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Performanec Prediction and Flight Impressions
by Zach Hoisington (E-mail).
Revised 2002/3/3.
Background
For the past 10 years I've been flying Pro Design paragliders.
The company has always been very kind to me and I feel they have a good product
line. However, I enjoy flying gliders
with ratings below DHV 2. Last year I flew the DHV 1 Effect (1-2 accelerated).
This year I've moved up to the DHV 1-2 class. Pro Design doesn't have a product
in this class yet. Therefore, I decided to look around for something else...
The new 1-2 gliders I considered were: Vibe, Oasis M,
Presta S, and Sport M. Like any normal engineer I ran to the computer to
speculate how the Gliders would do against each other. I did both a simple drag
build up and also a regression analysis. The simple regression analysis ended
up being as accurate as the more complex drag buildup. Therefore, the drag
buildup was shelved for another blown-out day. The results from the regression
are below:
|
Wing |
Best L/D |
|
Presta |
8.30 |
|
Oasis |
8.28 |
|
Sport |
8.18 |
|
Vibe |
7.80 |
In addition to glide, I tried to compare the sink rate and
flatness of the polar at high speed. This can be confusing because every
manufacturer recommends different wing loadings. As a first hack I ran a case
assuming that all gliders have the same wing loading. Theory says that the sink
rates (comparatively) would be :
|
Wing |
Min sink (m/s) |
|
Oasis |
1.08 |
|
Presta |
1.12 |
|
Sport |
1.14 |
|
Vibe |
1.23 |
History has shown that when applying the test above,
gliders with superior sink rates are better off when loaded heavier. This
causes the final sink rates to be closer together, but it allows the heavier
loaded gliders to have improved performance at high speed. Therefore, you would
expect from the above data that Gin would recommend the highest wing loading,
and he did, by about 5%.
My intent was to select the best glider for both safety and
performance. This is difficult with the
wide range that 1-2 covers. I think it is unlikely that the Vibe was intended
for the same class of pilots as the others.
I wanted a way to compare a top end DHV 1-2 with a low end 1-2.
Therefore, in an attempt to compare safety with performance, I made up a simple
parameter that approximates the hands-up safety of the glider. I compared this parameter
to the L/D and came up with an overall rating. The work above is so ridiculous
that the details aren't worth sharing, however the order went like this :
|
1st and 2nd |
Oasis and Vibe (nearly the same) |
|
3rd and 4th |
Sport and Presta (also very close) |
This can be very misleading because there are so many other
factors at stake, but it's fun to do anyway and could probably raise some
wonderful controversy. Again, this
paragraph should not be taken very seriously, but it was enough for me to
finalize my decision.
Construction seems fine to me. Inside the glider, I like
the absence of internal tension straps between the line attachments. This
allows all of the tension to be distributed to the fabric, making it a bit
tighter for the number of ribs. This is nothing new, and done by many others.
I'm also a fan of how the glider has line attachments on every third cell.
It takes a bit more effort to make a glider this way and
doesn't seem to improve performance a whole lot, but it looks clean. Porcher
Marine fabric is what I'm used to (Pro Design uses this and I've never worn out
a glider). Best part is just the smell
of it. I laid my glider out in my apartment as an air freshener (no joke).
Airfoil
So I took a few measurements. At the center it's about
18.7% thick. It tapers to around 17.5% at the tips. This is pretty common. The
shape of the nose is a bit different though. It has some resemblance to a
slightly thickened version of the LA2573A for those aero weenies (very rounded
and then a long slanty region).
Flight
The handling is good, with nice and flat turns. I was
looking forward to the 'fake' handling that I had heard the glider had a bit
of. I was actually a little disappointed that I didn't feel this tendency of
over-turning. I personally prefer this
quality (a little) because it allows the pilot to ride more outside brake in
thermals, increasing the feel of the angle of attack of the outside wing. Oh
well, as the glider is, ample outside brake can be used for a pretty clean turn
anyway.
Slight vibration at trim speed of the rear lines.
Considerable amount of undersurface vibration between 50% and 100% speed. I
don't have a feel for how much this impacts performance. I don't think it's too
much, but you have to wonder.
With the brakes 2 inches above stall the glider still
seemed to have a very good sink rate. I didn't feel too much warning before the
glider stalled, but it took quite a bit of brake deflection. (Hands at mid
buttocks with the hands through the brakes) I was able to hold the glider in
constant stall for a long drop without full stalling, but I doubt I could
repeat the trick 10 times in a row.
In general the glider felt quite pitch stable to me. This
may be in part from the long line length. I enjoyed the very slow pitch
rotations out of collapses, etc.
End
I dig the glider, but I haven't flown the other new 1-2's
yet so I haven't formulated a really strong opinion. I also could have some
hidden agenda to promote Super Fly
products now.