Drogue size?

Discussion in 'Recovery' started by RCGuyGR, Oct 6, 2019.

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  1. Oct 6, 2019 #1

    RCGuyGR

    RCGuyGR

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    Hi all,
    Building a Mad Cow Frenzy for my first HP dual deploy. Looking at around 5.5-6 lbs weight, using a 50" main chute. Can't seem to find much info on determining drogue size. Thoughts?
    TIA
     
  2. Oct 6, 2019 #2

    timbucktoo

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    I’d probably use a 12” Top Flight.
     
  3. Oct 6, 2019 #3

    Buddy Michaelson

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  4. Oct 7, 2019 #4

    Bat-mite

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    Some people recommend 20% the size of your main. That would be 10". However, I often use a streamer with rockets that size. A), it's more visible, and B) you get a faster descent rate while still keeping your parts separated.
     
  5. Oct 7, 2019 #5

    Onebadhawk

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    +1...

    Use a streamer..

    Teddy
     
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  6. Oct 8, 2019 #6

    Nathan

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    I like Rocketman drogue chutes. I use a 3 ft Rocketman Experimental Drogue chute on both of my 75 lb rockets. They're not made like normal chutes, not as much drag as a standard chute but much stronger which is what you need with a drogue. A big rocket descending at 60 to 70 mph under a small drogue puts a lot of stress on the chute. Try driving down the road at 70 mph and stick your arm out the window holding a parachute. No just kidding, DON'T DO THAT. But you get the idea. Drogue chutes don't need to be the most efficient but they need to be really strong.
     
    Last edited: Oct 8, 2019
  7. Oct 8, 2019 #7

    ep29030

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    Size is not that important, as the primary purpose of a drogue is not reducing the rate to travel. Its primary purpose is to put parts in the correct orientation so the main can open without hitting other parts of the rocket. Even a 12 inch drogue can do this. Falling at 80-100 ft/second is not the issue, orienting parts is the critical risk.
     
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  8. Oct 8, 2019 #8

    ep29030

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    Size is not that important, as the primary purpose of a drogue is not reducing the rate of descent. Its primary purpose is to put parts in the correct orientation so the main can open without hitting other parts of the rocket. Even a 12 inch drogue can do this. Falling at 80-100 ft/second is not the issue, orienting parts is the critical risk.
     
  9. Oct 8, 2019 #9

    jmwoody

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    All very good advice on sizing a drogue chute to rocket size/weight.

    Buddy's Rocketman Experimental Drogues are the best made in the market and will survive just about any event when other rocket parts won't ... just one mans proven opinion.

    I also use Rocketman streamers. I ran a 50'x6" steamer in my M1297 / 23lb fall weight after burn out / 4.5"x96" rocket at LDRS which went 11,500+ and landed 1 mile away from the launch pad on a moderately breezy day. The main was also a Rocketman 9' Pro Experimental chute which opened at 1200'.

    I do love to use streamers but, will use drogues just as often and I am a firm believer in Teddy's, OneBadHawk Kevlar Harnesses which I run in all my rockets.

    For your app RCGuyGR, you can't go wrong with one of Buddy's products and he will guide you to the right rig. Just give him a call or shoot him an email.

    BTW ... they will last you a long time and many rocket flights.
     
  10. Oct 8, 2019 #10

    Not Quite Nominal

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    TLDR: Top flight 6x60 or 7x70 streamer. Math below.

    My (possibly controversial) reasoning

    I think the drogue should be sized based on the surface are of the rocket, not the weight of the rocket.

    Specifically, I think the drogue should be 1/3 to 1/2 the side-on surface area of the rocket.

    Once the rocket separates, the tumbling rocket body itself will provide more than enough drag to slow the descent rate to a safe opening speed for the main. The point of the drogue then is just to stabilize the assembly. Just enough drag to keep the line from thrashing, not so much drag that the two pieces hang low and start tangling.

    https://www.rocketryforum.com/threads/drogue-sizing-thoughts.154776/#post-1917030

    A 4" Frenzy is 78" tall and 4" in diameter, providing approximately 312 sq in of side-on surface area. (Neglecting the fins/NC)

    For 1/3 the surface area a 12" diameter drogue is just about right.

    For 1/2 the surface area a 14" diameter drogue if you could find one.

    However:

    A streamer has about 1/4 the Cd of a sideways cylinder (0.2-ish vs 0.8-ish), so a streamer with an area just a little more than the side-on area of the rocket will give you that perfect 1/3 of the drag, while being significantly more visible.

    A 6x60 (360 sq in) or 7x70 (490 sq in) TFR streamer is perfect for 312 sq in of rocket. $8-$10, or $12-$15 for the reinforced Ultra streamers. Neon pink can be seen forever. Can't beat them!

    Rocketman streamers are pretty cool too, but the even the smallest ones are too big for this application.
     
    Last edited: Oct 8, 2019
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  11. Oct 8, 2019 #11

    GaryT

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    I just used this 1ft Pro Experimental Drogue Chute on Sat in my Dominator 3, Incredibly well made chute and worked perfectly on my Dom3,it also had quite a bit of cd for a 1' Chute. Pad weight was 9.5lbs

    I have the 1', 2' and 3' in the Pro Experimental Drogue series.
     
  12. Oct 8, 2019 #12

    jmwoody

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    What you have stated about streamers NQN is interesting and I don't find what you postulate controversial at all.

    A streamer utilized as a downward falling stabilizer based on smaller rockets surface area does work. Scaling up on larger free falling rockets requires a greater level of knowledge usually gained from experience over time and flights.

    With enough material (lengthxwidthxthickness) one could theoretically bring any size (did not say weight) rocket down safely on streamer only depending on the landing surface. As rocket weight goes up or the landing surfaces hardens a streamer only fall becomes problematic in the ...end.

    Back to the OP's question about a proper sized drogue ... Buddy suggested a 12" drogue and that seems to be a good size for the described rocket size and weight wise. Simple and straight forward.

    Ideas vary and that's what's great about our sport ... it's sporting
     
  13. Oct 8, 2019 #13

    Buddy Michaelson

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    Believe it or not John, I have brought down a 32lb rocket with a streamer only, granted it was a 268ftx10” streamer, but a lot of people out there say “once a streamer is so long it’s not scalable anymore.” Which that launch totally proved it wrong, would love to land a much bigger rocket with streamer only, nothing cooler than seeing your rocket from apogee all the way to the tall corn fields. Btw I bought the high res pics from Nadine of your rocket descending on my chutes at LDRS, will have to send them to you.
     
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  14. Oct 9, 2019 #14

    jmwoody

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    Thank You very much Buddy!!!!

    I checked her site and it's kind of old and not any updates? Do you have an inside to her work? I should pay her direct as it's copyrighted and only right that I honor her copyrights. Being a retired photographer I do understand copyrights very well ...lol
     
    Last edited: Oct 9, 2019
  15. Oct 9, 2019 #15

    Not Quite Nominal

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    For the main, agree. For the drogue, I think my rule holds. Specifically:

    Mains should be sized for the weight of the rocket - the target is a specific touch down speed.

    Drogues should be sized for the area of the rocket - the target is balancing drag between the rocket body and the parachute.

    Double the weight of a rocket (bigger motor/more payload), and you should double the area of the main, but the drogue size should remain exactly the same. It will just fall 40% faster, but even at the degenerate case (metal motor casing falling sideways) you've got enough drag.

    Absolutely agreed. Drag is drag is drag. An elliptical chute has a Cd of 1.6, a parasheet 0.8, and a streamer 0.2.

    So for the same amount of drag as a parasheet, you need half the parachute area if you get an elliptical, or four times the area if you use a streamer.

    In the case of a drogue where you don't need much drag and you're very high up/hard to see, the larger size of the streamer is beneficial.

    In the case of the main, the opposite is true: you're sized for weight, the streamer size will impose a weight/volume penalty. That being said, if you can bear the weight, a huge streamer is super cool!

    I'm actually thinking of buying one of Buddy's big streamers to use as a main in my MPR38. Not the most efficient choice, but it actually flies a little better with more noseweight (small fins, and I do like bigger motors), so the extra weight vs. a parachute is actually a plus.

    Agreed on that. Glad to see an actual parachute professional agree with my napkin math. 12" drogue or a 7x70 streamer should provide a perfect balance between drogue and body drag and give you the perfect stable "flying V"
     
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  16. Oct 9, 2019 #16

    Buddy Michaelson

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    Personally I like oversizing the Drogue, for me, walking an extra hundred feet is not an issue if I’m using a good tracker, or launching in open land like our club site (a very big sod farm), Blackrock or Hellfire. In the case that the main does not open, its better to fall around 70fps than 90fps. The less stress added to the main parachute from opening the better, my chutes can take a lot of stress though so I’ve never 2nd thought opening speeds, as I’ve never heard of any problems with thousands of chutes out there. At Balls this year, a guy had attempted a 2 stage high altitude attempt (not naming any names) but he only had enough room for a 3ft parachute for the top section, which was a Drogue Chute, it would had been fine being all aluminum, but the problem was the motor never lit on that stage, which was a O and probably was 30lbs or more, so the rocket landed very hard as it weighed 4 times more than expected and badly damaged the rocket. So always plan for more space than you think you’ll need, and always oversize your parachute, I always size for around 13fps for mains, and 65fps for Drogue because of my nice paint jobs.
     
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  17. Oct 9, 2019 #17

    Dave A

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    I'm with Buddy on over-sizing on drogues, slightly.
    I had a 50# IRIS which has big fins. Not really paying attention to its drogue descent, I would see the fin areas were large enough that the booster would come down horizontally, swapping place above and below the payload until the cords would get tangled.
    I flew all my 6" and larger rockets with a B2 Cert 3 drogue, obviously not large enough.
    My 9" Patriot did the same thing, next flight will be with a larger, ballistic Rocketman Drogue chute.
    Hopefully, everything will come down in the proper orientation.
     
  18. Oct 15, 2019 at 11:31 PM #18

    RCGuyGR

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    Wow! Tons of great information. Going to refer to this thread for future builds. Thank all who contributed.
     

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