Wingloading

[guest]

Does anyone have any views on the ideal wingloading for BASE?

The received wisdom appears to be a wingloading of .75 (i.e. exit weight/canopy size=.75)

However, I am coming to believe that an even lower wingloading (.65? lower? ) might be ideal.

Can anyone see any problems with extremely low wingloading? Will a more lightly loaded canopy open slower, or less consistently (aside from the fact that, being larger, it will open a bit slower regardless of what load it carries)?

What about turbulence? Will a more lightly loaded canopy be more susceptible to turbulence?

Does anyone have any thoughts, facts, ideas or conjecture on any of these issues?

--Tom Aiello
tbaiello@ucdavis.edu

[guest]

Hi Tom, As you know Consolidated Rigging recommends wing loads of between .7 and .8 lbs/ft^2 on the Mojos. Lower wing loadings can easily be used. We have repeatedly jumped at wingloading as low as .57 with no ill effects.

I can say from experience that the Mojo will perform well at wing loadings in the ~.6 range. However, a number of factors influence this including airfoil design, trim angle, inlet shaping etc.
However, not all canopies are created equal in this respect. Just like design factors allow us to load a contemporary skydiving canopy at 2.5, not every BASE canopy will have the same tolerance for lower (or higher)wingloadings.

Lower wing loadings will give you: Lower forward and vertical velocities, a lower stall speed, easier and more forgiving flare behaviour, shorter control range(however, this is usually negated by the proportionally larger canopy). All of these features equate to a more docile and easier to control canopy - Often ideal in a BASE environment.

Lower wing loadings will also give you: Lower dynamic pressure (q). This equates to higher potential for closed end cells, more suseptibility to turbulence.

These are facts. The degree to which the negatives will overshadow the positives is all related to the canopy design and to what extreme you lower the wingloading.

There are other factors beyond just wing loading to consider though. A larger canopy will weigh more. This will require more time to deploy because of the increased inertia at snatch and greater mass. So although you may want a huge canopy for the landing the freefall might dictate a smaller one.

In my experience it takes a size graduation of 2 (ie mojo 240 up to mojo 280)to begin to notice the extra mass though.

Another point I'd like to make while discussing wigloadings: I often see the exit weight underestimated or not even properly factored. For example, a jumper weighing 165# will have an exit weight of at least 185# and this can substantially impact the calculation of wingloading. Remember your rig is 15# plus, a helmet is at least 1# shoes/boots upto 3#, radios, cameras, stash bags, etc etc. It adds up fast.

Oh and BTW for a guy w/ a broken back and scrambled inards Go HUGE! ;-)


Adam
http://www.crmojo.com

[guest]

>I often see
>the exit weight underestimated or not
>even properly factored...
>...Remember your rig is 15# plus,

Isn't suspended weight the more relevant factor, not the exit weight?
If so you can subtract the canopy weight of 6 to 11 lbs from your calculations.

[Dwain]

>A larger canopy will weigh more. This
>will require more time to deploy
>because of the increased inertia at
>snatch and greater mass. So although
>you may want a huge canopy for the
>landing the freefall might dictate a
>smaller one.

In my experiences freefalling low objects (159'-180' range over hard earth) with Slim, canopy mass played a small role in opening height in comparison to how the p/c is placed into the airflow (with, for example, Slim using a Mojo 280 and myself using a Mojo 220).

Over many many low freefalls together it did not appear that I was averaging noticeably higher openings even though Slim's canopy was always significantly heavier than mine.

The only variation which produced noticeably different opening heights was the technique used to place the p/c into the airflow (other than the obvious one of different p/c sizes), and variations/fluctuations in cell presurisation.

This can be reasoned to the fact that the pull forces exerted by very large p/c's in low airspeed still well exceed the weight of the canopy. The speed at which the p/c starts working is the key factor.

If canopy weight is a key factor in your gear selection for survival reasons then you are about to do one hell of a low freefall. :-)

[guest]

Exit weight or system weight is the relevant number. You can't negate the mass of the canopy because the canopy has to suspend it's own weight in the system.

To draw a parallel to aircraft: Could you subtract the weight of the wings from an aircraft's gross weight rating?

Adam
http://www.crmojo.com