Thermocouple HPR payloads? Help please.

We can sit here and bicker epoxies and TG temps all day. I can theoretically compute how hot something gets at supersonic speeds using undergrad knowledge of compressible gas dynamics. You know what I really want is hard data on a flight test of supersonic Mach numbers vs thermocouple recorded temperatures. I’m brainstorming mounting any thermocouple to a aluminum tip nosecone and or getting a custom pitot tube tip. I don’t have the budget to do this experiment yet, but I want help from the forum on thermal data logging systems. I also have never set up a thermocouple outside of a university lab. Do you guys think we can find a portable logging system cheaply and cram it into a 54mm MD rocket nose? Then shove an L motor and push it over M2.3. Anyone have experience with J type thermocouples?

Some high end hobby altimeters record temperature. I would love to make a more serious flying thermo lab eventually and post results. I’m extremely interested in nose tip temperature and also eventually fin temp if practical, let’s start with nose temp first.

https://www.omega.com/pptst/OM-EL-USB-TC.html

Wanting opinions, advice, and input... Just a Saturday armchair forum open source thought experience.

I think I found a thermocouple.

https://www.automationdirect.com/ad...MIvf_ev4-84QIVhsDACh3nkQ_kEAQYASABEgJmq_D_BwE

I’d like to discount your first statement. No, we can’t bicker all day about TG temps.

Good luck in your quest though, sound like a hot topic.

I have the older version of this:

https://www.vernier.com/products/interfaces/labq2/

I could fit inside a 4" rocket. It has 3 analog ports that can take thermocouples. It's designed for STEM education so it's pretty robust and easy to use. It has variable data rate recording and has a built in accelerometer, temp, and microphone. My son used it as part of a load cell for a science fair experiment and it worked very well.

I've thought of trying to use it to measure both the nosecone temp and the fin leading edge. Nosecone is easy but the wiring to the fins it what has always been an issue. I'm working on a 4" CF rocket that would be a good candidate for a test, at least for the nosecone.


Tony

Sure, you can measure and record all sorts of data, and even transmit inflight telemetry.

Thermocouples can be slow to respond and take either a specific circuit to interface or a bunch of number crunching.

Look at an Arduino using a DS18B20 temperature sensor (or 8).

An Arduino Nano and hand full of sensors can measure various points on the rocket. Add an SD card for storage and you can collect a lot of data.

A little research, $20 in parts, a little time breadboarding to work this out and you can be ready to go.

Used these for surface temps on fins/airframes...with epoxy coat over them to seal. Might work on inside of cone/metal tip.

search around to find various sizes/temp range....you can get just about anything . [used 500degree]
great for motor case temps also, that was eye-opening.

https://www.google.com/search?q=tem...AUIDygC&biw=1150&bih=588#imgrc=zmig8XKtCewU2M:

These would be simple solution [cheap] to get you going till ya figure out the fancy space taking stuff.

Adafruit has a handful of great options. A feather with an appropriate breakout board would be a pretty easy and cheap way to accomplish this. I've used this for a couple of small projects:

https://www.adafruit.com/product/3263

Looks like someone has already given you Arduino options for the logger and TC transducer end of things. I was going to suggest that, so I will, too!

I remember a rocket called Don't Debate This Too that I think flew with a thermocouple in the NC. Maybe see if Mike published any data from the flight on any of the forums. It was a MD bird running an N5800, so the result should have been a decent temperature .

Before jumping at thermocouples, what temperatures are you expecting?

Thermocouples are great if you can use their wide range but not the best thing if you can't. Given the temperatures expected, simple thermistors are probably best. Cheap and small.

If you must use thermocouples, consider type E as they have the highest output.

I have one of these: Just need an RDAS to fly with it.

https://aeroconsystems.com/cart/flight-avionics/r-das-thermocouple-expansion-board/

Wow, that board is perfect. I still have and fly a RDAS compact. Both my MD 54mm and 98mm have an aluminum tip nose cone that should be easy to modify.

I’ll have to buy one for BALLS this year. Thanks for the link.


Tony

UhClem said:

Before jumping at thermocouples, what temperatures are you expecting?

Click to expand...

Upwards of 578 degrees Fahrenheit at nose tip according to compressible gas dynamics theory including oblique shock effects on the nosecone. What I really want to do is start comparing this theory to reality. That’s kinda why I jumped to thermocouples and am standing firm on that decision for its high temperate range. One sample every second of flight is fast enough sampling, imo.

Use thermocouples if you like, but be aware that there are RTDs that can go way over that temerature at a reasonable price, like 500°C for about $5 or better, and they're easier to interface.

As for wiring to a fin edge sensor, if on lays up one's own FG, then it should be no big trick to embed the sensor and leads. Let the leads emerge from the leading edge of the tab and then run up the airframe interior to the electronics. But you would have to look out for CTE mismatch; this method fails if the FG expands more that the copper and rips the wires off the sensor.

Paired with a Nano, this might work:
https://www.adafruit.com/product/269?gclid=EAIaIQobChMIjZ-vkNXh4QIVQuR3Ch2N2QYzEAQYBSABEgKgoPD_BwE

Just be aware that those nifty MAX thermocouple parts that do cold junction compensation assume that their temperature sensor is at exactly the same temperature as the cold junction. Which is wherever you make the change from copper to thermocouple wire.

So put that transition as close as possible to the IC and put the assembly in some sort of thermal insulation.

Eagle Tree’s eLogger is set up for three channels of temperature logging. https://www.eagletreesystems.com/index.php?route=product/product&path=62&product_id=54 The temperature sensors they sell are essentially thermocouples on a long lead.

I have never flown one of these in a rocket but have a couple of them (V2 and V3) in RC airplanes where I’ve logged the winding temperature of a motor in flight and and that sort of thing. The Windows interface software takes some learning but is very flexible. If you go as low as 1Hz you’ll be able to record many hours of data.

I have flown their standalone altitude sensor as a rocket altimeter back when I first got back into rocketry (10 years ago or so). It was a little awkward to package in a LPR but it worked just fine. You’d need to power the logger on the battery connection with a small 2s LiPoly or some such but that plus temperature sensors alone would work just fine.

Added later: I see that they rate their stock temperature sensors to a maximum of 250 degrees F. But I’ll bet that if you dropped them a line they could come up with something that would suit your purposes or help you interface whatever thermocouple you’ve already selected.