the "Priority Express"

[bjphoenix]

Somebody gave me some old E12 that likely had not been stored properly. Rather than build an expensive rocket to use them in, I am building a very cheap rocket. It will be using all found materials, the only purchased product I might use is a trash bag to make a parachute. In the photo you can see the main airframe which is a cut down Priority mail / Express mail triangular tube, a motor tube rolled from some brown paper using an empty E12 casing as a mandrel, a piece of D12 casing for a thrust block, a piece of cardboard cut to make a fin template, and some pieces from a cardboard cereal box cut and formed to make a pointed pyramid nose cone. I have to scrounge up another piece of cardboard to make some bulkheads and fins out of. I'm planning on building it with fins extended to the engine tube.
I did some crude modeling in Open Rocket to determine a ballpark size for the main tube and the fins. After I get more constructed I can take some weights to check stability margin. (I'm not sure if you can model a triangular airframe in OR so I modeled it with a round tube of the same cross section area, my triangle size is about equivalent to a 3" diameter tube.) I have a couple of E12-4 and E12-6. I think the size will be about right for an E12-4, E12-6 will deploy a bit lower but hopefully not too low.

 

[teepot]

29mm mount. Flies good. I use a G78-4. Nose cone is 1/8th ply. That's most of the nose weight.

 

[bjphoenix]

29mm mount. Flies good. I use a G78-4. Nose cone is 1/8th ply. That's most of the nose weight.View attachment 640868

That looks appropriate for a G. I started with a full size tube about like that, each side about 6" or a bit more. I cut the sides down to 4" each and the length to 27". My nose cone is about 5" long. I was working on the fin can today, actually the motor mount tube and bulkheads since I haven't cut the fins yet. Are your fins just one layer of cardboard or more than that? I was thinking of laminating 2 layers of cardboard together but I have to be a little bit concerned about weight.
Another thing- my fins will come out at the 3 corners. You can see one of the fin slots in the photo.

 

[BABAR]

I love cross sectional polygonal rocket designs.

Nose pyramids rule!

You may want to swing test this one, size of those fins is borderline by my MindSim, FWIW.

 

[teepot]

That looks appropriate for a G. I started with a full size tube about like that, each side about 6" or a bit more. I cut the sides down to 4" each and the length to 27". My nose cone is about 5" long. I was working on the fin can today, actually the motor mount tube and bulkheads since I haven't cut the fins yet. Are your fins just one layer of cardboard or more than that? I was thinking of laminating 2 layers of cardboard together but I have to be a little bit concerned about weight.
Another thing- my fins will come out at the 3 corners. You can see one of the fin slots in the photo.

I put a 2.6" BT up the middle. The fins are 1/8th" ply. I just looked at it. The nose cone is 1/4" ply not 1/8th". Nose cone has three sides and a bottom. I used a coupler to attach the nose cone to it. It's 36" long and weighs 38 ounces. I flew it first at home to make sure it worked before I flew it in public. It sure got a lot of attention when I took it to the LCO table. The LCO is the RSO. We are a real laid back group. I have taken other oddrocs to fly at our launches. He looked at it and told me what rod to use. It went straight up, chute came out. He looked at me and said, how did you do that? It makes it to about 600' on a G78-4. I call mine Priority Mail.

 

[bjphoenix]

I love cross sectional polygonal rocket designs.

Nose pyramids rule!

You may want to swing test this one, size of those fins is borderline by my MindSim, FWIW.

I haven't cut the fins yet, I can make them bigger. The proportions came from OpenRocket, the 4"x4"x4" triangle has the same area as a 3" diameter circle so I simmed it with 3" diameter tube. I don't know how well one equates to the other WRT stability calculations. Once I cut the initial fins I can get an overall weight and CG to compare with my sim file.

 

[BABAR]

I haven't cut the fins yet, I can make them bigger. The proportions came from OpenRocket, the 4"x4"x4" triangle has the same area as a 3" diameter circle so I simmed it with 3" diameter tube. I don't know how well one equates to the other WRT stability calculations. Once I cut the initial fins I can get an overall weight and CG to compare with my sim file.

If you are feeling adventurous, you can attach the fins parallel to the side, all either clockwise or anticlockwise.

Orientation is like the Gyskelion



You can either surface mount them or cut a slot. Since they will be glued to either the external wall (or internal wall if you do a slot) alignment should automatically be perfect.

The arrangement is what I call asymmetrically symetric, NOT a mirror image but balanced in such a way that it should NOT induce rotation, pitch, or yaw.

Putting the fins here places them further from the centerline, so the fins are more efficient.

It also accentuates the OddRoc vibe, but that’s a matter of personal preference.

 

[bjphoenix]

If you are feeling adventurous, you can attach the fins parallel to the side, all either clockwise or anticlockwise.

I originally thought about that. I've decided to go ahead with TTW fins.

 

[lr64]

Are you going to keep the original markings? You could paint the fins and nose cone to match. You could tell spectators that you were from the USPS and that this was for the new, discount "priority mail" program.
---------
Oddroc people with small fields could go for the cremated remains box. Many of the priority mail boxes are free
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I'll bet you could make the whole rocket, including fins, motor tube, centering triangle or square, etc. out of priority mail stuff. If you felt bad about taking advantage, you could buy some interesting stamps and never use them. Maybe some of this rocket-related stamp:
https://store.usps.com/store/product/buy-stamps/osiris-rex-stamps-S_484204

 

[bjphoenix]

Are you going to keep the original markings? You could paint the fins and nose cone to match. You could tell spectators that you were from the USPS and that this was for the new, discount "priority mail" program.

I'm keeping the original markings on the main body. The nose cone is mostly yellow, I want to keep it like that but I may decide it's just too awful. I don't have any spare cardboard yet for the fins. Depending on what cardboard I get I will have to decide whether to paint the fins.

 

[teepot]

My Priority Mail triangle came from Sticker Shock. Still has the shipping label on it. My fins are TTW.

 

[lr64]

TTW? I don't know every TLA yet.

 

[Art Upton]

Thru The Wall

 

[bjphoenix]

TTW? I don't know every TLA yet.

I know of 2 ways that through-the-wall fins are done, either way you cut slots in the body tube for the fins which are made longer than if they were to be surface mounted. One way the fin sticks through the slot and you can add glue fillets on the inside and on the outside of the tube. The other way, the way I always do it, is the fin root is made longer and extends through the slot in the outer tube and glues to the motor mount tube. There are multiple ways to actually implement this but for this build I put the fins, bulkheads and motor tube together as an assembly and then put the whole thing into the end of the main body using slots that extend all the way to the end of the tube. In the first photo you can see the entire assembly put together, and you can see the slots in the corners of the triangular body. In the second photo you can see the assembly partially slid into the body. It doesn't quite fit perfectly, I need to do some trimming. In the last photo you can see an assembly of everything. It should be ready to fly Sunday if the weather cooperates.

 

[lr64]

Looks good. If it was me, I might apply some epoxy to the surfaces of the fins, inside and outside the main body. I'd let it soak in for a few minutes and then scrape off what was left. Preferably an epoxy that dries fairly hard. For all I know, you're already doing something like that.

 

[bjphoenix]

Making more progress- now that I have all of the major pieces done I can weigh it and check CG location. And there are issues. As it sits with motor it weighs almost 12 ounces. When I dug out my old motors for weighing I found they are E9 and not E12. My earlier sim was to get the size where I thought it would work WRT aerodynamic drag and I wasn't concerned about weight, now it turns out to be too heavy for a single E9. I went into weight reduction mode by cutting off about 8" of tube and cutting a few other holes where I thought I could get away with it. My plan is to cover the holes with printer paper to maintain aerodynamic properties. If I can believe the sim using a round tube I'll have to add a bit of nose weight to maintain stability even though it doesn't need more weight, maybe 1/2 ounce will be enough. After massive cutting the weight with motor is just under 9 ounce. The sim shows optimum delay at 3.9 sec. and around 500-600' altitude. If I had planned better with my sim I would have known the weight problem and I could have scaled the tube down a little bit more. I'm putting fillets on the fins now, still have to add shock cord, launch lug and paper over the holes in preparation for a Sunday launch.

 

[modeltrains]

holes in preparation for a Sunday launch.

Holy, Sunday, that fits.

 

[lakeroadster]

And if it crashes and burns and the investment is lost.... ..... it's the United States Postal Service. (did you buy insurance... lol)

You should be able to do an all up swing test to determine nose weight.... and you may also be able to leave the openings as is and not cover them up.

Plenty of room to add some E or D motor boosters times 3. Why fly 1 BP motor when you could fly 4.

 

[BABAR]

Making more progress- now that I have all of the major pieces done I can weigh it and check CG location. And there are issues. As it sits with motor it weighs almost 12 ounces. When I dug out my old motors for weighing I found they are E9 and not E12. My earlier sim was to get the size where I thought it would work WRT aerodynamic drag and I wasn't concerned about weight, now it turns out to be too heavy for a single E9. I went into weight reduction mode by cutting off about 8" of tube and cutting a few other holes where I thought I could get away with it. My plan is to cover the holes with printer paper to maintain aerodynamic properties. If I can believe the sim using a round tube I'll have to add a bit of nose weight to maintain stability even though it doesn't need more weight, maybe 1/2 ounce will be enough. After massive cutting the weight with motor is just under 9 ounce. The sim shows optimum delay at 3.9 sec. and around 500-600' altitude. If I had planned better with my sim I would have known the weight problem and I could have scaled the tube down a little bit more. I'm putting fillets on the fins now, still have to add shock cord, launch lug and paper over the holes in preparation for a Sunday launch.View attachment 641467

It may be a wash, but paper pyramidal nose cones allow the following trick.

I make mine out of cardstock, for big ones I don’t know if the word is poster board (it’s not like foam board or depron) . So they weight almost nothing.

So here’s the trick.

You can make the really long, with very little weight penalty. NOW you can put any nose weight in the tip of the nose cone, and take advantage of the added length. In this way, a small amount of nose weight can have a strongly favorable effect on CG.

There is also an aesthetic factor. IMO long pyramid nose cones LOOK really cool on rockets with polygonal cross sections. I suspect the aerodynamic effect is neutral. Not sure. Maybe @neil_w can chime in on sims for cylindrical rockets. Specifically if you lengthen a nose cone with either no change in nose cone mass, or say for a thin walled plastic nose cone a corresponding increase in nose cone mass, how does it affect stability of rocket. Does the CG change of the mod exceed the CP change?

My mind sim for your particular rocket is that you likely move the CG forward more than CP with a longer nose cone with an equal or potentially lower rocket mass.

Of course, to make this work you are gonna need to eat a lot of Cheerios.

 

[neil_w]

Specifically if you lengthen a nose cone with either no change in nose cone mass, or say for a thin walled plastic nose cone a corresponding increase in nose cone mass, how does it affect stability of rocket. Does the CG change of the mod exceed the CP change?

I don't know, but it would be easy enough to fire up OpenRocket and test it out.

 

[bjphoenix]

It flew twice today. Last night I put printer paper over the lightening holes. I was concerned about the strength of the paper to resist ejection charge but that didn't seem to be a problem although an ember from the first ejection charge burned a 1/4" diameter hole through the paper. I launched using a 6' long 1/4" diameter rod and the rocket flew straight even though we had a good amount of wind. 4 sec. delay worked well. The rocket achieved its mission of using up the 4 old motors that I was given, although only one motor actually launched the rocket. The other 3 motors blew out their nozzles on ignition and the rocket stayed on the pad. Since I only got one good launch I put a new E12-4 in it and launched again. I couldn't tell that it flew any differently with the E12 but it didn't eject the parachute completely. The rocket was lost in high grass 300 yards from the pad even though I made many passes through there looking for it along with a couple of other people. Not having the parachute out to be visible probably didn't help either. The photo is of the launch with the E9.

 

[BABAR]

. The rocket was lost in high grass 300 yards from the pad .View attachment 641846

Should have gotten a tracking number.

Congrats on a successful creative design!

 

[jqavins]

The other 3 motors blew out their nozzles on ignition and the rocket stayed on the pad.

That's been my problem with old E9s. People talk about CATOs, but I've never had one of those, and I've had several nozzles blow out. I've learned what that sounds like so I was able to tell another rocketeer what went wrong with his even though my back was turned.

 

[lakeroadster]

That's been my problem with old E9s. People talk about CATOs, but I've never had one of those, and I've had several nozzles blow out. I've learned what that sounds like so I was able to tell another rocketeer what went wrong with his even though my back was turned.

A nozzle blowing out is a CATO... ​

 

[jqavins]

Not every launch failure is a CATO. In a nozzle blow-out, the rocket just sits there while the powder burns, no harm no fouls. Not catastrophic. Not like this:

 

[neil_w]

Not every launch failure is a CATO. In a nozzle blow-out, the rocket just sits there while the powder burns, no harm no fouls.

Hmm, I disagree here. Although I see where you’re coming from, I would still consider a “harmless” nozzle blowout to be a CATO, and reason to file a MESS report. Interested to hear what others have to say about this.

 

[lakeroadster]

Not every launch failure is a CATO. In a nozzle blow-out, the rocket just sits there while the powder burns, no harm no fouls. Not catastrophic. Not like this:
View attachment 642971

Catastrophic At Take Off. The nozzle separating from the paper tube qualifies as "catastrophic" ​

 

[neil_w]

From https://stason.org/TULARC/recreatio...TO-Is-it-CATO-pronounced-KAY-TO-or-CAT-O.html


Disclaimer: I don't know much about this FAQ.

 

[jqavins]

I acknowledge that there is ample room for interpretation here. That said, I nevertheless take issue with the definition above, for two reasons.

1. The first and second sentences contradict each other in the case of a nozzle blow-out. In my experience, both first and second hand, after the nozzle is blown, the propellant burns slower than planned, by quite a lot. Which should be expected, assuming the propellant's burn rate exponent is positive.
2. I reject the final sentence, that an ejection failure is also a form of CATO, since that happens long after take-off.

All of these things certainly merit MESS reports.

I can't find a reference, but I have long "known" that the term has been around referring to instances of unplanned rapid (and usually pyrotechnic) disassembly, dating back to many of these guys; events on or barely off the pad:

 

[BABAR]

darn, Neil beat me to the same quote (although from different source.). Interestingly Wikipedia has a slightly different interpretation which is however NOT sourced (so much for the Internet in general or Wikipedia specifically being the repository of all knowledge.)

A PRACTICAL definition may be: Motor failure that would justify a MESS report and likely spur manufacturer to replace the motor and possibly the rocket.

For black powder and single use composite motors I would say that a failure of the motor walls would qualify, so
1. the casing
2. Significant portion of nozzle
3. Premature failure of forward wall (basically a near instantaneous combustion of the whole propellant mass at ignition that blows out the front, usually either on the pad or a few feet above it.

I don’t fly reloads, so don’t know if this applies to failures of forward and aft closures.

Interesting that while the origin of the specific initials C. A. T. O. is debated, the assumption that it refers to “CATASTROPHE” seems universally accepted. If so, seems actually to frequently be wrong.

True, most if not all CATOs result in failed (or at least far from nominal) flights.

True that SOME CATOs destroy or nearly destroy the rockets.

But seems like many if not most CATOs do little or no damage to the rocket. Not that I am recommending them, but some are darn entertaining (I am thinking of a certain A10-0 Twin Factor flight with @kuririn snd @Ronz Rocketz a year or so back with three or four CATOs. Retrospectively might not have been the greatest idea to CHAD stage 4 motors to a two stage rocket, but we didn’t expect the majority of motors to CATO. Anyway, no rocket or property damage, no physical injury although may have stirred up my Post Iraq deployment PTSD for a moment.)

Anyway, I’m not convinced that all CATOs truly qualify with anyone’s definition of Catastrophe, despite that seeming to be the one universally accepted origin of the word.

Since the word is used so much and isn’t going away, I’d describe it as a post ignition containment failure of one or more motor walls (casing, nozzle, or if well prior to normal burning of delay, forward wall). Damages range from injury to reputation of the motor vendor to destruction of rocket, personal injury, and/or property damage.