How to calculate thrust required to lift a heavy rocket?

Discussions of motors from single-use and RMS solid propellants to hybrid propellants

Moderator: Moderators

vance2loud
Rocket Crew
Rocket Crew
Posts: 283
Joined: Wed May 14, 2014 12:44 pm
Location: Devonport, Tasmania

Re: How to calculate thrust required to lift a heavy rocket?

Postby vance2loud » Mon Sep 14, 2015 11:17 pm

If you are looking for something to use C6-0 motors in can I suggest something along these lines.
http://www.artapplewhite.com/fs.html
or an Estes Snitch if you can find one.
Both of those work well on a motor with no delay, have tumble recovery and tend to be a crowd favourite whenever I'm launching LPR.
TRA #15165 AMRS #50
I do it because i can, I can because I want to, I want to because you said I couldn't. - Unknown
I have not failed. I've just found 10,000 ways that won't work.
- Thomas Alva Edison

Lamp
Aged like a good scotch
Aged like a good scotch
Posts: 1103
Joined: Fri May 08, 2009 9:28 am
Location: Melbourne

Re: How to calculate thrust required to lift a heavy rocket?

Postby Lamp » Tue Sep 15, 2015 12:55 am

lucifer911 wrote:
Lister wrote:We tell you to read the instructions so you dont keep doing dangerous launches that you upload to youtube.. you are being reckless and dont understand that rocket motors arent toys and should be treated with respect. there is a reason motors come with instructions and there is no shame in reading them to understand things better especially when you have NO understanding of how and why they do what they do.. if you keep ignoring advice you will find it an expensive way to learn, and I would suggest you stop uploading to youtube the rockets you modify againt advice or instructions as your making us look like cowboys.


First off

Reading small pamphlets will not make me a rocket scientist and it doesn't contain all the information I need to know to become good at this hobby in 2-4 launches. Instructions do not contain everything I need to know just basic guidelines.


Some would say I have quite a bit of experience (it took me a lot more than 2-4 launches) and I am an L3 flier and a current Tripoli Technical Advisory Panel member... and I am not ashamed to say I still read all the advice and pamphlets that come with motors.
I might have assembled a particular motor a dozen or more times but if you see me at a launch putting a motor together you will also see me checking the instructions!

lucifer911 wrote: there were no guidelines about max weight of rocket on the back of the Estes package and my rocket is still technically a LPR


Because they are LPR motors designed to fly in kits and it is assumed the kits would be built as designed and not modified, they do not provide max liftoff weights with the motors but the kits contain recommendations for suitable motors. The recommended motors would exceed the safe liftoff requirement. It is assumed you would start flying the kits and therefore gain experience about how the motors perform before scratch building. As Vance posted, there are various resources available to help.


lucifer911 wrote: The higher the impulse of the motor - the more dangerous it becomes to people and property.. that is the way I see it.


This is correct and that is why there are safety codes to cover what we do at any power range we may use. They are there for a reason because all rocket motors are potentially dangerous! On the weekend as RSO at Serpentine, we launched a couple of "M" motors that were routine (proven rockets, suitable motors, correct safe launch distance) but I called a "heads up" (potentially dangerous) launch on an experimental cluster of 2 "C" motors. Because it is low power does not automatically make it safe! By the way, everyone agreed I was right to call the low power cluster a "heads up"!


lucifer911 wrote:I see this attitude in quadcopter operators too who usually put the blame on people new to the hobby for new laws being introduced restricting airspace when it is usually them who violate airspace laws. I have not touched any midpower rockets or motors above C... and this 100g rocket isn't exactly a military rocket...


Our hobby is quite safe if the person preparing and flying the rocket has sufficient knowledge and the correct procedures are followed. That does not mean you cannot experiment with design and performance but you have to do it safely!

We are so strict about safety because our hobby is potentially dangerous and possibly lethal even at low power. Failures occur, it is inevitable in this hobby, but we make sure the potential for damage or injury is minimised...if we do this the regulators are happy, if we don't the regulators will make sure we will no longer be able to fly and it could take as little as one bad incident for that to happen!
‘It takes sixty-five thousand errors before you are qualified to make a rocket.’ — Werhner von Braun
TRA 12286 L3
TAP member

lucifer911
Rocket Flyer
Rocket Flyer
Posts: 134
Joined: Sun Jul 26, 2015 12:49 am

Re: How to calculate thrust required to lift a heavy rocket?

Postby lucifer911 » Tue Sep 15, 2015 5:21 am

thanks Vance,

I plugged some data into the thrustcurve page and it produced a list of suitable motors I should be using for my rocket.
Here is the rocket I am currently using available from ausrocketry
http://ausrocketry.com.au/56er-model-rocket-kit.html

On that link it says:

DETAILS

The 56er was designed especially for new rocketeers, with little or no experience, and younger modelers.

As this is a Skill Level 1 model rocket kit, the ply fins and fin slots on the airframe are pre-cut for quick and easy assembly.

This kit includes illustrated instructions, parachute kit, and other parts needed to build this rocket. This rocket requires glue to be assembled, we recommend 2 part epoxy.

The 56er can be launched on Southern Cross Rocketry B6-4 and C6-5 model rocket motors.

Rocket dimensions: Overall length : 62cm
Diameter : 1.346" / 3.3cm(BT60)
Fin Span : 14.3cm
Weight : ~89grams


On the thrustcurve website it gives some conflicting data on motors I can use compared to the recommend motors on the ausrocketry link. The B6-4 motor (either Estes or SCR) will result in less than the required 15m/s launch velocity but the C6-5 motors is safe to use for the weight of my rocket. It also suggests I can use Aerotech D motors for a safe launch.

I have attached the thrustcurve recommended motors to this msg.


vance2loud wrote:If you search around there was a rocket building guide put out by Estes in the 70's or 80's.
It goes into a lot of the basics of design to give you a better start.
If I find the link I will post it here.
another good source of information is the videos from Apogee rockets.
I might update the motor list that I created and include the lower power Estes motors with a guide to (very rough) weight limits for some of the lower motors.

If you go to http://www.thrustcurve.org/guidepage.jsp you can enter your rockets details and it will let you know which motors will allow for safe lift off speed and rough altitude predictions. Not as good as doing a complete simulation in Rocksim or Openrocket but certainly better than nothing.
Attachments
Suitable motors.JPG

lucifer911
Rocket Flyer
Rocket Flyer
Posts: 134
Joined: Sun Jul 26, 2015 12:49 am

Re: How to calculate thrust required to lift a heavy rocket?

Postby lucifer911 » Tue Sep 15, 2015 5:45 am

One of my mistakes was (aside from not reading enough info) I assumed if a motor fits into a motor mount tube then it would / should work. All the black powder LPR motors A/B/C have a 18mm diameter and 7cm length so I thought each one would work because they fit. Obviously I made a mistake with the booster and should have waited for the C6-5 motor I won't make this same mistake again as I did put a lot of time into preparing my rocket only to get it damaged during this launch. The thrustcurve website has been very helpful in suggesting the safe motors I should use and also lists motors which are potentially hazardous. I will use this as a guide when deciding which motors to use for certain rockets.

Also I don't want to ask too many questions as I don't want to irritate you or the rest of the rocketry community so thats why I went off and launched it without asking.
I will try to be more responsible for future launches and will let you know before I'm about to do something new. I will discuss the other issues with you via sms :)


Lister wrote:
If you did some reading before building and subsequently shortening your shock cord on the black and gold rocket you wouldnt have lost the nose cone.

if you had of got the motors the 56er instructions said to use instead of getting booster motors and then flying them after I had told you it would deploy at motor burnout and likely damage yiur rocket and should wait till you have c6-5 motors you though bugger it and launched on a c6-0.. and damaged your rocket and lost the nose.

You didnt even ask if an A motor would be a bad idea, just saud that A motors are useless and youbwould use the rest for smoke bombs.

I know you think we/I am picking on the new guy but everyone of us when we start out get alot of constructive criticism, its how we learn without having so many failures and without launhing with no understanding of what we are doing. Your way definitely isnt "The only way to become good at this" the other way is to not tane advice as a personal attack and actually take on board what people say who know what they are actually doing.. we dont say these things for shits and giggles, you are in a hobby now that if not done in a responsible and safe manner can BLOW UP and potentially kill you or someone else in the vacinity.. I will also point out you dont call out a 5 second count down when launching which is in the insignificant pamphlet that contains all the safe launch procedures..the 5 count would be good for you especially so anyone near by can keep there heads up.. and with your history of falling rocket parts I would want to know when your launching.

No matter who the person is if they do something reckless or potentially dangerous or irresponsible they get pulled up on it and usually learn from it.. please dont be the other kind that judt does what they want coz what would anyone else know.

User avatar
jase
It runs on moonshine
It runs on moonshine
Posts: 1217
Joined: Wed May 11, 2011 11:06 pm
Location: 43° South

Re: How to calculate thrust required to lift a heavy rocket?

Postby jase » Tue Sep 15, 2015 9:10 am

Good that you've found Thrustcurve...

Can you see the advice that Thrustcurve gives you?

You've posted the advice above, in the screen shot - it is the best advice anyone can give you.

See where is says "...a quick simulation has been run to give you a rough idea..."

....and then;

"We encourage you to run a more complete simulation with any motor you plan to use;..."

...I've added emphasis, not to be condescending, but to point out the important aspects you've seemed to have missed.

Looks to me that you are at that critical point in the evolution of anyone who wants to get into rocketry where you now need to spend some time learning how to use simulation software. There really isn't any other safe way forward for you now...
Me and my rockets run on Moonshine.

User avatar
SpaceManMat
Astronaut
Astronaut
Posts: 2094
Joined: Mon Dec 15, 2008 9:56 pm
Location: Brisbane

Re: How to calculate thrust required to lift a heavy rocket?

Postby SpaceManMat » Tue Sep 15, 2015 9:27 am

Open rocket is a free simulator that most people here use, you've probably seen screen shots posted around. There are models available for a lot of rockets that you can download, but you should check the model against what you have actually built.
QRS: 124
AMRS: 32 L2 RSO
Highest Altitude: 13,647 feet
Fastest Flight: Mach 1.55
Largest Motor: CTI 1115J530 IM
Current Project: X Wing

lucifer911
Rocket Flyer
Rocket Flyer
Posts: 134
Joined: Sun Jul 26, 2015 12:49 am

Re: How to calculate thrust required to lift a heavy rocket?

Postby lucifer911 » Tue Sep 15, 2015 12:57 pm

yep I was a bit intimidated of using openrocket because I didn't know how to use it when I first opened it.

I have spent a few hours with this program now... and what helped me understand this program was I opened an example of a small rocket. From this I was able to modify the data and even found a way to produce the exact shape of my fins :) I have measured out everything and I think it looks good on the simulation. I selected motors which were available in Australia and which were suitable for my rocket based on thrustcurve. I even loaded up the C6 booster motor and openrocket made an accurate prediction of what really happened in my unsafe launch. The simulation even gave me a warning in the C6-3 motor and let me know the rocket will be travelling a little too fast during parachute deploy. This program is quite amazing and seems to be able to predict future launches with good accuracy.

I have attached a screenshot of the simulations I conducted.. it doesn't give me a safety warning on the A8-3 motor... but this simulation is without the payload bay. I do not know how to add a payload bay in openrocket. Would I simply just increase the body tube length to include the payload bay?





jase wrote:Good that you've found Thrustcurve...

Can you see the advice that Thrustcurve gives you?

You've posted the advice above, in the screen shot - it is the best advice anyone can give you.

See where is says "...a quick simulation has been run to give you a rough idea..."

....and then;

"We encourage you to run a more complete simulation with any motor you plan to use;..."

...I've added emphasis, not to be condescending, but to point out the important aspects you've seemed to have missed.

Looks to me that you are at that critical point in the evolution of anyone who wants to get into rocketry where you now need to spend some time learning how to use simulation software. There really isn't any other safe way forward for you now...
Attachments
Simulations.JPG

Lister
Engineer
Engineer
Posts: 967
Joined: Fri Jun 05, 2015 5:36 pm
Location: Bendigo, Victoria

Re: How to calculate thrust required to lift a heavy rocket?

Postby Lister » Tue Sep 15, 2015 1:59 pm

Thats fantastic, well done Ryan. Keep using OR and it becomes second nature. To add a payload bay make a new body tube the length of the payload bay and put it between the nosecone and body tube. add a coupler to it and make sure you select fibreglass for the coupler material. Too add the altimeter, add the mass component to the payload section and input the weight of your altimeter (can google altimeter 2 weight)


Return to “Propulsion”

Who is online

Users browsing this forum: No registered users and 1 guest