Torn Between Scylla and Charybdis

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mannyskid

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I want to start off by saying that my first year at college has been going decently well so far and I think I can start thinking seriously about this project and how I am going to go about it.

I am planning on building a 75mm minimum diameter rocket to fly at Black Rock sometime next summer, most likely at Aeronaut in August. I have done 75 mm MD successfully in the past before but not like this. The main goal of this project is that I want to make an attempt at breaking the Tripoli commercial M altitude record with a CTI 9977-M2245 Imax. This is the end goal, and there will be a few steps along the way of accomplishing that goal:

The first being that I have to work out a recovery system that I want to use and am comfortable with. I have tried tethers, line cutters and all that in the past. The main issue that I have with those types of systems is that my payload sections are always cluttered with wires and shock cord tangled in a ball by the time I'm done. That's why I am going to be building two rockets for this project. The first rocket is going to be very average hobby grade construction (FW fiberglass and west systems). I want to fly this rocket a few times to allow me to figure out how I want to work the recovery system. I may go with a line cutter, or I may go with a short main parachute bay; that depends of the results of the first few flights. I would also like to fly this rocket to a decently high altitude, preferably above 25,000'. My current plan at this time is to fly it on a CTI M2250 at Kloudburst. I'm not too concerned with this flight as I have done with flight combination with lesser construction methods and kept the vehicle together.

The second being that I have to keep this rocket together at speeds in excess of M3. This is the spot that I have had issue with in the past. Some of you may recall the two N motor rockets that I flew earlier this year that both shredded.

https://www.rocketryforum.com/showt...er-rocket-N3301-at-Kloudburst&highlight=N3301
https://www.rocketryforum.com/showt...osition-98mm-Minimum-Diameter&highlight=N3301

A major issue that was brought up was that the composite materials that I was using were not up to the task. I will have to admit, both of these rockets were built using very average hobby rocket techniques. That is going to change with this rocket. I want to use the best composite materials that I can get my hands on. Vacuum bagged carbon tubes using Aeropoxy, Cotronics Duralco 4461 for tip to tip, thick carbon plate fins (3/16" or 1/4"), and an improved nose cone. A major issue that has also been brought up is dynamic stability at high mach. From what I have both read and seen in the real world, it seems as though a low aspect ratio conical nose cone will be the best at high mach. There is one thing that I am confused on, why is that? Somebody correct me if I'm wrong, but Center of Pressure moves forward because of increased drag on the nose cone compared to the fins at high mach, so why wouldn't a high aspect ratio cone work better? This is an issue that I am going to look into. When I get back to campus, I am going to go straight to the library and see if I can find an answer. There are plenty of books on aerodynamics, many of which were written by Theodore Von Karman. If anyone has any insight on this please share. Also, I am working a 54mm MD though the school, and one of the seniors that I am working with is going to show the rest of us (well, there's only three people on the project) how to use Star CCM which apparently can determine dynamic stability. So maybe we will be able to run our own analysis on this.

Just from some very preliminary RasAero/OpenRocket simulations that I have run, I am thinking of going with a very ARCAS style rocket, with four fins. The design is still in the woodworks and nothing is finalized as of yet.

The last thing that I want to talk about in regards to the actual rocket is the name. The reason that I chose the name "Torn Between Scylla and Charybdis" is because of the real life implications surrounding this mythological tale. In The Odyssey, Odysseus is forced to chose which monster to confront, either Scylla or Charybdis. In the past, I have chosen the path of Charybdis that led to my ultimate doom. This time, I am going to choose Scylla possibly avoiding total disaster.

This time, I am going to be much more open to input given on this project because frankly, I'm going to need all of the help I can get! Also, this is going to be a very slow moving thread so don't expect too much action.

Manny
 
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Subscribed!

We also need to talk about the trip itself. Aeronaut 2014 is likely in my future as well. :wink:
 
Deployment bag and ARRD is my suggestion.

It's magic! Bare Necessiities oughtn't have deployed without a drogue (stripped off during the high speed separation) but it did nonetheless.
 
A major issue that has also been brought up is dynamic stability at high mach. From what I have both read and seen in the real world, it seems as though a low aspect ratio conical nose cone will be the best at high mach. There is one thing that I am confused on, why is that? Somebody correct me if I'm wrong, but Center of Pressure moves forward because of increased drag on the nose cone compared to the fins at high mach, so why wouldn't a high aspect ratio cone work better? This is an issue that I am going to look into.

Manny

Here is my opinion on this. And it is only my opinion.

If you get better results with a short conical nose cone you are probably using Rocksim for your simulations. Rocksim is putting too much emphasis on the exposed area of the nose cone. Try with Rasaero and you will likely get different results.

Also, read this excellent thread from our Australian friends. https://www.ausrocketry.com/forum/viewtopic.php?f=10&t=3659. They also conclude a longer Von Karman is preferred for high altitude.

Let us know what you find out.
 
Manny, building something smaller to help sort those recovery questions is a Smart Move!
 
Not sure what you're planning to use for a shock cord, but I have recently been plagued by tangling of smaller gauge Kevlar cord. I frequently use 1/8" TK in my 54mm rockets and it seems that the past 3 flights have all tangled in some form or fashion. I've taken measures to z-fold the cord and tape lightly, but it still tangles. Maybe this is something that you can solve in the testing phases and provide some feedback.
 
Not sure what you're planning to use for a shock cord, but I have recently been plagued by tangling of smaller gauge Kevlar cord. I frequently use 1/8" TK in my 54mm rockets and it seems that the past 3 flights have all tangled in some form or fashion. I've taken measures to z-fold the cord and tape lightly, but it still tangles. Maybe this is something that you can solve in the testing phases and provide some feedback.

My guess? Your recovery system is inducing spin.

Swivels have become very common, due to unbalanced parachutes, but they shouldn't be necessary.

-Kevin
 
My guess? Your recovery system is inducing spin.

Swivels have become very common, due to unbalanced parachutes, but they shouldn't be necessary.

-Kevin

Knotted, not spun together. It happens during deployment.
 
Subscribed!

We also need to talk about the trip itself. Aeronaut 2014 is likely in my future as well. :wink:

Awesome!!! It looks like Aeronaut 2014 is going to be dominated by the Illiconsin group! We will talk more about this down the road at a launch sometime, but if I were to have another driver, the trip wouldn't be so bad and might only take 1.5 days instead of 3.

Deployment bag and ARRD is my suggestion.

It's magic! Bare Necessiities oughtn't have deployed without a drogue (stripped off during the high speed separation) but it did nonetheless.

I'll look into that. I already have cable cutters from archetype, so I'm thinking about getting a deployment bag (made for cable cutters) from Fruity Chutes and going with a small drogue like what you guys did with Bare Necessities.

I should be starting the build of the first airframe in a few weeks after finals are over (2.5 weeks) and I can get the parts on the way home. I just have to nail down exactly what my design is going to be then I can move forward, but for now, study time...

Manny
 
Manny,

We should talk. I can share my lessons learned with the 3" min diameter Arcas since that is along the lines of what you want to do. I was planning on doing a retrospective build thread for it, but you can see how much progress I've made on that front :rolleyes: I also have pics of Jeff M's min diameter M2245 rocket that you might want to see :)

Chuck
 
I'll look into that. I already have cable cutters from archetype, so I'm thinking about getting a deployment bag (made for cable cutters) from Fruity Chutes and going with a small drogue like what you guys did with Bare Necessities.

I should be starting the build of the first airframe in a few weeks after finals are over (2.5 weeks) and I can get the parts on the way home. I just have to nail down exactly what my design is going to be then I can move forward, but for now, study time...

Manny

I sent an email to Gene asking about the cable-cutter-type of deployment bag, but I still couldn't figure out how they're supposed to work; the cable tie's breaking strength is like 10 pounds and I can't figure out a simple way for that to resist the force of a drogue trying to pull the deployment bag off.

If you figure it out, post an explanation.
 
I sent an email to Gene asking about the cable-cutter-type of deployment bag, but I still couldn't figure out how they're supposed to work; the cable tie's breaking strength is like 10 pounds and I can't figure out a simple way for that to resist the force of a drogue trying to pull the deployment bag off.

If you figure it out, post an explanation.

One solution is a three ring release like they use in skydiving.

-Kevin
 
Manny, know that you're quite possibly going to have some competition... I don't want to name names for them (I'm only tangentially involved, I won't be there most likely), but you won't be the only young'un showing up with an M2245Imax minimum diameter rocket... so be warned.

From what I have both read and seen in the real world, it seems as though a low aspect ratio conical nose cone will be the best at high mach. There is one thing that I am confused on, why is that? Somebody correct me if I'm wrong, but Center of Pressure moves forward because of increased drag on the nose cone compared to the fins at high mach, so why wouldn't a high aspect ratio cone work better?

That's certainly what I would have thought; there are lots of practical reasons why shorter cones are easier, though, namely structural on vehicles that have to maneuver extensively.

In other news, some opinions I will be repeating: above mach 1.5, everything other than RASAero is highly suspect; above mach 2, everything other than RASAero is totally made up; it can be very helpful to use the tabulated RASAero outputs and make a "drag power" plot in excell to see where in the flight profile you are actually suffering the most from drag losses, then modifying the design to reduce drag in that specific flight envelope; once you get past 6.5:1 or so, the drag difference of nosecones becomes pretty trivial but the CP displacement might not be; watch for shock waves causing local thermal erosion and failure of the fins; the AIM Xtra is well worth it's cost as a data recording and diagnostic tool, even beside the fact that it provides bulletproof apogee detection for deployment via GPS+inertial measurements and equivalent GPS-tracking capacity to the BigRedBee; deployment bags are pure magic for packing huge parachutes into tiny spaces; deployment gabs are magic for making darn sure the chute opens when it's supposed to and only when it's supposed to; and finally, that flame pan on your last tower was SICK so do it again plz. =)
 
I thought of that but couldn't figure out how that would work with the eyelets on the bag.

It may well require modifying the bag. In my opinion, many of the deployment bags offered in the hobby are lacking.

-Kevin
 
Manny, know that you're quite possibly going to have some competition... I don't want to name names for them (I'm only tangentially involved, I won't be there most likely), but you won't be the only young'un showing up with an M2245Imax minimum diameter rocket... so be warned.

Is this me or someone else?

I wont be flying MY M2245 project till XPRS 2015 at the latest I think. This year I'm just focusing on the PWF.

Best of luck, Manny. I'll be following along, of course.

Alex
 
Is this me or someone else?

I wont be flying MY M2245 project till XPRS 2015 at the latest I think. This year I'm just focusing on the PWF.

Best of luck, Manny. I'll be following along, of course.

Alex

Someone else; and I remembered after posting that their project isn't an M altitude attempt, it's a 2-stager. So nevermind.

Nonetheless, I'll be following this one. Looks really neat!
 
After an entire winter break of doing absolutely nothing rocket related, it's time to get moving on this project (a little).

Since school starts on Monday and I still have to buy my Statics of Engineering textbook (I registered for the class after the textbook reservation deadline) and I would like to beat the lines at the bookstore, I decided to drive back to Ames this morning. On the way, I stopped at the Wildman Rocketry world headquarters in Van Orin Illinois. All of the little elves are working hard to finish off Black Saturday shipments, but the factory workers had some time to help me get some parts that I needed.

I got all of the fiberglass parts that I need to build the first rocket. Charybdis will be the more risky conventional fiberglass, while Scylla will be the second all vacuum pressed carbon fiber rocket. Basically, I am building this first rocket as a deployment test vehicle. I will be flying this one multiple times. At least one low altitude flight (<7,000') for a flight test of the cable cutters, so that I can get used to using them. There will be at least one high altitude flight of this rocket (~30,000') at Kloudbust in Argonia in mid-April. For the high altitude flight I will be using a CTI 4 grain M2250 C*. The reason that I picked this motor (other than the fact that I have one) is that I have successfully flown this motor in a minimum diameter to 23,000' before. Attached below is a preliminary Open Rocket simulation. I have a RasAero file on my computer at home that puts it quite a bit higher but I forgot to take a screen capture of it. For now, until I can figure out how to partition the hard drive on my macbook, this is what I have to go with.

Screen Shot 2014-01-10 at 8.50.29 PM.jpg

The reason that I say this is preliminary is because I'm not sure nose cone shape I want to use. I still have some more research to do on this but will know soon enough.

Just for kicks, since I don't have a bath tub in my apartment at school, I had to take an obligatory "parts shower" picture....

IMG_1101.jpg

Here is a picture of all of the parts dried and on our breakfast bar.

IMG_1103.jpg

The Wildman world HQ has recently acquired a brand new CNC machine. This thing is a really slick set-up and was able to turn out the custom fin guides in just a couple minutes from design to completion. The rocket is going to have four very ARCAS like fins. 8" root, 3" tip, 3" height, 5" sweep and 1/8" thick. 48" of black fiberglass tube for main airframe. In the center, we have the parts for the custom motor adapter. This is going to act as a stand in motor case when I fly this rocket on a Crazy Monkey K630 Cloud9 propellant.

That's pretty much all I have for now. I don't have anything this weekend, so I will probably spend it covering my clean apartment in fiberglass dust and epoxy.

Meatball out.
 
Lookin' good, Manny! Glad yer back at the task! Keep us posted on progress :wink:
 
Thank you Jeff! You supplied the motor that will be this rocket's first flight.
 
Manny,
Could you post your Open Rocket file? I'd like to see how you packed your nose.
Thanks
 
Manny,
Could you post your Open Rocket file? I'd like to see how you packed your nose.
Thanks

Sorry I never saw your reply, here is my Open Rocket file. It's not EXACTLY how I'm going to do it, but it's a rough guess on how I'm going to pack it. I generally have to wait until I get the nose cone so that I can get a look at it and really play around with Av-bay ideas.

View attachment Scylla & Charybdis.ork
 
What does an Aerospace major at a large university have to do on a Friday night by the means of entertainment? Build rockets of course!

So I began construction today by tacking on two of the four fins. I first taped off an area of the tube that I wanted to attach my fins and added one inch. I then sanded that area thoroughly with 220 grit sand paper, as not to severely damage any glass fibers.

IMG_1133.jpg

I then proceeded with bonding (after cleaning the tube with Isopropyl alcohol :p ). For bonding the fins, I used Glenmarc G5000 High-Strength Rocketpoxy. First, I spread the fin guides out so that the fins were fairly loose so that I could spread the Rocketpoxy along the root of the fin. Then, using the rest of the epoxy I created somewhat of a small fillet. It's drying now, and I will glue the other two fins on in the morning.

IMG_1136.jpg

IMG_1138.jpg

After I am done attaching all four fins, a large radius fillet of Rocketpoxy will go over them. That's about it for now.

Manny
 
Just for kicks, since I don't have a bath tub in my apartment at school, I had to take an obligatory "parts shower" picture....

Not to take any unnecessary digs at your record or anything, but isn't that the photo you take after the rocket shreds?
 
Not to take any unnecessary digs at your record or anything, but isn't that the photo you take after the rocket shreds?

It's very rare that a post here make me laugh out loud (other that all of Gus' long rants) but that was hilarious! And yes, my record for this past year has been pretty piss poor, and I deserve at least some teasing. :D
 
Rocketpoxy for tacking, huh? I thought about it, and maybe I let Alex get into my head too much, but the Tg of Rocketpoxy and the temperature of a motor case don't seem to go well together in my head anymore. I'm going with Proline 4500.

I also thought about Aeropoxy for Laminating, with it's advertised Tg of 200, but Proline 4100 laminating resin claims a Tg of 250...but who knows for sure how accurate that is. That was off a data sheet that is still stuck somewhere on Tim's web server.


Thoughts pourin' out, see you at Aeronaut!

Edit: Re-reading this post I thought I should defuse it a bit, I wasn't posting to question your methods. I was more or less thinking out loud through my fingers. You've got way more experience in this field than I do, I just thought maybe I started over-thinking everything :wink:


Braden
 
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Not to take any unnecessary digs at your record or anything, but isn't that the photo you take after the rocket shreds?



AHAHAHAHAHAHAHA!!!!
:rofl::rofl::rofl::rofl::rofl::rofl::rofl::rofl::rofl::rofl::neeneer"
 
Rocketpoxy for tacking, huh? I thought about it, and maybe I let Alex get into my head too much, but the Tg of Rocketpoxy and the temperature of a motor case don't seem to go well together in my head anymore. I'm going with Proline 4500.

I also thought about Aeropoxy for Laminating, with it's advertised Tg of 200, but Proline 4100 laminating resin claims a Tg of 250...but who knows for sure how accurate that is. That was off a data sheet that is still stuck somewhere on Tim's web server.


Thoughts pourin' out, see you at Aeronaut!



Braden

You can post cure laminating Aeropoxy for a boost in tg if you have the resources for that.
 
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