Glide Performance without PC and bridle

[base311 0]

Hey,

Anybody have any numbers (or hell I'd even be interested in pure supposition) on how much a canopy's glide performance would be increased by removing the PC and bridle?

Scenario: Got an object with 3 possible LZs and only trees for outs. LZ 1 calculated necessary glide ratio (without counting turns - in other words straight from exit point to lz) is 1.86:1, LZ2 ratio is 2.05:1 and LZ3 is 2.36:1. These numbers DO already account for a conservative necessary opening distance (150' to allow for a fully open and pressurized flying canopy corrected to LZ heading), and the remaining calculations are conservative estimates based on solid altitude measurements.

If one removes the PC (and let's just say for the sake of convention the PC being removed is a non-vented zp 42") and bridle, how much do you THINK (know) that the glide performance would be increased?? I mean are we talking 100ths place behind the decimal? or could we see a tenth of a point increase? two tenths? Math wizzes?

Jumping a mojo loaded @ ~.75:1

It's one of those situations where 'more than likely you're probably gonna live,' but I'm now curious about the PC removed scenario and don't have any answers. BTW, the LZs are not visible from the exit point - everything just appears to be a sea of trees.

thanks,
Gardner

[DexterBase 0]

This is a subject I'm also interested in. I brought up a very similar question either on Blinc or here. I'll try and dig it up if I can. Good question though.

I hypothesized that removing the PC would remove a bit of parasitic drag and flatten out the glide somewhat. The question is whether it would be enough to make a noticeable difference. A 42" PC seems capable of generating enough drag to steepen the glide and slightly affect performance.

You're planning to D-bag or McConkey?

[base311 0]

Quote

This is a subject I'm also interested in. I brought up a very similar question either on Blinc or here. I'll try and dig it up if I can. Good question though.

cool, thanks

Quote

You're planning to D-bag or McConkey?

as yet undecided....

I'll surf blinc and see what I can dig up. I really should have posted this over there. chalk it up to brainfart.

gardner

[Dwain 0]

Gardner,

I used the term "noticeable" as I'm basing this on personal feel, not GPS data. While I do have some GPS data on glide ratio of various canopies, I don't have enough to make quantifiable statements on the effect of difference sized p/cs. Therefore all these comments are highly subjective and should be taken lightly.

Firstly, if your calculations are correct you should be able to make the first two landing areas easily (provided there is no wind or sink) regardless of what p/c you are dragging (within reason of course). The third one will be more dependent on canopy but it should still be OK with your Mojo (but not by a huge margin).

Flik, Troll, Ace and Blackjack all have great glide ratios (as far as modern day BASE canopies go).
A non-Vtec FOX (or Vtec with valves) also has great glide ratio (the standard FOX used to be known as the best BASE canopy for glide a few years ago).
Of everything commercially available the Troll probably has the edge in glide as its airfoil is the most advanced (slightly tapered, construction techniques which reduce the deformation of the inflated wing) in terms of an efficient wing when inflated, but only just, and that is when you fly it with the precise combination of riser and toggle input (it's angle of attack is slightly steeper than the Flik and so you need to compensate more with riser and toggle input to make it flatten out).
Mojo's and non-valved Vtec FOX's don't give the best glide. The same with Dragon's and Dagger's. Their glide ratio is still acceptable, just not the best compared to what is currently available if you are intent on making distant landing areas.
ZP top skin will make a noticeable difference if the canopy ride is long. F111 porosity will also make a big difference (a new F111 canopy will far outglide the same canopy with hundreds of jumps and some water landings on it).

The parasitic drag of the p/c will affect your glide ratio to some extent. Once again this effect only becomes noticeable over a long canopy flight.
A more noticeable difference is the effect that the p/c has distorting the top skin of your canopy from the bridle attachment point being dragged back.
The smaller the canopy and the larger the p/c, the bigger the effect this will have. For example a 48"p/c on a 220 canopy will create noticeable distortion to the top skin and performance will be very noticeable (if you are tuned into the way your canopy performs). A 280 canopy dragging, say, a 38" p/c won't really have any noticeable distortion whatsoever.
A canopy with a multi will reduce the distortion as the p/c drag is distributed to two cells (#3 and #5) rather than just the center cell (#4). (Note: The center cell on a multi canopy does not carry any of the p/c drag when in flight as the center multi line and the tail pocket line are not loaded).

One extreme example: A number of years ago I did a BASE jump with a 9,000' canopy ride under a Mojo220 (loaded at about 0.77) with a 52" ZP p/c. The canopy was severely distorted during flight. The leading edge of the canopy formed a V shape as the center cell was pulled back by the p/c. This became more enhanced during turns and front riser input (where the airspeed was higher). The canopy still flew and landed OK, but the glide ratio was noticeably poorer than usual. I have experienced (and heard a number of other jumpers commenting on) a difference in glide when going back and forth between a 32" p/c and a 48" p/c (e.g. when everyone jumps Eagles Nest after a day at Kjerag).

However, the biggest factor is the possibility of downdraft and cross winds. Even if there is no wind at exit or at the landing area you can sometimes experience downdrafts and cross winds during a long canopy flight in mountainous regions. This is where you can get hosed and end up in the trees. The general rule is to front riser through the down drafts, turbulence and strong cross winds (to minimize your time in them) and fly in half brakes in the updrafts (to maximize your time in them). Try to avoid crabbing in strong cross winds if you can avoid it and just focus on covering the distance while allowing the cross wind push you sideways. Usually the uppers are stronger than the lowers and so you should be able to make it back flying into the wind at a lower altitude rather than crabbing at a higher altitude (this is a very general rule though and following it to the letter will eventually get you into trouble).

The higher the wingloading, the less effected you will be by cross winds and downdraft. Glide ratio with a canopy theoretically should remain constant regardless of wingloading provided you are within certain limits. In other words if you have two identical canopies except for size, use the smaller one if there is any question in regards to downdraft, crosswind or headwinds. Use the larger one if you know you are going to get updraft or a tailwind.

Also minimize toggle input during the flight. Making a number of small corrections to direction during the flight will eat up much more distance than most people think.

If you do end up forced to land in the trees then try to hit the thickest, lowest tree you can find. Don't fly into a spindly one as it will just fold up your canopy and then drop you to the deck. Aim for the center of a thick one (the thicker and the lower the better) and fly straight into it. Flare, legs bent and feet together, shut your eyes tightly as you hit the foliage and then try to grab on to a branch to prevent falling. Getting your canopy out of the tree will be a bitch to say the least, but it's much better than laying broken and twitching at the bottom of a spindly one. Although most people come away from tree landings OK, it is still serious business. JM took a tree branch through the heart during a tree landing on his 300th jump. Aim for the friendly looking ones with bendy branches.

In summary, if you are not freefalling the object, and you are worried at all about making the landing area, you have the option of deploying without a p/c and you totally trust your non-pc deployment system (which is another topic entirely), then I would remove the p/c every time.

Hope this helps.

[motherhucker 0]

Gardner:
Don't be a pussy.
Go huck the fucker already!

[base311 0]

Dwain,

Thanks for your thoughtful response; I do think that the first two lzs are totally doable, but it is the third (and furthest) that is primo and the one I'd most like to make. Regardless of which I ultimately choose, thanks for your thoughts. I learned a long time ago not to try to stretch distance in an unpowered craft.


Huck,

I'm on it. Been waiting on bird bans, man...

What I really need are ten guys with ten chainsaws and about 5 minutes on sun. morning at sunrise.

Hope y'all are doing well.

Gardner

[Skinflicka 0]

Sir 311,

I can't help you with the chainsaws and I don't have that many friends but I do know a guy who can provide such a service with purple DaKine pants and a rake.

Try posting on Blinc.

Will that suffice?

Love n hugs,

Skin
PS "I learned a long time ago not to try to stretch distance in an unpowered craft."
Nice to see at least one lesson was gained by the historic and heroic capers of Felix Bumfondler.

$kin.

Prizes to anyone who gets to read my posts before Mr Aiello's son, Tom deletes them.

[QuickDraw 0]

This almost begs the question or catchphrase "What Would Felix Do ?"

-- Hope you don't die. --

I'm fucking winning