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Ultra micro skydiver for, say, less than 100 g?

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Old 11-16-2013, 02:44 PM
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Tom_1971
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Default Ultra micro skydiver for, say, less than 100 g?

I have read a lot here and around the web and it's time to start building something from scratch.
Since I don't have access to a large plane, I'd like to build something that can be lifted up by a small (less than 1 mt span) electric plane or even by a 450 helicopter. My target is to stay below, say, 100 g.
Electronics (RX, 2 servos, lipo) can be assembled easily within 20 g or so. The remaining weight could be for the chute and jumper body (doesn't need to be so realistic, at least not to start, a frame board with two "arms" could be enough for the first build). I already have more than 1 square meter of ripstop nylon 44g/mq available in my workshop...
However, I'm wondering which chute size should I select maybe around 50 cm span (may I assume that chute area scale proportionally with jumper mass?) and also if such a light skydiver could be actually flown and steered with success.
Is there someone already having experience with a similar ultra micro skydiver?
Which plan do you suggest? May Gitchel plan work after scaling? Is the very old plan #631 from RCM magazine worth to be bought?
Many thanks, I hope to be able to progress in RC skydiving and to add useful contributions to this forum in the future.
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Old 11-17-2013, 08:09 AM
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GaryV
 
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Hi,

Here are the specs on the ihl-junior.
The one I have weighs 200g without the receiver.
I haven't actually jumped it yet, still another project on the list. It is very light itself, and I think building one half that weight would be a task.
I'm not saying it couldn't be done, the chute on the ihl spans 56cm
I will try to upload some pics from the manual to maybe give you some ideas on what you need.

GaryV
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Old 11-17-2013, 01:46 PM
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Lot of information on the diver, nothing on the chute (apart the picture on the cover), that is what I need more... Do you have information to build the chute, too? Or even close up pictures of the chute?
Many thanks anyway.
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Old 11-18-2013, 07:58 PM
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The chute here is prebuilt there are no instructions for building it.The only other pictures are for packing the chute.

The cover gives the Span, chord and area of the chute, and the weight of the skydiver.
One could assume that to build a skydiver of 100g as you stated, that is roughly half the size of this one so you would need a chute half this size.
I am used to the Mike size divers which have a about a 5' span and are fairly easy to see.
I dropped this one Sunday from where I usually drop my Mike and couldn't tell the orientation to fly it, landed about a 1000' away.
Did two more drops a little closer and landed within 20' of where I was standing both times.

I 'm attaching a pdf of the Gitchel chute it was designed for a 2.5 to 3 lb. diver. I made a copy to 80% of the original and it worked good for a 1.5 lb. diver.
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Old 11-20-2013, 03:19 AM
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Thanks, Gary. That adds quite a lot wrt Gitchel .doc file I already had (without pictures).
By 80% scaling, I think you mean 80% span and cord (i.e. 64% chute area) right? In this way you are able to maintain a load of about 0.0019 to 0.0023 lb/sqinch i.e. approx 0.13 to 0.16 g/cmq as for the Gitchel chute (size of 49x26" applied to a weight of 2.5-3 lb), if I understand well. Could you please confirm?
If this is correct (and if nature scales linearly to whatever scale, that is not right the case...) the scale factor for a 100 g jumper could be around 30% span and cord with respect to your chute (1/7h of your weight) i.e. 25% with respect to Gitchel chute.
If everything is correct... bingo! I can go straight cutting the ripstop nylon!!! And the build log can start.
What do you think? Am I missing someting (that I should discover before the fist crash of my jumper)?


P.S. According to text and drawing, the Gitchel chute has 13 ribs + 2 tip ribs (i.e. 14 "channels", I don't know how to say better) but the title speaks of 7 "cells" chute. I'd say the cells are actually 14 (mmhh...) or maybe each "cell" is constituted by two adjacent "channels". Are the holes (for air pressure stabilisation, I think) present on each of the 13 ribs? Do you have a drawing of wiring to the diver, too?

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