Skydive-drop pilots, how to...

[Meatbomber]

How do you guys calculate wind correction for the exit point ?

We're flying the jumprun at 80 KIAS with the Skyvan, what we do to get the wind correction is:

a) get the wind up to 5000ft and use 0.1Nm/3Kts Wind (wind drift on the chute)
b) get Wind up at drop alt and use 0.1/6Kts Wind (wind drift in free fall)

Then consider that you're "tossing" them 0.5NM due to exit speed

e.g. 15 Kts up to 5000, 30kts at altitude, same direction (say 270) would give:

Jumprun heading 270:
0.5NM+0.5NM = 1NM after passing overhead, and due to the balsitics you give the green light at 0.5NM after passing overhead.

Now that's all nice as long as the Winds aloft and the wind on the ground is about the same direction, and as long as you don't have an exceedingly high number of exits. But how to deal with highly different wind directions, high number of exits (long jump run)

What i do if the wind is calm and i have a large number of exits (for example there was a freefly corse and we had something like 17 exits with 24 skydivers in the load) is to fly an arc at 0.5 around the field, that gives everybody a pretty reasonable distance to the field and the seperation is not a problem too...

Comments, suggestions, different experience ?
MB

[Leviathan]

Meatbomber,

With Regard to the "line" of your jump run suggest you get an aerial of your DZ and plot vectors outward from the peas for the winds aloft forecast, this allows you to visualise the winds and their effects, depending on your GPS's capabilities if the winds are awkward consider an "offset" jump run, which I always find useful.
For example if the winds are howling out of the North on the surface but out of the West aloft a westerly jump run will yield slowest GS (obviously) but an offset to the north will have your jumpers opening upwind of the peas.

The more complex issue of the depth of the jump run is primarily a function of the number of groups on board and as such in the Skyvan or CASA can be a problem.

Without getting into all the various permutations I'll give you a few tips that have helped me out,

Winds aloft forecast below 20kts. have negligible effect on freefall drift derived from experience. So basically if your dealing with winds <20 put your jumpers out straight up or allowing for the inevitable flappin' about on the gate maybe .2 prior.

Also,if surface winds are <12 kts and/or depending on the peformance capabilities of the canopies you could can buy some "space" by putting them out even further downwind, thus allowing a larger area of "distribution"
The first jumpers out may not like this because they have to hold into wind but I usually tell them to take it up with the jumpers at the back who may take issue with being put out 2 miles from the DZ!

The arc method you mentioned works fine as well, only the jumpers don't like the tailgate moving about so you have to be ginger with inputs etc.

The biggest problem I had was jumpers ignoring exit separation (another science in itself) There's nothing worse than steaming down jump run (especially no wind/low wind) and watching the GPS tick down and the jumpers back on the tailgate having a tea party before exit.

So, in general terms the less wind aloft the less separation, never less than 5 seconds though. Separation should be a function of Groundspeed, bearing in mind again freefall drift is negligible below 20 kts.

If you have a mix of disciplines on board consider freefliers first, RW next and tandems always last, a large RW formation should maybe go first with a longer than normal separation for them. I usually let the load organisers sort this out and try and get an idea of what we've got enroute to altitude and make corrections accordingly.

So basically, tricks up the sleeve are plot your winds outwards from the dz starting with surface winds. Offsets for awkward wind conditions, disregard freefall drift below forecast 20 kts aloft, consider downwind exit points (not too far downwind!) for low surface wind conditions, arc method. Talk to the jumpers especially first out/last out and get an idea of opening points so you can "dial" in the jump run.

E-mail me if you want to talk more about it,

Regards

Leviathan

[static]

Hi There!

We use the following method:

First run of the day, we throw a "streamer" out of the airplane at 2000ft directly above the dropzone. This streamer is simply a small piece of wood with a brightly coloured piece of cloth or paper attached to it.
Then you simply watch where it lands. This is a simple and accurate method of finding the ideal exit point.
It disregards the drift during freefall, but hey, if you`re such a hotshot skydiver you`ll be able to make up for that during your last 2000ft :)

Good Luck.

One last tip: Never, never let the jumpers decide on the exit point by their reference to the ground from the airplane. Only very rarely will you find a jumper that can accurately judge his position by looking down.

[Meatbomber]

Excellent tips Leviathan !

Regarding the wind drifter: in the times of GPS and therfor well known wind direction and spped plus canopies that have todays performance i guess they're pretty rarely used.. especially out of the big planes (like the Skyvan, Casas etc..)

unless you plan static line round canopy drops :)

Leviathan:

when you fly an offset jumprun, say 0.5 offset to the north on a 27/09 runway / Jumprun (wind aloft being from the west, OR the dropzone very narrow (had that as well) where do you start your drop ? afer all it's slant range then..

[Leviathan]

Hi Meatbomber,

Yes I was afraid you'd ask me that!

To use your example winds aloft are less than 20 kts, surface winds are 15-20 out of the north and the DZ is oriented east west trees either side (seems like that always eh?)

A .4 .5 offset for what are pretty high surface winds would work nicely, a westerly jump run distributes everybody a long a line upwind of the peas, allowing everybody to make it in but like you say the offset complicates the exit point.

At any given time you'll never get any closer than .5 nm or "abeam" to your waypoint so think of .7 prior as being .2 prior and say .8 past as .3 past you desired exit point etc. The amount of distortion mathematically is negligible because of the relatively small distances involved. These distortions however magnify if you get into offsets bigger than .7

So you want to distribute the jumpers equidistant EITHER SIDE of the abeam or .5 offset you plan to fly, so as to keep everybody as close to the DZ as possible. Exception winds aloft >20 then you go deeper.

The success of your offset jump run is also dictated by the Update rate of your GPS.

Again the critical element is the number of groups as you know 12 groups of 24 freeflyers is a challenge to get everybody in to the DZ and I have in the past made two jump runs to facilitate these situations. (boss didn't like that)

To re-cap winds aloft <20 will have little effect on freefall drift (except large rw formations), The amount of offset will be dictated by surface winds, try .5 for 15-20 kts and adjust up or down as necessary, be wary of offsets greater than .8

The main thing is to fly the PLANNED jump run and get feedback so you can dial it in as necessary. It's a bit of a black art If everybody makes it in on the first load of the day you're the man!!

With reference to the WDIs as you say they are useful when doing static line drops from say a Cessna but for operational and economic reasons not practical in large aircraft skydive ops.

Regards

Leviathan

[javelin]

Guys, don't get too technical. Lets go to basics, if all your jumpers are using square mains and reserves then the exit point becomes less critical in winds up to 15 - 20 kts. Start with a WDI and work out the upper winds from the met forecast. As a rule, they veer with altitude so if you calculate the spot from the WDI, the exit point should be deeper and further right in the northern hemisphere ! Get an aerial photo, divide it into squares, use a grid system and alter the spot accordingly during the day - ie C7 maybe moves deeper and right to D9. Use the GPS and spot from the front, espescially if your Van doesn't have a side door. The other technique as used in the States is to calculate a deep ish spot and run in cross wind - then all the groups have a chance of getting in as they simply funnel back towards the DZ. Message me for more info and we can chat if necessary. Yes Javelin's are the best kit !!

[Meatbomber]

Javelin: That's just not feasible with our operation, as we're flying from different drop zones prety much every week. Besides the Skyvan doesn't give me any view down and to the sides uneless you're banking it very hard.. not good for skydiver stomaches :)

Mind to explain the crosswind method a bit closer ?

Cheers
MB

[javelin]

Sure,
A modern square has a speed of 20 - 40 mph, it is capable of a good range in its glide, so is the reserve. Establish the depth of the spot either by a wind drift indicator or by calculation of drift in 2 minutes from opening against the ground and 2000' winds. Now run in crosswind at that depth of spot. The first group exit 500 metres short of the centreline of your DZ and groups follow at 5 -10 second intervals depending on size. Use gps for first spot and then modify as you go. If the local area demands a run in into wind, simply approach the run in at 70 degrees and intercept the run in about 500 metres short of the DZ. As you roll onto the run in, use a close in point and distance point on the horizon to aim for and in winds up to 20 knts give the cut as you cross the DZ. The first group will exit 5 secs later and then at 5 - 10 sec intervals - no problem! Give the last group some Schilling coins for the phonecall back to the DZ ! Don't worry about the turns, they are used to it and if not you can always hose out the back of a Van - I was used to 206's etc Private mail me with a contact and I will call you.

[gravity victim]

What's all this about pilots deciding who gets out where anyway? In my day, it was strictly the jumpmaster's responsibility, and should there be an unfortunate coming together of canopy and high voltage lines, the pilot could proceed to the bar for end-of-day refreshments with an untroubled conscience.

The longest walks I ever had to make carrying a parachute were inevitably the result of letting the pilot pursue his own theories about the exit point!

[Meatbomber]

LOL gravity victim i've had more than once a "didn't i say so" with jumpers who tried to spot on their own accord rather than going at the green light :)

[gravity victim]

You must excuse the ramblings of an old buffer from the Jurassic age of parachuting, Meatbomber. I can appreciate that in the days of square canopies and bigger turboprop aircraft taking lots of bodies to altitude, the pilot handles the exit point.
I guess that GPS has probably done for the fine art of spotting what it has done generally for navigation skills - but when we had to steer round canopies into tiny DZ's, it was something that a lot of attention was paid to, and very satisfying to do well.

I know that you probably fly experienced ******s, but I'm sure that keeping the beginners in the same County remains the formal responsibility of the jumpmaster/instructor, at least I hope so.

I will admit to having landed in the wrong County, and on a display at that!
:)
(Strange - the pprune censortron has rejected the word s k y g o d .) Is this a side-effect of the ban on religion and politics, I wonder?

[ 03 October 2001: Message edited by: gravity victim ]

[Meatbomber]

Subject: Calculated Air Release Point (CARP)


Hi,

dropping guys and it's all worked out by the talking GPS who sits behind me.

I'm all for keeping it simple as some of the replies to your thread seem to suggest but if you have a large stick and / or a small DZ there has to be some better method of coming up with the goods.

CARP for freefall is made up of:

Green-on to Off-Sill (GOS) - how long it takes the guys to get out of the aircraft.

Still Air Forward Throw (SAFT) - distance travelled by the jumper, due to the forward airspeed of the aircraft.

F/eefall Drift - depends on time in the air from end of SAFT to opening height and mean windspeed for that height range.

Canopy Drift - depends on time under canopy and mean wind speed for that height range

We have made up an Excell programme that takes 101+ variables into account and comes up with an offset in yards and bearing from the impact point.

(For static line we miss out Freefall Drift and use Canopy Drive as an equation function)

Taking into account the size of the DZ we also come up with a Parachute Cut-Off Time (PCOT). If the last guy isn't out of the aircraft by that time, in seconds, after the "Green-on" then the Red goes back on.

If you haven't much down view from the aircraft, either because of superstructure or higher drop heights it's simply a case of listening to the Nav or flying to the GPS position and getting them out.

As the driver I'm not fully sure of the numbers used but I'll look into it and see if I can come up with some ballparks, or if you can come back with some of your numbers as examples I'll give the problem to one of my guys as a project.

Rgds

Art

Hello Art!

Sorry i couldn't reply to your mail, i just got it bounced back as undeliverable...

From your response i'm gathring you're a military driver, Herc i suppose ?

You're right we don't have much of a down view from the Skyvan , especially considering that our standard jumprun is at 15.000 feet. And due to the fact that most skydivers are used to side exit a/c they don't get the spotting right at most of times... GPS drop is the best approach i think, and as far as i got from Leviathan in his response they are using the same procedure in their Casa.

But as you said the difficultie lies in the number of varibles !

You guys do mostly round canopies i suppose ?
I've been to germany 2 month back and we did some dropping on an airfield that had also a Transall from the german AF dropping sticks of 20 round canopies, they get out pretty fast which is a good thing, we do have the problem that in a load of up to 25 folks you can have as many as 25 exits! Having that many is somewhat unusual tho ;) but 10-12 exits is a normal number. The seperation is supposed to be in the 5-7 seconds range between exits.

For an example:

Jumprun at FL150
85 KIAS
12 exits

DZ allignment 27/09
say 1000 yards long and 100 wide

Winds on the ground:
180/15
5000 feet to 15000 feet
360/30

I actually had that situation.
Really looking forward to what you and your guys come up with ! I'd be especially interested on what variables you take into account.

Cheers
Phil
a.k.a MB