Drogue Parachute Sizing

The Rocketry Forum

Help Support The Rocketry Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.
Interesting conversation. I try to size my drogue based on my simulation results. I usually try for about 50-60 fps descent rate on the drogue, not only to bring it down a little quicker, but also to reduce the load on the main when it deploys. I also keep in mind that it's possible the rocket will land on drogue only.
On some of my smaller rockets, I'll use a streamer for the drogue to avoid drifting. That also helps to keep the parts from banging together.

Phil L.


Agreed, Openrocket's a good source of data for making assumptions.
My only wish is that it could take some account for the booster's falling drag. I haven't had any luck generating a good profile for a drogueless descent. It always makes it ballistic.
 
Thanks again for all the comments. So here is some more fodder for discussion on this. My ~50 lb rocket (pad weight with motor) went to 7400 ft. I used a 30" Cato chute as a drogue. Stratologger data said it was dropping at ~90 ft/sec. Both the top and btm AFs were pointing down based on the on-board video (fins down and NC pointing down on the upper AF). The upper AF was top heavy. The entire rocket is fiberglass. There was turbulence as the upper AF was twisting around. Neither were anywhere close to parallel with ground but stayed close together pointing down. When the first charge fired at 1100 ft, there was an extremely fast rotation...faster than I've ever seen. A slight tangle on the deployment bag prevented the 12' Rocketman main from opening. Only the 24" pilot chute was out. Rocket came in on only the drogue and pilot chutes fortunately landing in soft soil so no damage. Your thoughts based on the observation that the two pieces were hanging straight down.
 
You need the drogue to do two things:
1 - stabilize or otherwise arrange the parts as they fall so they are not banging into each other.
2 - slow decent sufficiently so that you don't pop the main when it inflates.

#2 is clearly dependent on matching the decent speed to the capability of the main chute.
 
There needs to be enough drag on the front end (harness and NC) to stop the back end (airframe) going nose down and ballistic. I normally don't have that problem but my last flight (4" rocket, 3m long) did suffer from that. As it rolled over the top the NC separated normally. The rocket managed to point downhill a bit, and with the assistance of some windmilling, the harness wrapped around the airframe and left the NC following in the lew of the airframe. Things started not quite entirely pointing straight down, but after about 7 seconds there was a step up in descent rate, so totally nose-down (with NC behind). Main was still safely waiting inside the airframe.

The main came out as scheduled and stopped everything in its tracks. 290 kph (180mph) to almost standstill in a very short time. Not much damage.

The learnings from that are that I (and maybe other people :wink:) need to have some small amount of drag attached to the NC, but not too small. I did have a chute protector, attached like a handkerchief by one corner, which has worked well up until now. Next time I will probably run a small (12"?) drogue. That should stop the blunt end of the airframe going south.
 
There needs to be enough drag on the front end (harness and NC) to stop the back end (airframe) going nose down and ballistic. I normally don't have that problem but my last flight (4" rocket, 3m long) did suffer from that. As it rolled over the top the NC separated normally. The rocket managed to point downhill a bit, and with the assistance of some windmilling, the harness wrapped around the airframe and left the NC following in the lew of the airframe. Things started not quite entirely pointing straight down, but after about 7 seconds there was a step up in descent rate, so totally nose-down (with NC behind). Main was still safely waiting inside the airframe.

The main came out as scheduled and stopped everything in its tracks. 290 kph (180mph) to almost standstill in a very short time. Not much damage.

The learnings from that are that I (and maybe other people :wink:) need to have some small amount of drag attached to the NC, but not too small. I did have a chute protector, attached like a handkerchief by one corner, which has worked well up until now. Next time I will probably run a small (12"?) drogue. That should stop the blunt end of the airframe going south.

I would say your best validation is going to come from a couple of 3-4k flights that you can observe from the ground. On board video is also very helpful but both would be ideal.

My typical config is to use a three loop harness with the third loop being about three feet, and the third loop is a couple of feet away from the nosecone.

In my mind this allows the chute to get out of the slipstream and do it's thing.
 
Flight was to 17k', so attitudes etc were determined from the data logged by the TeleMega.

The chute worked as intended and as usual (drogue pulled main out of bag). It was the drogue-less NC that tucked in behind the airframe for the express ride down. Main deployment was clear and clean (and very sudden!).
 
Hi Over ThTop,

I am confused. Were you not flying in a standard dual deployment mode where an apogee charge releases a small drouge Chute from the booster?
 
Apogee deployment blows the NC off the front and remains attached to the rocket by the harness (attached to the avionics bay). Rocket normally comes in quite flat at that stage. Main deployment blows the deployment bag out of the airframe (upper section) which releases the drogue into the airstream, and then the drogue pulls the main out of the bag. Main harness is attached directly to the airframe (at the avionics bay, and not on the same harness as the NC).
 
Hi Over The Top,

I am still confused. In a standard dual deployment the apogee charge seperates the booster from the AV Bay. Then either a drouge Chute or shock cord is deployed if a drouge-less deployment is being used. They are deployed from the booster.

You are are stating that your nosecone is seperated by the apogee charge. Do you mean that your nosecone and the upper payload tube are seperated from the booster section by the apogee charge? This sounds like a drougles deployment.

When your main Chute charge fires where is the main parachute being deployed from? The booster or the payload section of the rocket? It sound like you are calling your pilot Chute that pulls your main Chute out of the deployment bag a drouge Chute.
 
I should do a sketch of this one day...

At apogee only the NC is blown off, by charges in the NC, controlled by the TeleMega. This is attached to the rest of the rocket now by a harness. The rest of the rocket consists of the altimeter bay, with the rear airframe behind it, and the upper airframe in front. These are all bolted together and in one piece. The main sits snugly in a deployment bag in the upper airframe, but will not fall into the airstream of its own accord. Charges on the end of the altimeter bay blow the deployment bag out of the upper section of airframe into the airstream. Drogue is lightly held under the flap of the deployment bag and once in the wind it inflates and pulls out the main. The main is connected by its own harness to the main rocket assembly.
 
Thanks for explaining that. A diagram would be very helpful in trying to explain this to others. What made you decide to dream up a completely different style of dual deployment? Have you flown similar rockets with one using your personal technique and the other utilizing standard dual deployment? Does your method reduce wind drift better than a standard small drouge?
 
I have done standard dual deploy, single-ended dual deploy (various techniques), drogue and drogue-less. It is really my personal preference. Rather than splitting the rocket I just knock the NC off. Might be a shade faster descent than drogue, but as I found out last flight it may be a little less predictable. Main always comes out nicely, which is a good thing!

I will consider each rocket on its merits. I am open to other peoples' ideas, so I am happy to try different techniques along the way, if they make sense to me. I tend to be leaning towards single-ended deployment a little.

As was said earlier, drogue sizing is a bit of an art.
 
The Skyangle cert 3 stuff is very sturdy. I would not hesitate there.

You could go with a Rocketman Pro XP or Ballistic Mach II chute. Good stuff too.

The Top Flight Ultra X or Crossfire chutes are good options too.

Ok, so my L3 project is 48 pounds dry and my plan was to go with a B2 L3 24" drogue. However, Open Rocket says the descent rate with a 24" chute with their advertised drag coefficient is 112 ft/sec.

Should I believe that or should I believe the hype about the B2 chutes and assume it will be well below 112 ft/sec?

If I believe Open Rocket, then I will need a 32" drogue for an 85-90 ft/sec descent. The catch there is that none of the sturdiest drogues come in that size. The best/toughest one I can find in that size is the B2 Classic II. I would think that would be tough enough, but can anyone expound upon that from experience?
 
Ok, so my L3 project is 48 pounds dry and my plan was to go with a B2 L3 24" drogue. However, Open Rocket says the descent rate with a 24" chute with their advertised drag coefficient is 112 ft/sec.

Should I believe that or should I believe the hype about the B2 chutes and assume it will be well below 112 ft/sec?

If I believe Open Rocket, then I will need a 32" drogue for an 85-90 ft/sec descent. The catch there is that none of the sturdiest drogues come in that size. The best/toughest one I can find in that size is the B2 Classic II. I would think that would be tough enough, but can anyone expound upon that from experience?

My F200 is 55# w/out the motor. My first two flights, I used a std. TFR PAR36 for a drogue. The shroud lines were not sufficient, and one set ripped. I then bought a PML 60" with spill hole, which makes it more like a 48". This may be a bit big, but not enough experience to know for sure.

If I were you, I would go with a 36", but something very heavy duty, like a Rocketman. And make sure there is plenty of time between the drogue deployment and main deployment. My mistake last time was to keep a 1000' main deployment altitude on a 1300' flight. Rocket did not have enough time to stabilize under drogue before the main came out (which may have been a little early, too), and thus main got a little tangled on the harness. Still got 90% of main open, and a nice landing.

See the video.
[video=youtube;il9FiXM4bqE]https://www.youtube.com/watch?v=il9FiXM4bqE[/video]
 
Hi Glen,

I just completed a lot of research for the parachutes for my Level 3 project. It came in at 48 pounds with the motor. I ended up using a Rocketman 36 and 48 inch 1.9 ProXP parachutes. The larger Chute was recommended by Rocketman. I will use the 36" Chute if it's windy on launch day. Too many trees at Potter. The ProXP chutes are made out of ballon fabric and therefore are extremely strong.

My my main is a 96" Iris Fruity Chute. I agree with John. Be sure to allow enough time for the drouge to stabilize the rocket before the main deployment.

Good Luck with your Level 3 flight.

Sincerely,
Bob
 
The 24" Skyangle will be too small based on what I have seen. I would consider a 32" or 36" classic 2- I think that should work.
 
36 pounds after burn with a SkyAngle 24" drogue yielded 76 fps.
 
I always add an extra drogue to my openrocket sims. I call it "Airframe Drogue." It's a zero weight drogue. I calculate the area of the largest section (usually the booster) and make that a virtual drogue. Doing that, I've been able to get sims to match real data within 5 to 10 percent. Then, I adjust the real drogue in my sims to get the desired descent rate.
 
I always add an extra drogue to my openrocket sims. I call it "Airframe Drogue." It's a zero weight drogue. I calculate the area of the largest section (usually the booster) and make that a virtual drogue. Doing that, I've been able to get sims to match real data within 5 to 10 percent. Then, I adjust the real drogue in my sims to get the desired descent rate.

Brilliant.
This trick may be what I need to get accurate Chute Release sims. I tried getting accurate descents on my Leviathan with a CR, but OpenR would take the delayed chute opening as delayed deployment, calculate its fall as ballistic, and give me *Excessive velocity at Chute deployment!* warnings. In reality, the nose was blown, the bundle was out, and it fell almost perfectly horizontal until the chute was released.

Do you include Area for only 2/1.5 fins (cardboard cutout style), or do you include all fins?
 
Brilliant.
This trick may be what I need to get accurate Chute Release sims. I tried getting accurate descents on my Leviathan with a CR, but OpenR would take the delayed chute opening as delayed deployment, calculate its fall as ballistic, and give me *Excessive velocity at Chute deployment!* warnings. In reality, the nose was blown, the bundle was out, and it fell almost perfectly horizontal until the chute was released.

Do you include Area for only 2/1.5 fins (cardboard cutout style), or do you include all fins?

I count the total area of the cylinder plus half the area of the fins (making the guess that half of the fins are tumbling in the wind at any time. Has seemed to work perfectly fine for me. Remember to use a drag coefficient of 0.75. That as the drag coefficient reported through some CFD calculations of a cylinder (I think I found that from an Apogee article).
 
Have you checked out Rocketman MACH 2 Chute? I'm using an 24" for my 42lb dry rocket. Not worried about decent rate only that the booster is falling below payload which it does.

ImageUploadedByRocketry Forum1503921820.495973.jpg
 
Just adding my two cents here, I did my level 3 with a 96" fruity chutes iris and a 36" fruity chute classic elliptical. Rocket was 53lbs on the pad if I recall correctly. perfect flight and descent, I sized the chute for a <100 fps descent under drogue in rocksim, using CD numbers off of fruity chutes website.
 
Reviving this thread as I am about to use a drogue for the first time. Several people suggested the Rocketman chutes, I am wondering has anyone used the adjustable decent rate on the Rocketman chutes? That is the slide with lock on the shroud lines?
 
Do you mind if I use your L3 certification package as a guide for my L3 package? I just bought a 4" Madcow Frenzy that I am going to build for my L3 cert.

I certainly hope he says yes to you lol

You won't go wrong following along with his calculations that's for sure.
 
Back
Top