MPR chute as a drogue?

Onebadhawk
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Nathan

Nathan

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I need to select a drogue to use with my 35 lb Formula 150. According to OpenRocket a 24" drogue will give me a descent rate of about 105 fps which I think is good. The only chutes I have that are that small are normal lightweight chutes like the kind that come with MPR kits. I have used a 18" MPR chute as a drogue on my 17 lb Frenzy and it worked fine but not sure if a chute like that will be strong enough for the 35 lb rocket. Is it okay to use a MPR chute as a drogue on a big rocket? Or do I need to buy yet another Fruity Chute?
 
What is wrong with a SkyAngle Cert 3 for $27.50? Works for my 42 pounder.
 
If you don't want to buy another chute, check with your current chute's mfg. to find out the tensile strength of the shroud lines and the stitching. They should know that. Gary of TFR has given me that info in the past.
 
I don't know the mfr, I just have a bunch of smaller chutes that came with various kits. I think I will just go ahead and buy a real drogue, maybe the Skyangle. I have to buy a new main anyway because my biggest one is 72", which would be big enough for the Formula 150 if it lands in nice soft sod farm grass but not if it lands in sod farm gravel parking lot.
 
It's just fine to use an MPR chute as the drogue. If it opens at apogee it just limits the terminal velocity of the rocket until the main opens. If it opens at high velocity the MPR chute might lose a shroud line, but that's better than zippering your body tube. Quite a few flights fly without a drogue. The stronger your drogue the more damage to your rocket. I would rather damage a $10 chute than a more expensive rocket.
The exception to what I have written above is if you're wanting to make sure that a failure of the main to deploy will not result in damage; then people use a larger, stronger drogue.


[emoji1010] Steve Shannon [emoji1010]
 
With that weight you will probably have a large main chute, so you should calculate how large the drogue has to be to slow down the rocket enough so that it will withstand the opening shock of the main chute.

Fshock = cd *cx * A * rho *v^2

A surface area
v velocity
cd drag coefficient
cx opening force coefficient for the skyangle around 1.2
rho density of the air at deployment

this is somehow a worst case model since it assumes a infinite rocket mass, but controlled deployment.
More you can find in the parachute design manual from Knacke
 
I respectfully disagree. As long as apogee deployment has split your rocket into an aerodynamically unstable configuration your rocket and your main needs to be able to withstand the deployment of your main. If you need to reduce the shock of the main opening there are a number of techniques to help with that, including taping shroud lines, using a slider, or different methods of folding your main that allow it to open more slowly.


[emoji1010] Steve Shannon [emoji1010]
 
You do not really disagree, for example a slider changes the opening force coefficient, which can of course help.
But one has to consider that the velocity is the only component in the opening shock which has a quadratic impact.
 
Check out Spherachutes, their HD drogues and Apex Drogues are top shelf and come in a wide variety of sizes to fit any profile.
Julie is great to deal with and also does repairs and custom work
 
I took a look at the Apex drogue- that is a neat design. Anybody here used one?
 
I used a small umbrella skin with shroud lines ziz-zaged about 1.5" up each seam for a drogue on my L3. It worked just fine. In fact it had too much drag. I will need to use a smaller one.
The point is that umbrella's are built with seams that are much weaker then even MPR parachutes would have. I've been using umbrella skins as drogues and main chutes for about 10 years now an the only one that ever failed was being used as a main chute when a motor ejection fired right at the end of burnout and the rocket was traveling about 400 mph. It only ripped open 3 of the 8 seams which surprised me, I expected more damage.

I know that's not direct evidence, but I have been using smaller MPR and nylon LPR chutes as drogue's for a long time and with the success I've had with umbrella skins, I wouldn't worry about using a MPR chute as a drogue.
 
Handeman said:
I used a small umbrella skin with shroud lines ziz-zaged about 1.5" up each seam for a drogue on my L3. It worked just fine. In fact it had too much drag. I will need to use a smaller one.
The point is that umbrella's are built with seams that are much weaker then even MPR parachutes would have. I've been using umbrella skins as drogues and main chutes for about 10 years now an the only one that ever failed was being used as a main chute when a motor ejection fired right at the end of burnout and the rocket was traveling about 400 mph. It only ripped open 3 of the 8 seams which surprised me, I expected more damage.

I know that's not direct evidence, but I have been using smaller MPR and nylon LPR chutes as drogue's for a long time and with the success I've had with umbrella skins, I wouldn't worry about using a MPR chute as a drogue.
Click to expand...

+1!
 

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