Altitude prediction?

Onebadhawk
Shop deals on ebay
The Rocketry Forum

Help Support The Rocketry Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.
Bat-mite

Bat-mite

Rocketeer in MD
Joined
Dec 5, 2013
Messages
11,959
Reaction score
2,798
Location
Maryland
Aside from computerized simulators, is there an easy to predict altitude based on impulse and weight? I'm not talking perfect--just ballpark.

A guy at URRF who had just bought a Leviathan and an H133 motor for his Level 1 cert asked me, "With this motor, how high will it go?"

Of course, out on the field with no computer, I told him to look at the package, see what it tells you for a G80, then extrapolate for an H133 (given the known total impulse for both).

Anyone know of an easier way? Be nice if there was a web site with a table that lists common total impulses by rocket weight and a resulting rough avg. altitude.
 
As a SWAG, going up an impulse doubles altitude.

For example, if a rocket flew 2,000' on a 50% H, you can reasonable expect 4,000' from a 50% I.

If you want more granular than that, look at the ratio of the impulses in Ns. Moving from a CTI J244 (867 Ns, a 68% J) to a CTI K660 (2437 Ns, a 95% K) would give 2437/867=2.81 x the altitude.

Roughly. Mach influences or excess drag from a rough finish not factored in. :)


All the best, James


<edit> PS: Ha. I see from the OP you were aware of this already. In this case, based on purely weight and impulse, I am no help.
 
Last edited:
azzie said:
Get Smart Launch app for iPhone.
Click to expand...

A good program but not exactly what the OP is looking for.

If someone doesn't point you in the right direction, you could put together a graph to show published info and data you can generate when you're at a computer. It may not be comprehensive but you could carry some info to describe approximate ranges.

So, did the impulsive flyer get his L1? Good suggestion to extrapolate; did he understand what you meant? :confused:
 
https://www.thrustcurve.org/

Put in the basics - rocket diameter, weight, and MMT size. It gives you a table of altitudes and delay times. You can access it with a smartphone as long as you have cell signal at the launch site
 
There's a few smartphone apps that'll ballpark it. With the availability of phones at launches, it's really the way to go....and they already exist.
 
DizWolf said:
There's a few smartphone apps that'll ballpark it. With the availability of phones at launches, it's really the way to go....and they already exist.
Click to expand...

I know I'm silly, but I don't have a smart phone. But I like the thrust curve thing. I could print out a spreadsheet for each of my rockets.
 
Or you could model each of them In openrocket and run the sims...what is the objection to this approach?


Sent from my iPhone using Rocketry Forum
 
Bat-mite said:
Be nice if there was a web site with a table that lists common total impulses by rocket weight and a resulting rough avg. altitude.
Click to expand...
At first, I thought "no way" because you know nothing about drag from this info. But, you could run sims for a generic rocket (20:1 L:D, 3FNC) and see what the range of variation is; perhaps you could come up with a reasonable approximation for sub-sonic flights.
 
The Madcow app (no longer available) was not bad in giving a rough estamate of altitude and performance. You entered the rocket diameter and weight, selected aerotech or CTI, and entered the motor diameter. It would pull up a list of motors and listed recommended delays and predicted altitude. For standard 3 fins and a nosecone designs it actually gave a decent estimate much of the time.
 
Last edited:
The MadCow App is still available, I just checked.

There are currently 7 apps for available for iPhone, including TRF. I started a thread previously listing them. I will try to find and update.



So many rockets, so little time, and money.
 
terryg said:
You entered the rocket diameter and weight, selected aerotech or CTI, and entered the motor diameter.
Click to expand...
With that much info (and data from ThrustCurve.org), you can actually do a quick simulation, which is what the Motor Guide does.

For those interested in this further, I put together an example mash-up accessing the API from JavaScript and wrote up the basics of flight simulation.

However, the best thing would be for this to be part of the regular flight simulators: a new feature that ran a simulation with every motor that fits (possibly narrowed down by manufacturer), since they have a much more complete representation of the rocket and a more sophisticated simulation technique.
 
wfcook said:
Or you could model each of them In openrocket and run the sims...what is the objection to this approach?


Sent from my iPhone using Rocketry Forum
Click to expand...

If the person has never used simulation software and just wants a rough altitude, that's a lot to ask. Heck, it takes a lot of hours to learn how to correctly simulate a rocket. We're talking relatively quick answer, here.

But to say "Go to thrustcurve.org, click Motor Guide, and fill out the form" is more like what I'm looking for. That's a good enough answer for me. I just didn't know thrustcurve.org could do that.
 
Aerotech has these nomograms, though personally I find 'em a tad hard to read. I'm considering making some simplifying assumptions and rolling my own.
 
Lowpuller said:
The MadCow App is still available, I just checked.

There are currently 7 apps for available for iPhone, including TRF. I started a thread previously listing them. I will try to find and update.



So many rockets, so little time, and money.
Click to expand...

Still available, but unfortunately it does not work on any modern droid os. It has never been updated. Rocket Motor Guide is good but it was nice to have a program for where there is no online access.
 
Last edited:
Zeroignite said:
Aerotech has these nomograms, though personally I find 'em a tad hard to read.
Click to expand...

Eyes are bleeding.:cry:

Probably better to run a few simulations with each of your rockets and different motors and put the altitudes in a notebook :)

However, would it be possible, given a motor's total impulse and average impulse (no thrust curve) and a rocket weight (including motor), to generate altitudes using a simple equation or simple numerical model?

It could then be easy to generate 3 altitudes. One for a rocket with a reasonable low drag coefficient (high rocket length to fin length ratio), one for a rocket with a high drag coefficient (der red max?) and one in the middle. Then, based on a rocket's weight and a general idea of it's drag coefficient, one could have a basic idea of just how high it will go.

I realise this is still far from what the OP is asking but it made me try to think about the minimal set of parameters you need to estimate the maximum height.
 
Last edited:
morlock said:
... it made me try to think about the minimal set of parameters you need to estimate the maximum height.
Click to expand...
Yeah, that's basically what the ThrustCurve.org Motor Guide is. (There's no reason not to use the full thrust curves, since they're easily available.)
 
JohnCoker said:
Yeah, that's basically what the ThrustCurve.org Motor Guide is. (There's no reason not to use the full thrust curves, since they're easily available.)
Click to expand...

No reason except to have some fun and small programming project on the side.

That is, another one :)
 
bobkrech said:
RSOs have charts for estimated apogee for rockets of various weight, airframe diameters, installed total impulse and Cd. An example of an RSO check list and chart package can be found at https://www.tripoliwisconsin.org/launchforum/pdfs/Rso.pdf

Also found at https://www.info-central.org/?article=114

Bob, you beat me to that RSO doc on the Tripoli Wisconsin site. It should cover a large portion of rockets.

Bob
Click to expand...




Mark Koelsch
Sent from my iPhone using Rocketry Forum
 
PML has sheets that show how high each of their rockets will fly and the best guess for delay time for various motors. I take printouts to launches. Pick one of their rockets that has a similar mass and diameter to your rocket and you should be close.
 
Andy Greene said:
I am very curious as to that answer as well ??? If not what happened ??
Click to expand...

Oh, sorry for the lack-o answer. No, he had not built the rocket yet. He was curious how high it would go on the motor he bought. And yes, he understood.
 
Bat-mite said:
I know I'm silly, but I don't have a smart phone. But I like the thrust curve thing. I could print out a spreadsheet for each of my rockets.
Click to expand...
No need for a smart phone. iOs rocketry apps will run on an iPod touch also, with no monthly fees. :)
 
Call me crazy, but I run through the sims BEFORE I plop down a couple hundred bucks for a HPR rocket and motor combo. I would hope that L1 and L2 wannabes are capable of some basic simulations to ensure a safe flight.

The inputs are basic: mass, thrust profile, drag coefficient, frontal area, air density. Solving the equations either in closed form or numerically requires some calculus. The CAD features of RockSim and Open Rocket help you design a rocket but are not needed to predict altitude.

I like Coker's Motor Guide on Thrust Curve.org to get estimates for many motors very quickly. I also like to print out the RockSim results and carry a notebook to the launch.

Several years ago, an old timer parked next to me at a launch chided my use of simulation notes before each of my flights. He gruffly told me "that computer stuff is a bunch of crap. Trial and error is the only way." All my flights that day were perfect. His large, complex project crashed in spectacular fashion due to a poor choice of motor and delay. I smugly said nothing.
 
Buckeye said:
Call me crazy, but I run through the sims BEFORE I plop down a couple hundred bucks for a HPR rocket and motor combo. I would hope that L1 and L2 wannabes are capable of some basic simulations to ensure a safe flight.

The inputs are basic: mass, thrust profile, drag coefficient, frontal area, air density. Solving the equations either in closed form or numerically requires some calculus. The CAD features of RockSim and Open Rocket help you design a rocket but are not needed to predict altitude.

I like Coker's Motor Guide on Thrust Curve.org to get estimates for many motors very quickly. I also like to print out the RockSim results and carry a notebook to the launch.

Several years ago, an old timer parked next to me at a launch chided my use of simulation notes before each of my flights. He gruffly told me "that computer stuff is a bunch of crap. Trial and error is the only way." All my flights that day were perfect. His large, complex project crashed in spectacular fashion due to a poor choice of motor and delay. I smugly said nothing.
Click to expand...

As someone just getting back into rocketry, I like running the simulations. In the past month, I've ordered a couple kits and already made a spreadsheet of the motors I'd like to use in them. For now, I'm just using OpenRocket, and I know it's not exact, but I'm only selecting motors with a large enough margin of error to be safe. Now I have my list of motors, delays, and projected altitudes ready to go. Just having that at my next launch will help tremendously because I can easily select motors and recoveries that work for that day's conditions. I remember 20 years ago when it was all guesstimating based on similar motors. It wasn't horrible, and a sensible person could figure out what to use. However, I also remember seeing a LOT more close calls, zippered rockets, and crashes back then. A smart man learns from his mistakes, a wise man learns from the mistakes of others, and the wisest man uses every resource available to him...
 
You could use wRASP32 which is very easy. Just enter the diameter, weight, Cd (usually 0.6) and add a motor. It's pretty close. The motor.eng file it uses for engine data is a text file so you can copy any of the Thrustcurve RASP files into it to add them to your motor selection.

If you have AeroLab, you can export drag profiles and import them into wRASP32 so you get accurate sims past 75% Mach. You don't need that for ball park sims.

Try this link https://tccnar.tripod.com/sims/082_wRASP32_221.zip This link was found on the TCC NAR Competition Primer
 
Buckeye said:
Handeman:

Is this the AeroLab of which you speak?:

https://www.softpedia.com/get/Science-CAD/Aerolab.shtml

Any reason you like AeroLab + wRASP instead of RASAero? RASAero will do the Cd profile and flight simulation in one package, and Chuck seems active in keeping the software up to date. I am not buying or selling, just curious.
Click to expand...

That's the one.

It isn't so much that I like the Aerolab + wRASP32 as much as I like wRASP32 for quick ballpark sims. Fill in three values, select a motor and sim the flight. You don't have to "build" a model first or load files or anything else. Editing the .eng files is also very easy. Just cut and paste the RASP file from Thrustcurve. If you do an Aerolab drag profile, you can save a model file and then reopen whenever you want to sim a new motor.

BTW, I do have and use RASAero too, and have started using Open Rocket. Those are good when you are working a specific project, but I still prefer wRASP32 for quick sims.
 

Similar threads

diyaerospace
ARC 2024
Replies
1
Views
766
PhlAsh
PhlAsh
GAP
Leave No Doubt: An M2020 to Mach 3 (ish)
Replies
8
Views
1K
kjhambrick
K
Adrian A
StratoSpear: 38mm 3-stage for complex L record attempt
2 3 4
Replies
100
Views
11K
waltr
W
RGClark
Attempt towards an amateur orbital rocket.
5 6 7
Replies
183
Views
12K
bad_idea
bad_idea
AeroTech
EVENT TRATECH Tripoli Technical Conference Presenters & Schedule at LDRS-39 - UPDATED 5/20/21
Replies
2
Views
2K
dvdsnyd
dvdsnyd

Latest posts

Back
Top