Separating the tail instead of the nose, considerations?

[jahall4]

I’m working on a 4” HPR project, custom design, where I can (a) separate the nose from the [body tube and tail cone] OR (b) separate the tail cone from the [body tube and nose]. I have read some strong arguments for doing (b) with all rockets, but for convenience and simplicity (e.g. drag separation issues to name just one) it is not the “traditional” way.

I have 3 specific reasons for using this configuration:

1)The primary ejection charge (apogee/single event) is in the nose forward of the chute (backup is the motor’s charge).
2)I would like the tail cone to contact the ground last, which is sort of “backwards”, but if the tail cone is where the nose would be during recovery configuration (b) makes sense.
3)Try something different where there is a benefit in doing so.

Are there any inherent problems I may not be considering?

 

[Handeman]

I have 3 specific reasons for using this configuration:

1)The primary ejection charge (apogee/single event) is in the nose forward of the chute (backup is the motor’s charge).

There is some difference in how things will deploy with the charge in the nose vs. the motor. If you use shear pins or have a tight joint without the recovery gear being a tight fit, the differences between the two positions become less because the pressure in the tube becomes much more important than any effect you get from where the charge is located. I'm not sure I would put a lot of weight on charge location when deciding how/where to separate the rocket. There are ways to mitigate any effects of charge placement.

2)I would like the tail cone to contact the ground last, which is sort of “backwards”, but if the tail cone is where the nose would be during recovery configuration (b) makes sense.

This is an interesting design requirement and I think the key issue you are asking about. I have to ask why tail cone last? If you want to reduce the energy of impact by reducing the speed of impact on the tail cone by taking some of the weight off the chute so it can slow more before the cone lands, then you don't really have a choice in your design. You have to separate in a manner that leaves the least amount of weight with the tail cone. You have to separate with as much body tube attached to the nose cone as possible.

3)Try something different where there is a benefit in doing so.

Are there any inherent problems I may not be considering?

Trying something different is always a good thing IMHO. It's what moves the hobby forward and keeps each of us interested and active.

Good Luck

 

[jahall4]

the differences between the two positions become less because the pressure in the tube becomes much more important than any effect you get from where the charge is located. I'm not sure I would put a lot of weight on charge location when deciding how/where to separate the rocket.

I agree and I'm not, just a bonus.

This is an interesting design requirement and I think the key issue you are asking about. I have to ask why tail cone last? If you want to reduce the energy of impact by reducing the speed of impact on the tail cone by taking some of the weight off the chute so it can slow more before the cone lands, then you don't really have a choice in your design. You have to separate in a manner that leaves the least amount of weight with the tail cone. You have to separate with as much body tube attached to the nose cone as possible.

It is and yes that is the foremost reason. I want to reduce the likely hood of breaking a swept fin. but there is another reason you might want to do this with every rocket... recovering from a tree canopy. Keep in mind that one could still do that with configuration (a).

 

[Handeman]

It is and yes that is the foremost reason. I want to reduce the likely hood of breaking a swept fin. but there is another reason you might want to do this with every rocket... recovering from a tree canopy. Keep in mind that one could still do that with configuration (a).

I can see your point on this, but I'm not sure it really makes that much difference. If you are so far off the landing area that you are in the tree canopy, it is almost certainly because the winds are high. The result of high winds isn't the nose cone dropping though the canopy, but the recovery harness draping across the tops of the trees because of the speed of the rocket when it contacts the tree tops. The nose cone stops and the chute drags the rest of the harness across the tops of the trees. I don't see the configuration of the recovery, nose cone down first or tail cone down first having any real advantage when you end up in the trees.

 

[jahall4]

If you are so far off the landing area that you are in the tree canopy, it is almost certainly because the winds are high.

Really? Tell it to this guy: https://www.check-six.com/images/Jenny38057-poster.jpg.

Must be nice having a treeless plain to launch on where you can set up anywhere you please. Apparently you weren't at NSL this year. Beyond that I'll give you a specific example... PMW has a 7 sq. mile recovery area of forest and large fields separated by draws and other features, if I remember correctly, the primary area is 1.5 sq. mile approx. We have guys that launch to 24,000 feet. The wind at that altitude can easily take a rocket out of the primary area (even on a drogue), but wind speed at the ground could be 5 or 10 mph.

In your scenario what "stops the nose cone"?

 

[fyrwrxz]

I have a 3" w/Cf fin can that breaks at the can. It's basically a NC and fins using a short length of shoulder and a coupler The reason is so i can vary the length of the body tube based on the size of the motor to maintain CG. I have very small shear pins thru blue tube with brass shim cutters to prevent drag sep as a couple of variants have mass differences that concern me. The first test flight was w/ I280 demo DMS motor w/o pins as the NC/body tube was slightly lighter than the CF can with motor retention.I made sure it was tight, but not binding. (I use graphite on the faying surfaces). Only a few thousand feet so it stayed in visual all the way. You have to rig your harness and chute to land in the order you want. I have a conical with extra weight imbedded so i wanted that to hit last. Still stuck the nose. Remember the load on the chute shifts when other parts contact the ground. Recovery train is approx 25' long. Try it-you'll like it! Straight smoke and good chutes!

 

[jahall4]

I have a 3" w/Cf fin can that breaks at the can. It's basically a NC and fins using a short length of shoulder and a coupler The reason is so i can vary the length of the body tube based on the size of the motor to maintain CG. I have very small shear pins thru blue tube with brass shim cutters to prevent drag sep as a couple of variants have mass differences that concern me. The first test flight was w/ I280 demo DMS motor w/o pins as the NC/body tube was slightly lighter than the CF can with motor retention.I made sure it was tight, but not binding. (I use graphite on the faying surfaces). Only a few thousand feet so it stayed in visual all the way. You have to rig your harness and chute to land in the order you want. I have a conical with extra weight imbedded so i wanted that to hit last. Still stuck the nose. Remember the load on the chute shifts when other parts contact the ground. Recovery train is approx 25' long. Try it-you'll like it! Straight smoke and good chutes!

This rocket sounds a lot like my project and with similar concerns about drag sep, CG, and in my case dampening ratio. Do you have a photo(s) you could post?

 

[fyrwrxz]

This rocket sounds a lot like my project and with similar concerns about drag sep, CG, and in my case dampening ratio. Do you have a photo(s) you could post?

I'll see what i can do.