Interesting simulation results from a custom payloader

View attachment 202 rocket.rktHello,

For a college engineering project, I am working on building a rocket to loft the digital flight recorder I have designed. I am designing the rocket using RockSim 9, and although I seem to have reasonable 1-1.5 caliber stability on both 1 and 2-stage configurations, the rocket, during simulation, is shown to be massively overstable, weathercocking like nothing I've designed before.

EDIT: .rkt file included. OOPS!

There must be something I am missing. How can I fix this?

As you can see this is my first post on this forum - I am not really sure if I should put this here or in the scratch-builts subforum, so if i'm not on the right track please let me know I welcome and appreciate any help you can give me!

Post again, or edit your post, choose "Go Advanced", scroll down to "Manage Attachments", and upload your .rkt file so we can look at what you have going on there.

Oops, I'm sorry, there you go!

aside from the centering rings having the wrong inner diameter...looks to me like a leadership problem, the rocket lacks proper motivation. seriously, open rocket didn't have issues with stability, it did say that I needed a much longer rod (at a guess about 10') with an effective length of 60" this bird was doing a whopping 20 mph*...there is your weather vaning problem, it is just too slow. you either need to put it on a diet, or give it more power.
*I tried it on a pair of E12s
Rex

Agree with Rex R on the weight problem. If this is the as built plan, go single stage and use an Aerotech F32 instead of Estes motors. If you have to use Estes, go with a 29mm motor mount and use the new F15s. The F32 should give you a nice flight without much weathercocking. Even the F15 will weathercock a bit, although less than an E12. That design is way too heavy for the E9, and is marginal on the E12. Note that the E9-0 has never been available for sale.

Where did you guys find the .rkt file? What did I miss?

Thanks, guys. I have never flown anything larger than an E12, though, and I'm cautious to make my first time on that size to be a custom. Would you guys be able to recommend a kit?

considering the plethora of kits out there...you're need to be a bit more specific in your desires . like price, engine size(and type), overall size of rocket etc. so we can narrow the field a bit. the Estes ps2 birds are nice.
Rex

I looked at the PS2 E2X Ascender, and it looks relatively cheap for one of those bigger rockets too. Might that work?

In order to satisfy the requirements of this project, I need to fly my instrument suite to at least 1,000 feet, with a payload section of at least 1.8" diameter. I don't have experience with anything larger that an E12, so I have the means to fly that engine size, but, if there is a good entry kit on something larger, I'd love to expand my horizons. Overall rocket size doesn't really matter as long as it has a large enough payload section. Of course I would like to keep my costs down.

Thanks

okay now that I know what you need... a quick and dirty design (more or less) says that you'll need an F50/F52 motor 29mm to get the results in some thing like this. this would of course not be a kit.
Rex

View attachment spev29mmv2.rkt

That is great, Rex, thank you! I think I will use that design as a starting point. Seeing as this will be my first flight of one of these powerful motors, can you offer any tips/advice to help me make this a success? In terms of sourcing parts/construction/launch. What are some common pitfalls one might fall in when "graduating up" to the 29mm engine?

Thanks for all your help.

I'd suggest looking up the instructions on a 29mm kit, such as the Argent, just to get a feel for it. Buying a kit wouldn't be a bad idea either.

A lot of guys suggest JB Weld for attaching the parts that will be in direct contact with heat/flame from the motor.

That doesn't look too bad. Will the portal-pad E and the E launch controller I already have suffice to launch this? Where would you get your parts from to build a custom of this size?

I've heard some people say the JB-Weld epoxy putty is good for making large fillets. Is this true?

Thanks!

if the budget allows, I would suggest something like the big daddy or the mega mosquito for your first foray into, thru the wall fins and composite motors(E20s work nicely in them). yes jb weld can make fillets, no it is not a good idea for mid power birds (way to heavy). the porta pad E is not sturdy enough for Fs and Gs, if for any reason an F powered bird got stuck on the pad it will burn though the blast deflector(and the pad under it). not sure about the controller(you'll need at least 30' of wire) probably need to modify it for 12v.
got alot of my parts from Semroc(tubes, nose, couplers)...one could order what you need from Estes(aside from fins). the key is Do not over Build. you want to keep it light.
Rex
oh, right the design built into a nice rocket...that nearly teleported off the pad with an F52(no payload), it has also flown on an E16 (much lower)

acegard said:

I've heard some people say the JB-Weld epoxy putty is good for making large fillets.

Click to expand...

Rex R gave you the correct info on fillets.

Start with well-fitted parts and tight fits on dry parts. Snug fit is #1, #2, and #3 on your list.

Gobs of goo will not make good structural joints, this will only add weight. Internal joints do not need any fillets. External fillets (for aerodynamic purposes) can be made with lightweight spackle (the "no slump" kind with microballoons mixed in) and toughened with a few drops of CA. If you must.

For a basic research project like yours, I recommend skipping the bells and whistles (like fillets). They are going to add to your build time with little benefit. The advantage you gain will be an insignificant gain in altitude, on the order of tens of feet at most (don't expect any hundred-foot payoff). And that is if they are done "right." You could just as easily shape some poor fillets and add to a base drag problem and lose a few tens of feet of altitude.

Thanks. I read on the Estes website that the E controller would work - Does the sonic igniter only work on 12 volts?

The E controller should work for firing one of them. Their minimum all-fire current is 3.6 Amps and from their internal resistance I can calculate that the 9V controller will deliver that.

The Estes "E" controller is (for all practical purposes) the same thing as their regular launch controller but with longer lead wires to the pad.

The NAR safety code calls for a 15 foot standoff between you and the launch pad for low-power motors up through D impulse class. This is a good, common sense safety measure. For larger motors (starting at E impulse class) the safety code increases this to a 30 foot standoff. Aside from that, the Estes E motors are still loaded with blackpowder propellants and still use the same igniters as Estes blackpowder low-power motors.

These Estes igniters are not the same as the igniters needed for motors loaded with composite propellants like the Aerotech motors. The Estes E launch controller may or may not be compatible with the igniters you use for composite motors.

I don't know how much of that you already knew; hope some part helps.

Open rocket, at least, check the distance scale which is different for horizontal and vertical.

I ran the sim and lengthened the rod and didn't help that much, although cutting all wind did. The odd thing is it's showing it goes straight for the first 30' or so -- even anti-weathercocked slightly, and then curves suddenly at about 50'. Odd. Is it somehow responding to the end of the initial thrust peak?

This is w/ no payload, though, right? May just need a lighter rocket, although if total is still over a pound, need composite or cluster. Note composites are a LOT louder and more aggressive.

It seems to me that the E controller will light the F15 motors, which is what I think I'm going to use (Because you get two per package - keeps costs lower - and they're just about what I am comfortable with flying right now power wise). Thank you guys so much for your help!

As I mentioned in a earlier post, an Aerotech F32-6 would work as well. The motor will fit in the same motor mount as an E12. The F32 should put the rocket well over 1000'. You will need a 12V controller, though.

Note that the F15 is actually lower peak thrust than the E12. The F15 tends to be too slow off the rod, E12 too little impulse and altitude (single staged) with weight. An E20 can safely fly more weight than either, and composites mostly go up from there.

I'll keep that in mind, and simulate both. With larger black powder and composite motors getting sort of expensive, I'm trying to balance altitude and cost. With a derivative of the design Rex gave me, 'm cracking 1300 feet on an F15. I'll need to check angle of attack in OpenRocket (since RockSim doesn't have the F15 to simulate) to make sure it's not keeling over.

^^-- https://www.thrustcurve.org/motorsearch.jsp?id=1010

Rocksim imports RASP files ... also exports them I think, but isn't always fully RASP-compatible.