Jolly Logic Altimeter 3 odd data chart

[solid_fuel]

I had an anomaly in the data chart for one of my flights last month. I was flying a Estes Vagabond on an Aerotech E18-7W, the flight returned an altitude of 1819 feet with a nearly 11 second delay and said that was early, also shows a weird altitude spike. I am thinking from looking at the chart the actual altitude was just over 1600 feet. ThrustCurve runs this combo to 1584 feet with a 7 second optimal delay. I have attached screen grabs of all the Alt 3 data. my airframe in this rocket has vent holes for the altimeter, the altimeter 3 was just tied to the shock cord and flew free during the decent. Any thoughts as to what may have caused the spike? the final picture is a close up of the spike.

 

[BDB]

I don’t know the answer, but I can commiserate. I’ve had some weird data from my A3 lately. But mine is getting pretty crusty from multiple fights and ejection charges, so I assumed that was the issue. I once had data like yours from my son’s Hyperbat. We stuck the A3 in the payload bay and it moved around in there, so that is what I attributed to the post-apogee spike. Despite these rare issues, I love my A3 and can’t wait for the release of the A4.

 

[BEC]

That sure looks like a violent spike in the barometric data at ejection. It was either a big charge or a much more violent than usual snap-back or collision between the A3 and some other part of the rocket. Rattling around in a payload bay (as BDB mentioned) will do this, too.

What does the accelerometer data look like? (Turn on at least the total acceleration trace and show us the graph with that on it as well as the altitude data.)

It is unusual for an A3 to get confused by a spike like that and report it as the max altitude. It has, in my experience, pretty good filtering on spikes in the data.

That the second page of tabular data says the ejection took place at 1806 feet, to me, corroborates my theory. The graph to me says the ejection was 2.5 seconds too late and very violent (and that the delay was more than 7 seconds). Again, the accelerometer data will shed some more light on this.

 

[Buckeye]

That sure looks like a violent spike in the barometric data at ejection. It was either a big charge or a much more violent than usual snap-back or collision between the A3 and some other part of the rocket. Rattling around in a payload bay (as BDB mentioned) will do this, too.

Yes, it could be any of these things.

I don't understand dangling a sensitive piece of electronics from a shockcord and then expecting to get meaningful data from it. An altimeter should be fixed rigidly in a bay and sealed from ejection charges.

 

[Larry Curcio]

The data themselves look perfectly normal to me.
Ejection spikes are the result of ejection shock. They are usually (usually) not the result of pressure anomalies - just shock. They are noise: variable in size but common.
Don't read stuff into them. Don't get bent out of shape.

I agree that the interpretation of the data by the software is off.
No biggie. Ignore the interpretation and let the graph speak for itself.
Cleansing breath!

 

[Lloyd Leichentritt]

In response to Buckeye, I don't have any rockets with a Av\bay so using a small JL Altimeter is a great way to getting this data without having to go to HPR or a rocket that was designed with a Av\bay. I'm looking forward in getting mine. I have one HPR but no Av\bay so I will be using a JLA3 for it. I think it a nice alternative to not having one. If I would go to L2 or L3 cert then maybe that would be a better option and would agree with you to having it fixed.

 

[solid_fuel]

It does have a loop to be tied on to the shock cord for use in rockets that down have an Avbay. It also has a mounting base for it you have something to mount it too.

 

[markkoelsch]

It does have a loop to be tied on to the shock cord for use in rockets that down have an Avbay. It also has a mounting base for it you have something to mount it too.

If it is barometric it should not be exposed to ejection gases. This is common sense. The pressure spikes from charges can cause issues. It also is going to get crusty with bp residue, which can cause corrosion.

I am with Buckeye on an altimeter belonging in a bay sealed from ejection charges.