About the limiting conditions for acceleration and dynamic pressure

SpaceNaruto

Member
Joined
Sep 8, 2022
Messages
5
Reaction score
2
Location
Japan
Nice to meet you.

We are currently using a simulator to develop a small rocket that can reach an altitude of several kilometers.
At this time, we are having trouble knowing how much acceleration and dynamic pressure we should limit in order not to destroy the fuselage and on-board sensors.

According to data on large rockets, it is common to set the acceleration to 4G or less and the dynamic pressure to 50kPa.
This is to protect the passengers and the expensive and sensitive payload.
Also, from the standpoint of efficiency, it is normal to reduce thrust and accelerate slowly while atmospheric density is high.

However, small rockets do not seem to care much about such conditions when compared to large rockets.
In fact, calculations using a simulator show that the speed increases rapidly and exceeds 4G and 50kPa due to the light weight of the vehicle.

If anyone knows of a document that describes the standards for small rockets, I would be very happy to hear from you.

Thank you in advance.
 

dhbarr

Amateur Professional
TRF Supporter
Joined
Jan 30, 2016
Messages
8,293
Reaction score
2,717
Most of the materials and build techniques in hobby rocketry are far too heavy/sturdy.

Has your team built many high power rockets already?
 

Steve Shannon

Well-Known Member
TRF Supporter
Joined
Jul 23, 2011
Messages
7,929
Reaction score
5,795
Location
Butte, Montana
@SpaceNaruto: A Tripoli member from Japan named Sumio Sawa is traveling to the USA to fly his Tripoli L3 flight at BALLS next week. Find him on Facebook and ask him for help. He would be a valuable resource for you.
The answers you want are already discussed numerous times within theses forums and part of the education that accompanies High Power Rocketry experience. Ranges of deceleration of 30 gees during deployment are not uncommon. Rockets are required to have at least three times as much thrust on liftoff as they weigh and are recommended to be at least five times. They’re usually even higher, sometimes much higher.
Good luck researching.
 
Last edited:

SpaceNaruto

Member
Joined
Sep 8, 2022
Messages
5
Reaction score
2
Location
Japan
Most of the materials and build techniques in hobby rocketry are far too heavy/sturdy.

Has your team built many high power rockets already?
Thank you, dhbarr.

No, we have not.
We have only built small rockets that can fly a few hundred meters.

This is our first attempt at a large rocket that can fly several thousand meters.
We are planning to mount various sensors, so we would like to know more about dynamic pressure and acceleration.
 

SpaceNaruto

Member
Joined
Sep 8, 2022
Messages
5
Reaction score
2
Location
Japan
@SpaceNaruto: A Tripoli member from Japan named Sumio Sawa is traveling to the USA to fly his Tripoli L3 flight at BALLS next week. Find him on Facebook and ask him for help. He would be a valuable resource for you.
The answers you want are already discussed numerous times within theses forums and part of the education that accompanies High Power Rocketry experience. Ranges of deceleration of 30 gees during deployment are not uncommon. Rockets are required to have at least three times as much force as they weigh and recommended to be at least five times. They’re usually even higher, sometimes much higher.
Good luck researching.
Steve Shannon, thank you for your reply.

We did not know about SAWA and will try to find him.

Thanks also for the information on acceleration.
I searched the forum but had trouble finding it because there is so much information.

We will continue to try the simulation.
 

Steve Shannon

Well-Known Member
TRF Supporter
Joined
Jul 23, 2011
Messages
7,929
Reaction score
5,795
Location
Butte, Montana
Steve Shannon, thank you for your reply.

We did not know about SAWA and will try to find him.

Thanks also for the information on acceleration.
I searched the forum but had trouble finding it because there is so much information.

We will continue to try the simulation.
Here is a link to Sumio Sawa: https://www.facebook.com/sumio.sawa.5
 

Bill Hanson

Well-Known Member
TRF Supporter
Joined
Nov 22, 2018
Messages
190
Reaction score
162
Location
New Mexico
Which simulator are you using for your calculations? If you aren’t using it already, I’d highly suggest OpenRocket

I’ll add that overloading the fuselage (airframe or body tube) is probably the least of your worries. Even a thick cardboard tube has considerable strength longitudinally (compression due to g-forces at launch), and in flight, the airflow largely goes along the tube so there isnt enough dynamic pressure to crush it in any reasonable range of velocity (less than Mach 2).

Now, air loads and flutter are a real concern for your tail fins. But I’d suggest you first think about just how high you want to go and then develop an aerodynamically stable rocket that will get you there with a given motor. It’s pretty easy to “what if” a design in OpenRocket. Then you can check to see if your design is strong enough to handle the expected conditions and reasonable variations. Then you can look at your sensors to see if they will have issues in that flight regime. Vibration is something you will absolutely need to consider.

You mention that you want to go several kilometers. Say it’s between 3 and 10 km (approx. 10,000 to 30,000 feet). Something that goes that high is a very advanced project and in the US would require a Tripoli or NAR Level 3 certification (which is what Mr. Sawa is trying to achieve). The contestants for the Spaceport America Cup fly to either 10,000’ or 30,000’ so you might want to look at the videos and presentations from the teams to get an idea of what they are doing.

Good luck with your project!
 

SpaceNaruto

Member
Joined
Sep 8, 2022
Messages
5
Reaction score
2
Location
Japan
Which simulator are you using for your calculations? If you aren’t using it already, I’d highly suggest OpenRocket

I’ll add that overloading the fuselage (airframe or body tube) is probably the least of your worries. Even a thick cardboard tube has considerable strength longitudinally (compression due to g-forces at launch), and in flight, the airflow largely goes along the tube so there isnt enough dynamic pressure to crush it in any reasonable range of velocity (less than Mach 2).

Now, air loads and flutter are a real concern for your tail fins. But I’d suggest you first think about just how high you want to go and then develop an aerodynamically stable rocket that will get you there with a given motor. It’s pretty easy to “what if” a design in OpenRocket. Then you can check to see if your design is strong enough to handle the expected conditions and reasonable variations. Then you can look at your sensors to see if they will have issues in that flight regime. Vibration is something you will absolutely need to consider.

You mention that you want to go several kilometers. Say it’s between 3 and 10 km (approx. 10,000 to 30,000 feet). Something that goes that high is a very advanced project and in the US would require a Tripoli or NAR Level 3 certification (which is what Mr. Sawa is trying to achieve). The contestants for the Spaceport America Cup fly to either 10,000’ or 30,000’ so you might want to look at the videos and presentations from the teams to get an idea of what they are doing.

Good luck with your project!
Thank you Bill Hanson, I am very happy to hear from you.

I see that OpenRocket is your recommendation.
We are using one, but need to get more familiar with it.

All of your specific advice and suggestions are very helpful.
Even if they seem trivial to you, they are really important information for us beginners.

We have contacted Sawa and received some valuable advice.
We will check the information about the Spaceport America Cup carefully.

Thank you so much!
 
Top