Max Velocity and Acceleration at Drogue Deployment

[Sailfish1957]

In an effort to have my LOC Hyper Loc 835 land relatively close to the launch site, I am (of course) employing Dual deployment with a 13" Drogue and 50" Main. Rather than have the drogue deploy at apogee, I thinking of using a considerable delay - to the point where the rocket is at about 4500', having descended from 8200'. The velocity at deployment, according to RockSim, is about 240 mph. Maybe a dumb Q, but will that speed tear the rocket/chute completely apart? Epoxy, SS hardware, etc....

 

[Buckeye]

That's about 3x to 6x the speed of a typical main deployment. You are probably looking at least a zipper through the cardboard tube.

Consider a streamer for the drogue and deploy at apogee. The descent rate of a streamer is faster than a parachute and often faster than drogueless.

 

[jderimig]

Thats alot of kinetic energy ~3700*W ft-lbs (where W is weight of the rocket) to dissipate. Do you have a plan to where all that energy is going to go?

 

[David Schwantz]

I zippered a full length CF tube when chute deployed after burnout. that cardboard tube don't stand a chance.

 

[Sailfish1957]

That's about 3x to 6x the speed of a typical main deployment. You are probably looking at least a zipper through the cardboard tube.

Consider a streamer for the drogue and deploy at apogee. The descent rate of a streamer is faster than a parachute and often faster than drogueless.

Great idea! I will do that. Any advice on the size (dimensions) of the streamer? Haven’t tried them. The rocket is 4” and 74 inches long (overall). I don’t have a weight just yet.

 

[Sailfish1957]

I zippered a full length CF tube when chute deployed after burnout. that cardboard tube don't stand a chance.

Roger that.

 

[Sailfish1957]

Thats alot of kinetic energy ~3700*W ft-lbs (where W is weight of the rocket) to dissipate. Do you have a plan to where all that energy is going to go?

Looking at advice on using a streamer instead of drogue.

 

[Buckeye]

Great idea! I will do that. Any advice on the size (dimensions) of the streamer? Haven’t tried them. The rocket is 4” and 74 inches long (overall). I don’t have a weight just yet.

Hard to say. Streamer design is not as straight-forward as a parachute. Look at Apogee's website for some tech tips and articles.

I just use a long length of caution tape on some of my HPR rockets.

 

[Handeman]

If it's coming in ballistic, then that speed is probably closer to 300 mph. I did have a rocket that failed to deploy a drogue (my mistake) and the main deployed at 400 ft at about 300 mph. It was made of phenolic tubing and the chute and everything survived without zippers or shredding, but the main opened so low to the ground the fin can slapped the ground after slowing some. It still busted up the whole fin can.
It's possible everything will survive if you have a slow opening main where the opening of the rocket and shock cord drag can slow it down significantly before the main opens.

Skydiver open their chutes at about 200 mph and the sliders slow the opening, not to protect the chute, but to protect the fragile human on the end.

As an RSO, I'm not sure I would allow that flight profile to fly, at least no where near the flight line, maybe the away cells with a 5° - 10° tilt away from the flight line. That would kind of counter your desire for a short walk.

 

[Sailfish1957]

Hard to say. Streamer design is not as straight-forward as a parachute. Look at Apogee's website for some tech tips and articles.

I just use a long length of caution tape on some of my HPR rockets.

I just ran RockSim with a 54" x 4" streamer and it deployed at apogee @ 28 mph. That's great. And, it reduced the range by a ton. Thanks for the info!

 

[Conway Stevens]

In an effort to have my LOC Hyper Loc 835 land relatively close to the launch site, I am (of course) employing Dual deployment with a 13" Drogue and 50" Main. Rather than have the drogue deploy at apogee, I thinking of using a considerable delay - to the point where the rocket is at about 4500', having descended from 8200'. The velocity at deployment, according to RockSim, is about 240 mph. Maybe a dumb Q, but will that speed tear the rocket/chute completely apart? Epoxy, SS hardware, etc....

I fly flights to well over 30k ft quite often with minimum diameter rockets. I try to bring them back close. I deploy my drogue at apogee. The biggest issue people have is running way to large of drogue. On my 54mm rockets its a 3 to 4 inch drogue. On my 3 inch to 4 inch diameter rockets its usually a 5 to 6 inch drogue max. Its more about a controlled decent not a huge reduction of speed. I usually bring them down around 125ft per second on drogue. Then kick the main out at 1000ft. You might chose different altitude thats lower as i pick my altitude so i can get a GPS fix to the ground from such flughts in the jet stream ive recovered flights from around 28 to 31k as close as 200 yards from the pad and as far as 5 miles... (high jet stream wimd speed that day) at NSL west i flew a 54mm min diameter to 31,374 and recovered 4900ft away. I understand your flight isnt as extreme but its realtive with the distance in mind.

 

[Sailfish1957]

I fly flights to well over 30k ft quite often with minimum diameter rockets. I try to bring them back close. I deploy my drogue at apogee. The biggest issue people have is running way to large of drogue. On my 54mm rockets its a 3 to 4 inch drogue. On my 3 inch to 4 inch diameter rockets its usually a 5 to 6 inch drogue max. Its more about offing a controlled decent not a huge reduction of speed. I usually bring them down around 125ft per second on drogue. Then kick the main out at 1000ft. You might chose different altitude thats lower as i pick my altitude so i can get a GPS fix to the ground from such flughts in the jet stream ive recovered flights from around 28 to 31k as close as 200 yards from the pad and as far as 5 miles... (high jet stream wimd speed that day) at NSL west i flew a 54mm min diameter to 31,374 and recovered 4900ft away. I understand your flight isnt as extreme but its realtive with the distance in mind.

Thanks, I’m thinking streamer on this bird.

 

[kjhambrick]

+1 @Conway Stevens

I am still doing the 'classic' ( aka 'old timey' style ) dual deploy with a mid-body AV-Bay, drogue in the fincan and main in a tube up top by the nose.

My drogue is attached to the tail of the AV-Bay and I try to size my drogue so that the fincan -vs- the drogue+AV-Bay+main-tube+nose have about the same effective CD on either side of the drogue shock cord.

This way the two sections can fall from apogee to the drogue deployment altitude with the shock cord fully extended and fly as horizontal as posible.

Sometimes it takes a little tuning to nail a good drogue size but as you said, the drogue can be surprisingly small -- on my rockets, thats something like the planar area of two fins, depending on the relative tube lengths and weights on either side of the drogue shock cord.

I am doing a 34mm ( BT-55 ) rocket now and I am trying a streamer which sims about right.

I've never tried a drogue streamer but I think this will work well with the streamer attached to the base of the AV-Bay instead of a 1 -or- 2 inch drogue.

-- kjh

 

[Sailfish1957]

+1 @Conway Stevens

I am still doing the 'classic' ( aka 'old timey' style ) dual deploy with a mid-body AV-Bay, drogue in the fincan and main in a tube up top by the nose.

My drogue is attached to the tail of the AV-Bay and I try to size my drogue so that the fincan -vs- the drogue+AV-Bay+main-tube+nose have about the same effective CD on either side of the drogue shock cord.

This way the two sections can fall from apogee to the drogue deployment altitude with the shock cord fully extended and fly as horizontal as posible.

Sometimes it takes a little tuning to nail a good drogue size but as you said, the drogue can be surprisingly small -- on my rockets, thats something like the planar area of two fins, depending on the relative tube lengths and weights on either side of the drogue shock cord.

I am doing a 34mm ( BT-55 ) rocket now and I am trying a streamer which sims about right.

I've never tried a drogue streamer but I think this will work well with the streamer attached to the base of the AV-Bay instead of a 1 -or- 2 inch drogue.

-- kjh

I like your thinking on this. I think the streamer will work well when attached at the avbay as you say. I will go with the deployment at apogee, and the main at anywhere between 1000 and 500 depending on the local wind conditions. I’ve RockSimmed this arrangement and I like the results. Thanks!

 

[David Schwantz]

Wow, never seen a 1 inch drogue.

 

[kjhambrick]

Wow, never seen a 1 inch drogue.

Yeah, me neither

But someone here on TRF mentioned that they sewed a triangular cup in the end of their streamer.

I might go there if the CD of my streamer turns out to be too small ...

-- kjh

 

[Conway Stevens]

Wow, never seen a 1 inch drogue.

At that point not really worth it. Might as well go drogueless

 

[DaHabes]

Put a chute release on the drogue. The rocket will essentially fall drogue-less until the chute release opens. I would hesitate to use a streamer, they are harder to model than a parachute and they can get surprisingly big since they are not nearly as effective as a parachute.

For that matter, if the two sections of your rocket are of about equal mass (with the AV-Bay being attached to the payload after apogee deployment), you can consider going drogue-less (it will fall flat with roughly even weights). If the weights are uneven, the heavier section will lead going down - not good if the heavier section is the payload section.