Drogue to Main Ratio?

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Trooper

Trooper

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If I have a main of 24", what size should the drogue be? How do you determine the drogue size; is there a ratio?
 
If your main is 24", that would be a time for either drogueless or a streamer.
 
CarVac said:
If your main is 24", that would be a time for either drogueless or a streamer.
Click to expand...

Its a Madcow DX3, which is designed for only a main. Should I go with a larger main and a very small drogue?
 
Trooper said:
Its a Madcow DX3, which is designed for only a main. Should I go with a larger main and a very small drogue?
Click to expand...

The drogue would have to be something absolutely tiny, to the point where the airframe and fins of the rocket will overwhelm that area.

Making the main larger won't be doing anything to change that.
 
If doing dual deploy, the drogue only needs to be large enough to keep the payload above the fincan during descent, so when the main deploys it's above everything & out of the way for getting entangled.

Is this a DD project?
 
I'd highly recommend running a sim on your DX3's descent speed with the 24", the parachute in mine was woefully undersized.
 
What I'd recommend is to weigh your finished rocket, add in the heaviest empty motor you plan to fly, and sizing the main for that. Then, for the drogue, figure a descent rate of 75ish FPS, and size appropriately. Assume nothing, and don't get too attached to that 24" 'chute; you may find it's inappropriate for safe recovery of this rocket--but might do for something else...


Later!

--Coop
 
blackjack2564 said:
If doing dual deploy, the drogue only needs to be large enough to keep the payload above the fincan during descent, so when the main deploys it's above everything & out of the way for getting entangled.
Click to expand...

Exactly!

Sometimes a slightly larger drogue so the fincan hangs below it and adds its weight to the drogue will get it down faster then just holding the payload above the fincan as it tumbles below and to the side. That also stops the fincan from getting into the flying mode and pulling the whole thing sideways.
 
How high you plan on flying this rocket. Do you have a small field, a cement parking lot, a lot of wind.
 
Size the drouge to keep the upper section higher than the fins-- heck yes, but also make sure you still have enough descent velocity to actually get the main to open. I've witnessed larger rockets with sizable drogue chutes come down slowly enough that the ejected main flaps about and doesn't get dragged through the air quickly enough to inflate. In the case of this smaller rocket you probably won't have this issue, if you do, the drogue will be big enough to act as the main!

N
 
The descent velocity is inversely proportional to the diameter of the parachute.

If the main chute descent velocity of a 24" chute is between 15-20 fps, then a 6" chute would provide a descent velocity of 24/6 = 4 times that of the main or 60-80 fps. The fly in the ointment is the cross-sectional area of the rocket. If the rocket hangs down below the parachute you most likely will obtain that velocity, however if the airframe is horizontal rather than vertical, the airframe drag may well exceed the drag of a 6" chute so drogueless recovery is probably an option.

Bob
 
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I almost never recommend a drogueless recovery. If you don't use a drogue, you are not controlling the decent. It doesn't matter how large your main is, if the payload is below the main when it opens and falls into it, tangling the main, the whole thing will drop to the ground without a chute. I usually start with a large drogue and reduce the size until the payload is starting to level with the fin can on the way down, then I go up a little larger on the drogue.

If you only need a 24" chute for a main, you probably only need a 4" x 48" streamer for the drogue. As I've said, you need to adjust the drogue to get the right fall profile.
 
Handeman said:
I almost never recommend a drogueless recovery. If you don't use a drogue, you are not controlling the decent. It doesn't matter how large your main is, if the payload is below the main when it opens and falls into it, tangling the main, the whole thing will drop to the ground without a chute. I usually start with a large drogue and reduce the size until the payload is starting to level with the fin can on the way down, then I go up a little larger on the drogue.

If you only need a 24" chute for a main, you probably only need a 4" x 48" streamer for the drogue. As I've said, you need to adjust the drogue to get the right fall profile.
Click to expand...

The rocket is a standard 2.56" DX3, with the added weight of a Madcow Altimeter bay. The DX3 ships with a single 24" parachute, which I assumed was ample. However, I'd like to try dual chutes, and so I'm looking at larger mains now for a softer landing--especially after people have voiced concerns about the chute being too small.

I don't like the idea of a drogueless recovery either. The drogue will be deployed with the motor ejection charge, so I need to secure the nosecone and have it separate at the av-bay to prevent tangling?
 
Trooper said:
The rocket is a standard 2.56" DX3, with the added weight of a Madcow Altimeter bay. The DX3 ships with a single 24" parachute, which I assumed was ample. However, I'd like to try dual chutes, and so I'm looking at larger mains now for a softer landing--especially after people have voiced concerns about the chute being too small.

I don't like the idea of a drogueless recovery either. The drogue will be deployed with the motor ejection charge, so I need to secure the nosecone and have it separate at the av-bay to prevent tangling?
Click to expand...

My recommendation would be to use the altimeter to do the apogee deploy and use the motor ejection as a backup. Just make sure it will be longer then when apogee will occur. The whole issue with motor ejection is inaccuracy. The altimeter is reading the altitude and will eject at apogee. Then your drogue controls the decent until the altimeter ejects the main.
 
+1 for all said above.

I'll also add that sims will take a lot of the guess work out of what the rocket will do on the way up/down.

Sim software takes a little time to learn but even a basic understanding should get your sims in the ballpark.

https://openrocket.sourceforge.net/ and https://www.rasaero.com/ are free. RockSim is the one I use most but it's not free.
 
... Removing, due to being incorrect. What I read wasn't what was written. My bad.

Gerald
 
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