Cypres set in a moving vehicule

[Phlip 0]

I believe the cypres measures the pressure for the altitude and the change in pressure for the speed.
Our landing area is 450 feet above the airport, so we need to set the altitude to 450up on every jump.

Is it bad to set the cypres to 450up in a moving car that is (and stays) at the airport's level?

Phlip

[Cornholio 0]

Hey Phil, if you are talking about the van ride back to the airport from the lz, I think it is a gradual descent from point A to point B. Maybe once you get within 1/4 of the dz, does it start to level out to the airport altitude.

Ask Seabazz....he should know the answer to this.

Butthead: Whoa! Burritos for breakfast!
Beavis: Yeah! Yeah! Cool!
bellyflier on the dz.com hybrid record jump

[hookitt 1]

Simple answer... yes it's bad. Can it be done? Probably. You happen to be near a very famous faultline, so I doubt that it's as level as you think. Besides, what would you save by setting it in in the Van?

Stick with the routine of setting back at the Airport.

My grammar sometimes resembles that of magnetic refrigerator poetry... Ghetto

[Phlip 0]

ok ok

I know the van goes down since it has to go from the landing area (450up) to the airport!
The question was : "if the car is at the same altitude as the airport and stays level".

I agree with you it doesn't make sense to take a risk to save 1 minute, that will be in another thread

I guess I also wanted to understand more how this thing work.

[hookitt 1]

There have been cypres test, where the aircraft flew level at 4000 ft to fool the cypres.

Yes it can be done.

My grammar sometimes resembles that of magnetic refrigerator poetry... Ghetto

[billvon 2,996]

>The question was : "if the car is at the same altitude as the airport and stays level".

And the windows stay closed - then yes, it can be turned on and it will calibrate normally.

[diverdriver 5]

Quote

>The question was : "if the car is at the same altitude as the airport and stays level".

And the windows stay closed - then yes, it can be turned on and it will calibrate normally.

Well, I'm not so sure about that. Wouldn't a low pressure be created inside the vehichle with increased driving speed? It would probably be miniscule but then again has anyone messured it? I would think with the windows up it would be a greater error than the windows down but I do see your point.

Simple answer, stick to the plan of setting it back at the packing area. Don't they pay a quarter to a kid anymore to redo all the Cypreses there still?

Also to add....I base my points on the fact that when you use the alternate static source in a C-172 and add power you will get a "bump" in pressure and an reading error because the source is inside the cockpit. The flowing air around the fueselage creats a lower pressure inside the cabin.

Chris Schindler
www.diverdriver.com
ATP/D-19012
FB #4125

[billvon 2,996]

>Well, I'm not so sure about that. Wouldn't a low pressure be created
> inside the vehichle with increased driving speed? It would probably
> be miniscule but then again has anyone messured it? I would think
> with the windows up it would be a greater error than the windows
> down but I do see your point.

Depends on where the venting system is and how it's ducted. Most cars have vents that operate even when the 'vent' gaspers are closed. If more of the vents face forward, pressure inside is higher than ambient. If more of the vents face rearward, pressure inside is lower than ambient. Since modern cars pay pretty careful attention to venting (it affects things like defrost, car audio sound, and perception of road noise) I would be willing to bet that a car's vents give you a more accurate pressure than what you get when you roll the windows down, due to the natural "alternate-static-air" venturi effect.

But in any case, what a cypres cares about is a stable pressure, not neccesarily an accurate one. Being off by +/- 50 feet is not even observable; that's within the error band of the cypres' sensor. However, a rapidly changing pressure, such as what you get with a car's windows down, will cause it to not calibrate properly or at all. The ultimate example of this is to open a sunroof in a car but prevent that little 'wind deflector' from popping up. Often you'll feel a booming or a shuddering, which is the mass of air in the car resonating at a very low frequency. Depending on the design of the cypres and the frequency of resonation, this could keep you from turning the cypres on at all.

[diverdriver 5]

Thanks Bill.....oh yah and.......NERD ALERT! We're such geeks.

[Rdutch 0]

I think a cypress wont calibrate if it picks up a big variation in height while calibrating anyway.
I once had 2 newer jumpers behind me, and one of them asked me to help them. They were trying to turn the one's cypress on while climbing to altitude, and it kept resetting. I let them know how bad an idea this was, and that if he was going to jump it would be without a cypress. When I got to the ground I checked the guy's gear just to see if it was a low battery that kept making it reset, and it counted down to an almost full battery (which I confirmed by the packing data card was a new battery). Later I was told that they make them that way to avoid this situation. Haven't heard it from the manufacturer but it makes sence.

Ray
Small and fast what every girl dreams of!

[diverdriver 5]

Quote

I think a cypress wont calibrate if it picks up a big variation in height while calibrating anyway.
I once had 2 newer jumpers behind me, and one of them asked me to help them. They were trying to turn the one's cypress on while climbing to altitude, and it kept resetting. I let them know how bad an idea this was, and that if he was going to jump it would be without a cypress. When I got to the ground I checked the guy's gear just to see if it was a low battery that kept making it reset, and it counted down to an almost full battery (which I confirmed by the packing data card was a new battery). Later I was told that they make them that way to avoid this situation. Haven't heard it from the manufacturer but it makes sence.

It's in the User's Manual. You can't set a Cypres on the way to altitude. Why would you want it to set? It would set at the altitude you happened to be at at that very moment. It would basicly fire high if it didn't have the inhibit logic.

Chris Schindler

[r2hubert 0]

Actually windows closed or open the difference will be very minimum, or I guess I will see the difference on my altimeter also, right?

--
Renaud SMA #9
"Mind is like parachute. It only functions when it's open."

[diverdriver 5]

Quote

Actually windows closed or open the difference will be very minimum, or I guess I will see the difference on my altimeter also, right?

Next time you are cruising along at highway speeds open up one of your windows. Do you feel a pressure change? I believe that the pressure inside a truck/van/car will be lower than the outside ambient airpressure thus possibly calibrating at a higher altitude to fire than it would normally had it not been in a moving car. Again, the easiest thing to do here is just wait to calibrate it at your departure point and then adjust it for any variation in landing altitude. Takes out the "what ifs" of this situation.

Chris Schindler
www.diverdriver.com
ATP/D-19012
FB #4125

[Sebazz1 2]

Hence why I've told you guys not to set your Cypress's on the van ride, but nooooo nobody lsitens to Seb...

[hookitt 1]

Just pack up in the van, Set the cypres later :)

My grammar sometimes resembles that of magnetic refrigerator poetry... Ghetto

[Craig 0]

[replyBut in any case, what a cypres cares about is a stable pressure, not neccesarily an accurate one. Being off by +/- 50 feet is not even observable; that's within the error band of the cypres' sensor. However, a rapidly changing pressure, such as what you get with a car's windows down, will cause it to not calibrate properly or at all. The ultimate example of this is to open a sunroof in a car but prevent that little 'wind deflector' from popping up. Often you'll feel a booming or a shuddering, which is the mass of air in the car resonating at a very low frequency. Depending on the design of the cypres and the frequency of resonation, this could keep you from turning the cypres on at all.

[r2hubert 0]

I guess we were not really concern about this small variation because we are setting our Cypress to 450up or 420up (depend of people) and the landing area is ~300up or something, but there are some hills surrounding the area. So I think it's really hard to determine what settings we need. So my guess is that's why we are not really concerned about this little deviation.
But I totally agree it's safer to take is time and set the cypress at the packing area.

--
Renaud SMA #9
"Mind is like parachute. It only functions when it's open."

[Phlip 0]

see talk back: "what about this extra minute"

[Craig 0]

Quote

I guess we were not really concern about this small variation because we are setting our Cypress to 450up or 420up (depend of people) and the landing area is ~300up or something, but there are some hills surrounding the area. So I think it's really hard to determine what settings we need. So my guess is that's why we are not really concerned about this little deviation.
But I totally agree it's safer to take is time and set the cypress at the packing area.

What altitude difference does your altimiters read between the landing area and the airport? There is the altitude difference, pretty darn close anyway. In my opinion you really should set your AAD as close as possible to what you landing area will be. Lets use your settings as you stated above. The landing area is 300 feet above the airport but yet you set the AAD for 450 above. Now, as long as the CYPRES works as stated you just set it's activation altitude for 900 feet AGL. If I remember correctly the CYPRES can fire at up to 1,200 ft AGL if you are going through the opening sequence at about this time (example pull at 1,500 ft). Now raise these numbers 150 ft...1,350 and 1,750 respectively. I would really be hoping to not have a need to "take it a little lower" for whatever reason and especially hope not to have a snively opening. On the other hand, if you set the CYPRES for and altitude lower than the landing zone....well you get the idea. Just some things to think about I guess.