thoughts on flying a PerfectFlite FireFly on the shock cord?

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Donnie

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The literature says at one point that you can do it "if accuracy isn't of paramount importance," but at another point implies that doing so can degrade the accuracy of the pressure sensor over its lifetime due to pressure spikes and hot gas temps.

Still incredibly new to this, so i might be worried about nothing, but what are your thoughts?

We bought this altimeter (my first) so that my little girls and I can get more data (and unique data for our locale) for 4-H Rocketry entries. We purchased some Quest Payloader One's from Apogee as well, since they have a payload bay. Now we're curious about the other rockets we have already built, that don't have a payload bay. I'm sure adding a bay isn't toooo difficult, but we really don't have any supplies on-hand for modifying stuff. I did a couple test flights with the altimeter and an 808 keychain cam taped to the outside of a rocket, and then did a test flight of the same rocket with the altimeter tied onto the nose cone's shock cord mount. I drilled some static ports into the body tube of the rocket, and all seemed to work just fine.

BUT, do you guys think I'm doing damage to the altimeter? How could I tell if it's affecting it over time without flying it with another altimeter side-by-side? I know these things are cheap, but people seem to always be running out of them, lol.

As a note, I've been EXTREMELY impressed with the altimeter. It's amazingly lightweight, and have had zero issues. Looks like that's the norm with them from other opinions on this forum.

If it was something that just "worked or didn't," I'd just keep using it on shock cords of rockets without bays and see if it eventually "didn't." But, I also want reasonable accuracy, so I don't want to be affecting it a little at a time...

I'm aware of the Jolly Logic stuff and its rugged simplicity, but the weight and size make of the firefly make it much more attractive in something like an Estes Crossfire...

Thanks in advance!
 
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The literature says at one point that you can do it "if accuracy isn't of paramount importance," but at another point implies that doing so can degrade the accuracy of the pressure sensor over its lifetime due to pressure spikes and hot gas temps.

Still incredibly new to this, so i might be worried about nothing, but what are your thoughts?

We bought this altimeter (my first) so that my little girls and I can get more data (and unique data for our locale) for 4-H Rocketry entries. We purchased some Quest Payloader One's from Apogee as well, since they have a payload bay. Now we're curious about the other rockets we have already built, that don't have a payload bay. I'm sure adding a bay isn't toooo difficult, but we really don't have any supplies on-hand for modifying stuff. I did a couple test flights with the altimeter and an 808 keychain cam taped to the outside of a rocket, and then did a test flight of the same rocket with the altimeter tied onto the nose cone's shock cord mount. I drilled some static ports into the body tube of the rocket, and all seemed to work just fine.

BUT, do you guys think I'm doing damage to the altimeter? How could I tell if it's affecting it over time without flying it with another altimeter side-by-side? I know these things are cheap, but people seem to always be running out of them, lol.

As a note, I've been EXTREMELY impressed with the altimeter. It's amazingly lightweight, and have had zero issues. Looks like that's the norm with them from other opinions on this forum.

If it was something that just "worked or didn't," I'd just keep using it on shock cords of rockets without bays and see if it eventually "didn't." But, I also want reasonable accuracy, so I don't want to be affecting it a little at a time...

I'm aware of the Jolly Logic stuff and its rugged simplicity, but the weight and size make of the firefly make it much more attractive in something like an Estes Crossfire...

Thanks in advance!

Anyone have experience with using the Firefly on a shockcord?
 
Mike,

I haven't flown my Firefly yet, but I've repeatedly flown PNuts (old and new version, also made by Perfectflite) and Micropeak simply tied to the shock cord. My teammates have also flown Adrels this way. We've never had a problem. I've always tied them to the shock cord, just below the nosecone, so they sit above the parachute (or streamer) and wadding. Only real concern is that ejecta from the engine will directly impact the barometric sensor but that is extremely unlikely, and I've never had it happen. Honestly, I wouldn't (and don't) worry at all about tying them to the shock cord.

As for the accuracy of the flight data flying them this way, the PNuts and Micropeak give a graph of the flight data and I've never had cause to believe they were not reading correctly.

Finally, the Quest Payloader One is an awesome, extremely underrated rocket.

Steve
 
I have a FireFly installed in an Alpha like that right now awaiting a chance to fly it. I did use a sharpened 3/32 brass tube to create some static ports in the body, and I have a little sleeve of sheet foam over the FireFly with the idea that it will protect it from being rattled around some. Since the whole device is covered in pretty thick heat shrink tubing (I had to cut a bit of it away to even get to the holes to use for the kevlar tether I made), and since of course you want the FireFly above wadding, shock cord and 'chute inside your Crossfire or whatever, I think PerfectFlite is being conservative in their instructions.

But that's all theory. Practice awaits a launch opportunity. Right now our club launch this coming Saturday looks like it will be rained out..... :(

I have flown multiple FireFlies in one model as well as flying them alongside other devices and I am impressed with them also. VERY consistent with one another and with Jolly Logic devices in particular.
 
Bernard,

Of interest is that the Firefly, Micropeak, and Adrel all use the same barometric sensor. In international competition we fly the Adrels without any venting ports at all. I know it's hard to understand how they could possibly work without vent holes, but they do. As it has been explained to me by the manufacturer of the Adrels, there is enough ambient air leak in all but the most hermetically sealed models to allow these ultrasensitive altitude altimeters to sense data. In fact, they work worse (lots of static) when any vent holes are used and we had lots of no-reads until we stopped using ports.

Since the three altimeters I mentioned all use the same sensor, one would think the others would be fine without vent holes as well, but I've not tried it. And if you are flying record-trial flights NAR rules require vent holes.

Steve
 
That is interesting. Certainly the pressure inside the model under those circumstances will lag the pressure outside in time, but since the model actually spends quite a bit of time right near apogee in a ballistic trajectory, as long as the lag isn't several seconds so that the inside pressure never bleeds down close enough to the lowest from pressure (presumably at apogee) before it's fallen too far and the pressure is rising again, it will be OK. Simple physics says that the rocket will spend two seconds within 16 feet of apogee (in earth's gravity and in a ballistic trajectory, neglecting drag).

I see that Adrel also recommend some tiny static ports when the rocket "is hermetic":

Adrel BMP instructions said:
Ventilation holes
For rockets S1 do not have ventilation holes (if the rocket is not hermetic)
For rockets S1 to be done two or three holes with a diameter of 0,1 mm – 0,2mm – (if the rocket is hermetic)
For rockets S5 to be done two or three holes with a diameter of 0,1 mm – 0,1mm

You actually are suggesting - indirectly - an R&D project where one could try to find out just how "leaky" the rocket has to be in order to give "close enough" apogee readings (within 1m I suppose would be "close enough"). I don't need any more projects right now :eek: :)
 
Based on the little bit of digging I have done it seems like the Firefly is a pretty new product and there's a bit to learn regarding how it behaves under various circumstances. I was considering adding an ebay to the nosecone of the Estes V2 I am building and using it to install the Firefly but maybe I'll just tether it to the nosecone. Using John Coker's method he demonstrated in his video I'd cut off the bottom of the cone and add a couple pieces of 1/8 plywood to act as a base and a point to connect the recovery system. Doing so would add about 14 grams. The clay nosecone weight that comes with the kit is 7 grams. Maybe adding an ebay to a rocket of this size is overkill.
 
I've personally used the FireFly tied to the shock cord (or directly tethered to the nose on a short kevlar leash) many times and with uniform good results as long is there is some venting. One of my TARC teams found out the hard way that they will read substantially too low - 30% or more - if there are no vent holes at all in a BT-80 size model. Smaller diameter models should equalize a lot faster since a much smaller volume of air has to seep past the shoulder. Would love to see this quantified but like Bernard I don't have time for any more projects.
 
So cool to see this thread finally come to life. Thanks, all!

We ended up mostly flying it in the payload bay, but nice to finally know we won't be hurting anything if we fly on the cord, as long as we have plenty of wadding.

Thanks again!
 
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