[FREE] 48" Rotafoil Parachute Pattern

[AlphaHybrids]

I have a Masonite rotafoil parachute pattern. It is a single piece, no gores needed. I use it on 3 pound rockets. I'm local to Colorado, if anyone is interested.

Here is a picture:



Edward

 

[AlphaHybrids]

Taken!

 

[shotoneup]

Is there an advantage in using this type of parachute?

 

[AlphaHybrids]

I find that they have less drift, and per area of fabric they can carry more mass at a certain velocity. With the three pound rocket the descent rate is ~10 fps. I flew to 2200' twice this weekend and walked less than 300' for it both times.

Edward

 

[Handeman]

I find that they have less drift, and per area of fabric they can carry more mass at a certain velocity. With the three pound rocket the descent rate is ~10 fps. I flew to 2200' twice this weekend and walked less than 300' for it both times.

Edward

What were the wind speeds? I had an apogee deployment at 6,400 ft and walked about 500 ft after a 5+ min decent and also had 5200 ft flight with DD deploy at 400 ft where I walked about 2,000 ft. It's about the surface and upper wind speeds much more the the chute.

Just telling us how far you walked doesn't tell us much.

 

[TopRamen]

That's really cool, and I do like makind parasheets/chutes, so I saved the image, but do you have a picture of an actual chute for three dimensional reference. I've never seen or heard of it before, but maybe it could be useful to those of us that fly in smallish fields?

It is certainly noted on my list of research items. Thanks for sharing.

 

[AlphaHybrids]

What were the wind speeds? I had an apogee deployment at 6,400 ft and walked about 500 ft after a 5+ min decent and also had 5200 ft flight with DD deploy at 400 ft where I walked about 2,000 ft. It's about the surface and upper wind speeds much more the the chute.

Just telling us how far you walked doesn't tell us much.

The wind speeds were variable, but approximately 5-7 mph to the southeast. Of rockets launched at the same time and approximately the same size and apogee, I walked about 1/2 the average distance that they did to recover. I don't know their descent rates, but this did recover much slower.

Edward

 

[Handeman]

The wind speeds were variable, but approximately 5-7 mph to the southeast. Of rockets launched at the same time and approximately the same size and apogee, I walked about 1/2 the average distance that they did to recover. I don't know their descent rates, but this did recover much slower.

Edward

So you're saying it was drifting down longer and slower but didn't go as far as other rockets?

The only way that is possible if if it has some forward speed going into the wind. If not, it will move with the air mass just like other chutes and if it takes longer to come down, it will move further with the air.

 

[TopRamen]

I found this Apogee PDF by Allison Van Milligan. "Spinning Parachutes: Do They slow The Descent Rate?"

https://www.apogeerockets.com/downloads/PDFs/Spinning Parachutes.pdf


The conclusion is :

"13
Launch Conclusions:
I found out that the spinning parachutes did not fall as slowly as the non-spinning parachute. But in real launches, the non-spinning swung back and forth more than the spinning chute. I would use a spinning chute when I wanted to have a more vertical descent, like an egglofting altitude rocket. The reason is that it makes the rocket come down straighter and a little bit quicker.
One thing you might worry about is that the spinning chutes can tear easier because they are already cut"

 

[Jeffmhopkins]

So you're saying it was drifting down longer and slower but didn't go as far as other rockets?

The only way that is possible if if it has some forward speed going into the wind. If not, it will move with the air mass just like other chutes and if it takes longer to come down, it will move further with the air.

Parachutes can operate in one of three descent modes: Restrained, oscillating, and gliding. Obviously a higher Cd is with gliding, and lower with oscillating modes. A non spinning parachute due to shroud line lengths and loading might tend to be in the oscillating or gliding modes.

A spinning parachute would probably operate less in the oscillating and gliding descent mode, being a more stable performing parachute when compared to non-spinning parachutes which might develop a gliding descent mode and drift a long way. You obviously need to keep in mind that the holes etc lower the Cd etc, but yeah

More information found here: http://www.nakka-rocketry.net/paracon.html#Basic

"The gliding nature of a parachute is another reason that using Cd as a measure of the effectiveness of a parachute can be misleading (Fig. 1). When a parachute descends, it may have both a downward component of velocity as well as a horizontal component (in other words, rather than descending straight down, it will descend at an angle). Air flowing around the parachute at a certain velocity (V) generates both lift and drag forces -- the drag (D) acting opposite to its line of motion, and the lift (L)acting perpendicular to this, tending to reduce the descent rate, Therefore, the drag coefficient measured from free fall "drop" tests may indicate a significantly higher Cd (than, say, that measured in a wind tunnel), as a result of this gliding phenomenon."

 

[Handeman]

A spinning parachute would probably operate less in the oscillating and gliding descent mode, being a more stable performing parachute when compared to non-spinning parachutes which might develop a gliding descent mode and drift a long way. You obviously need to keep in mind that the holes etc lower the Cd etc, but yeah

What I've found is that standard parachutes that oscillate then to not glide at all, other then going one way then the other which cancels each other out. So they tend to come down with zero total glide and slightly faster then the calculated values you would get based on chute construction. Chutes that glide and don't have a control mechanism tend to take off in a random direction. They may go off a long ways or they may come closer and closer to the pad. It is random and with enough examples, they will also average the same as a chute without glide.

In either case, they move with the air mass because they can not do anything else. Even a spinning chute has to come down in the moving air mass. You have to remember, relative to the chute, there is NO wind. If the air mass is moving 10mph relative to the ground, then the chute is going to move at 10mph relative to the ground.

Assuming the release point of the chute is directly over the pad and at the same altitude, the only way a rocket touches down closer to the pad without an upwind glide component, is if the chute allows a faster descent rate.

If your spinning chute was consistently landing closer to the pad, then it had to be consistently weather-cocking into the wind, releasing at a lower altitude or coming down faster then the other rockets, or some combination of those three. The chute cannot land closer if it had a slower decent rate if the other two items are the same.

 

[ep29030]

Rotofoil chutes are mentioned in Knacke's Parachute Manual. They have a high Cd, but they are limited to a max size of about 4 feet diameter. They also have a low opening force coefficient, IIRC.

 

[Jeffmhopkins]

Handeman, I mostly agree with everything you've stated, just a few comments.

Is an oscillating mode it can occur in one axis or both axis, and can have a rotational axis as well.

In a single axis oscillation there can still be a glide component in any direction, the oscillation might just be higher on one side than the other. Again in multiple axis oscillation (ie coning) there can still be a horizontal glide component in a direction. Only when adding the rotation to an oscillation can we then start to have the effect negate the possible glide component.

This glide (even very slight) will make the rocket land further from the parachute deployment location 100% off the time at zero wind speed, and approach a 50% closer /50% further as the limit approaches infinity.

If the radial frequency is higher, this glide affect can be negated.

I imagine that overall glide is slight in most parachutes to be negligible, but a parachute with a high radial velocity will decently help negate it.

A lot of people on smaller parachutes have shroud lines to two places on the canopy, with the middle being the location of whatever connection to the rocket, tied with a knot or other hardware. This is not the best option for insuring equidistant shroud lines and non gliding canopies.

Now, after all that, I agree that the effect is probably negligible in a proper constructed parachute. But maybe his other parachute had offset lines and just wants to fly

Oh, and there can be wind for the parachute in the air column

Gusts. They'd of course negate out over averaging, but still.... Just because you're floating down in the air column doesn't mean wind speed doesn't change, your inertia would insure there would be some wind before the parachute speeds up to match

 

[shockie]

porosity increases parachute stability, ie reduces oscillations parasheets and circular parachutes by their very nature are unstable hence the oscillations, rocking back and forth, etc on the other hand, porosity also reduces the Cd leading to higher descent rate the increase stability of parachutes can be seen by using spill holes ......or some combination of slots around the periphery of the parachute.....or you could just a t-Pin and poke a series of holes in a pattern around the parachute to accomplish the same.