Much is being said on airflow in light aircraft, but we rarely have the opportunity to verify.
We availed ourselves of our recent stays at Darois to perform a few visualization flights with the help of some MCR boys.
See also Michel Bosek's tuft experiment at the bottom of this page.
During our first weekend in Dijon-Darois (october 2005), the arrival of JJH prompted the quick setup of our first experiment. Thanks to Jean-Jacques !
Within a few minutes, the MCR 4S is equipped with tufts at strategical places, air inlets, fin to stabilator junction, rear of wing-root, wing tips (winglet).
After a quick briefing, the 4S took to the air, followed by JJH with this writer and Dyn Aero's camera.
JJH comes into close formation with IF. First observation : the 4S is no sluggard !
After a few photo attempts, DA's camera battery quit altogether ;-(
During this time, Igor in IF (with a working camera ;-) takes pictures of the photographer's airplane, and of the tufts at the winglets
As one can see, wingtip vortices concern only a small portion of the winglet. The intensity of the vortices gradually increases towards the tip.
The formation flight ends with a brief run at 100% power, "just to see". Measurements are taken on the fly and weights are not accurately known, but airspeed calibration is obviously not the same in the two aircraft.
Somewhat disappointed for having been unable to take useful pictures, we took the opportunity of a familiarization flight with Nicolas next day, to try visualizing the airflow with used motor oil.
"Ingredients" were kindly supplied by the local FBO, Aero Restauration Service ;-)
DA's camera had not fully recovered from its battery replacement. But looking closely....
Streamlines can be made out on the fuselage side, with the contraction observed on the previous day.
On the corner and the bottom of the fuselage, the lines are straight. We still have to determine the flow behaviour at the change of direction : boundary layer separation ?
With close attention, one can discern the marked curve of the streamlines on the flap.
Starting chordwise, they then turn towards the fuselage.
Please note we used the flaps on landing, which of course must have influenced the oil pattern.
When we came back to Darois, we had the opportunity to fly formation with F-PRTR, flown by Philippe.
Our aircraft configuration has changed somewhat since the previous tests : the new fuel tank access covers are recessed a few millimeters, with sharp edges. This modification on the 10 covers will definitely affect performance, but will not change the airflow we intend to check.
The airplane is tufted only in the left wing-root area.
Prolonged formation flight with F-PRTR at 220 km/h IAS.
Like the first time, two runs at 75% then 100% power, in order to quickly compare the performance of the two aircraft, in spite of the different loads (two in TR, with not much fuel, three plus 120 liter avgas in IF).
On board TR, I carefully make sure the cruise revolutions stay at 5000 RPM, and not 5200 as usual, due to a loose pitch lever.
An observer from DA does the same on board IF, but our levers do stay where you set them ;-)
After a small trip in formation, we land at Til Chatel to say hello to the club, then Igor takes everybody back to Darois in TR, while I'm flying back direct to Vienne with our bird.
Michel Bosek owns an MCR 01 Club. He made a detailed video tuft study, and kindly allowed Contrails ! to publish some screenshots.
The flow leak at the flap-root, seems to disturb the airflow on part of the fuselage.
Note that the low pressure tends to suck open the canopy. Retightening the locks would slightly decrease drag.
Excerpt of Michel Bosek's video.
To be continued...
Contact the author