Vent holes in nosecone

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Champkai32

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Hello, in my high power rocketry build I have placed the altimeter in the nosecone. Do I need small holes in the nosecone for the barometric sensor get precise data and work well? Is this practise viable and will it cause any problems in rockets going above Mach 2?
 

SpaceX76

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Yes you need some way for the external air pressure to get to your barometric pressure sensor, to get any altitude data that is besides ground level.
 

David Schwantz

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Have you ever built a rocket before? I ask this as if you are planning a Mach 2 flight, you should already know the basics. Might want to try a couple LPR and then MPR first. But as Spacex76 said, yes you will need vent holes. Good luck.
 

Champkai32

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Have you ever built a rocket before? I ask this as if you are planning a Mach 2 flight, you should already know the basics. Might want to try a couple LPR and then MPR first. But as Spacex76 said, yes you will need vent holes. Good luck.
I have launched three Estes rockets before and want some experience for high power rockets! also thanks for confirming! :)
 

rharshberger

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Just be aware there will be nothing "precise" about any logged data (if using a recording altimeter) in the nosecone. The events will happen at the proper times (ejection at apogee and main at lower altitude) but the data will be so noisy as to be useless due to the turbulent airflow over the static ports. Your level of experience needs to increase a fair bit before flying much less building a M2 rocket, if all you have flown are Estes rockets.....or are you trolling the members of TRF?
 

Champkai32

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Just be aware there will be nothing "precise" about any logged data (if using a recording altimeter) in the nosecone. The events will happen at the proper times (ejection at apogee and main at lower altitude) but the data will be so noisy as to be useless due to the turbulent airflow over the static ports. Your level of experience needs to increase a fair bit before flying much less building a M2 rocket, if all you have flown are Estes rockets.....or are you trolling the members of TRF?
Nah not trolling, but thanks for the info will look into it, any ways to reduce the turbulent airflow? any specific hole location in the nosecone?
 

Tractionengines

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My personal thoughts are:
There are false high-pressure areas where the nosecone is pushing air out of the way, then behind that is the turbulent areas were readings jump around. By then you are aft of the nosecone.
So, best option is to put the (3)static ports in the upper end of the bodytube behind the nosecone sholder. Then vent thru the bottom of the nosecone into the body tube with (1 or 2 moderate size holes).
This will give the altimeter in the nosecone smooth pressure changes, and you get nice data to review later. Just make sure the holes in the body tube are sized for the volume being equalized and your good.
As they say though YMMV ("Your milage may vary" just in case you did know the abbreviation. )
Mike
 

Grog6

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Does anyone have a good formula for atmospheric heating of a nosecone vs mach speeds?
I'm thinking of a Sprint missile model. And how hard I need to push it to need a ceramic shell.
 

Champkai32

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My personal thoughts are:
There are false high-pressure areas where the nosecone is pushing air out of the way, then behind that is the turbulent areas were readings jump around. By then you are aft of the nosecone.
So, best option is to put the (3)static ports in the upper end of the bodytube behind the nosecone sholder. Then vent thru the bottom of the nosecone into the body tube with (1 or 2 moderate size holes).
This will give the altimeter in the nosecone smooth pressure changes, and you get nice data to review later. Just make sure the holes in the body tube are sized for the volume being equalized and your good.
As they say though YMMV ("Your milage may vary" just in case you did know the abbreviation. )
Mike
Thx
 

Mike Haberer

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Yes you need some way for the external air pressure to get to your barometric pressure sensor, to get any altitude data that is besides ground level.
If the bottom of the nose cone is straight, in line with the body tube, put them there. Ports placed on the tapered part of the nose cone will be "noisy" and only the ground and apogee readings are likely to be valid.
 

alexzogh

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Does anyone have a good formula for atmospheric heating of a nosecone vs mach speeds?
I'm thinking of a Sprint missile model. And how hard I need to push it to need a ceramic shell.
Now, this is trolling!
Might want to create your own thread for this subject.

In general:

1632745243559.png



T is ambient temperature, Teff is the effective temperature experienced by the nose cone, V is the velocity of the rocket relative to air, m is the "average" mass of air particle, and kB is the Boltzman's constant.

More specifically,

Q = 345 ρ0.8 M2.8/x0.2

Where:

  • Q is the heat flux in BTU per square foot per second.
  • ρ is the free stream air density, in slug per cubic foot.
  • M is the mach number.
  • x is the distance from the tip, in feet.
If you plot this out, you get:

1632745616157.png



Of course, you will need material properties and part dimensions to convert the heating rate into a peak flight temperature of the part of the nosecone you care about. Suffice it to say, this is a lot of heat


Second half of this data was stolen from here, which is great reading: https://sugarshotsolidworks.wordpress.com
 
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Champkai32

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If the bottom of the nose cone is straight, in line with the body tube, put them there. Ports placed on the tapered part of the nose cone will be "noisy" and only the ground and apogee readings are likely to be valid.
Ok! :)
 

Grog6

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I'm not intending to troll the forum; I've been watching youtube videos and stuff with some severe wonder and speculation.
There's a lot of nice reading there; I wonder how many lists I just made by ordering a book on tactal missile design, lol.
 

Grog6

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Here is what inspired me to ask the question:

<iframe width="560" height="315" src="
" title="YouTube video player" frameborder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture" allowfullscreen></iframe>
 

Grog6

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Amazing to know that those flight computers were mainframes, and could really only track one missile incoming, and the first nuke blinds the whole system...
 

beeblebrox

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Just as a note, Mach 2 produces more heat than you would expect. I flew a G300 with tiny fins and a nose cone made of oak. (29mm) The rocket was flown at night with photographic measurement of velocity. V Max was 2408 ft/sec. about Mach 2.1 The motor only had propellant and no smoke/delay element. AFTER burnout a clearly visible orange streak appeared as the nose cone caught fire...
 

RocketRev

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Hello Champkai32,

I would like to first echo post #11 from Mike in NE Ohio. Put the pressure equalization ports thru the bottom of the nose cone into the airframe itself. If you put the pressure equalization ports anywhere on the surface of the nose cone you will end up with absolutely false readings. The pressure on the surface of the nose cone, and there fore thru any ports thru the nosecone, is going to be greater than anywhere else on the rocket simply because it is the surface which is pushing the air aside. Any readings you get from ports thru the NC are going to be false readings. And even if you only go just past ******, it will spell disaster for any kind of barometric deployment electronics. Mach-2 plus is taking you thru a "whole 'nother critter."

Placement of the ports on the airframe itself is also important. In order to get clean readings without any false pressure spikes, you need at least three ports spaced evenly around the airframe. The old rule of thumb as I was taught it was a minimum of a full caliber behind and in front of the closest gaps in the airframe. In this case that gap would be between the nosecone and the airframe. This rule was very effective for rockets flying under ******. But you are planning on going a whole lot faster than merely breaking ******.

Going mach means that you are going to go thru the transonic region that is the transition between below mach speed and greater than mach speed. Funny things happen with pressure on the surface of an airframe traveling thru the transonic region. At least one very sizeable pressure wave will actually travel over the surface of the airframe from front to back as the rocket goes from below mach to above mach speeds. And depending on your design, there may be more than one pressure wave traveling back and forth along the airframe at the same time. Think along the lines of Chuck Yeager breaking the sound barrier for the first time. In his own words the airplane seemed to loose control during what we now know was the transonic region, but that control was reestablished once the airplane broke thru into the mach+ region of speed. There is a great deal of violent turbulence in the transonic region and it is not very easy to predict what it will do to your rocket.

Then you need to think about what kind of electronics you are going to be using. Not all of them are capable of working properly thru the transonic region and into multiple mach speeds. In the earlier days of electronics a whole bunch of them failed because they were not designed for mach speeds. Most of them these days, use a kind of false reading inhibitor to keep from reading these false pressure wave spikes as apogee and trying to deploy the recovery system, usually at Max-q which is always disastrous, at least in my experience.

There are other things that one can do, but please be careful. Going mach 2 plus can be a very challenging thing to attempt. I was in one of Tim the Wildman Lehr's N-10000 drag races out at LDRS 29 with 6" diameter Wildman kits on the 98mm Cessaroni N10,000 motor. I only have data for my rocket which hit mach 2.6 going straight up. I was not the first off the pad, but I did hit 14881 feet which was the highest recorded altitude of the group. Check it out on youtube at "wildman's N10,000 drag race" or cut and paste the following into youtube. For whatever reason I'm having a hard time getting the link to appear all I can get is the text.

So I speak with some experience. It can be done, but it is a challenge. And if you don't do it right.....? Well, be prepared for the consequences. And honestly, if you've just got three Estes rocket flights in your experience portfolio, you are no where near ready for ****** let alone any further. I wouldn't want to be on the same field with you making an attempt right now.

Brad, the "Rocket Rev.," Wilson
 

Grog6

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The Sprint had active cooling; some floro refrigerant was sprayed on the inside, apparently.

Maybe it was to put the fire out. :)
 

Grog6

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I'll start a thread; sorry about the thread hijack.
Thanks for the links and formula.
 

Donnager

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So, best option is to put the (3)static ports in the upper end of the bodytube behind the nosecone sholder. Then vent thru the bottom of the nosecone into the body tube with (1 or 2 moderate size holes).
This is what I've done. Vent the bottom of the nose to the airframe, and vent the airframe.
 

jderimig

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Alot of speculation, handwaving and hypothesizing going on in this thread. Here is a plot of barometric versus inertial altitude of my Balls 29 flight to Mach 2.3 with 2 vent holes on the nosecone placed on a VK nosecone near the point where the curvature goes to constant diameter. Yes there is some turbulence noticeable on the baro curve but it is hardly disastrous.

1632782067247.png
 

watheyak

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John’s post brought up a theme in some recent posts that’s been bothering me.

BREAKING THE SOUND BARRIER IN A ROCKET ISN’T A BIG DEAL!

Almost a non-event. No shocks. No vibration, no Hollywood movie buffeting drama. Just a minor increase then decrease in CD.

There, I said it.

Here’s data beyond John’s to support this. This rocket went Mach 3.5 with vent holes at the very near the tip of the nosecone, flagrantly pointing into the relative wind. *gasp*

The baro is the blue line. Pardon the poor resolution, I’m not at home where the full resolution file resides.
41051302-0FE8-44F3-AC03-03F752A31D72.jpeg

Maybe I’ll start a whole new thread. A PSA of sorts.
 
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rocket_troy

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Here’s data beyond John’s to support this. This rocket went Mach 3.5 with vent holes at the very tippy-tip of the nosecone, flagrantly pointing into the relative wind. *gasp*
If it was at the "very tippy-tip", doesn't that mean at the very tip pointing upwards? I'm guessing I'm missing something? Can you possibly attach a photo or even a rough sketch illustrating the position on the NC?

I house my electronics in my NC and have 2 opposing vent ports about 1 calibre down from the shoulder, but they're quite large and the resulting baro spike at the transonic is much more pronounced than John's. I can probably reduce their area significantly, but I'm really curious about your method and the reasoning behind positioning it where you do.

TP
 

watheyak

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If it was at the "very tippy-tip", doesn't that mean at the very tip pointing upwards? I'm guessing I'm missing something? Can you possibly attach a photo or even a rough sketch illustrating the position on the NC?

I house my electronics in my NC and have 2 opposing vent ports about 1 calibre down from the shoulder, but they're quite large and the resulting baro spike at the transonic is much more pronounced than John's. I can probably reduce their area significantly, but I'm really curious about your method and the reasoning behind positioning it where you do.

TP
By tippy tip I meant a few inches behind the tip. I was exaggerating for effect, I suppose. I’ll change the original post. 😬

I put the electronics as far forward in the nosecone as I could because the parachute and recovery harness were also housed in the nosecone.

This thread explains it all-
 

Buckeye

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John’s post brought up a theme in some recent posts that’s been bothering me.

BREAKING THE SOUND BARRIER IN A ROCKET ISN’T A BIG DEAL!

Almost a non-event. No shocks. No vibration, no Hollywood movie buffeting drama. Just a minor increase then decrease in CD.
I agree with you. The Mach speed occurs in the first seconds of the flight, so you just blinked and missed it. But, there was nothing to see anyway. An acelerometer is required to measure it with any accuracy, not the run of the mill baro altimeters. Sorry to harsh the buzz, but in fact, the simulation of speed is likely more accurate than any measurement. The rocket is not going to fly apart and shred at M=1 in Hollywood fashion. Any well-constructed cardboard, wood, or fiberglass rocket will be just fine. Here's the CD response to M=3. Meh.

1632829608809.png


CP moves around a little bit at supersonic speeds, but unless you are on the bleeding edge of stability, the effect is minor.

I will say that temperature increase above M=1 can be an issue, as in this thread:

 

jderimig

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If it was at the "very tippy-tip", doesn't that mean at the very tip pointing upwards? I'm guessing I'm missing something? Can you possibly attach a photo or even a rough sketch illustrating the position on the NC?

I house my electronics in my NC and have 2 opposing vent ports about 1 calibre down from the shoulder, but they're quite large and the resulting baro spike at the transonic is much more pronounced than John's. I can probably reduce their area significantly, but I'm really curious about your method and the reasoning behind positioning it where you do.

TP
My opinion is the shoulder is not an optimum location as it can be below where flow can separate. A location on a converging surface may be better.
 
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