rodbailey

The Value of a Test Flight
by Jérôme Daoust ( http://www.expandingknowledge.com/ )
Revised 2007/4/23

Some familiar sayings after a paraglider test flight…

- A pilot flew a wing with a higher certification level than his normal wing, lands with big smile saying "Not even a small collapse, it's great" and is ready to buy it.
- A pilot lands and says "That's a scary wing, it moves around a lot. Collapses must get really ugly".

So how much value is there in a test flight, and what are appropriate conclusions we can gather from it?

First, what we can not conclude from one day of flying:

- From how "nervous" it feels overhead, you cannot predict:
-- The collapse recovery behavior (and general safety level).
--- When I changed from a Gin/Oasis (DHV 1-2) to the Nova/Aeron (DHV 2) I was surprised that the DHV 2 wing was so dampened overhead (maybe more than the Oasis) and rarely collapsed, but was consistent with DHV 2 recovery behavior when it did. Then when I switched from the Aeron to a Nova/Tattoo (same DHV 2 class) the increased requirement for active piloting was striking from the first flight, but it recovered noticeably better from collapses (trim and accelerated). I flew an Advance/Omega 6 (DHV 2-3) that felt less "nervous" than the Tattoo (DHV 2) I had at the time. My current Nova/Ra (DHV 2) is nervous in pitch and yaw (but much dampened in roll) yet is the most relaxing DHV 2 wing I have tested when recovering from accelerated collapses (even rated 1-2 on frontal at max speed).
--- There are wings of a lesser DHV class which require more active piloting than some of the class above, yet a pilot should not assume that he automatically has the skills to manage the collapse scenarios of the higher DHV class wing. Chances are you can test fly a competition wing and land with a big smile.

-- A wing's collapse resistance.
--- Wings which are less dampened and move more overhead as a whole, do not necessarily get more asymmetric or frontal collapses. Rapid adaptation to the changing air mass is not necessarily a bad thing, and you do get a sense of the air's "texture" so you may actually be more on you grads to prevent collapse than a more dampened wing.

- You cannot predict fully accelerated collapse behavior from tests at trim or ½ speedbar.
-- Most pilots will not dare test fully accelerated collapses to get a taste of what will likely happen to them later during ownership, so they try to extrapolate the behavior from their observations at trim or ½ speedbar. But the reactions of a wing follow the square of the airspeed prior to a collapse, so good-natured collapse recovery lesser speeds is no guarantee of full-speedbar behavior.
-- Thinking that full speedbar collapse recovery is not important, is fooling yourself. The next time you need full speedbar to penetrate, you will be at risk and entering uncharted territory.

- You cannot predict a wing's collapse resistance after a few hours airtime.
-- It requires about 40 hours before a sense of how collapse-resistant a wing is. Before that the sampling time is insufficient. There have been days where I though the air was nasty to me and a friend thought it was fine, while the reverse happened just as well. Collapse-inducing air is location and time specific.

- Construction quality.
-- Some judge how good their wing is by how big/thick/rigid specific components (fabric, risers, pulleys, leading/trailing edge reinforcements) are. Real longevity is difficult to estimate.

What we can get an idea of:

- If you are OK with the level of active flying required.
-- Although we said above that a "nervous" a wing is no indication of poor recovery behavior or low collapse resistance, and that there are benefits to feeling the air, it remains that such a wing will require more input from you, making the ride less relaxing and drawing some of your focus away from other flight goals. Be aware that after about 10 hours with a new wing, you will have developed new reflexes (maybe from new neural connections established during sleep) and you will start feeling significantly more at ease with it.
- Best sink rate
-- First you need to locate the amount of safe/usable brake pull for minimizing the sink rate.

- L/D at trim at accelerated.
-- Difficult to measure or get a sense of unless there is a significant (at least 0.5) difference. Comparisons with friends flying at your side can be spoiled by many variables like: Wing loading, model size (a larger size of the same wing typically has 0.25 better L/D), amount of drag at the pilot level, how each wing reacts to air disturbance.

- Efficiency at thermalling.
-- Some wings dissipate more energy than other during constant turns or change of directions.

- Behavior of typical worst-case scenarios.
-- One cannot predict the worst thing that can happen to him. But some bad scenarios are more common than others, for example stall are not as likely as a collapse while fully accelerated. Some say they solve the issue by avoiding to use their speed system but they will still end up using it to avoid being blown back and often close to terrain, which is not the time to test recovery skill if needed. I like to do 2 (to avoid getting off easy on the first one) of each of these (with lots of altitude) and feel that if I'm not willing to do it in relatively safe conditions, I should not be flying this wing:

- Fully accelerated frontal.
- Fully accelerated asymmetric.
-- Related discussions:
- Limit yourself to 1/2 speedbar?
- How to be comfortable flying full speedbar on your new wing?
- Likelihood of arm fatigue on long flights.
-- Arm fatigue sets in more quickly if you elbow can not be kept under your hand (hand often needs to be at/below your shoulder), and compounded by the brake line tension for your favorite airspeed. Wings with higher certification levels (DHV 2 and above) are often easier on the arms.

What we can get a true sense of:

- Turn response to brake input.
-- It is when you just switched to a different wing that you are most aware of this, as your muscle memory of your previous wing is most fresh.
- Airspeed
-- You can measure it. But be aware that it is significantly dependant on altitude: The rule-of-thumb is that each 1000 m increment gives you at least 2 km/h more.
-- You can compare with a friend flying at your side (if you are at a similar ratio into your respective weight ranges).
- Ease of inflation and kiting.
-- But most recent wings do that well.
- If the accelerator system is easy and smooth to fully use. Some require more effort.
- If the rucksack that comes with the wing is big enough for all your gear.

Happy testing and demo-ing.