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Jump Run Direction

 

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kallend  (D 23151)

Feb 19, 2004, 5:59 PM
Post #26 of 57 (872 views)
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Re: [diverdriver] Jump Run Direction [In reply to] Can't Post

In reply to:
In reply to:
And additional factors that influence jump run direction are such things as avoiding lakes, oceans, swamps, rivers, etc. These are constraints that vary from DZ to DZ.


Now you REALLY are getting into the "art" of spotting. We could argue the flat open ground all day long. But when you take into account group size and type, topography, aircraft size (total jumpers), canopy types commonly jumped at that DZ, and ATC climb requirements/constraints you have to put it all together.

I spent lot of time studying a master.Wink


ZoneRat  (D 26968)

Feb 19, 2004, 10:26 PM
Post #27 of 57 (857 views)
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Re: [diverdriver] Jump Run Direction [In reply to] Can't Post

Ok. I'm going to do some research on Hooks and 308's statement because I don't want to take another swing at what is likely a very dead and beaten horse... I smell a laymans trap there. I find the phrase 90 knots "Indicated" interesting. Seems like that means speed of wind over wing rather than distance travelled (otherwise, I'd still have a valid point up there... I think)... but I'll try to look it up in a thread somewhere. I respect your time enough to do that before I answer back.

But regarding the art of spotting... (black art?):
I can see where canopy types make a dif. Same with load compliment. And I can see where different aircraft have different capabilities/ requirements regarding how much time you have vs need to exit jumpers so they can deploy in the Happy Cone...

But topography like lakes and rivers? A good spot's a good spot. Right? Just more pressure to make sure it really is right. Because there's more at stake when a jumper lands off. Might get eaten by a croc, or land in a river or somethin'..

Mountains... I can see that making a dif topographically speaking. But a swamp?

The Happy Cone probably doesn't care what's beneath it for the most part.

I'd guess.

(btw: I really do appreciate your helping me in this. I'm not trying to just argue... I do want to understand.)


sundevil777  (D License)

Feb 19, 2004, 10:38 PM
Post #28 of 57 (854 views)
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Re: [ZoneRat] Jump Run Direction [In reply to] Can't Post

Iindicated air speed means uncorrected for pressure changes at altitude, or something like that. True air speed - TAS vs IAS.


velo90

Feb 20, 2004, 1:51 AM
Post #29 of 57 (837 views)
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Re: [ZoneRat] Jump Run Direction [In reply to] Can't Post

Quote:
The Happy Cone probably doesn't care what's beneath it for the most part.

Quite right, but your happy cone is rather big. An aircraft flies in straight lines (or maybe there is a hook turn in there). This means that in reality the jump run cannot use all of that cone. If the pilot knows there are swamps and crocs to the left of the cone he can fly the aircraft more to the right of the cone.
Quote:
A good spot's a good spot. Right?
A good spot can turn into a bad one if the jumper has a mal.Unsure


pccoder  (A 43773)

Feb 20, 2004, 4:43 AM
Post #30 of 57 (826 views)
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Re: [diverdriver] Jump Run Direction [In reply to] Can't Post

In reply to:
In reply to:
Regardless of speed, doesn't the plane have to worker harder to maintain altitude if going with the wind than against it?

No.

So, just clarify for me. Quite simply, not some huge explanation. If the planes heading is North and wind is from the North, does the plane have to use more fuel to maintain the same altitude as if the wind is from the South? Or is it the other way around?


kallend  (D 23151)

Feb 20, 2004, 7:36 AM
Post #31 of 57 (811 views)
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Re: [pccoder] Jump Run Direction [In reply to] Can't Post

In reply to:
In reply to:
In reply to:
Regardless of speed, doesn't the plane have to worker harder to maintain altitude if going with the wind than against it?

No.

So, just clarify for me. Quite simply, not some huge explanation. If the planes heading is North and wind is from the North, does the plane have to use more fuel to maintain the same altitude as if the wind is from the South? Or is it the other way around?

The plane doesn't know which way the wind is blowing over the ground unless it's on the ground.


bmcd308  (D 27472)

Feb 20, 2004, 7:37 AM
Post #32 of 57 (811 views)
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Re: [ZoneRat] Jump Run Direction [In reply to] Can't Post

Think of an airspeed indicator as a device that measures how hard the air is pushing against it. When you stick your head out to spot, your smiling mug is an airspeed indicator. The amount of wind you "feel" is what determines your indicated airspeed. If you held a child's windmill out the door and counted how fast it was spinning, you would have made a primitive airspeed indicator. As each molecule of air moved past the windmill, it would push it some.

True airspeed is the rate that individual molecules of air move past a specific point. This is a little harder to feel on your face, since you are not good at detecting changes at the molecular level. So TAS winds up getting calculated based on IAS and the density of the air, which is a function of altitude and temperature. TAS is the speed you are actually moving through the air - or the speed at which individual molecules of air are moving past a specific point.

Why not just talk about TAS? Because IAS ("felt" speed) is what generates lift.

Think about the windmill out the door in a plane that will fly a constant true airspeed. As the plane goes higher, the less dense air pushes less and less on the windmill as the air moves past the blades, because there are fewer molecules to actually do the pushing. So the windmill turns more slowly, even though the speed of the plane through the air (its TAS) remains the same. In order to figure out how fast the individual molecules of air are moving through the windmill, we have to take into account the fact that there are fewer molecules pushing on the windmill blades.

Now take the plane up higher still. Eventually, you will notice that the thinner air is pushing less and less on the windmill, until it is hardly turning at all. At this point, you will hear a funny buzzing noise and a bunch of profanity from the cockpit. The buzzing was the stall warning. The profanity was the pilot. The pilot will do some cool pilot stuff, and pretty soon, your windmill will be spinning along quickly again.

For purposes of being a "cool" skydiver, it is important to recognize the distinction between IAS and TAS, but to act as if it does not exist when talking to pilots. This is because they understand this on an instinctive, gut level, and they do not even have to think about it. Arguing with them about it will only make you look silly. And they are used to dealing with people who do not understand it, so they won't really judge you for appearing not to have a clue. It is only when you try to appear to have complete command of the concept but do not that you look like an azz.


Brent


ZoneRat  (D 26968)

Feb 20, 2004, 7:37 AM
Post #33 of 57 (809 views)
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Re: [velo90] Jump Run Direction [In reply to] Can't Post

In reply to:
Quote:
The Happy Cone probably doesn't care what's beneath it for the most part.

Quite right, but your happy cone is rather big. An aircraft flies in straight lines (or maybe there is a hook turn in there). This means that in reality the jump run cannot use all of that cone. If the pilot knows there are swamps and crocs to the left of the cone he can fly the aircraft more to the right of the cone.
Quote:
A good spot's a good spot. Right?
A good spot can turn into a bad one if the jumper has a mal.Unsure

Both good points. I would prefer a spotter, Pilot or otherwise, who hedged their bets.


bmcd308  (D 27472)

Feb 20, 2004, 7:37 AM
Post #34 of 57 (808 views)
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Re: [pccoder] Jump Run Direction [In reply to] Can't Post

Neither


pccoder  (A 43773)

Feb 20, 2004, 7:44 AM
Post #35 of 57 (805 views)
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Re: [kallend] Jump Run Direction [In reply to] Can't Post

doesn't it know which direction it is blowing in the air?

and my question had nothing to do with the speed of air on the ground.


(This post was edited by pccoder on Feb 20, 2004, 7:47 AM)


velo90

Feb 20, 2004, 7:48 AM
Post #36 of 57 (802 views)
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Re: [pccoder] Jump Run Direction [In reply to] Can't Post

Quote:
doesn't it know which direction it is blowing in the air?

Scroll up a few post's and you will see that Kallend has already answered that question.


ZoneRat  (D 26968)

Feb 20, 2004, 8:13 AM
Post #37 of 57 (796 views)
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Re: [bmcd308] Jump Run Direction [In reply to] Can't Post

Brent, I want to thank you for your TAS/ IAS post. Very nicely written... Your examples were excellent. I can see where IAS/ TAS would really effect spotting on a high alt jump. I can also see where your explaination of those two concepts would be a great primer when helping someone understand why a canopy will fly differently at a Colorado DZ vs a sea level DZ.

And, I think it gives me the piece of the puzzle that allows to complete my "Why? Why you do dat?" post earlier up.

There are several concepts that have been brought up so far in my part of this thread. I'm gonna think on them a bit and post a set of tentative conclusions.

That should be good.Wink


sducoach  (D License)

Feb 20, 2004, 8:58 AM
Post #38 of 57 (782 views)
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Re: [diverdriver] Jump Run Direction [In reply to] Can't Post

Chris is the best at explaining the aircraft spotting and Quade gave a great example of the "cone".

Think of spotting in the context of ground speed and time. Upperwinds effect the ground speed of the aircraft which effects the time you have available in the "cone" to exit the aircraft.

More detail if requested

Blues,

J.E.


Premier billvon  (D 16479)
Moderator
Feb 20, 2004, 9:18 AM
Post #39 of 57 (776 views)
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Re: [pccoder] Jump Run Direction [In reply to] Can't Post

>If the planes heading is North and wind is from the North, does the
> plane have to use more fuel to maintain the same altitude as if the
> wind is from the South?

No. This misconception comes about because planes need to use more fuel to maintain the same GROUNDSPEED if they have a headwind. The plane takes the same amount of power (and hence fuel) to maintain a given airspeed, but if the air's moving, airspeed is not the same as groundspeed. That's why you will sometimes hear airline pilots mention that they can compensate for a headwind by burning more fuel. But if you just want to maintain altitude, there's no difference in heading into the wind or away from the wind.


velo90

Feb 20, 2004, 9:24 AM
Post #40 of 57 (774 views)
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Re: [billvon] Jump Run Direction [In reply to] Can't Post

Quote:
That's why you will sometimes hear airline pilots mention that they can compensate for a headwind by burning more fuel.

In my experience you just end up late at the airport and miss your connecting flight Unimpressed


pilotdave  (D License)

Feb 20, 2004, 9:32 AM
Post #41 of 57 (772 views)
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Re: [pccoder] Jump Run Direction [In reply to] Can't Post

Picture yourself on a moving sidewalk or giant treadmill. You can walk normally in any direction you want. Your actual MOVEMENT, relative to the fixed earth, will not be the same as your movement relative to the sidewalk.

Wind is just like the moving sidewalk. Does it take any more energy to walk AGAINST a moving sidewalk as it does WITH the sidewalk? Well, if you walk at a fixed rate (ie the same airspeed regardless of the wind), then no.

I think you're confusing the fact that if you want the plane to fly at the same speed relative to the ground while flying into the wind, then yes, more power will be required. But otherwise, the plane is just an ant on a treadmill. It doesn't care which way the wind is blowing.

Dave


kallend  (D 23151)

Feb 20, 2004, 9:33 AM
Post #42 of 57 (771 views)
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Re: [pccoder] Jump Run Direction [In reply to] Can't Post

In reply to:
doesn't it know which direction it is blowing in the air?

and my question had nothing to do with the speed of air on the ground.

Imagine you are in a hot air balloon floating above clouds so you can't see the ground. Would you be able to tell the wind speed and direction by, say, smoking a cigarette and watching which way the smoke blows? Or by watching the clouds? Remember, you will be blowing along with the wind, just like the clouds.


pccoder  (A 43773)

Feb 20, 2004, 9:56 AM
Post #43 of 57 (763 views)
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Re: [kallend] Jump Run Direction [In reply to] Can't Post

OK, I guess most of your last few explanations have made more sense to me.

Thanks for the clarification.


hoym  (D 12622)

Feb 20, 2004, 3:19 PM
Post #44 of 57 (747 views)
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Re: [ZoneRat] Jump Run Direction [In reply to] Can't Post

Okay, in the past I've scanned the discussions about exit order and spacing between loads. I decided to try to play with some numbers just for fun.
Someone one reading this can tell me if my math is correct or if this has already been considered.

BIG DISCLAIMER!
THESE IDEAS ARE FOR DISCUSSION AND THEIR ACCURACY HAS NOT BEEN VERIFIED!!!

I think the most important thing for skydivers to understand is the concept of ground speed (GS) and also the variables that affect GS. (IAS, TAS, wind direction, direction of flight).

Most pilots measure airspeed in knots (nautical miles per hour). Most skydivers understand statute (normal drive your car type of) miles so my calculations take this into consideration.

One nautical mile is equal to 1.15 statute miles (the unit of measure most of us state side folks use).

What we need to know in advance.
Ground Speed in Knots (GSK). This should be supplied by the pilot.
Distance desired between groups of skydivers. This should be dictated by the DZ, DZO or S&TA.
What we want to calculate.
TIME in seconds. The amount of delay needed between each group of skydivers to give the desired distance between groups.

With the GSK and desired distance information, we should be able to calculate the amount of delay needed between each group of skydivers on a given load.

A knot is a measure of nautical miles per hour. Because we want to calculate time of delay between groups in a measure of seconds, the first thing to do is convert the GSK (ground speed in knots) to a measure of distance of statute miles per second.

So Ö.
If the GSK is 80 then
80 * 1.15 = 92 miles per hour
92 / 60 = 1.5333 miles per minute
1.5333 /60 = 0.02555 miles per second

OrÖ
80 * 1.15 / 60 /60 = 0.02555 miles traveled per second.

Now for discussion purposes, letís say that you want .5 (one half) mile(s) between each group of skydivers. And here is THE BIG QUESTION (for all of us Jaywalk Allstars)Ö How many seconds do we wait to get a half mile of separation between each group of skydivers?

Take the distance desired and divide distance traveled per second and it will give you the amount of time the next group should wait before exiting the airplane.

.5 / .02555 = 19.569 (or about 20 seconds)

Letís look at two more examples with a hypothetical headwind and tailwind component put in to change the groundspeed. To try to keep it brief, Iím not going to change the desired amount of separation distance. You can decide to use whatever you want there.

So for this example, consider a 30 knot headwind so that now our airplane has a 50 knot ground speed.
50 * 1.15 / 60 / 60 = 0.015972
And (for half mile separation distance)Ö
.5 / 0.015972 = 31.3 seconds of delay between groups.

And now turn the airplane around so that thereís a 30 knot tail wind (110 knot ground speed).
110 * 1.15 / 60 / 60 = 0.035138
And for half mile separation distanceÖ
.5 / 0.035138 = 14.2 seconds of delay.


Now, letís go back to our 80 knot GS, half mile separation example where we need 20 seconds between each group. Letís say that there are 10 two-ways on this twin otter. If every group takes exactly 20 seconds between each exit, that should be 180 seconds of jump run from the first group exit to the last group exit.

If the plane with an 80 knot ground speed takes 180 seconds and it travels 0.02555 miles per second, then the jumpers will be spread out over 4.6 miles.

Just some ideas to consider.
If anyone would like to verify the math, that would be great.

BIG DISCLAIMER AGAIN!
THESE IDEAS ARE FOR DISCUSSION AND THEIR ACCURACY HAS NOT BEEN VERIFIED!!!

(Edited to make the incorrect 10 into a 20.)


(This post was edited by hoym on Feb 20, 2004, 7:29 PM)


Premier billvon  (D 16479)
Moderator
Feb 20, 2004, 3:27 PM
Post #45 of 57 (744 views)
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Re: [hoym] Jump Run Direction [In reply to] Can't Post

A reasonable approximation. As long as the winds are from the same direction at opening altitude, that formula will give you safe results. The only time it will fail is if winds are from the opposite direction at opening altitude, which is (fortunately) rare.


prost  (D 24959)

Feb 20, 2004, 4:45 PM
Post #46 of 57 (737 views)
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Re: [ZoneRat] Jump Run Direction [In reply to] Can't Post

Ok lost in the aerodynamics lesson is the original point.


There are times that jump run is not best into the wind. We have an 6500 foot long runway and the airport goes much farther in each direction. The airport is not nearly as wide. There are a lot of swamps around us. We almost always run jump run north of south (direction of the runway) and off set it in the direction the wind is coming out of. This way worst case scenario, everyone can at least land of the airport.


kallend  (D 23151)

Feb 20, 2004, 6:27 PM
Post #47 of 57 (734 views)
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Re: [hoym] Jump Run Direction [In reply to] Can't Post

Quote:
Now, letís go back to our 80 knot GS, half mile separation example where we need 20 seconds between each group. Letís say that there are 10 two-ways on this twin otter. If every group takes exactly 10 seconds between each exit, that should be 180 seconds of jump run from the first group exit to the last group exit.

I must be missing something here. If they need 20 seconds between each group, why do you then say they take 10 seconds between each exit? If it were me and I needed 20 seconds for separation, I'd wait 20 seconds.

I also think 1/2 mile separation between 2-ways is overkill.


hoym  (D 12622)

Feb 20, 2004, 6:49 PM
Post #48 of 57 (729 views)
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Re: [kallend] Jump Run Direction [In reply to] Can't Post

Quote:
If they need 20 seconds between each group, why do you then say they take 10 seconds between each exit? If it were me and I needed 20 seconds for separation, I'd wait 20 seconds.

I also think 1/2 mile separation between 2-ways is overkill.

Oops, the 10 second note was a typo. The math was right though, 9 segments of 20 seconds each equals 180 seconds. (I've fixed that in the other post.)

As for the 1/2 mile for a two way, you may be right. Here is what I said...
Quote:
Letís look at two more examples with a hypothetical headwind and tailwind component put in to change the groundspeed. To try to keep it brief, Iím not going to change the desired amount of separation distance. You can decide to use whatever you want there.

My post was long enough the way it was. I just used a half mile example throughout for consistency sake.

There are a lot of variables as mentioned, and as you suggest, that should be added into the equation to determine the appropriate distance of separation between groups. Size of the formations, type of formations (big way rw, small way rw, freefly, tandem, aff, crw, wing suit, etc.).

That would be quite an administrative task to try to get each type of skydiver to know the subtleties of exit delay calculations to the extent of knowing... IF you are a two way and following another 4 way or smaller (which is NOT a skysurfer or wing suit flyer) THEN take a 10 second delay BUT if you are following an rw group of 5 to 12 then take a 15 second delay or 12 or larger then take a 20 second delay, blah, blah, blah, , blah, blah. (Again, don't use these number, its for discussion. Make your own decision.)

It seems that it might be more simple for the operator to post a note someplace like the loading tent or near the door of the aircraft that for today the delay is X.

Remember one of the things I said was that you need to determine what distance you want and then the math will help with determining the amount of delay. If you don't know what distance you want for separation and you don't know the ground speed, you will never be able to know how many seconds to delay between groups.

Who knows how would be the best way to implement a safe delay between groups. Continue researching and teaching I guess.

(Thanks for finding the typo/mistake.)
-mh.


(This post was edited by hoym on Feb 20, 2004, 8:14 PM)


diverdriver  (D 19012)

Feb 21, 2004, 7:18 AM
Post #49 of 57 (704 views)
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Re: [ZoneRat] Jump Run Direction [In reply to] Can't Post

Ok, without looking at any other responses I will try to answer.

Indicated airspeed is just that. What we see on the guage. It DOES NOT mean what we are actually flying through the air. When I'm in the Otter I fly initial jumprun at about 85 knots KIAS (knots indicated airspeed). But I'm ACTUALLY traveling through the air at about 100-105 knots TRUE AIRSPEED. KTAS is corrected for non-standard pressure (at altitude it is less than on the ground) and temperature (combined you get air DENSITY).

So, on a no wind day I will see a groundspeed of about 100-105 knots. This helps me judge my climbout spot, potential "throw", and exit seperation estimation.

Yes, swamp, river, highway, farmer McNasty all plays into selection of jumprun direction / offset. At SDC we have a river flowing north to south along the east side of the airport. Most times when I am flying I run a parallel JR to the river and offset for drift. When someone cuts away it is likely their gear will land somewhere on the airport or at least on the west side of the river. This is important because if you always run into the upper winds you will have people balking at climbing out of the plane on the east side of the river. You have then waisted LOTS of valuable exiting space. People shouldn't have to fear losing their gear so if I can take away one mental factor from the equation I will do it.

Now, if the winds are honking (technical midwestern term for wind speed. We have Honking, Cranking, and Screaming) I will run directly into the upper winds as my "cone" is no longer a cone usually. It has turned more into a narrow "channel". I know it's hard to describe without diagrams really but that's the best wording I can come up with right now.

Help any?


kallend  (D 23151)

Feb 21, 2004, 7:28 AM
Post #50 of 57 (702 views)
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Re: [hoym] Jump Run Direction [In reply to] Can't Post

In reply to:

Who knows how would be the best way to implement a safe delay between groups.


-mh.

Me.

http://www.iit.edu/~kallend/skydive/ and click on "Resources"


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