those connectors listed now, but these innards seem similar: https://hobbyking.com/en_us/2mm-gold-connectors-10-pairs-20pc-1.html

2mm bullets are practical to use and take little space. Preparing for flight I connect the minus and install the battery to the battery bay. the plus wires hand beneath the model and the bay. Just before the launch I connect the plus to, and am ready to rok!

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« Reply #23 on: September 06, 2017, 05:10:59 AM »

I am using the same procedure as Tapio to get ready for starting, that's why I like divided connections.

For the weight-sensitive between you. The pictures show 2 types of 2mm connectors with a weight ratio of 1:3. And E-36 is a weight-sensitive class! You may find a very illuminating post from Yak52 in the Bungee glider topic about span limited classes. The bottom line says you can only play with weight and wing aerea in such a class if you like to optimise the flight envelope.

Urs
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