Quantcast

Fly-Away Rail Guides (54mm) - What Did I Do Wrong?

The Rocketry Forum

Help Support The Rocketry Forum:

RocketPro

Well-Known Member
Joined
Jun 21, 2014
Messages
62
Reaction score
12
This weekend at ROC, I used the 54mm Fly-away rail guides for the first time. It did not go well...

My rocket is a 54mm, Madcow Tomach. This rocket has flown before with rail buttons. I have both diameter sets of 54 mm rail guides, the smaller one would now even "close" enough to to get the rocket onto the rail. The larger diameter one was a loose fit. Not sloppy, but the rocket would easily slide inside of the guide. I used one of the supplied rubber bands per the instructions. In a ground test, it slid nicely and popped right off.

This weekend I loaded it up with a AT K545 (DMS) for a test flight of some recovery electronics and the guide. The guide slid down the rail nicely (good job by ROC of keeping their rails clean!). The rocket was sitting on the stop at the bottom of the rail and I positioned the guide right on top of the fins (touching).

At ignition, the rocket appeared to start up the rail but jammed. It then carried the 50lb pad up into the air about 20 feet and at a significant angle before the whole shebang crashed into the playa. At this point the buttons broke off of the guide and the rocket, still under some thrust careened across the playa for about 100 yds. After the buttons broke off, the guide actually opened up, and both it and the rubber band were intact and in a normal post-flight condition. The buttons were still on the rail, but could be easily slid up and down. A post-mordem of the buttons show that there was considerable loss of nylon (nylon "strings" on the rail).

My assessment is that the fins on the Tomach, which have a shallow sweep angle, pried open the guide creating the jam on the buttons. The lack of friction between the guide and the airframe just made this bad enough to jam the buttons. Does this sound right?

Don't mis-interpret...I don't think that the guide design is necessarily at fault. It is certainly strong enough to lift a 50 lb pad off the ground! I just want to not make any mistake that I made again!

Thanks for any feedback.
 

cerving

Owner, Eggtimer Rocketry
TRF Sponsor
TRF Supporter
Joined
Feb 3, 2012
Messages
3,977
Reaction score
1,222
I was concerned about that happening when I used one with my 38 Special and a Mongoose 29 (I put a 29mm-38mm cardboard motor adapter slit in half to make it fit). Had four flights no issues with it, but they weren't on a K545 either. The Mongoose 29 went on an I205, so the acceleration was pretty significant.
 

fyrwrxz

latest photo
Joined
Jun 6, 2011
Messages
6,575
Reaction score
45
Back in the day when you had to make your own fly away guides, I used that expanded rubber pad you put in tool box drawers or use as a kitchen shelf liner. Super grippy and you can trim a significant amount off to adjust/shim with. 3m spray or contact glue works. Most dollar stores have it with the kitchen goods. HF also carries it.
 

mpitfield

Moderator
Staff member
TRF Lifetime Supporter
Global Mod
Joined
Jul 7, 2013
Messages
4,900
Reaction score
430
Location
Toronto, Ontario
I was lucky enough to purchase my 54mm fly-away-rail-guide from Bill, the manufacturer, at NYPOWER in May and he personally set them up on my 54mm Tomach. One thing Bill mentioned when he set them up was to make sure that the fin was not directly lined up with the hing part of the guide, but off to the side. I launched it twice at that launch and had no issues at all following those guidelines. Not that 2 launches constitutes a big enough sampling to be conclusive, but that part to take away is that the manufacturer felt it important not to line up the fins with the hinge, so you may be onto something with your postmortem.

I could be wrong but I believe he may of also recommended that I use 2 bands as well as to make sure that I open and close the guide a couple of times to make sure that the bands naturally move to the correct location on the hinge. Performing his setup procedure I tested the resistance on the rail both vertically in the slot and the resistance the bands would naturally have on forcing the rail apart, and in both cases it was very minimal. He also recommended that we do a dry run, so while the rail was in the near horizontal position, we slid the rocket all the way down then simulated it launching slowly to see if there was any binding and the guide just popped off at the top of the rail.

Not sure if this procedure differed from yours or would of had any effect but this was what Bill and I did out at the pad.

Lifted the pad, wow!
 

wfcook

Mayhem Rocketry, LLC
Joined
Nov 15, 2013
Messages
1,030
Reaction score
6
This weekend at ROC, I used the 54mm Fly-away rail guides for the first time. It did not go well...

My rocket is a 54mm, Madcow Tomach. This rocket has flown before with rail buttons. I have both diameter sets of 54 mm rail guides, the smaller one would now even "close" enough to to get the rocket onto the rail. The larger diameter one was a loose fit. Not sloppy, but the rocket would easily slide inside of the guide. I used one of the supplied rubber bands per the instructions. In a ground test, it slid nicely and popped right off.

This weekend I loaded it up with a AT K545 (DMS) for a test flight of some recovery electronics and the guide. The guide slid down the rail nicely (good job by ROC of keeping their rails clean!). The rocket was sitting on the stop at the bottom of the rail and I positioned the guide right on top of the fins (touching).

At ignition, the rocket appeared to start up the rail but jammed. It then carried the 50lb pad up into the air about 20 feet and at a significant angle before the whole shebang crashed into the playa. At this point the buttons broke off of the guide and the rocket, still under some thrust careened across the playa for about 100 yds. After the buttons broke off, the guide actually opened up, and both it and the rubber band were intact and in a normal post-flight condition. The buttons were still on the rail, but could be easily slid up and down. A post-mordem of the buttons show that there was considerable loss of nylon (nylon "strings" on the rail).

My assessment is that the fins on the Tomach, which have a shallow sweep angle, pried open the guide creating the jam on the buttons. The lack of friction between the guide and the airframe just made this bad enough to jam the buttons. Does this sound right?

Don't mis-interpret...I don't think that the guide design is necessarily at fault. It is certainly strong enough to lift a 50 lb pad off the ground! I just want to not make any mistake that I made again!

Thanks for any feedback.
Holy #$%*&!

This is definitely a first. Let me consult with a couple of my beta testers on this one. I will of course happily replace the guides but I want to try to figure out why this happened. Even under a LOT of torque trying to open the the guides they should still roll right up the rail because the buttons are designed to spin, and should not jam.

Bill _/)_
 

NateLowrie

Well-Known Member
Joined
Jun 28, 2016
Messages
667
Reaction score
4
This weekend at ROC, I used the 54mm Fly-away rail guides for the first time. It did not go well...

My rocket is a 54mm, Madcow Tomach. This rocket has flown before with rail buttons. I have both diameter sets of 54 mm rail guides, the smaller one would now even "close" enough to to get the rocket onto the rail. The larger diameter one was a loose fit. Not sloppy, but the rocket would easily slide inside of the guide. I used one of the supplied rubber bands per the instructions. In a ground test, it slid nicely and popped right off.

This weekend I loaded it up with a AT K545 (DMS) for a test flight of some recovery electronics and the guide. The guide slid down the rail nicely (good job by ROC of keeping their rails clean!). The rocket was sitting on the stop at the bottom of the rail and I positioned the guide right on top of the fins (touching).

At ignition, the rocket appeared to start up the rail but jammed. It then carried the 50lb pad up into the air about 20 feet and at a significant angle before the whole shebang crashed into the playa. At this point the buttons broke off of the guide and the rocket, still under some thrust careened across the playa for about 100 yds. After the buttons broke off, the guide actually opened up, and both it and the rubber band were intact and in a normal post-flight condition. The buttons were still on the rail, but could be easily slid up and down. A post-mordem of the buttons show that there was considerable loss of nylon (nylon "strings" on the rail).

My assessment is that the fins on the Tomach, which have a shallow sweep angle, pried open the guide creating the jam on the buttons. The lack of friction between the guide and the airframe just made this bad enough to jam the buttons. Does this sound right?

Don't mis-interpret...I don't think that the guide design is necessarily at fault. It is certainly strong enough to lift a 50 lb pad off the ground! I just want to not make any mistake that I made again!

Thanks for any feedback.
Do you have video or pics of the launch, setup, or post-mortem? I would be helpful for root failure identification.
 

wfcook

Mayhem Rocketry, LLC
Joined
Nov 15, 2013
Messages
1,030
Reaction score
6
A couple of boilerplate questions:

(1) Did the rocket have any other buttons or protrusions on it
(2) Was it a one-piece rail or a two-piece rail
(3) Is there any video?
 

RocketPro

Well-Known Member
Joined
Jun 21, 2014
Messages
62
Reaction score
12
I will check the club to see if there's any video...I don't have any.

This a minimum diameter rocket. Protrusions:
1) Aeropack retainer at the aft end of about 0.0625", and
2) a set of low-profile pan-head screws at the upper joint. The screw heads protrude less than 0.080".
Note that the rocket slid onto the rail easily as the amount of offset from the guide created a clearance for the retainer. I noticed this because on my previous flight with regular rail buttons, I had to add a spacer to the buttons to clear the retainer. I was happy that I didn't have to add any spacers to clear it.

The rail is a one-piece extruded piece of aluminum (1010-style), six feet.

I'll provide some photos of the pieces when I get home tonight.
 

RocketPro

Well-Known Member
Joined
Jun 21, 2014
Messages
62
Reaction score
12
Bill...
While I appreciate the offer, you do not need to replace the guides...this is a learning process for everyone. It's most probably a user error of some sort so even if I'm the first to do something that we discover is something to not do...the knowledge will help others in some way.

I can send you the parts if you'd like to have them for analysis (my treat). I'm always trying to help out our creative vendors and manufacturers because it's you folks that advance the hobby and I get the fruits of that! Send me an address via regular email (allen@alumni.duke.edu) and I'll box them up for you.
 

manixFan

Not a rocket scientist
Joined
Feb 15, 2009
Messages
1,908
Reaction score
881
Location
TX
Rocket Pro,

Are you saying that the rocket was a slip fit inside the guide? I've been testing my guides for some very high performance flights at BALLS. One of the things that I found that seemed to be a possibility is that if there is not a positive fit (grip) between the guide and the rocket, the rocket may actually 'fly into' the guide. In my test case the tip-to-tip fiberglassing extended slightly ahead of the fins which caused a tapering increase in thickness as the tube approached the fins. When I tested the combo on a rail I found that if there was any kind of bind in the rail, the rocket would slide up into the guide and that extra body tube thickness forced the guide open a bit which caused the rail buttons to bind on the rail, which then allowed the rocket to slip further into the guide spreading it further open and binding the guides even more. My take-away is that for that rocket and guide combo there needs to be a non-slip fit between the guide and rocket to prevent what I described from happening.

This was just me testing the guide in my garage with a 6 foot length of rail so I don't know what would happen in the field. But it happened the very first time I tried it with that particular rocket. So it seems to me there should be a non-slip fit between the guide and the rocket. I am testing a variety of techniques to provide a positive grip between the guide and rocket.

Just my thoughts on the subject,


Tony
 

RocketPro

Well-Known Member
Joined
Jun 21, 2014
Messages
62
Reaction score
12
Tony
Yes, it was a slip fit. You have described what I think is happening...but I don't have the experience to be definite. Bill is looking into it to see if there's a lesson for us all, but it does seem to be a good idea to make sure that the guide is snug to the rocket.
Allen
 

RocketPro

Well-Known Member
Joined
Jun 21, 2014
Messages
62
Reaction score
12
One other item...it was 100+ out there when I launched.
 

manixFan

Not a rocket scientist
Joined
Feb 15, 2009
Messages
1,908
Reaction score
881
Location
TX
Tony
Yes, it was a slip fit. You have described what I think is happening...but I don't have the experience to be definite. Bill is looking into it to see if there's a lesson for us all, but it does seem to be a good idea to make sure that the guide is snug to the rocket.
Allen
I should have said in my first post that I agreed with your assessment based on my testing. I was really wanting to give you another data point to help with your analysis.

One of the rockets I am using with the guides with is a Rocketry Warehouse carbon fiber 54mm Mongoose. It does have very swept fins that may cause the same kind of issue that you had. I have a lot of room between my guide and the rocket so my plan is to use rubber bands on the guide to fill the space. If figure that the rubber bands will provide very good grip between the guide and the rocket. For the 3" rocket I had to sand the interior of the guide a bit for clearance so I am thinking of a light coat of high-temp gasket seal RTV on the interior of the guide to provide a non-slip surface. I am testing that this week.

Thank you for your report, it will certainly help me make sure I don't run into the same issues and may help Bill pass along some suggestions to other users as well.

For what it's worth I've seen a couple of other instances where a rocket using regular rail guides bound on the rail. One carried the rail into the air and actually had a nearly nominal flight. The other got about halfway up and just stuck there. So it's not a phenomenon unique to the fly-away guides. But still good to figure out what we can do to prevent it from happening again.


Tony
 
Top