maximum usable altitude of Perfectflite SLCF

Does anyone have any flight experience with the SLCF above 50K feet? I'd like to use one as a backup altimeter on a flight that sims to about 70K feet.

I know the SLCF is advertised to work to 100,000 feet and this is plausible because the MS5607 barometric sensor provides data to that pressure, although I think that accuracy may degrade as altitude increases. But at some point the sensor will be producing a really low value and apogee deploy may be triggered by noise, depending on how aggressively the the readings are filtered and what sensor oversampling rate is in use.

I've asked Perfectflite but haven't gotten a response yet.

I could do a vacuum chamber test but it's hard to get pressures that low with what I have.

It's my understanding that the issue with going above 50k (up to 100k) is more about the electrolytic capacitors boiling off. If you look at the Missileworks RRC3- that's the difference between the normal one and the extreme altitude one:

https://www.missileworks.com/rrc3/

That being said, the SLCF has an electrolytic on it (according to the pictures), so I don't know how they work when MW claims that their standard RRC3 doesn't.

djs said:

It's my understanding that the issue with going above 50k (up to 100k) is more about the electrolytic capacitors boiling off.

Click to expand...

I think the concern about this has been overstated a little, we're only talking about a couple of minutes of vacuum exposure.

Tell us how goes, someone has to be first....

Even if the software allows for it, I would think accuracy would degrade somewhat at the tropopause.

The TE/Meas-Spec sensors (the MS5607, MS5611, and the MS5637) are rated at 300 mbar at full precision, that works out to a little above 30,000'. The extended range, in which they will operate with a reduced precision, is 10 mbar, which is about 85,000'. It's in the data sheets...

cerving said:

It's in the data sheets...

Click to expand...

I'm well aware of the sensor data sheets, but it becomes a system question that can't be answered without the details of the processing as to whether apogee deployment will work reliably down to 10 mbar, which is why I asked for actual experience.

It's not just the sensors. It's how temperature and altitude are related. In the troposphere, temperature declines with altitude; in the stratosphere, temperature first remains constant with altitude, and then it increases. The temperature patterns affect the way the pressure data have to be rendered to yield altitude. The points where the temperature regimes change is variable, and it isn't easy to sense ambient temperature in a moving rocket - so even if the software can handle the equations, you have to know when to use which. Therefore, I speculate that accuracy declines somewhat when the rocket gets out of the troposphere.

But for apogee detection all that is required is that pressure decreases monotonically with altitude. Accurate conversion of p to altitude is not required.

jderimig said:

But for apogee detection all that is required is that pressure decreases monotonically with altitude. Accurate conversion of p to altitude is not required.

Click to expand...

Agreed. I think of usability differently than most, I guess .
Accuracy is affected, for what that is worth.

From what I've been told, a few thousand feet at 100K and above doesn't make much difference in terms of deployments, the air is so thin that the additional drag that an early drogue deployment may cause is fairly minimal. I added an extended timer to the original Eggtimer because somebody wanted to use it for a high altitude flight and they decided that a timer was the most reliable deployment mechanism. I don't know how that flight went, however...