Rocketman chutes (in real life)

Curious... Are Rocketman parachutes really that bad?!?

In looking at their website, the weight chart shows 6 to 12 lbs for an R9C. This weight is about equivalent to a 72" hemispherical from Spherachutes (which has an opening of approx. 60" and matches this decent rate calculator), yet the R9C is HUGE, much bigger than the Spherachute.

It could be that Rocketman just very conservative with the chart on their website? (Which would be unlike Ky's personality)

What have you found in real life? Are the specs conservative?

Take a look at ther discussion that has been going on chutes. I make both the cupped Parabolic, which is very much like the RocketMan chute, and I make a Hemi Elipse and there is a great deal of difference in the CD of the two chutes. It takes a Cupped of almost twice the open diameter to equal the same CD as a Hemi elipse.

Well, yes, I know that, but then how do you explain Skyangle chutes decent rate chart where again about a 60" chute does the 8 to 12 pound range. A Skyangle chute looks an awful lot like a cupped parabolic. I guess the answer is that a Skyangle chute is more like a hemispherical.

Originally posted by dixontj93060
Curious... Are Rocketman parachutes really that bad?!?

In looking at their website, the weight chart shows 6 to 12 lbs for an R9C. This weight is about equivalent to a 72" hemispherical from Spherachutes (which has an opening of approx. 60" and matches this decent rate calculator), yet the R9C is HUGE, much bigger than the Spherachute.

It could be that Rocketman just very conservative with the chart on their website? (Which would be unlike Ky's personality)

What have you found in real life? Are the specs conservative?

Click to expand...

Where did you find the dimensions of the R9C to interpret that it is "HUGE"?

Originally posted by plasticpaul
Take a look at ther discussion that has been going on chutes. I make both the cupped Parabolic, which is very much like the RocketMan chute, and I make a Hemi Elipse and there is a great deal of difference in the CD of the two chutes. It takes a Cupped of almost twice the open diameter to equal the same CD as a Hemi elipse.

Click to expand...

Respectfully....

Be careful. Open diameter is meaningless. Parachute Cd is based on fabric area not open diameter. Current published information suggests that parabolic Cd is HIGHER than hemis or ellipses.

I plan to some drag testing with the cupped parabolic once the weather cooperates up here.

Originally posted by jderimig
Where did you find the dimensions of the R9C to interpret that it is "HUGE"?

Click to expand...

The Rocketman chutes are sized in inches, not feet.

An R9 is 96" Not 9' That makes it a 8' chute.

R14 is 144" or a 12' chute

R18 is 180" or a 15' chute....

Take that into consideration, and remember that a round parachute has a much larger CD. Rocketman chutes are only four lines called an X-Form with a lower CD.

Originally posted by jderimig
Where did you find the dimensions of the R9C to interpret that it is "HUGE"?

Click to expand...

I have both an R9C and a 72" Spherachute (actually an R7C and a 60", 96" and 120" Spherachute also). I was doing some mix/match with the drouges I have for my L2 build. I knew it always seemed like the Spherachutes packed so much better. Now I know why... I never actually compared them side by side. The Rocketman chute is HUGE in comparison. That is why I wanted to get some real life examples of using Rocketman chutes--model of chute versus project size just to see if the weight specs published by Rocketman were correct. I saw a ton of large projects with Rocketman chutes at LDRS for instance--maybe nobody on this site though... Maybe I should ask this question on another forum...

Actually Erik should know...

In your experience, are the Rocketman chutes pretty true to their published weight specs or is the chart conservative?

-Tim

Originally posted by jderimig
Respectfully....

Be careful. Open diameter is meaningless. Parachute Cd is based on fabric area not open diameter. Current published information suggests that parabolic Cd is HIGHER than hemis or ellipses.

Click to expand...

I understand where you are coming from and I respect your ideas, in this case however I have to respectfully disagree with you. If I made a chute with a very tall skirt to the point where it looked like a tube the vertical sections of the tube/chute would not help with the efficiency of the chute. It would however be used in the CD calculation of the chute. This makes no sense to me because the extended skirt does not make the chute any more efficient. However if we were to calculate CD based on sq inches of fabric the cupped parabolid chutes still have a lower CD because they use more fabric due to the 4 vertical "ears" that replace some of the shroud line length. There may be information indating I am mistaken but I have pics of my kids playing with my chutes in the wind that would show I am right....LOL, LOL

Originally posted by plasticpaul
I understand where you are coming from and I respect your ideas, in this case however I have to respectfully disagree with you. If I made a chute with a very tall skirt to the point where it looked like a tube the vertical sections of the tube/chute would not help with the efficiency of the chute. It would however be used in the CD calculation of the chute. This makes no sense to me because the extended skirt does not make the chute any more efficient. However if we were to calculate CD based on sq inches of fabric the cupped parabolid chutes still have a lower CD because they use more fabric due to the 4 vertical "ears" that replace some of the shroud line length. There may be information indating I am mistaken but I have pics of my kids playing with my chutes in the wind that would show I am right....LOL, LOL

Click to expand...

I will collect the data. As a parachute descends there is air velocity horizontally as air spills from the chute. The vertical cups of the cupped parabolic offer drag to this airflow and thus contribute to the drag of the chute overall. All of the relative airflow in the chute is not perpendicular to the ground.

That makes sense in terms of it spilling out. I wonder if they have looked into how much the "flaps" interfere with air flowing into the chute. I am just having a hard time getting past what I have seen with the chutes I have made. I guess I am just really hard headed.

Then again I wonder if we aren't beating the dead horse. All the chutes out there work and bring down our rockets safely. It's just a matter of which one each person likes. I'm sure some are made better than others though......

Originally posted by plasticpaul
That makes sense in terms of it spilling out. I wonder if they have looked into how much the "flaps" interfere with air flowing into the chute. I am just having a hard time getting past what I have seen with the chutes I have made. I guess I am just really hard headed.

Then again I wonder if we aren't beating the dead horse. All the chutes out there work and bring down our rockets safely. It's just a matter of which one each person likes. I'm sure some are made better than others though......

Click to expand...

Paul,

I think the horse is way past dead

Search some of the parachute tech reports on stinet. You will see that parachute modeling is one of the most complicated problems in aerodynamics. It can be hard to predict what a chute will do until you put in a real airflow at the speed it will operate at.

I'm with you, the hemi's seem to do better in the tug test than others. However normalized for fabric used they seem to be equivalent. Since you are in a better climate than me right now maybe you can do a simple experiment. Make smallish cupped parabolic and ellips. chutes with equivlent fabric area and do a drop test. I'll bet a nickel they hit the ground at about the same time.

(I have also sent a PM from a private source on the matter).

I really do look forward to meeting you this summer. It was 6deg at my Mom's house this evening and 46 here.......

I will have to take some measurements and see what I have for sq inches on some of these.