Replies to This Discussion

Permalink Reply by Varga András on August 11, 2009 at 10:50am

I would use a parafoil kite, that's the cheapest.

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Permalink Reply by UFO-MAN on August 11, 2009 at 10:58am

Hi Andreas. Any links or pictures to what you mean?

I need to deploy the chute with a servo based release mechanism controlled by the flight computer. The parachute will be stored inside the fuselage and eject out from a hatch. I am thinking of spring loading it. I need a parachute design that does give a slow rate of decent (1kg tot weight) of approx 0,5 m x sec^-1 max. and as good stability as possible. As little lateral drift as possible (want it to descend straight down). I also need high likelyhood of chute deployment.

Do I normally need a drogue chute for this application?

UFO_MAN

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Permalink Reply by Varga András on August 11, 2009 at 1:02pm

I mean this method:

Based on this kind of two-hand-controllable parafoil kite:

http://www.hiflykites.co.za/kite-online-shop/power-kites.htm
But this is maybe not the best if you want a completely vertical descend.

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Permalink Reply by UFO-MAN on August 11, 2009 at 1:45pm

Hi, may be a good candidate. However I tend to think that the half sphere designs with a small vent at the top are the most stable. I would like to locate a shop that sells 2,5 - 3 meter parachutes. I need a low ROD.

UFO_MAN

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Permalink Reply by Wendi Smol on August 11, 2009 at 3:03pm

Hi, you should remember that a slow decent and little drift don't go together. You can only have one or the other. And especially a decent rate of 0.5m/s is impossibly slow. Normal decent rates are about 3 to 5m/s. When it comes to UL rescue parachutes the decent rate can even be higher.
Perhaps you should have googled for model rocket parachutes?
Here is one I found in ten seconds flat:
https://www.discountrocketry.com/parachutes---recovery/flight-84in-... .
I'm actually working on a UAV rescue system. For safe deployment at (nearly) all situations you will probably need more than just a "Jack out of the box" mechanism. I'll put a little sketch of my system into my photo album.

Have fun

W.

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Permalink Reply by Scott James on August 13, 2009 at 12:15am

I found this a while ago?

Hope it helps! Cheers.

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Permalink Reply by UFO-MAN on August 13, 2009 at 1:30am

Hi Wendi. OK that slow descent and low drift don't go together on the same type of parachute with significantly different sizes. However, a parafoil for example, has inherent "drift" as it is designed to have lateral speed as far as I know. A spherical design with a vent should only drift from wind, mainly.

What I am after is a design that will give low ROD and move as straight down as possible (wind drift I can't control of course). I am lazy and don't want to chase the UAV far away after it has recovered. Especially in snow that is very important.

I might reconsider the ROD requirements as it is based on a square law in terms of the parachute loading (area to weight) so at some point the reduction in ROD is not worth the extra weight and volume required.

I took a look at your sketch here: http://diydrones.com/photo/photo/listForContributor?screenName=2mbb... and it looks cool. It looks fairly complicated as well. Is the two arm mechanism idea something like this: 2) Get it away from the fuselage and tail, 3) Slingshot the parachute out, 4) descent ? How do you plan to implement it?

Have you made any prototypes?

I was thinking of ejecting under the craft to get away from the tail, prop and horizontal stabilizer. The attachment to the fuselage will be at CG above the wing.

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Permalink Reply by JvdB on August 13, 2009 at 2:01am

http://www.aeroconsystems.com/chutes/index.htm

I would go for a super reliable pilot chute / balute (no tangled lines)

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Permalink Reply by UFO-MAN on August 13, 2009 at 4:04am

Hi JvdB. That 60" chute looks fairly bulletproof. However, I need to find a way to eject it from the fuselage without too much complexity. I am contacting aeroconsystems regarding this. Any other suggestions are welcome.

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Permalink Reply by Wendi Smol on August 14, 2009 at 6:56am

Have you seen how heavy it is?

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Permalink Reply by UFO-MAN on August 14, 2009 at 7:08am

Not yet ... the total weight of the whole craft is 1 kg so it cant weigh much ...

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Permalink Reply by Wendi Smol on August 16, 2009 at 8:57am

They also have a much lighter version of 60", costs $ 20.00 and weighs around 340gram.
Comparing that with the drogue chute I would guess the latter will weigh at least 500gr.

W.

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