Hi All.

I have recently ordered one of each 50"x36" sized sheets of Spectra ballistic grade 1000 sheet and Spectra/Carbon Fibre hybrid sheet to carry out some testing with to see how practical it will be in my airship project.

Now my intention is to hopefully be able to use the Spectra as the outer shell of the airship that will go over the rigid framework, however although it will be suitable when not infused with resin I would like to be able to infuse it to create a more solid and smoother outer shell at least for the gondola. There are a number of reasons for wanting to do this; a smooth outer surface would significantly reduce any drag on the airship as it moves through the air because of its large surface area, also there will always be the ever present risk that someone may want to take a pot-shot at it with something like an air rifle for example (this has happened on an earlier test balloon) so the Spectra would be more than enough to protect the internal gas bag and components.

So I would like to ask if anyone has had any hands-on practical experience either infusing Spectra with resin and even attempting to laminate more than one sheet of it together ? Also I should note that because of it final use it will still need to be a UV stable end product so the use of vinylester and polyester resins will probably be essential unless anyone can point out anything different ?

Any help and advice would be greatly appreciated, and any trials carried out will be videoed or photographed and posted on here for all to see if they too are interested.

Jim

You don't necessarily need to use UV stable resins if you are coating it with a UV stable paint or lacquer.   Depending on how weight critical your plans are, you may find the extra weight of a layer of lacquer is offset by the added strength and benefits a higher performing resin brings.

Maybe some small test peices might help you. 

Also the spectra material is a woven cloth, recommended by the manufacturer for use in composites so no reason why it wouldn't laminate ok.

Obviously how you process it, be it wetlay or a vacuum process will determine its final performance.

You would need to test it's ballistic properties are adequate. A single layer may well not be enough for some projectiles. For example, most modern armour uses multiple layers of ballistic material.

Should be quite easy to find out from a airgun enthusiast what the likely velocity drop off and hence impact energy would be at likely "engagement" distances.  You could even shoot a test piece if you are really worried!

You wouldn't want it going down like the Hindenburg!!

Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant

Hi Warren,

What would be your recommendation be for UV stable paint or lacquer to use on the Spectra ?

As for testing its ballistic properties I have a Daystate Mk III PCP air rifle and land with permission to shoot over so testing to .22 air pellet at variable distances shouldn't be a problem with test materials, it is more the case of how to produce that best material and structure to do so with first.

I have been in touch with the supplier just now and from his data sheet (all in ounces and inches ... US for you !) I have finally worked out its weight at approx 85 grams per square metre so compatible with your lightweight carbon fibre sheet, however unlike carbon fibre Spectra is an excellent insulator but a complication is that it is also completely invisible to radar which might have implications (or stealth/killer airship advantages ...lol) at a later date but for now with an estimated cloth to resin ration of 60/40 it will still come under the weight limits I need for final build for a surface area of 18 metres squared which will come to approx 2.2kg on an airship with 7kg all up lift, and depending on the weight of the paint or lacquer this could also be added.

Jim

Stealth Airship LOL.  Secret weapons platform!!

In lacquer terms generally any automotive 2 pack will be UV stable.  Other paints you need to look up the manufacturers details.  You may want a semi flexible paint if these panels are super thin.

Its radar absorbing/reflective properties will change once wetted out with resin and/or painted anyway!

Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant

why does it need to be a ballistics material?

Hi Warren.

Just been looking up the lacquers you recommended on the internet and can see they are readily available in places like Halfords and similar auto-stores so won't be a problem trying out some of them to see there effect with Spectra, thank you, also it will be interesting to see the effects of both polyester and vinylester resins too.

Can you imagine the real world implications of a true stealth airship ? !!! ... lol. I wish.

Hi Compositepro

The use of Spectra in my airship project is to produce a tough and durable outer shell that will go over the rigid framework; as a choice of material it has many advantages but its basic ballistic properties are an added bonus that will help to protect the lifting gas and the internal components.

Jim

so no one is firing anything at it?

Hi Compositepro.

A previous test model was shot down by a local idiot with an air rifle, this was a basic framework of 1.6 m diameter sphere with an helium inflated balloon and ground tethered, and was a test to see if a basic framework could be lifted. You can never account for the stupidity of some people and the things they might do !

The next design will be 2.6m in diameter and made from carbon fibre laminate framework and covered with spectra material for the outer shell assuming it is suitable for the task. It will also have a pay-load of motors, batteries, and on-board telemetry/camera system for FPV and the estimated cost for a completed airship will be approximately £4000 all in, so the need to protect the airship at all time is a priority but hopefully not an eventuality.

Do you think that there may be a concern from someone that an aerial vehicle with a level of ballistic protection is likely to be flying ?

Jim

kids and CHAVs with air rifles will shoot at it.  Thats the kind of messed up society we live in now.

Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant

every material has some level of ballistics protection.

Ballistics materials are not restricted in this country.

Im sure some PC doo gooder will be "concerned" after all you could strap a bomb to it....... but if we listened to them, we'd ban all RC aircraft from civilian use.

Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant