Super DX3 DD quick chute question

I am simulating my DD Super DX3 with the chutes I currently have. However, it is stating that the main at 700feet is deploying too fast at 61.7 mph. This is my current setup:

Drogue: Apogee deploy with 10'' chute. Backed up a few seconds later with motor eject.

Main: 36'' chute deployed at 700 feet.

I have been reading a few posts for other setups and people state that I should be between 60-80 mph. I just want to make sure that the drogue is effective enough.

I do not think 61.7 mph is too fast. You want it moving to get your main inflated. I have seen several rockets over the years descend too slow and have the main flutter in the breeze.

Actually how the chute is deployed is the most important part of deployment.

In other words imagine the difference in traveling 60 mph in your car and slamming the brakes on as hard as you can versus slowing applying the brake pedal until you stop.

Parachute deployments can act the same way. If the canopy portion inflates before the lines and all webbing are taunt it's like slamming the brakes on and is likely to damage your rocket.

If the lines and or webbing, shock cord, etc.. are taunt prior to canopy inflation it equates to easing the brake pedal on.

This is very important to skydivers as a hard opening can break your neck or back or even worse result in death.

Deployment bags or other devices are designed to prevent the canopy from opening prior to "line stretch". If you don't have a deployment bag this can be accomplished through packing or even through the use of a few strategically placed rubber bands. Skydiving rigs use rubber bands to control deployment.

An easy way is to wrap the canopy with the lines so they actually the canopy from inflating until they unwind.

However as mentioned by the early poster it is possible to over control the opening and snivel in but frankly this is highly unlikely with a "round" canopy and is more likely caused by poor packing they traps canopy fabric in the lines and prevents inflation.


So many rockets, so little time, and money.

Don't forget that the rocket itself is going to add drag at higher decent rates. When I did DD in the past I tried to shoot for 100fps under the drogue.

Thanks everyone! I agree that enough speed is a good thing. I have been programmed to fix all errors I see in simulation lol. Another quick question, I use shear pins for both sections right? Or do I have to do shear pins for only the main section? I read somewhere that you use sear pins for both sections but it seems a bit much to me to have the lower section shear pinned unless it was rocket using a booster stage.

you usually only use shea rpins to hold the nosecone on during the decent of the drogue to prevent premature ejection of the main chute.......

Just as I thought.... Thanks!

I use shear pins on both ends of everything. My 4" DX-3 has three 2-56 nylon pins top and bottom. Shear pins are more "consistant" regarding the force needed for separation.

My typical drougefall is between 90-120 fpm (61-81 mph) depending on altitude.

In terms of reducing shock loading, the highest benefit you can have is by adjusting drogue size appropriately. The objective is to have the fin can and nose section roughly horizontal, separated by the shock cord as it falls from apogee.

In this configuration, when the parachute opens, the fin can swings down from horizontal until suspended under the nose section, dramatically extending the time duration of the impact, which in turn reduces shock.

Having too large of a drogue can actually be bad, as the rocket experiences droguefall strung out perfectly vertical. This ensures a high shock load as the entire load stops simultaneously.

Determining the correct size drogue usually takes a couple of flights. Asking around will get you in the ballpark.

All the best, James

It depends on the fit of the coupler and the lower airframe plus how draggy is the motor section. Looking at the Super DX3 IMO the aft is not that draggy so it depends on how tight the coupler is. You should be able to pick up a fully loaded rocket by the forward section and it should not separate without some shaking. If your rocket acts like that you should not need shear pins on the drogue just the main. However you can do what Titan II does and not worry about it.
Above all ground test.

Thanks again! I just did a test holding the forward end of the rocket and the aft end doesn't separate. I'm going to think about the shear pins for the drogue section.

Fdog- Thanks for a detailed explanation. I will hopefully get to try my first DD and Level 2 cert. in a few weeks at White Lake. I hope to see you there!