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gorillaparks

Front Risers in Head wind

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If I find myself in a strong headwind too far from my spot on (final) leg of landing pattern (200-300ft) with danger below me, could I GENTLY use front risers to get more penetration and make it to safety? I realize the variables, but wondering if this is a reasonable solution.

PS- I realize that this situation is entirely avoidable with good planning. But that is useless once in the situation. Thanks for any advice! :)

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I have done it and I believe I achieved good results. In a completely avoidable situation I found myself about 600 feet above a house and coming straight down in a strong head wind. I used front risers to get some penetration to land in the backyard. To either side or turning around were not options due to obstacles. I learned my lesson there.

Long story short, avoid ever setting up over anything you don't wish to land on, but front risers can be used to get penetration yes. As for starting that at 200-300 feet, that's questionable and determining if it is safe depends on a lot of variables.
"Are you coming to the party?
Oh I'm coming, but I won't be there!"
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Thanks for the input. Yeah, several times Ive come up short of the mark due to a mis calc in headwind. I agree that 200-300ft could be sketchy for the front risers. I suppose its a judgement call, you know..balancing the risk of not fulling recovering and coming into land super hot, or coming straight down on some power lines.

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If the headwind is that strong that you aren´t covering any ground anymore in full flight, it is obvious that you´ll be able to fly further by applying frontriser input.
Way more interesting is the question how strong the headwind needs to be to make frontrisers the input of choice.
Here´s an example:
(sorry that I´m using meters not feet, if you wanna have the numbers in feet multiply the meters by/with three, take the result and add another 10%...)
Full flight:
Opening altitude: 720m
Rate of descent: 4m/s
Forward speed: 12m/s
Glide ratio: 3:1
Headwind: 10m/s (not that much that you aren´t covering ground in full flight)
Groundspeed: 2m/s
Time under canopy: 180 seconds
Distance flown till touchdown: 360m
Frontriserinput:
Opening altitude: 720m
Headwind: 10m/s
Rate of descent: 6m/s (+50%)
Forward speed: 16m/s (+33%)
Glide ration: ~2.5/1 (2.66 to be exact)
Time under canopy: 120 seconds
Groundspeed: 6m/s
Distance flown till touchdown: 720m
Twice the distance!
You could argue that 10m/s (=20knots) of headwind is still quite a lot for a canopy of average loading and seize and I would have to agree to this objection.
But if you do the calculations for any strenght/speed of headwind you´ll figure out that you´d travel the same distance no matter whether your choosing full flight or frontrisers if the headwind is 4m/s.
In other words:
If the headwind is any stronger than 4m/s you´d be better off using frontrisers.
If the windspeed on the ground is 2-3m/s (4-6knots), you´ll have a reasonable chance that the winds at opening altitude are exceeding 8 knots - making frontrisers the weapon of choice to fight a headwind.
The headwindspeed that is asking the pilot for frontriserinput is way lower than most people would expect.
If you need to fly far in a headwind or if you have to clear an obstacle - don´t let the high rate of descent fool you - apply serious frontriserinput!

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Remember : Your canopy does NOT know anything about the meteo wind ... it only knows about relative wind. For any give control input your canopy Airspeed is constant irrespective of which direction that it is pointing!

(.)Y(.)
Chivalry is not dead; it only sleeps for want of work to do. - Jerome K Jerome

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If the headwind is that strong that you aren´t covering any ground anymore in full flight, it is obvious that you´ll be able to fly further by applying frontriser input.
Way more interesting is the question how strong the headwind needs to be to make frontrisers the input of choice.
Here´s an example:
(sorry that I´m using meters not feet, if you wanna have the numbers in feet multiply the meters by/with three, take the result and add another 10%...)
Full flight:
Opening altitude: 720m
Rate of descent: 4m/s
Forward speed: 12m/s
Glide ratio: 3:1
Headwind: 10m/s (not that much that you aren´t covering ground in full flight)
Groundspeed: 2m/s
Time under canopy: 180 seconds
Distance flown till touchdown: 360m
Frontriserinput:
Opening altitude: 720m
Headwind: 10m/s
Rate of descent: 6m/s (+50%)
Forward speed: 16m/s (+33%)
Glide ration: ~2.5/1 (2.66 to be exact)
Time under canopy: 120 seconds
Groundspeed: 6m/s
Distance flown till touchdown: 720m
Twice the distance!
You could argue that 10m/s (=20knots) of headwind is still quite a lot for a canopy of average loading and seize and I would have to agree to this objection.
But if you do the calculations for any strenght/speed of headwind you´ll figure out that you´d travel the same distance no matter whether your choosing full flight or frontrisers if the headwind is 4m/s.
In other words:
If the headwind is any stronger than 4m/s you´d be better off using frontrisers.
If the windspeed on the ground is 2-3m/s (4-6knots), you´ll have a reasonable chance that the winds at opening altitude are exceeding 8 knots - making frontrisers the weapon of choice to fight a headwind.
The headwindspeed that is asking the pilot for frontriserinput is way lower than most people would expect.
If you need to fly far in a headwind or if you have to clear an obstacle - don´t let the high rate of descent fool you - apply serious frontriserinput!



Where did you get your glide ratio numbers from?
...

The only sure way to survive a canopy collision is not to have one.

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I'm sure it's a mythic and made up one, yet, it's certainly close enough as a generic example and has the advantage of being easy to work with.

3:1 is ballpark and "close enough" for most canopies.

The one that I'm curious about is the delta on his front riser glide ratio since that would depend quite a bit on how far he pulls them down. I also like how in the parenthetical he says "2.66:1 to be exact" as if front riser input is exact.
quade -
The World's Most Boring Skydiver

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I'm sure it's a mythic and made up one, yet, it's certainly close enough as a generic example and has the advantage of being easy to work with.

3:1 is ballpark and "close enough" for most canopies.

The one that I'm curious about is the delta on his front riser glide ratio since that would depend quite a bit on how far he pulls them down. I also like how in the parenthetical he says "2.66:1 to be exact" as if front riser input is exact.



Well, THAT is the whole point. The delta is what gives the change in range. SO guessing a delta and then using it to determine the break-even wind speed is totally bogus.

Without knowing the lift/drag polar of the canopy/jumper combination all you have is a guess, and wrapping it up in math doesn't alter the fact that it IS a guess.
...

The only sure way to survive a canopy collision is not to have one.

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Ok, so I couldn't care less which one of you is smarter...you guys can figure that out on your own. I do however appreciate your confirmation that front riser input will indeed increase my ground distance in a strong head wind. I wanted some experienced advice on how practical this approach would be. So thank you.

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Ok, so I couldn't care less which one of you is smarter...you guys can figure that out on your own. I do however appreciate your confirmation that front riser input will indeed increase my ground distance in a strong head wind. I wanted some experienced advice on how practical this approach would be. So thank you.



Honestly, if you find yourself in that situation, you've already lost the battle and you're having to fight hard and fast to win the war (and land safely).

Although having this tool in your tool box can help you when you're behind the ball, so to speak. To figure out what will do you the best, you'll need to dedicate some hop-n-pops to this, play with input and the accuracy spot. The problem is, it still won't be accurate due to ground speed and not being able (or willing) to recreating a bad situation in training.

Do you have a local canopy mentor that can help you out while you try to learn some of these more advanced skills?
--"When I die, may I be surrounded by scattered chrome and burning gasoline."

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Ok, so I couldn't care less which one of you is smarter...you guys can figure that out on your own. I do however appreciate your confirmation that front riser input will indeed increase my ground distance in a strong head wind. I wanted some experienced advice on how practical this approach would be. So thank you.



We (the PD Factory Team), don't generally find this to be true,nor do we teach people to use fronts to cover ground in a headwind. We do find, however, that if the winds are so strong as to consider this approach, that fronts will get you out of the air faster, and thus spend less time subjected to moving with the airmass.

Generally, in a strong headwind, full flight is your best option to cover the most ground.

YMMV.

Ian
Performance Designs Factory Team

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confirmation that front riser input will indeed increase my ground distance in a strong head wind.



We (the PD Factory Team), don't generally find this to be true,nor do we teach people to use fronts to cover ground in a headwind. [...]
YMMV.



I'm surprised at the latter. But it can depend on the circumstances we are talking about -- both answers can be right:

a) If you are trying to cover a lot of ground and generally fight back through moderate wind, what Ian says may be right. (eg, 30 mph forward speed, 15 mph headwind) The extra speed you get from front risers probably may not make up for the increased descent rate.

b) But if you are trying to get 50 m forward just to get past a line of trees, doing 30 mph in a 30 mph wind, who cares about the descent rate. Getting an extra 5 mph out of the canopy will save you, screw the descent rate.

To understand all this you do need to understand glide polars, how to shift them to account for wind, and typical skydiving canopy glide polars.

And whether or not you understand that, at least understand the 'accuracy trick' to estimate glide angle over the ground when you are actually there in the air and can test out fronts to see whether its gonna help or hurt you.

And as far as doing front risers low, that's OK. But watch out for: a) applying fronts suddenly if in turbulence (although whether there's a problem with turbulence and fronts may be debatable), and b) letting up too suddenly where you lose too much speed just when you are about to want to flare. That gets into the whole issue of recovery arcs. You either want to let up high enough to regain normal speed, or low enough to transition right into a swoop style landing if you know how to do that.

Explaining everything about recovery arcs and glide polars is a whole other job.

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You are correct for your option b scenario. However, it's worth noting that the forward speed increase is, relatively, minimal compared to the altitude loss.

If you're in 30pm headwinds are just above a treeline and need fronts to clear it....you've made some pretty bad decisions leading up to that moment (including the decision to jump in those kinds of winds near tree lines - not to mention the turbulence a pilot can expect to find around objects/trees in the conditions you cite) :)
In all but the most extreme cases, the canopy is moving forward over the ground in full flight. In these cases the loss of altitude is rarely, if ever, worth the extra few mph if the pilot decides to go to fronts.

Ian

Performance Designs Factory Team

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Ian:
Ok, looks like we are basically in agreement.

This is one of those cases where the question and answer have to be broken down more for a full understanding. So both can be right: "Front risers in a headwind is often a waste of time" and "Front risers in a headwind can be very useful."

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I'm going to disagree with a lot of people, but I call BS on extending a glide with front risers. It cannot be done.

When you pull both front risers down, your airspeed will increase, but only because you have re-trimmed the canopy for a steeper glide. The canopy goes faster down a steeper hill, but the bottom of that hill is closer in than the bottom of the full flight hill. You will not fly further by going down a steeper hill.

If you happen to be backing up, in that one case, you will back up a shorter distance by landing sooner, but only in that one case.

If you are coming straight down, or making any headway at all, you're best bet will depend on your canopy, but the only choices will be full flight, or some rear risers.

Full flight is the safest bet, however some canopies may experience a reduction in drag with a slight input to the rear risers. Enough to offset the reduction in airpseed, and allow you to fly further into the wind.

The full flight trim of a canopy is not selected based on the coefficient of drag, but the desired airspeed and turn recovery characterisitcs of the canopy. Especially in the cases of higher performance canopies, with their super steep trims, often times the lowest drag will be at a slightly shallower trim than full flight. How this applies to any one canopy is for the pilot to determine either through expereince, training, or some sort of testing. Using too much rear riser in high winds will increase the drag, and decrease your ground speed, so proceed at your own risk.

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Theoretically, but possibly not practically, you could increase the glide distance over ground.

Example 1: 30 mph head wind with a full flight airspeed of 30 mph

In Ex. 1, without any input to the canopy and pretending the head wind is consistent your ground speed would be 0 mph. If you were to flair a little you could decrease your airspeed to 25 mph, causing your ground speed to be 5 mph. This would be going backwards, of course.

If you were to pull down on the front risers you could increase your airspeed to 35 mph. This would again cause your ground speed to be 5 mph, however it would be in a more desirable direction. This would, however, cause your descent rate to increase.

In the example it would clearly be beneficial to use front riser input if you found yourself over an object you didn't wish to land on. If necessary, flaring could also be used if the object didn't extend behind you. With a PLF, of course.

Example 2: head wind 27 mph with a full flight airspeed of 30 mph

In this example your full flight ground speed would be 3 mph. Flairing the same about as in Ex. 1 would cause your ground speed to be 2 mph., flying backwards. Pulling down your front risers, again the same amount as in Ex. 1, would cause your ground speed to increase to 8 mph.

This is where it gets complicated. Your ground speed has increased, however the angle at which you are approaching the ground has also increased. What you would need to determine is: can you cover more ground distance at 3 mph and a 45 degree angle, or can you cover more ground distance at 8 mph and a 60 degree angel?You could create an equation to determine at what altitudes, airspeeds, and ground speeds each method would work but I will leave that to someone else. There are, of course, other factors such as the recovery arc after releasing the risers, changing wind speeds, how you plan on landing, etc.

The easiest thing to do is not put yourself in a situation where you are over an undesirable landing area without an easy way to clear it. Even if that means not jumping on a particular day due to high winds, etc. If you do end up in that situation use your judgment on what the best case scenario for avoiding the object is.

With that said, my money is going on Ian's advice that in most circumstances full flight is your best bet!

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I have to say I´m very sorry, but the delta is not a guess.
A whole lot of testjumps has been done in Germany over the last two years likely collecting the most detailed data ever of parachute flight.
(Maybe with the exception of the X-38
http://en.wikipedia.org/wiki/NASA_X-38
but one of the jumpers has been part of the X-38 program).
They are working with a company that is specialized in collecting all kinds of flightdata.
There systems are not only using GPS and airpressuredata but combining those with INS.
http://en.wikipedia.org/wiki/Inertial_navigation_system
In addition they are even monitoring the toggleinputs (how long - inches and time - the input is and what forces are necessary to apply those inputs).

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If you are interested how this looks like you can scroll through this document:

http://www.metatag.de/webs/dfv/downloads/1_-_KATE-Projekt_im_Detail_mit_ersten_Ergebnissen.pdf

I know it´s in german language and you´ll likely don´t understand the details but it will give you an impression what it is all about.
They are even monitoring turnrates...
Once again it doesn´t take a headwind that strong that "he" is killing all of your groundspeed to cover more distance with frontrisers. Do the math (not by guessing, we got the data) or just give it a try....

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O.K now that 'looks' like good maths ... but when you say that the canopy full flight speed is 30m.p.h - surely (?) that is not in the direction of across the ground BUT Down the Flight Path (into Relative wind) so will be a reduced component of the 30 m.p.h - So the Ground Speed component.

(.)Y(.)
Chivalry is not dead; it only sleeps for want of work to do. - Jerome K Jerome

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Yeah, in this whole conversation, we're generally all just using forward speed casually without always being clear about the difference between forwards speed and flight speed along the velocity vector.

(And thanks to Morris for the link to the KATE experiments -- neat stuff as I used to do some canopy tests with anemometer and variometer.)

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You're missing a key aspect of this whole thing, that being drag.

There are two types of wind, the relative wind, and the real wind. In zero wind conditions, you still have the relative wind of your movement through the still air effecting the canopy, but when you add 'real' wind, you now have two factors to deal with.

When I mentioned the 'least' drag flight mode for a canopy, I'm speking with reagrds to the real wind. When you apply double front risers, your angle of attack decreases, but so does the angle of the relative wind as the glide path becomes steeper so the drag increase is only due to the increase in airspeed.

Now when you consdier the effect of the 'real' wind, you have another story. The 'real' wind moves horizontally, and that does not change when you change the angle of attack of your canopy. So when you honk down on the front risers, you 'show' more of your topskin to the 'real' wind, and increase drag.

So if you are going straight down, with zero groundspeed, adding front risers will not give you more forward speed into the wind. It will give you a steeper glide angle, and steeper than zero (aka going straight down) is a negative value (aka going backwards).

This effect is why you can sometimes go further into the wind with some rear riser input. If your canopy is trimmed such that it is not fully 'streamlined' into the 'real' wind, if the trim is steep enough that the topskin is exposed to that wind, flattenting out the trim will put more of the canopy 'behind' the nose as opposed to out in the wind. While you can never get the realtive wind to match the 'real' wind, bringing the two clsoer together reduces the overall drag on the canopy.

The basic idea with canopies is that they are unpowered craft, but you could consdier gravity to be a source of thrust, so maybe you could call them 'non-adjustable' powered craft. Without the ability to add or subtract power, every input you make to the canopy will have a trade off. It's the same thing in an airplane until you touch the throttle. At a single power setting, you can trim the aircraft though a variety of configurations, but they all have a trade off. You can trim the nose up for a longer glide, but you'll sacrifice airspeed. You can trim the nose over for more airpseed, but at the expense of a reduced glide (sound familiar?).


All of this is with the exception of a 'best glide' speed. All aircraft have a published figure that reperesents the power off speed at which the AC will glide the furthest. This is determined and provided for the case of engine failures, it allows the pilot to set the airspeed to best glide, and offer himself the most options for choosing a landing site. This best glide speed is above the stall speed, which is the slowest speed the aircraft can fly.

So just going as slow as the AC can go will not buy you the most time aloft and in turn offer you the most options for landing, and the reason is drag. The best glide speed is where the lift over drag ratio is the lowest, and it's somewhere a few ticks above the stall speed. All of this is similar to my assertion about canopies flying into the wind benefitting from some rear riser. Full flight does (or may) not optimize the L over D, so coming closer to that will actually fly you further into the wind.

Even if the rear riser theory is not correct, the fact remains that you don't ever fly further by pulling on the front risers. It's just not how things work.

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Don´t mix true (in relation to the ground) and relativ (in relation to the air) glide!
In nowindconditions both are the same, and in nowind you are right that frontriserinput will never let you fly further, you´ll end up shorter.
But with wind it´s a whole different story.
In my example the relativ glide for full flight was 3meters forward for ever meter down, the relativ glide for frontrisers was 2.66meters forward for every meter down, resulting in less distance covered - in nowind. In a headwind as strong as in my example the true glide for fullflight is down to 0.5meters forward for ever meter down while the true glide for fronts is 1meter forward for ever meter down, resulting in twice the distance.
You are saying that by pulling down the fronts you would increase the drag as there would be more topskin presented to the headwind. Sorry, but that´s just not true.
The canopy always flies in relation to nothing but the surrounding air, the relative wind will hit the canopy always from the exact same direction if the same input is applied, winds are not affecting relativ glide at all, they are only affecting true glide.
Your canopy is flying in relation to the surrounding air always as if in nowind (as long as we don´t take/bring turbulences into the picture, but that´s another story/aspect, don´t let us mix those two).

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The canopy always flies in relation to nothing but the surrounding air, the relative wind will hit the canopy always from the exact same direction if the same input is applied, winds are not affecting relativ glide at all, they are only affecting true glide.




You cannot discount the effect of the 'real' wind on the canopy.

For example, in no wind if you fly your canopy due west, the realtive wind will come from the east and your ground track will be due west.

Now add a stiff north wind. The relative wind as far as the canopy is concerned is still coming from the east, however there is an added component in the north wind, and the groundtrack is now southwest.

The 'real' wind has a real effect on the canopy in relation to the ground. The real wind does not have an effect on the flight characteristics of canopy when not considering the ground. Flying above a cloud deck in 50mph winds or 5mph winds will always be the same, but once you get below the cloud deck and the ground comes into view, the two wind scenarios will produce two very different canopy rides with realtion to the ground.

Trying to increase your ground track with double fronts certainly involves the ground, and as such the real wind needs to be considered.

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