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What is a cross brace tri cell
Where did the idea come from
What are the advantages
What does this mean to you
How noticeable is this extra lift
Other flying characteristics
Disadvantages of this canopy design
Several years ago we decided to get serious about making an all out high
performance canopy that would be a significant step up from anything currently available.
When a ram air canopy inflates the canopy surfaces bulge between the ribs with the air pressure. This both effects the airfoil shape and draws the ribs closer together reducing the span of the canopy (and therefore the surface area). The more ribs we have, the less distortion and shrinkage occurs but bulk and line drag increase. On a conventional canopy not only do the cells bulge they also zigzag up and down between load bearing and non-load bearing ribs, further distorting the canopy and reducing its span/area even more.
To quantify this, bulge distortion alone reduces a 9-cell canopy area by 9% and zig zag distortion by a further 4%. Say you are jumping a PIA measured 100sf canopy, you are actually flying around with 87sf of wing area above your head.
With the EXTreme-FX you still get the bulge distortion (reduced slightly through 21 chambers instead of 18) but zig zag distortion is eliminated completely. On a 100sf EXTreme-FX, bulge distortion will reduce your area by only 8% and that is all. So you still have 92sf of wing above your head (compared to 87sf), 5% more lifting area and no extra drag (less in fact).
Now that you have this concept in mind, consider this.
Dynamic Distortion Back to Menu
When you look at a photo of a conventional canopy flying on full drive the zig zag appearance is obvious, but look at a landing canopy photo and you will see the zig zag appears much more pronounced - IT IS !
During your flare your canopy is both, slowing down and pulling more load, which is reducing the supporting pressure within your canopy and pulling it further out of shape. In fact, during your flare your zig zag distortion will increase a further 7-9%, to around 12%. Add to this our bulge distortion and our 100sf canopy is now giving us 79sf of lifting area when we land.
Now look at the photo on the cover of our brochure. As you can see, even at the very end of the flare there is no zig zag distortion at all. You are landing with 92sf of lifting area, compared with 79sf. A MASSIVE difference of 16.4%.
Our figures come from physical measurements taken of models inside the wind tunnel and have been proven in practice through building very useable small canopies, to date down to 69sf. Imagine landing a 69sf conventional construction canopy.
"AH HA !!" you think, why not just buy a 16% larger conventional canopy ? It will still land me softly, pack down smaller and save me a bundle" - and you would be right except for one thing. This larger canopy would also have 16.4% more drag therefore you would fly slower, turn slower and swoop in for landing slower than the EXTreme-FX and (as well as being less fun) this airspeed is what you are using to produce your landing lift.
Spanwise Consistency Back to Menu
On an aeroplane wing the airfoil usually gets proportionally thinner towards the wing tips to help reduce some induced wingtip drag. On an elliptical canopy the cells are usually the same width right across the canopy. At the wing tips the canopy is shorter meaning the cell is proportionally wider and thus will proportionally bulge more and produce a proportionally deeper airfoil at the tips - exactly what we don't want. Often designers have dealt with this by adding extra non load bearing ribs into the end cells to help contain this distortion.
On the EXTreme-FX we have gone one step further by keeping every cell on the canopy at an equal aspect ratio. If you compare the cells in the center with the wing tips you will see they are narrower and the airfoil depth does remain totally consistent over the span of the canopy.
In summary, the EXTreme-FX will totally eliminate both zig zag and dynamic distortion, marginally reduce bulge distortion and will deliver spanwise consistency to reduce wingtip drag.
What does this mean to you? Back to Menu
As with previous steps forward in parachute design the extra performance is realised by being able to reduce the size of the canopy.
When jumping a similar size canopy you will actually lower your decent rate and therefore fly and turn slower. Although this technically represents an improvement in performance it is not what we were trying to achieve.
Reducing the canopy area by say 10% over your conventional elliptical ZP canopy will give a good benchmark for comparison. With a 10% reduction in area you would find:
How noticeable is this extra lift? Back to Menu
On a lightly loaded canopy the extra performance generally isn't that noticeable but when we get to extremes and the canopy is 'heavily loaded' it becomes very noticeable.
This is the same for most performance steps. For example, the difference between an F-111 230 sq. ft. and ZP 230 sq. ft. canopy is not that much but you can imagine the difference when a 95 sq. ft. F-111 canopy is compared with a 95 sq. ft. ZP.
By 'heavily loaded' we don't just mean a big person under a small canopy. When a canopy is being flown hard and the person under it is pulling a lot of G's their weight in the harness is greatly increased. At that time extra little bits of performance really start to add up.
You may have noticed conventional elliptical landing performance starts to drop off at a steady flight wing loading above about 1.7 PSF (pounds per square foot). They are more radical and still easily useable but not as efficient. This is due in part to the parasitic drag of the jumper, and other non lift producing objects. As a canopy reduces in size this drag becomes a larger proportion of the flying unit as they do not reduce relative to the canopy's size reduction. The performance drop on a conventional canopy is also due to the effects of dynamic distortion.
With the EXTreme-FX this landing performance drop off does not start occurring until a steady flight wing loading of around 2.00 PSF is reached. (In testing we have taken them to 3.1 PSF.)
During a landing manoeuvre you may be pulling 1.5G's, and say 1.2 G's at the beginning of your surf. This is where you realise the extra performance.
Going to a smaller canopy has a compounding effect: Smaller canopy = more manoeuvrability = greater airspeed = more G's = canopy maintains performance = canopy responds = can go smaller etc....until you reach this performance drop off.
We are not suggesting you load your canopy to 2.00 PSF, but just demonstrating that the "performance envelope" carries further and becomes more noticeable.
If you are wanting to jump a canopy of 1.2 PSF or below then there is not that much of a performance gain. You are probably better off sticking to conventional canopies (we make them too). But if you want to jump a canopy above 1.4 PSF you will notice this improved performance considerably.
Openings Back to Menu
For us, the biggest hurdle to designing a zero-p cross brace tri-cell has always been the openings. We've had a lot of trouble with them ever since we just about maimed ourselves under the first one we made five years ago. We spent a lot of time getting them first acceptable then improving them to the stage we have them now.
The EXTreme-FX openings are mainly controlled by the nose configuration and are very slow and progressive. As soon as the canopy comes out of the bag it starts to inflate immediately and slowly. You know things are happening straight away and you can monitor the opening as it slowly grows into a full canopy. You won't be screaming earthward with a streamer at line stretch wondering when things are going to happen. Openings take a long time but do not use much too much height as the majority of the opening sequence is waiting for inflation to finish rather than inflation to start.
Most elliptical canopies have a high proportion of off heading openings and the EXTreme-FX is no exception. However by slowing down the opening sequence we have managed to eliminate the steep dive that commonly occurs with conventional ellipticals immediately after opening. With the EXTreme-FX, off heading openings are quite tame as the canopy is either streaming and not flying at all, or is growing and has stopped flicking around, meaning the canopy has time to settle before it tries to fly. Off heading openings on the EXTreme-FX are therefore not such a big problem and will cause less malfunctions, as well as leaving your nerves intact.
Another reason we made the openings this slow is because zero-p canopies tend to get occasional rogue openings (these are sometimes put down to line dump ). By slowing down the entire opening sequence we've made those rogue openings acceptable and not a killer. That balances it out.
Overall, the openings are better than under any other ellipticals we've jumped, although not as nice as you would get under a 500 jump F-111 7 cell. The state of the art is not at that stage yet, for any high performance elliptical canopies.
Other flying characteristics Back to Menu
The disadvantage with the small recovery arc many modern canopies have is that you need to (dare I say it) "hook lower" to get the full force of the canopy to carry you down to the ground on full drive. In contrast, the EXTreme-FX has been designed to have a large recovery arc which means you can hook higher, get a lot of speed up from your hook and maintain it longer on full drive until you are ready to flare. You have lots of time to make fine adjustments as you get closer to the ground. Also - the larger the recovery arc, the higher you can do your hook, and the bigger the final height difference will be between full brakes and full drive. Your hook height will need to be higher but does not have to be judged as accurately or as quickly to remain safe.
When changing from one canopy to another, it is worth getting a serious feel for the flying characteristics of the new canopy before committing yourself to any landing manoeuvre.
Disadvantages of this canopy design Back to Menu
There are a couple of unavoidable trade-offs with this design. Jumpers went through the same issues when ZP canopies first came out. The pack volume and price will no doubt put a few people off.
We have some advantage in New Zealand because the NZ dollar is weak. This means our manufacturing costs are relatively low compared to many other manufactures but this still does not bring the costs down to conventional ZP prices.
Manufacture Back to Menu
At NZ Aerosports we computer cut all our canopies with a CAD/CAM (computer aided design/computer aided manufacture) system. We use no patterns or templates and program each order individually into our computer system to customise colours, size and options.
Every model of canopy is available in ANY SIZE you wish. Our cutter marks, labels, then cuts and seals each panel as well as calculating and generating line lengths.
As you can imagine, in an elliptical canopy there are many different shaped panels rather than the same shapes being repeated. With the EXTreme-FX this is even more pronounced as many more panels must be cut and placed to an individual shape and location in order to form a canopy of this structure. To do this by hand would become totally impractical. (Generating the prototype shapes initially took us months of CAD work on a customised canopy design program.)
Each panel is cut to an accuracy of 0.2 millimetres. A high degree of accuracy is required because some of the angles in the cross brace are so acute that if positioned incorrectly the whole parachute will not be shaped correctly. This would defeat the whole purpose of the cross braces pulling the canopy into true.
On all our canopies we use a doubled patch at every line attachment point to eliminate lower surface damage.
Conclusion Back to Menu
The EXTreme-FX is not for everybody - it's not an all round canopy or of much advantage at light wing loadings.
But if you're a bit of a canopy connoisseur who likes flying a canopy and enjoys a radical turf surfthen maybe you should consider the EXTreme-FX.
At high wing loadings it will out perform any canopy currently available, it's expensive, it's bulky but it opens great and is a pleasure to fly and land.
This may be the canopy for you.
All prices quoted are in Australian Dollars and are subject to change without notice.
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