Model parachute

5 January 2024

Ram-air foil? A rectangular block to distance the plastic skirts, including sticking at the correct positions. This skirt separate the top foil and bottom foil and birdle connects.

Or use the birdle strings to pass through the top and bottom foils and secure? Front and Back sets.

27 September 2021

Simplify, simplify.

The parachute needs some dimensional stability when it is an inverted U-shaped, maybe corrugation works but need it be fully corrugated throughout the span?

One idea is to have corrugation at the tips, it will bend easier and helps to maintain the inverted U-shape and the corrugation at the tips gives it some chordwise stiffness.

Another idea is to forgo the concertina-corrugation. Curl tips will have similar effect.

In any case, if mid span needs more spanwise support, a sliced plastic straw, additional layer of paper or overlap the leading and trailing edges on the centre portion of span? 

Photocopy paper at A4 dimensions should be stable enough with just curled tips. If CG shall be 20% back from leading edge, then tips of 40-50% (forward raked, should be enough).

As a start of the experiment, parachute glider can be an A4 paper with 1/8 span tips, leaving 3/4 span flat.. Why the need for long bridles, for a glider, to check the dimensional stability and flying stability: insert bamboo stick through both tips, say at 15% with a small weight.

A less simple but convenient test model

The paper parachute might not work. To give it the best chance of success, maybe step back to a 'half' parachute. The parachute has to be secured anyway, instead of a single bamboo stick, maybe a foam strip as that will hold the angle of parachute. Since there is a foam strip and the foam strip looks a bit like a long aspect ratio wing, a foam fuselage might be added to the foam strip, it will be good to adjust weight and add fins and horizontal stabiliser too. And once it glides ok, it can be modified to accept the RC gear. It will become something like an autogiro with wings and tail, if tail is needed (most likely).

 

But, if that's the model, then why not make the wing high lift and lower aspect? Then without the parachute, it flies, with the parachute it flies slower, and if the parachute flying fails, an additional top wing can be added to make it a biplane. But then, if I made the wing wider, how do I know if parachute fails or if the flying was because of the wing?

So, same fuselage, add beam for parachute, if need tail, make the tail big enough. If it glides well enough, add RC and motors. When bored, remove parachute, glue on rear halves of wing. If RC flies ok, and when bored, add top wing. When bored, remove rear halves of wing, add rotor.

Oh no, if the wing is a flap, it will fly nose down and need elevator control. High camber will also nose down but not as much as flap down, maybe it will be ok with stabiliser.

Slow Flying

The idea of parachute model is not just because it's cool, it is also because it is slow flying and steep but slow descent. So are the ideas of an autogyro or rogallo. There's another type that can probably accomplish that: high lift like a ground effect vehicle. Obviously, the model will not be in ground effect, but having the wing at a high angle of attack would make it fly slowly as well. Maybe the beam can be a thicker piece of beam with leading edge sanded. The chord extension can be paper curled or creased to introduce curvature like permanent flaps. The paper can be glued to the underside of the thicker beam, the straight cut trailing edge of the thicker beam can act as a KF foil. The root can be glued to the fuselage and tip or intermediate span can have ribs to keep the paper foil. The foil can also be glued on ribs so that the foil are set off from the bottom of the thick beam, giving it a slot effect. I wonder if a slot in this configuration is a plus or a minus. Paper foil can also be altered to give wash-out effect too.

24 September 2021

Plastic of a shopping bag is too flexible. Concertina paper is too heavy? I can imagine plastic film buckles and the whole model crashes, it need reinforcement chordwise.

Maybe plastic straws can be glued/looped to the tips of the parachute, that'll prevent chordwise collapse to an extent.

Mid-span collapses can be done by pasting paper strips chordwise? If mid-span needs more support, substitute with plastic straw?

The planform might as well be tapered, thick in the middle to create the most drag/lift.

Bridle can be paper strips, rather than strings and the gondola can be held in position in cardboard pieces.  

Gondola can be the same as the one I did for parasol. This time round, check the receiver is functioning properly, remove the hotglue, drill holes and thread the motors on the tongue-depressor.

If tips collapses, then maybe it is necessary to have struts spacing out the tips from mid-span.

Just tried checking the receiver, the motor spins up and down by itself and very soon both LED are blinking. I have put the cell to charge. Next I take out a known workable E010 and see if it is the receiver that is damaged. After the cell is charged when the charger LED switched off.

Okay, I tried again when I thought the cell is charged. The E010 blinks after a few seconds, seems I have not charged the cell. The E010 flew weak, probably because of the weak cell, but the motor spin was consistent to the throttle input, so it means that my E010 board on tongue-depressor is kaput.

To tear up a good E010 or not to, that is the question.

13 September 2021

A paper concertina/zig-zag/z/accordion fold is a continuous parallel folding of paper. A rectangular piece of paper concertina looks a bit like the wing for parachute gliding.

The real parachute has many air-filled cells and the shape allowed the wing to glide/float rather than descend like a traditional parachute. The concertina has chord-wise strength to support the foil, and standing far, far away, it gives an impression of a supported sail. It can probably be done with tissue but the lack of support will be more of an issue. Plastic film is probably unsuitable because it is too flexible.

A parachute will probably glide ok with a straight airfoil, but if it has an under-cambered with reflex airfoil it ought to be better because drag is not such a bad thing in a sinking object? Parachute gliding appears to hang in the air, the emphasis is how slow it appears to float down and forward, and covering a small distance. Because it is slow, it is more susceptible to air disturbances and gusts than a traditional aeroplane. However if wind is eliminated, like in an indoor environment, wouldn't it be ideal?

One idea of a reflexed under-cambered paper foil is a half and half: fold down the ridges on the leading edge ad fold up the valleys on the trailing edge. The ridges become under-cambered, the valleys become reflexed.

A distinct idea is to treat the parachute as the wing of a plane and to invert fold up the centre bay like before or to do that to a paper extension which then has a longer tail moment and acts as a horizontal tail. Parachute can have a trailing chute for better direction stability and this arrangement mimics that. Yet another idea is to cut slits in the valley/valleys of the trailing edge and invert the ends, This can also be done at the ridges of the leading edge to give an under-cambered airfoil.

As the foil is high above the thrustline, a draggy foil is desirable to allow changes in angle of attack due to the changes in thrust. A straight airfoil is less draggy than the reflexed under-cambered foil and although the induced drag is smaller, the concertina fold and induced drag is sufficient to allow changes in angle of attack.

For controlling the angle of attack and directional changes, a twin motor is enough and is the simplest. Controlling foil shape is also possible but it is more complicated and at what point does direction change due to lift or more induced drag?

Many ideas to consider:

• Rectangular or curved planform
• Parallel folds, equal width throughout
• Non parallel folds at tips
• Ridge and valley folds to what extent and to how many bays
• Extra fold along leading edge for denting resistance but I don't think so
• How many points of rigging
• CG location
• and more.

Rigging can be done over a wooden block with nails to ensure that the strings are identical. Alternatively, I think paper with tape can be used too, Paper triangulars has the advantage over strings because it is slightly structural and will hold the angle of attack better in more conditions.

I think CG is most important (duh!) and a simple flat paper glider of the same planform can be done first to determine it.

Then maybe I can make the concertina model from a single A4 sheet of paper and use an old KF606 to provide the differential thrust. The KF606 is 10gram (advertised), maybe the critical parts weighs 7gm (3gm for the model), so it should be ok, but if it proves too heavy, maybe 2 sheets of A4 paper or a single sheet of A3 paper?