Kframe
Well-Known Member
One of the things I like doing in rocketry is modifying kits to make them stronger and/or take bigger motors, converting to dual deployment, trying new things with what I have on hand and also building new projects from scratch with specific goals in mind.
Over last winter I got the idea to make a rocket using Estes BT-60 tubes (Big Bertha diameter) that would be capable of breaking Mach 1 or more, and fly to at least ten thousand feet.
As far as looks I wanted something that resembled a flechette or an anti-armor kinetic penetrator and would be about the length of the Estes Vapor.
Around this time I also discovered that the inside diameter of a Estes BT-60 coupler is about the same as the outside of a 38mm case.
So I decided was building a minimum diameter 38mm project!
(Up til then I had been thinking 29mm in a minimally upgraded airframe.)
I started in RockSim, actually using the Vapor .rkt file for initial spitballing and found that some I and J motors would do it.
The sims also showed that the rocket would have to endure 40-75 G's depending on the motor (that G number decreased as the mass increased once I actually started plugging in real material and component weights, but still, I knew it was gonna rip!).
Therefore, some serious beefing up was going to be needed, while keeping the weight as low as reasonably possible.
I had previously used Soller Composites fiberglass sleeving to glass my L2 4" tubed project, so I turned to them again and this time chose the lightweight carbon fiber sleeving (the lightweight was not a good choice, as you'll see).
I'm going to skip over a lot of the initial build stuff, as this thread is actually supposed to be about what happened and what I'm doing about it.
What I ended up with is this:
Just over 47" tall, can take up to a 38/1320 case, has a 3D printed (PETG) av-bay containing an Eggtimer Quasar for dual deployment and GPS tracking.
The as mentioned Estes BT-60 tubes sleeved with one layer of the lightweight Soller carbon sleeving, is drogueless, has a piston in the forward section that protects and pushes out a lightweight 3 foot chute (Cd 2.2) and is topped with an aluminum tipped (for CG and Mach reasons) PETG nosecone that holds a Featherweight transmitter for backup GPS tracking. Oh, I also tucked a Jolly Logic Altimeter 2 in with the chute. for more data collection.
Fins are 3/16" G10 that are aggressively beveled and are JB Welded to the airframe.
With chute, electronics and batteries but without motor it has a mass of 850g, or under 1.9 pounds.
I dubbed it "Max-Q" for fairly obvious reasons.
Now I did launch it first on an H242, I didn't want to go nuts right off the bat.
On that it had a perfect flight, going about 480mph and reached about 4000 feet.
To my eye it looked undamaged upon recovery (whether it was structurally weakened from force or heat, I don't know).
Well the next week I headed to Airiest XXX in Kansas (from MN) and I had a 24 year old J570 for it.
I also brought a new J270 that I seriously considered using instead, but hey, it's Airfest, go big or go home, right?
On the J570 it sim'd to 14,000', 1200mph with an initial punch of 65 G's!
By comparison, the J270 would have been about 11,000', 900mph and only 25 G's.
Quite a difference.
Launch ready the rocket now totalled 1750g, the motor weighed more than the rocket!
So it got loaded onto pad 42 on Day 2 and when the countdown hit zero it lit immediately and leapt off the pad.
All looked good and straight until it was about a thousand feet up and it suddenly folded in half and then spun out of control as the motor burned out.
It looked like a shred as there were some pieces that looked like they departed, more about that later.
The main sections stayed together and cartwheeled down between two pop-up shelters behind the flight line.
Thankfully nobody was hurt and no vehicles were hit!
In one spot was most of the rocket, but the nosecone and the forward shock cord were missing.
I also realized later that the piston, most of the forward kevlar shock cord, the parachute and the JL altimeter were lost, those things and some chunks of nosecone skirt must have been the pieces that were spotted when things went awry.
Amazingly, my phone was still picking up the Featherweight and I tracked that to a spot out by the 50's pads, and the rest of the nosecone was found a few feet from that. The chute, shredded, was found another five hundred feet away in a different area. Never found the piston nor the JLA2.
The Quasar was also still alive. So really, it could have been much much worse.
Below is the rocket back at base, I've opened up the undamaged av-bay to power down the Quasar.
At that point I put the remains in the trailer and focused on other rockets for the rest of the weekend.
When I got home and started looking at things I decided that it was repairable and with some strengthening I could make another stab at a successful flight to 1000mph and at least 10K feet.
It really seems to be a case of too many G's in too lightweight of an airframe. It just couldn't hold up.
In retrospect maybe it was foolish to think a single layer of CF over thin wall cardboard could withstand that much kick, but you often learn more from failures than successes so..... c'est la vie.
Neither charge fired. What I think happened is that under stress it crumpled on one side of the tube and as the forward portion whipped to the side as the booster tried to pass itself the weight of the nosecone pulled it out of the tube, yanking the chute and JLA2 with it and at several hundred MPH the chute shredded and yanked on the eyebolt on the base of the cone breaking that before snapping the cord, the piston and JLA2 went somewhere and everything else just spun to the ground. (well I'm sure the piston and altimeter landed too, you know what I mean
)
First thing I did was cut off the damaged area.
Luckily I happened to have a spare section of carbon fibered BT-60 left over from the original construction, and it was the right length!
I attached the new section to the rest of the booster with that red coupler and TiteBond II.
But that was just the start.
Most of the booster is filled up with a 1080 case, but there was about 6-8 inches between the case and the shock cord mount and where the av-bay mates that is likely the weakest.
It is above all the thrust, but below most of the weight of the cone, electronics and recovery gear.
I decided to add another layer of something. I didn't have any more CF sleeving on hand but I did have some fiberglass sleeving that was quite a bit heavier.
Of course I prepped the surface to take hold of new resin.
It was white, but once it was wetted out with resin it would basically became transparent.
Here it is with the shrink wrap already on it.
After a day or so I peeled off the shrink wrap and the transition is pretty good. Not perfect, but it passes the ten foot test lol.
This really increased the unsquishability of the airframe, but to go a step further I also slid about six inches of coupler inside the forward end of the booster and epoxied that in place.
The attachment for the recovery line was in the part that had to be cut off so after the coupler had cured in place I made a new part.
Two layers of 3/16" aircraft plywood glued together, cut into a circle and fitted with a forged eye bolt.
I also put in vent holes but I don't actually plan on using motor eject.
The glue isn't dry yet but here's a peek inside.
In this version I seated the mount way deeper, before the rocket could have taken a 38/1320 case but now it is restricted to a 1080 case, so it can still take the J570 or J825.
In that above picture you can also see the internal coupler that was added for more strength.
I don't have a way to quantify how much sturdier this is now, but it has very little squish when squeezed now.
While that's drying I am printing a new nosecone to replace the one that was torn apart.
Again, shocked that the Featherweight wasn't destroyed when it was ripped out of there!
I also have made a new piston out of loose fitting blue coupler, 3/16" plywood, and sealed with CA.
So, the repairs are nearly complete, and I hope to find another J570 to try again!
I have a J270 but that's really not the same G load range at all and I want to see if my repairs were enough.
Another option if I can't source a J570 before MWP is to use an I500T.
It would push with about 40 G's, and go 10,000' and about 900mph.
More than one person has asked 'why don't you just buy 38mm fiberglass tubing for your airframe?'
Well, I do stuff the hard way, I guess.
-Kris
Over last winter I got the idea to make a rocket using Estes BT-60 tubes (Big Bertha diameter) that would be capable of breaking Mach 1 or more, and fly to at least ten thousand feet.
As far as looks I wanted something that resembled a flechette or an anti-armor kinetic penetrator and would be about the length of the Estes Vapor.
Around this time I also discovered that the inside diameter of a Estes BT-60 coupler is about the same as the outside of a 38mm case.
So I decided was building a minimum diameter 38mm project!
(Up til then I had been thinking 29mm in a minimally upgraded airframe.)
I started in RockSim, actually using the Vapor .rkt file for initial spitballing and found that some I and J motors would do it.
The sims also showed that the rocket would have to endure 40-75 G's depending on the motor (that G number decreased as the mass increased once I actually started plugging in real material and component weights, but still, I knew it was gonna rip!).
Therefore, some serious beefing up was going to be needed, while keeping the weight as low as reasonably possible.
I had previously used Soller Composites fiberglass sleeving to glass my L2 4" tubed project, so I turned to them again and this time chose the lightweight carbon fiber sleeving (the lightweight was not a good choice, as you'll see).
I'm going to skip over a lot of the initial build stuff, as this thread is actually supposed to be about what happened and what I'm doing about it.
What I ended up with is this:
Just over 47" tall, can take up to a 38/1320 case, has a 3D printed (PETG) av-bay containing an Eggtimer Quasar for dual deployment and GPS tracking.
The as mentioned Estes BT-60 tubes sleeved with one layer of the lightweight Soller carbon sleeving, is drogueless, has a piston in the forward section that protects and pushes out a lightweight 3 foot chute (Cd 2.2) and is topped with an aluminum tipped (for CG and Mach reasons) PETG nosecone that holds a Featherweight transmitter for backup GPS tracking. Oh, I also tucked a Jolly Logic Altimeter 2 in with the chute. for more data collection.
Fins are 3/16" G10 that are aggressively beveled and are JB Welded to the airframe.
With chute, electronics and batteries but without motor it has a mass of 850g, or under 1.9 pounds.
I dubbed it "Max-Q" for fairly obvious reasons.
Now I did launch it first on an H242, I didn't want to go nuts right off the bat.
On that it had a perfect flight, going about 480mph and reached about 4000 feet.
To my eye it looked undamaged upon recovery (whether it was structurally weakened from force or heat, I don't know).
Well the next week I headed to Airiest XXX in Kansas (from MN) and I had a 24 year old J570 for it.
I also brought a new J270 that I seriously considered using instead, but hey, it's Airfest, go big or go home, right?
On the J570 it sim'd to 14,000', 1200mph with an initial punch of 65 G's!
By comparison, the J270 would have been about 11,000', 900mph and only 25 G's.
Quite a difference.
Launch ready the rocket now totalled 1750g, the motor weighed more than the rocket!
So it got loaded onto pad 42 on Day 2 and when the countdown hit zero it lit immediately and leapt off the pad.
All looked good and straight until it was about a thousand feet up and it suddenly folded in half and then spun out of control as the motor burned out.
It looked like a shred as there were some pieces that looked like they departed, more about that later.
The main sections stayed together and cartwheeled down between two pop-up shelters behind the flight line.
Thankfully nobody was hurt and no vehicles were hit!
In one spot was most of the rocket, but the nosecone and the forward shock cord were missing.
I also realized later that the piston, most of the forward kevlar shock cord, the parachute and the JL altimeter were lost, those things and some chunks of nosecone skirt must have been the pieces that were spotted when things went awry.
Amazingly, my phone was still picking up the Featherweight and I tracked that to a spot out by the 50's pads, and the rest of the nosecone was found a few feet from that. The chute, shredded, was found another five hundred feet away in a different area. Never found the piston nor the JLA2.
The Quasar was also still alive. So really, it could have been much much worse.
Below is the rocket back at base, I've opened up the undamaged av-bay to power down the Quasar.
At that point I put the remains in the trailer and focused on other rockets for the rest of the weekend.
When I got home and started looking at things I decided that it was repairable and with some strengthening I could make another stab at a successful flight to 1000mph and at least 10K feet.
It really seems to be a case of too many G's in too lightweight of an airframe. It just couldn't hold up.
In retrospect maybe it was foolish to think a single layer of CF over thin wall cardboard could withstand that much kick, but you often learn more from failures than successes so..... c'est la vie.
Neither charge fired. What I think happened is that under stress it crumpled on one side of the tube and as the forward portion whipped to the side as the booster tried to pass itself the weight of the nosecone pulled it out of the tube, yanking the chute and JLA2 with it and at several hundred MPH the chute shredded and yanked on the eyebolt on the base of the cone breaking that before snapping the cord, the piston and JLA2 went somewhere and everything else just spun to the ground. (well I'm sure the piston and altimeter landed too, you know what I mean
)First thing I did was cut off the damaged area.
Luckily I happened to have a spare section of carbon fibered BT-60 left over from the original construction, and it was the right length!
I attached the new section to the rest of the booster with that red coupler and TiteBond II.
But that was just the start.
Most of the booster is filled up with a 1080 case, but there was about 6-8 inches between the case and the shock cord mount and where the av-bay mates that is likely the weakest.
It is above all the thrust, but below most of the weight of the cone, electronics and recovery gear.
I decided to add another layer of something. I didn't have any more CF sleeving on hand but I did have some fiberglass sleeving that was quite a bit heavier.
Of course I prepped the surface to take hold of new resin.
It was white, but once it was wetted out with resin it would basically became transparent.
Here it is with the shrink wrap already on it.
After a day or so I peeled off the shrink wrap and the transition is pretty good. Not perfect, but it passes the ten foot test lol.
This really increased the unsquishability of the airframe, but to go a step further I also slid about six inches of coupler inside the forward end of the booster and epoxied that in place.
The attachment for the recovery line was in the part that had to be cut off so after the coupler had cured in place I made a new part.
Two layers of 3/16" aircraft plywood glued together, cut into a circle and fitted with a forged eye bolt.
I also put in vent holes but I don't actually plan on using motor eject.
The glue isn't dry yet but here's a peek inside.
In this version I seated the mount way deeper, before the rocket could have taken a 38/1320 case but now it is restricted to a 1080 case, so it can still take the J570 or J825.
In that above picture you can also see the internal coupler that was added for more strength.
I don't have a way to quantify how much sturdier this is now, but it has very little squish when squeezed now.
While that's drying I am printing a new nosecone to replace the one that was torn apart.
Again, shocked that the Featherweight wasn't destroyed when it was ripped out of there!
I also have made a new piston out of loose fitting blue coupler, 3/16" plywood, and sealed with CA.
So, the repairs are nearly complete, and I hope to find another J570 to try again!
I have a J270 but that's really not the same G load range at all and I want to see if my repairs were enough.
Another option if I can't source a J570 before MWP is to use an I500T.
It would push with about 40 G's, and go 10,000' and about 900mph.
More than one person has asked 'why don't you just buy 38mm fiberglass tubing for your airframe?'
Well, I do stuff the hard way, I guess.
-Kris
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