I'd be interested in seeing that if you could bring it to the next launch.

I could drive they keying with the spare switched output on the Parrot, but then it wouldn't be a factory-standard altimeter. I would also have trouble squeezing in code to have it periodically transmit my call sign.

Warren,
Man that is small. Was that off the shelf, or did you build it?

Gregs stuff can be flown on 3v or so which means a three stack of those wee 50mAH NiCds will power it for some time, and easily fit a 17mm if not 13mm tube.without adding a lot of length, while weight is well below useable ballast--bout 10 grams or so.

I bought it. It's a standard module, runs on 3-6 VDC and provides 250 mW of output power. It's made in the UK for long range remote controls and supports a bit rate up to 128Kbaud. Since it has CMOS inputs, it can be driven analog as well. There is a matching receiver module. Built into a device with a PCB antenna, they guarantee 1850' of range on the ground. Airborn with a properly cut wire antenna it should do far better. Basic tests indicate 2 miles minimum, though I haven;t flight tested it.

I'd be glad to bring it with me. I'll look for the data sheet on the set and send you the PDF or post it where you can get it.

Warren

By the way Adrian, put me down for one of those altimeters when you've got one that will do at least Apogee deployment. Without electronic deployment, you really can't optimize for altitude.

Grr. Bill, you got me thinking, which is a dangerous thing. I've been planning for my first deployment altimeter to have lots of bells and whistles like an on-board arm switch, continuity checks, pyro current measurements, 6 Amp output current, and lots of programmability for the 3 deployments. But what would it take to just fire a single apogee deployment using the Parrot and its single cell battery, if it's just a bare-bones implemenation? Turns out the answer is that it probably just takes replacing a very extremely tiny part with an extremely tiny part. I think I could have fit it on the existing board. Then I could support a 3 Amp firing current for a short duration. The next question is, is it worth throwing away $180 in boards and delaying for another week, given that the end product would have a number of limitations:

No terminal blocks. I'd solder a pig-tail for the pyro output
No continuity checks.
No arm switch
No programmability, just apogee deployment. Maybe a mach inhibit based on accel-derived velocity.
3 Amps max into a 1 ohm load
Discharging the Li-poly cell for a short time at way over its spec (continuous) rating.

I should already know this, but what's the resistance and all-fire current for a low-current ematch? The Parrot, as is (with a couple extra lines of code) could be a 3.6V source in series with a 4.25 Ohm resistance.

Adrian,

The specs on the M-Tek ematches that Tim carries are at:

http://www.electricmatch.com/product.html

I bought a handful to do ground testing. I also ordered some filament canisters from Pratt Hobbies (similar to Quickburst's Hot Coils, but tested with "normal" altimeters).

Ken

Most E-matches on the market today have an all fire current in the range of 500mA or less, with somewhere around 1 ohm resistance. It should fire pretty easily.

By the way, Adrian, if you do design your altimeter to deploy, and want to show people the light regarding long burn motors in slightly larger diameter rockets, I have a G25-5 that I could give you for an altitude attempt. I have had designs in rocksim where it simmed at over 9500 feet. It's a 29mm standard length G, with about a 5 second burn and 125Ns. Should be fairly decent at getting the record, and I have no doubt about it's ability to clear 8k or more pretty easily in an optimized rocket (it should stay subsonic too :))

It still won't touch a 24mm G55... which I will be flying before December 31st when it goes out of certification.

Warren

me too. The closest animal extant is the Ellis 24mm SU G37 which has a tad over 110N-s but a longer burn, making it a near replacement for the vaunted G55.

It still won't touch a 24mm G55... which I will be flying before December 31st when it goes out of certification.

Warren

From all my sims, it more than touches it, it well surpasses it with a well optimized rocket. I've never simmed a G55 at over 8500, while I've simmed the G25 at well over 9k. One sim approached 10k, but I have doubts about its accuracy. Keep in mind that even though the frontal area is increased by 46% with the 29mm rocket, the coefficient of drag can easily be half of the cd of the 24mm rocket for a decent portion of the flight simply because of the lack of mach flight. Still, it doesn't matter that much - it'll all come down to which actually flies higher, which we shall see at some point in the relatively near future.

I have sims with the G55 that push slightly past 10K and reliably sim in the mid 9K range. The crux is that your G motor is 29mm whereas the G55 is a 24mm motor - a major change in drag. Of course I'm not about to release the details of the rocket until I fly it for the record.

By the way, a reminder to ALL altitude record aspirants - You MUST declare the flight to be an altitude record attempt BEFORE the button is pushed. No exceptions.

Warren

The other crux is that the G55, in an optimized rocket, will be at minimum in the transonic if not the supersonic, while the G25 will not. That is also a major change in drag. Which one is the greater effect remains to be seen - I have no doubt that both can break the current record though.

I've looked at too many sims not to know that keeping a rocket subsonic is almost always best, unless you blast thru in a hurry. Thats where IMO F and G records seem to behave odd and a 29mm slowburner can outperform a 24 mach buster. As Chris indicates its from the rapid rise in Cd. A great illustration of this phenomenon is his data from the I600 blast when Cd rises from the low .4 range to approx .7

One way to think about it is terms of a work function. Work against gravity is constant depending only on the endpoints, while work on drag is not a state function, (in math speak, instead its a line integra) that very much depends on path, or in this case velocity. So if 4 seconds of a flight where say 5000 ft of altitude are gained is done at a Cd of .7 or so, the energy lost to drag will be almost twice that of the same rocket which stays below say 800fps ascending the same 5000 (and taking 7 seconds to get there). So the 45 percent increase in drag due to greater surface area is more than repaid. This is straight forward physics.

The next few launches look like they will be very interesting 8)

One way to think about it is terms of a work function. Work against gravity is constant depending only on the endpoints, while work on drag is not a state function, (in math speak, instead its a line integra) that very much depends on path, or in this case velocity. So if 4 seconds of a flight where say 5000 ft of altitude are gained is done at a Cd of .7 or so, the energy lost to drag will be almost twice that of the same rocket which stays below say 800fps ascending the same 5000 (and taking 7 seconds to get there). So the 45 percent increase in drag due to greater surface area is more than repaid. This is straight forward physics.

Actually, it's even a bigger factor than that. The Cd is just the coefficient in the drag equation F = 1/2 pV^2*Cd*A. So if the velocity doubles to put the rocket into the transonic region, you'll not only get almost a doubling of the Cd, you'll also get a factor of 4 in the velocity term, for a total of almost 8 times drag force for the same area. That's a lot of leverage to overcome the area increase. On the other hand, gravity losses are worse the longer it takes to get to apogee, but all this is accounted for in Rocksim, which shows a subsonic F rocket just crushing the TRA record.

As I said though, if you have a way to deploy with it, you can have my G25-5 for an altitude attempt (I wish I had a G25-15, but the 5 second was hard enough to find as it is). From my sims, you should crush the TRA G record fairly easily, as it should outperform the F10 in a similar design to your F rocket (just lengthened slightly). 10k might not be out of the question, putting you almost as high as the current H record.

By the way, the G25, like the 55, goes out of cert on 12/31/07, so you would want to do it relatively soon...

I don't want this to come out wrong and I don't want this to come out smarmy (that was a disclaimer) but simulating something and flying it are two totally different animals. The TRA "F" record hasn't stood for as long as it has because it is a chump record. I have heard many folks say online and in person that they have an F rocket simmed to 8K or 9K. I also have stuff simmed that high. On game day, they just don't fly as high as they are simmed. Some sim files are just inherently bad.

The Ellis L330 is another weird one. My rocket "beLLwether" (built especially for that motor) sims to 28-29K. I've flown it three times on L330s, and each time I got about 23K. Ditto for the K250s. The single-use 29mm Aerotech G motor files seem to be notorious for bad simulations.

Bottom line is that every one of us (me included) has at one time or another gotten AGU (all geeked up) about some stupendous motor/rocket combo that goes a zillion feet high in Rocksim. I've found that my actual mileage DOES indeed vary -- and almost always to the downside.

BTW, I have found many of the AeroTech and CTI reloadable sims to be uncannily accurate. For some reason, the bugs seem to be in the aforementioned loads, with only a few exceptions. I'm not sure how Apogee loads perform? I've never flown one...