H Motor World Record Build

flyguy614

Matt Dahle Photography
Joined
Apr 6, 2022
Messages
16
Reaction score
31
Hi all!

I'm new here, my name's Matt, and I recently broke the H motor world record. I thought it might be fun to make a quick post on the design of the rocket, and some future improvements to be made!

Build​

The rocket is a minimum diameter cardboard H13 build with carbon fins, a styrene nosecone, a 3d printed tailcone, and lots of 100lb kevlar line. I used an EasyMini on Apogee Redundant mode for charges, and a Featherweight Tracker for tracking. The chute is a 9" nylon chute.

A unique (in my opinion) part of the design is that the tailcone is permanent, and the fins are mounted to it. I wanted to put the fins as far back as possible to be able to make them as small as possible while still having a stable rocket. I thought it'd be a fun and clever design consideration to work around, and it ended up working out really well. The rocket uses an H13 with no thrust ring, and the motor gets loaded in the front. The shock cord is kevlar line, which is tied in a loop on the body-tube end. the loop goes around the H13 longitudinally, and ties/wraps once around the nozzle to make sure it doesn't slip up around the motor. The kevlar around the motor creates a good friction fit for the motor in the body tube, it takes a good 60lbs+ to get the motor in or out. With the maximum thrust peak on the H13 being about 10lbs, it's a light and reusable way to retain the motor for this purpose! It also is what holds the shock cord in place, no need for an eyebolt, bulkhead, epoxy, etc.

The avionics go in the nosecone, and are held in by yet another kevlar string. This kevlar string is epoxied into the top of the nosecone, and is tied around a 3D printed coupler that fits into the bottom of the nosecone. Once tied, you tie the other end of the parachute's shock cord to that loop, and voila! You've got a rocket.

Note: I ended up finding out later that I probably could've made my fins a little bit smaller than they were, but I think I'll keep them that size to keep the stability with it being such a small and dense rocket.

1666112414144.png

Pain​

This is the rocket after a paint job. This rocket in particular ended up weighing about 80g dry, about 290g wet. Unfortunately, I was putting the motor into this rocket the day before I left to Black Rock, and grabbed/pushed too hard in the wrong place. I ended up crumpling the rear end. I had some thick tube left over, and elected to rapidly build another bottom half using it instead of using thin tube. The thick tube rocket was not polished and not as aerodynamic as the first one. It was also a bit heavier, weighing in at 99g dry and 309g wet, but at least I had a rocket.

1666112230778.png

I thought it'd be funny to write on the rocket in crayon, and call it "unfinished cardboard tube."

Launch​

Anyway, I launched it from a tower I designed out at UROC's UR NUTS launch at Black Rock. Unfortunately, it went pretty sideways about 40ft AGL. It was positively stable, so it flew straight after that, but why it did that was a mystery. We thought it was weathercocking at first, but we found out later that it does that in zero wind as well. At maxV, it was going 917ft/s up, and 439ft/s sideways. Regardless of this, it still reached an apogee of 15,257' AGL. I certainly think it could reach 17k if it went reasonably straight up, but that's hard for a rocket like this.

We found out that it wasn't weathercocking when I launched it again a couple days later. In zero wind, it did the same exact thing but in a different direction. Relative to the rocket, it could've been the same direction, as I didn't pay much attention to what the orientation of it was when I put it in the tower. But when plotted out, their flight paths to apogee look almost identical, with the second flight not being as good as the first. The second flight ended up reaching an apogee of around 14,870 or so. Also worth noting that the second flight's landing seemed to be a bit harder, as some of the fillets' adhesion broke from the fins. This is probably partly due to me having rushed the fillets. Glad they worked out fine on the first launch, but definitely worth having some better fillets (amongst other fixes) next time.

Potential Improvements​

Some hopeful fixes for next time:
  • Longer tower
  • Better designed tower braces (may have interfered with the rocket's exit)
  • More stiff tower tiedowns (was paracord)
  • 3D printed Von Karman NoseCone (heavier, but shoulder should fit into the BT better, eliminating possible NC tilt)
  • Trapezoidal fin shape to reduce the chance of impact damage
  • Fins will have tabs that go into the tailcone for a "through the wall" type support and (hopefully) better fin alignment when used in conjunction with a fin jig.
  • And of course, the next one will be properly painted and polished for better aero.
I also intend to use the next iteration as a sustainer to go for the complex H and I world records. We'll see how that goes!

Thanks for reading!

1666115239072.png 1666115251262.png 1666115269442.png 1666115280342.png
 
Last edited:

waltr

Well-Known Member
Joined
Jul 17, 2021
Messages
1,197
Reaction score
701
Location
SE Pennsylvania
Wow, nice design and congrats on the record. Any video?
Too bad the first one got damaged when you loaded a motor.

Could it have been a fin fluttered or bent causing the path deviation?
 

flyguy614

Matt Dahle Photography
Joined
Apr 6, 2022
Messages
16
Reaction score
31
Wow, nice design and congrats on the record. Any video?
Too bad the first one got damaged when you loaded a motor.

Could it have been a fin fluttered or bent causing the path deviation?
Not sure, I feel like it's going too slow during that time. I'm wondering if there's some vibration in the conduit I'm using for the tower that causes the rails to contact the rocket in unexpected ways. That, or even just a fin misalignment.


View attachment Matt_Dahle_UR_Nuts_2022_H13_GoPro_launch1.mp4

This is the only video the site will let me upload for some reason.
 

Attachments

  • Matt_Dahle_UR_Nuts_2022_H13_GoPro_launch1.mp4
    47.9 MB

BDB

Absent Minded Professor
Joined
Aug 22, 2015
Messages
2,410
Reaction score
708
This is spectacular! Thanks for sharing.

I'm interested in the 3D printed tailcone. What material did you use, and how did you determine the optimal shape?
 

flyguy614

Matt Dahle Photography
Joined
Apr 6, 2022
Messages
16
Reaction score
31
This is spectacular! Thanks for sharing.

I'm interested in the 3D printed tailcone. What material did you use, and how did you determine the optimal shape?
I used PETG, and it did a pretty good job of not melting!

I messed around in OpenRocket for a good amount of time just messing with the measurements, and the profile is a tangent ogive just because it's easy.

But that's all in simulators, and real life sometimes gives you better information! When I got the rocket back, the tailcone had charring/soot about 2mm up on the bottom of the outside. This indicates to me that the flow is separating there, so the next iteration will have a tailcone that's truncated to exactly where that flow separated.
 

3stoogesrocketry

Well-Known Member
Joined
Feb 26, 2012
Messages
1,769
Reaction score
546
Not sure, I feel like it's going too slow during that time. I'm wondering if there's some vibration in the conduit I'm using for the tower that causes the rails to contact the rocket in unexpected ways. That, or even just a fin misalignment.


View attachment 542292

This is the only video the site will let me upload for some reason.


This almost looks like your motors ignition fault . The motor is a cored end burning design . If your ignitor is touching only one side of the core wall ( yes i know its only 3/8 inch deep or so ) the thrust will be slightly augmented till the core burns flat. Also being right at the nozzle , any miss alignment in thrust will do that .
 

flyguy614

Matt Dahle Photography
Joined
Apr 6, 2022
Messages
16
Reaction score
31
That's an interesting idea, definitely plausible. Any idea on how to mitigate that?
 

flyguy614

Matt Dahle Photography
Joined
Apr 6, 2022
Messages
16
Reaction score
31
Hotter igniter with a flat tip? Just speculating here. Nice flights!
Good thinking, the igniter that comes with the H13 is pretty tiny and miniscule. I wonder if it's just igniting grain in a small local area first. I wonder if using a bigger igniter would ignite more grain, faster, and give it a better kick out of the tower too?

I don't know if that's even how that works, I'm not very educated on that matter at all.
 

OverTheTop

Well-Known Member
TRF Supporter
Joined
Jul 9, 2007
Messages
8,010
Reaction score
6,307
Location
Melbourne Australia
I wonder if it might be tower too. The tower is relatively tall and skinny. There will be compression loads on the rods from the tie-down. Mr Bernoulli's principle says that a high velocity flow is low pressure, so maybe the tubes bow in as the rocket rises through them. Food for thought, as is the asymmetric thrust idea.

Congrats on the record too :cool: .
 

Sandy H.

Well-Known Member
TRF Supporter
Joined
Mar 20, 2009
Messages
2,059
Reaction score
1,455
Good thinking, the igniter that comes with the H13 is pretty tiny and miniscule. I wonder if it's just igniting grain in a small local area first. I wonder if using a bigger igniter would ignite more grain, faster, and give it a better kick out of the tower too?

I don't know if that's even how that works, I'm not very educated on that matter at all.

I'm not a competition expert for sure, but I've flown with the local club on a few competitions just to help fill out the roster. Anyway, one year we had a competition where I used a piston launcher (Estes B motor, I believe). I was amazed at the difference in altitude and speed it made compared to just launching from a tower.

I know 100% that launching an HPR for a world record is totally different than that, but I'm curious if using a piston launcher in the tower could help you get up to speed quicker? Not even sure what the limitations are for setting a record, honestly.

Very cool to launch something like that, I'm sure! Great job!

Sandy.
 

flyguy614

Matt Dahle Photography
Joined
Apr 6, 2022
Messages
16
Reaction score
31
I'm not a competition expert for sure, but I've flown with the local club on a few competitions just to help fill out the roster. Anyway, one year we had a competition where I used a piston launcher (Estes B motor, I believe). I was amazed at the difference in altitude and speed it made compared to just launching from a tower.

I know 100% that launching an HPR for a world record is totally different than that, but I'm curious if using a piston launcher in the tower could help you get up to speed quicker? Not even sure what the limitations are for setting a record, honestly.

Very cool to launch something like that, I'm sure! Great job!

Sandy.
Woah, I've never seen those! I'll have to look into that, thank you!
 

waltr

Well-Known Member
Joined
Jul 17, 2021
Messages
1,197
Reaction score
701
Location
SE Pennsylvania
The uneven end burn idea is interesting idea. A better igniter may help that.

In the video it looks like classic wind-cocking into the wind. A longer tower and ensuring minimum drag through the tower to get maximum acceleration.
A sim shows 20m/s (65f/s) off a 6 foot rail which should be plenty fast unless there was excess friction in the tower.
 

flyguy614

Matt Dahle Photography
Joined
Apr 6, 2022
Messages
16
Reaction score
31
The uneven end burn idea is interesting idea. A better igniter may help that.

In the video it looks like classic wind-cocking into the wind. A longer tower and ensuring minimum drag through the tower to get maximum acceleration.
A sim shows 20m/s (65f/s) off a 6 foot rail which should be plenty fast unless there was excess friction in the tower.

I'd normally agree, but the second day I launched looked identical and the wind was d-e-a-d dead. The rocket fell almost exactly straight down haha
 

JamesS

Well-Known Member
Joined
Dec 6, 2019
Messages
132
Reaction score
88
When I got the rocket back, the tailcone had charring/soot about 2mm up on the bottom of the outside. This indicates to me that the flow is separating there, so the next iteration will have a tailcone that's truncated to exactly where that flow separated.
I was reading recently about the Krushnik Effect and your comment reminded me a bit of it. I don't know if it actually applies to your build but maybe look into it when you consider the next iteration of your tailcone. You may be loosing thrust.

Awesome job though and thanks for sharing! Looking forward to your next version!
 

rcktnut

Well-Known Member
Joined
Oct 26, 2009
Messages
1,932
Reaction score
523
Location
Sheboygan WI
NICE FLIGHT!!
I'll vote for too slow out of the tower. The fins are pretty small. How long is the tower? At 1 second into the flight looks like the rocket doesn't have much altitude meaning your not getting the ft/sec. you need before stable flight.
 

flyguy614

Matt Dahle Photography
Joined
Apr 6, 2022
Messages
16
Reaction score
31
NICE FLIGHT!!
I'll vote for too slow out of the tower. The fins are pretty small. How long is the tower? At 1 second into the flight looks like the rocket doesn't have much altitude meaning your not getting the ft/sec. you need before stable flight.
Tower is 5ft tall, rocket has about 13% body length of stability. I  am going to make the tower longer, but I've seen other H13S builds leave shorter rails and go straight. My build is still the lightest one that I know of...

But I don't disagree with you necessarily, I'm probably going to extend the tower by at least a foot. Again, shotgun method for fixes lol
 

flyguy614

Matt Dahle Photography
Joined
Apr 6, 2022
Messages
16
Reaction score
31
I was reading recently about the Krushnik Effect and your comment reminded me a bit of it. I don't know if it actually applies to your build but maybe look into it when you consider the next iteration of your tailcone. You may be loosing thrust.

Awesome job though and thanks for sharing! Looking forward to your next version!
I think it does apply, and it's something that I'm curious/worried about. I didn't look into it TOO much though, but with some time to spare until my next attempt, I'll certainly be looking into it!
 

rcktnut

Well-Known Member
Joined
Oct 26, 2009
Messages
1,932
Reaction score
523
Location
Sheboygan WI
Go through the video a "click" at a time. Rocket starts moving at 15 sec. almost takes 1 sec. to clear the tower. At 17 sec. not much more than a few towers high. It looks the same looking at the longer range also. Good luck with next launch!
 

StreuB1

Well-Known Member
Joined
Aug 28, 2007
Messages
1,046
Reaction score
1,211
Location
Illinois
Wonderful flight and great design.

Longer tower, double the length, and tighter fitting to the body. Depending on your CP/CG, one little 'dink' to the rocket at it leaves can very easily cause a rotation. The faster it is going, the less time (dt) the 'dink' from the tower will act upon the rocket. Thus, cause any rotation, to be very slight overall. That weeble wobble looks like an oscillation from an external force acting upon the body and without enough forward velocity, it was able to rotate about its CG.
 

Collan Fraser

Member
Joined
Nov 4, 2018
Messages
18
Reaction score
22
Not sure, I feel like it's going too slow during that time. I'm wondering if there's some vibration in the conduit I'm using for the tower that causes the rails to contact the rocket in unexpected ways. That, or even just a fin misalignment.


View attachment 542292

This is the only video the site will let me upload for some reason.
looks like changing cg as the propellant burns and the weight changes, short rockets do this
 

SolarYellow

Well-Known Member
TRF Supporter
Joined
Aug 6, 2022
Messages
721
Reaction score
513
Location
First country to put a man on the moon.
Especially as you lengthen the tower, maybe add a couple of rings to hold the rods in position w.r.t. each other. Will make the whole thing stiffer, and keep any one of them from vibrating as much due to a little ping as the rocket bumps it.

Also, on stability, check the detailed, step-by-step output of whatever sim software you're running. I have had rockets that said they were GTG on the main design screen, but when you look at the step-by-step output, they come off the rod well below 1 caliber. Especially a risk if you're playing with optimum weight to maximize apogee, and additionally risky with a slow-burn motor. As others have said, add in some bumping around in the tower, and that could explain it.

It seems logical that the end-burn motor could demonstrate the characteristic of gaining stability as it burns even more than a more typical motor design.
 
Last edited:

teepot

Well-Known Member
TRF Supporter
Joined
Dec 7, 2019
Messages
3,391
Reaction score
3,667
Location
Pahrump, Nevada
I know the gentleman that won the Hamster Dance. He enlarged the motor core a little and got better velocity off the rail. At least I think he used a rail. Might have been a tower though. He said he used a 1/8 drill bit to make the bottom bit larger. He also used a H13.
 
Last edited:

James Kobel

Well-Known Member
Joined
Nov 8, 2021
Messages
49
Reaction score
35
Tower is 5ft tall, rocket has about 13% body length of stability. I  am going to make the tower longer, but I've seen other H13S builds leave shorter rails and go straight. My build is still the lightest one that I know of...

But I don't disagree with you necessarily, I'm probably going to extend the tower by at least a foot. Again, shotgun method for fixes lol
I don’t know what the tower was made of, but I’ve used aluminum pipe for a tower and has turned out really great and stiff. Also, maybe Kevlar would be a good material to use to tie down the tower?
 

AlexBruccoleri

Well-Known Member
TRF Supporter
Joined
May 11, 2021
Messages
468
Reaction score
229
This is fantastic. One question. What do you mean by trapezoidal fins? Your shape actually looks fairly optimal in that it pushes the CP back with as little area as possible.

Cheers, Alex
 
Top