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Old Jun 23, 2012, 05:28 AM
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France, Lorraine, Montigny-lès-Metz
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Hello,
I find the Neos discution great, I would like to know the angle between the wing and elevator ° V Thank you in advance Patrick
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Old Jun 23, 2012, 11:01 AM
G_T
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Thomas,

Things which might have an effect are how long the wing is left alone before removing it from a mold or bag (% total cure) and whether there is a post cure elevated temperature cycle before it is removed, and lastly whether the wing is cooled completely before it is removed.

Going a full cure cycle and post curing are the enemy of production rates...

As you've noted, Kevlar also doesn't like moisture. Ideally the wings should be made from dry fabric in a low humidity environment. I think that's actually a requirement for aerospace work with Kevlar but I don't have any documentation to support that and haven't researched it.

One last thing that can be going on is the use of an epoxy system which, given how it is processed/cured, can take a deformation over time when exposed to a relatively small load - one below failure point. MGS is one of the better systems in this regard; West is one of the worst.

Gerald
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Old Jun 24, 2012, 08:39 AM
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Hong Kong
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Hi Patrick, the angle is 0degrees.

Gerald, thanks for the suggestions. Currently we don't have elevated temperature curing, only room temperature (although it does get quite hot!). Curing cycle is 24 hours I believe (need to double check) before taking it out of the bags.

Leaving it in for 48 hours would be great, but don't have room at the moment. I wonder if that is the culprit?

Wings are made in a climate-controlled environment so humidity inside the workshop itself isn't an issue, would it have any affects outside of the workshop where it is extremely humid? Perhaps during transportation, etc?

All wings are stored quite carefully on flat surfaces at my office (where i DO have enough space to do that for the 1-2 days before they get shipped out )

Using the same process, there hasn't been any problems with the carbon wings, they seem to be much more resilient.

Thomas
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Old Jun 24, 2012, 01:24 PM
G_T
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Carbon is far stiffer and stronger in compression than Kevlar. So the epoxy matrix would have less effect on a carbon wing.

Lack of a post cure is almost certainly the culprit. Very few laminating resins will reach full cure without a post cure cycle, and the only ones which comes close in a reasonable ammount of time (that I know of) are MGS and West. West just isn't suitable for our use for making wings or fuselages - wrong physical properties. So your epoxy probably seems hard after 24 or even 48 hours but it is not quite done curing. Most shrinkage occurs in the latter part of the cure cycle... So here comes the warps. That may take up to a week if you don't elevate the temperature!

If you can do something to get the temperature up to even just 120 degrees F for the duration of your cure cycle, the results should be quiet a bit superior. Some laminating resin systems are going to require that just to get a good initial cure. For others, such as MGS, that is enough to achieve most of the possible properties of the resin system alleviating the real need for a post cure cycle.

BTW, if you use MGS and use slow cure hardener only, you have to elevate the temperature to get a full cure.

0.02c

Gerald
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Old Jun 24, 2012, 01:35 PM
G_T
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PS - I forgot to mention...

There is this little annoying thing of Tg, the glass transition temperature. Epoxy is a semi-crystalline plastic. As the temperature is raised, it undergoes a phase transition when the temperature hits Tg. At that point, the structure changes from semi-crystalline to amorphous, with an associated change in physical properties. The properties do not change in a good direction...

The glass transition temperature of an epoxy system is a function of the post cure cycle and of the particular epoxy system. In most cases the glass transition temperature is a little above the peak temperature used in the post cure heat cycle.

On a hot summer day, our planes can get pretty hot sitting on the ground. If the post cure cycle doesn't raise the temperature of the wings to within 20 degrees or so of the temperature they'll get in use, then the wings will likely warp a little. You have to look up the recommended post cure cycle duration for the particular epoxy system you use, and look up the changes in physical properties between using a post cure cycle and not using one. In particular, look at the Tg.

West won't post cure, the Tg is low, and that is what makes that system unsuitable for making our wings and fuselages.

So, to reiterate, there are two sources for warps. (1) Insufficient initial cure so that the resultant final shrinkage occurs after the part is demolded. (2) Insufficiently high Tg.

Gerald
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Old Jun 24, 2012, 10:04 PM
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Neos Carbon

Light air day flying the Neos.........flight report soon
Just think about camber! Zone V2 ya baby!
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Old Jun 24, 2012, 10:50 PM
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Got a ride on Dave's carbon Neos today for about 5 minutes. This one comes with the following comment. HIGHLY RECOMMENDED and what ever he said.
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Old Jun 24, 2012, 11:16 PM
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Gerald, thank you. We'll take another look at the elevated temperatures, will likely need to find room to put it! May be even more important for our moulded wings coming in the next little bit. We've done some experimentation with different resins and found the current one best for our needs from the ones we've tried, including, but we are planning on trying one more in the next little bit with ridiculously good specs rivaling and surpassing the MGS in some aspects (on paper anyway).

Dave, man oh man! YES camber is AWESOME on the Neos

David, what did you think from your 5 minute test drive? By the way, your stuff is shipped, will send you the tracking in a couple minutes
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Old Jun 24, 2012, 11:43 PM
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The Carbon Neos felt light and active and it is fast. I just could not grasp how such a light ship can maintain such momentum so easily. I watched it next to my Topsky in light lift and it just rose away like it was in a hurry or something. In the short flight I had I could not formulate a great discription of the Neos but as I stated in the last post HIGHLY RECOMMENDED. You have a winner with the Carbon Neos.
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Old Jun 25, 2012, 12:16 AM
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Any updates of when my 2 neos will be ready Thomas ?
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Old Jun 25, 2012, 12:22 AM
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Kane, they're both ready pending on the fuselages. The last shipment which had your fuselages in them got hit by the post office, I'll keep everyone posted as soon as I get my next batch in.
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Old Jun 25, 2012, 03:14 AM
Team Hong Kong F3K
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Update:
All future kits will ship with extra spread-tow fabric for the wing joint and vertical/boom joint rather than the glass we've been shipping out, yay!!
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Old Jun 25, 2012, 03:21 AM
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No worries take your time, just checking on a rough date ? Carbon tails and extra carbon sounds great . I prefer strength over weight
Lookin great and brilliant flight reports !
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Old Jun 25, 2012, 03:29 AM
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Kane, think we're looking at receiving them around July 4th.
I might have been unclear in my wording! I meant that the FG cloth we have been including to join the wings and vertical to the boom is now replaced with some STF cloth.
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Old Jun 25, 2012, 08:31 AM
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Kane, two of these are yours and one's for Jun!
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