Estes Altimeter, Holes

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ArthurAstroCam

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I was just reading the instructions for the Estes Altimeter. They are calling for 3-4 evenly spaced 1/8" holes to be put 2 " from the opening in the body tube. What impact will this have on the performance of the rocket itself? I know the altimeter works on barometric pressure- are the holes necessary? I will be launching with an AstroCam.
 
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mg444

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I just purchased the Jolly Logic Altimeter Two. I haven't had a chance to read the instructions yet, but do all rockets need these holes for proper altimeter readings? It makes since that they would - I just really don't want to drill holes in my rockets. Thanks.
 

neil_w

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I just purchased the Jolly Logic Altimeter Two. I haven't had a chance to read the instructions yet, but do all rockets need these holes for proper altimeter readings? It makes since that they would - I just really don't want to drill holes in my rockets. Thanks.
If you want to get flight data for the "up" part of the flight, then yes. Holes. For typical LPR rockets they're barely more than pinholes.

I you only want to know apogee and descent data then you can get by with hooking the altimeter to the shock cord, and it'll get valid readings post-ejection.
 

GlenP

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I just purchased the Jolly Logic Altimeter Two. I haven't had a chance to read the instructions yet, but do all rockets need these holes for proper altimeter readings? It makes since that they would - I just really don't want to drill holes in my rockets. Thanks.
Yes, while not airtight by any means the rocket might leak pressure at a slower rate without vent holes. So, you would get an internal pressure measurement that lags the actual atmospheric pressure around the rocket, then the ejection charge goes off.
 

ArthurAstroCam

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Yes, while not airtight by any means the rocket might leak pressure at a slower rate without vent holes. So, you would get an internal pressure measurement that lags the actual atmospheric pressure around the rocket, then the ejection charge goes off.
OK, holes it us, although the body tube of my rocket will certainly not look as elegant now.
 

BEC

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Yes, there needs to be a path for the air pressure outside to get to the altimeter in a timely fashion. Holes near where the altimeter will be installed is the simplest way. Here is MUCH more detail (small apologies for blowing my own horn): https://www.apogeerockets.com/education/downloads/Newsletter543.pdf

The Estes Altimeter is fussier than some about needing good venting to work properly. Also be aware that, unlike just about any other, it does NOT lock in its reading after a flight, so that if it sees lower pressure (say when removing it from a payload compartment while accidentally covering the static ports) it will change it's displayed apogee value.
 

ArthurAstroCam

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Yes, there needs to be a path for the air pressure outside to get to the altimeter in a timely fashion. Holes near where the altimeter will be installed is the simplest way. Here is MUCH more detail (small apologies for blowing my own horn): https://www.apogeerockets.com/education/downloads/Newsletter543.pdf

The Estes Altimeter is fussier than some about needing good venting to work properly. Also be aware that, unlike just about any other, it does NOT lock in its reading after a flight, so that if it sees lower pressure (say when removing it from a payload compartment while accidentally covering the static ports) it will change it's displayed apogee value.
Well, for better or worse, that's the one that I have. So I will try to engineer holes that will make it work. In absolutely no rush. The AstroCam's camera keeps me plenty busy and entertained!
 

ArthurAstroCam

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I know they are hard to see, but if you just extend a line up from the fins you can see the holes for a variety of stuff. Makes finding a hole for a 2-56 shear pin on a black rocket much easier.
Very cool- thank you. The AstroCam body is so small, the holes will probably be much more noticeable. But going to give it a shot.
 

BEC

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Well, for better or worse, that's the one that I have. So I will try to engineer holes that will make it work. In absolutely no rush. The AstroCam's camera keeps me plenty busy and entertained!
I would be a little nervous about the Estes Altimeter in the Astrocam....not because of vent sizes but because of the complication of having that in with the 15 inch 'chute and the line to the nose cone tip.

I fly the FlightSketch Mini in many models, including my Astrocam (venting is done with holes made by a big t-pin — much smaller than 1/8 inch). Just getting everything out and open properly was complicated by having the Mini (in one of the little fleece pouches I use) in with all the rest of that stuff. I figured out after a few tries that tying the altimeter to the loop where the 'chute attaches, rather than to the base of the nose cone, led to fewer failed deployments (and related body tube damage).

The Estes unit is bigger and MUCH heavier....so if you try to fly in in your AstroCam setup it will be "interesting".

Here's what one can do with flight data from a recording altimeter and video from AstroCam and a piece of software to overlay the data from the altimeter onto the video:
 

ArthurAstroCam

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I would be a little nervous about the Estes Altimeter in the Astrocam....not because of vent sizes but because of the complication of having that in with the 15 inch 'chute and the line to the nose cone tip.

I fly the FlightSketch Mini in many models, including my Astrocam (venting is done with holes made by a big t-pin — much smaller than 1/8 inch). Just getting everything out and open properly was complicated by having the Mini (in one of the little fleece pouches I use) in with all the rest of that stuff. I figured out after a few tries that tying the altimeter to the loop where the 'chute attaches, rather than to the base of the nose cone, led to fewer failed deployments (and related body tube damage).

The Estes unit is bigger and MUCH heavier....so if you try to fly in in your AstroCam setup it will be "interesting".

Here's what one can do with flight data from a recording altimeter and video from AstroCam and a piece of software to overlay the data from the altimeter onto the video:
I think it is worth a shot! A
 

icyclops

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Yes, there needs to be a path for the air pressure outside to get to the altimeter in a timely fashion. Holes near where the altimeter will be installed is the simplest way. Here is MUCH more detail (small apologies for blowing my own horn): https://www.apogeerockets.com/education/downloads/Newsletter543.pdf

The Estes Altimeter is fussier than some about needing good venting to work properly. Also be aware that, unlike just about any other, it does NOT lock in its reading after a flight, so that if it sees lower pressure (say when removing it from a payload compartment while accidentally covering the static ports) it will change it's displayed apogee value.
Can you place a hole/port cover like below over the actual hole to cover it up yet allow air inside from the bottom. Or will the airflow over the body tube create a negative airspace and give the altimeter an improper reading. I worry that 1/8” holes in the body tube will allow airflow into the inside of the rocket and inflate it or mess with ejection pressure Under the wrong circumstances.
Anybody try this out?

1641612897212.jpeg
 

BEC

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Or will the airflow over the body tube create a negative airspace and give the altimeter an improper reading.
THIS is the issue with anything like that. I've not intentionally done this, but I have seen some very interesting things from air leaking in at the base of the rocket around the motor/mount. See my presentation at the upcoming vNARCON for an example or two of that.

How big the holes need to be are really a function of how big a volume the altimeter is riding in and to some degree on how fast it's going to go. See the article I wrote in the Apogee Peak of Flight newsletter linked in my post #11 above for the details.

On something the size of the AstroCam (BT-50-based) with the altimeter in with the recovery stuff, I'd do no more than three 3/32 inch holes, which I punch with sharpened brass tubing (also shown in that article). Then flow a little thin CA into the hole edges and then use some fine sandpaper to smooth out the outer surface.

No worries about all but the wimpiest of ejection charges. I'm not sure what you mean by inflating the rocket...

Ejection gases will leak out through those holes. See GlenP's picture above and the soot below the hole right above the rocket's name.
 
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I find the holes look better before painting. If the rockets has no vents, I tend to use the Estes altimeter. Also I’m down to one Flightsketch Mini and one damaged Mini that looks like it’s still works but Russ has been out of stock for the past several months.

There can be other issues with altimeters.

 

TheTank

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Here's what one can do with flight data from a recording altimeter and video from AstroCam and a piece of software to overlay the data from the altimeter onto the video:
I like that overlay! HPTuners is a race car parts company (logo in lower left). Did you pull that down from their website?
 

BEC

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I like that overlay! HPTuners is a race car parts company (logo in lower left). Did you pull that down from their website?
Yes. I was looking for an alternative to DashWare that would run on my Mac and found their RaceRender to be my main option. It took some fussing around to get things to work but I got there eventually.

I have to get a paid version of the software to get rid of the big logo in the corner :).
 

ArthurAstroCam

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Can you place a hole/port cover like below over the actual hole to cover it up yet allow air inside from the bottom. Or will the airflow over the body tube create a negative airspace and give the altimeter an improper reading. I worry that 1/8” holes in the body tube will allow airflow into the inside of the rocket and inflate it or mess with ejection pressure Under the wrong circumstances.
Anybody try this out?

View attachment 498832
It calls for three holes. Even if I was able to drill them close enough to be "covered" with such a part, not quite sure where I would get such a part. I may just wait till I build a rocket with a wider tube.
 

icyclops

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It calls for three holes. Even if I was able to drill them close enough to be "covered" with such a part, not quite sure where I would get such a part. I may just wait till I build a rocket with a wider tube.
You can fold a very small piece of BT into a flap…simple paper airplane type of fold. Folks with 3D printers could print something also….doesn’t have to be exactly like the picture, that is just all I could find to show an example of a protective port.
 

new2hpr

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Can you place a hole/port cover like below over the actual hole to cover it up yet allow air inside from the bottom. Or will the airflow over the body tube create a negative airspace and give the altimeter an improper reading. I worry that 1/8” holes in the body tube will allow airflow into the inside of the rocket and inflate it or mess with ejection pressure Under the wrong circumstances.
Anybody try this out?

View attachment 498832
I'm worried that you're all creating a solution for a nonexistent problem. Just poke a few evenly spaced holes (visually hide them if desired, but don't alter/block aerodynamically). Been done this way for quite some time without issue.
-Ken
 

tjkopena

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I you only want to know apogee and descent data then you can get by with hooking the altimeter to the shock cord, and it'll get valid readings post-ejection.
Maybe worth noting for people just starting to play with altimeters, that using this approach without holes and thus only getting accurate samples post-ejection won't necessarily get you the apogee, though it is hopefully close. You want ejection to happen as close to apogee as possible, but for a simple timed ejection on stock delays, you're going to be slightly (or more than slightly...) over or under the ideal. This approach should get the apogee if you happen to eject prematurely, but that limits your altitude and seems to me likely to be more stressful on the rocket. So in practice you're aiming to choose a motor delay that's just slightly over the ideal, meaning the rocket will have fallen somewhat from apogee before ejecting. In this setup your max altitude reading would thus be below apogee, although hopefully close.

Other than some satisfaction of hitting whatever altitude or speed, the most valuable thing I get from an altimeter is actually looking at exactly that timing. I'm not sure what data the Estes altimeter provides, but I most often use a Jolly Logic 2. It has a similar form factor as the Estes and also doesn't do any fancy data logging & export. But at least as useful to me as the apogee altitude is that it also reports the duration of the coast phase and duration from apogee to ejection (as well as the height at ejection and just a couple other things). Those durations are very useful toward evaluating if the delay on the motor is providing a long enough coast to maximize the flight, yet not being too long. Technically I guess it could and might time those durations w/ just accelerometers and the vent holes might not be strictly necessary to measure them accurately, but I wouldn't assume that.

I totally get not wanting to drill into a finished rocket once it's done if you didn't include vent holes beforehand, but it's fairly easy to do so cleanly and won't be noticeable at all. For one of my best looking & best performing rockets I 100% forgot about the altimeter holes until I was packing the rocket at the field for flight. Wound up basically gouging them out in the back of my car w/ a less-than-new hobby knife, which I definitely cringed at doing. But even those aren't noticeable, the rocket works great, and the data is spot on the manufacturer's flight predictions.
 

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