QuickTalk 6 - COMPOSITE NEWS
- Category: Q-Talk Articles
- Published: Sunday, 31 October 1982 06:11
- Written by Jim Masal
- Hits: 1420
/Not surprisingly, designers of canard aircraft have taken an interest in rain-induced flying difficulties. Most will agree that some degradation can be expected with laminar flow airfoils, but the degree of severity appears to vary among individual aircraft. Recently, several organizations addressed this issue. Their comments are of interest./
(QBA reported in its last issue the crash of Owen Billman's Quickie, N39QB. Since that time, QAC and Rutan Aircraft have commented on this accident and we have reprinted their letters.)
I was extremely saddened when I learned of your incident returning from Oshkosh...In reading your report I see all the seeds of the mishap in place.
1. Obviously when the aircraft did not take off normally, the takeoff should have been aborted.
2. While moisture on the canard will indeed cause a longer takeoff roll, I do not believe that this was the primary cause.
3. Your static RPM was 2900, this is at the bare minimum for the 18 HP (RE: newsletters).
4. You state that the empty weight of your airplane was 309 lbs; you also state that the pilot weighed 180 lbs; that you were carrying 6 gal. (36 lbs.) of fuel; that you were carrying a small duffle bag (we estimate 5 lbs.). I assume that the 4 lbs of oil were included in the empty weight. This would put your "all up" weight at 530 lbs.
The gross weight of the 18 HP Quickie is, always has been, and always will be no more than 480 lbs. Anyone flying an 18 HP Quickie above 480 lbs is not flying a Quickie; it's just that simple. I personally discussed this matter with your F.A.A. inspector and I emphasized to him that 480 lbs was the limit for an 18 HP Quickie.
Why 480 lbs? Did we pull this number out of the air? Certainly not. The 480 lb gross was determined on extensive flight tests. This limit was based on takeoff and climb performance.
An 18 HP Quickie at V-min will climb adequately at 480 lbs. At 530 lbs this margin will be greatly reduced. I estimate that the additional 50 lbs plus would have increased your takeoff roll by at least 20% (canard wet or dry). I am certain had your aircraft not been carrying the extra 50 lbs plus it would not have touched back down after initial life off. I also feel your initial climb rate would have been 75 to 100 FPM higher canard dry, perhaps more canard wet.
5. It is obvious that there was some difference between the left and right sides of your canard since you had a roll input upon entering rain. This may have affected the performance of your airplane. Two Quickies on the way to Oshkosh flew in rain at a density altitude of 13,000 ft with no loss of airspeed or altitude and both were 22 HP conversions.
We at Quickie have done extensive tests (18, 22 HP) on takeoff performance both with just a dew wet canard and in rain. We have not conducted such tests above the gross weights of the respective versions, and I do not plan to. We at Quickie have never authorized anyone
Losing something one has spent so much time and effort to construct is always a heartbreak. Hopefully we can learn something from incidents such as yours.
Gene Sheehan, QUICKIE AIRCRAFT CORP.
The subject of rain-induced boundary layer transition and its effect on trim and performance is one that we have been investigating for several years now. Tests have included fixed and free transition measurements of six different airfoil shapes on the VariEze, Long-EZ, Amsoil racer and Defiant. Full-scale moisture tests have been conducted in the NASA Langley 30 x 60 wind tunnel. I have not published an account of these tests because they still contain some contradictory results. For example, theoretical predictions call for the largest trim change to exist on the well-contoured aircraft that normally have the most extensive laminar flow. Just the opposite is true - the best contoured ones have the least trim change in rain!
The trim change of the Long-EZ and VariEze in rain is generally mild. Most trim down in rain, about 25% of the VariEzes trim nose up. There have been several report a strong nose down trim change; outside of the pitch trim capacity. In general, these have been fixed with a correction of canard incidence or elevator shape. I know of no rain-induced accidents with the VariEze or Long-EZ, however several have reported extensive increases in takeoff rotation speed and take-off distances....
Concerning your Quickie and others that have near equal-area tandem wings, we have not conducted fixed transition or moisture tests on these, but based on your and others experience, it appears that the transition effect on maximum lift is more severe. This is apparently due to the double effect of loss of CL and the inability to trim to an adequate angle-of-attack.
Burt Rutan, RUTAN AIRCRAFT FACTORY
***EVEN THE DRAGONFLY***
(Reprinted from DRAGONFLYER newsletter #8)
...We carry almost two-thirds of the aircraft weight on the canard...When the laminar flow is disturbed..the drag increase causes a loss of speed of around 7 mph in the worst case ..and a pitch down. Since it requires more aft stick for level flight under this condition, you reach the aft stick stop at a higher airspeed, which produces an increase in the minimum airspeed..(about 8-10 mph in the worst case). The only potentially dangerous thing that I noticed is if the aircraft is waiting for takeoff in the rain and has a good coat of wax on the airfoils, it will produce giant-sized drops...The takeoff roll may be as much as 50% longer...Once the aircraft is up to speed and the huge drops blow away, the small drops will only produce the minor pitch change we've seen before...
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