First test flight report
MW9 Plank G-CKAA Flight Testing
1st flights 5-10-19 at Shotteswell, present MW, George Haffy, Andy, Chris O’Donnell, EFC
4 hops
Directional control on the ground is excellent, brakes good, turning circle less than the runway width at Shotts. The seating position is comfortable and the cock-pit environment pleasant.
Acceleration on the ground with existing engine and prop is good.
The nose can be raised at about 40IAS with a clean lift-off at about 50IAS, sometimes strip bumps could gave an earlier lift-off.
There is very little yaw control in the air, pitch & roll control through small angles is good.
Throttling back at approx 15ft & 50-60IAS gave enough time for a controlled round out, flair and gentle touch down.
The brakes were effective in limiting the ground roll.
For the take-off, either for a hop or for a committed flight, the aircraft needs to be running straight and central on the runway under nose wheel steering before lift-off. After lift-off and when a few feet off the ground gentle roll can be used to maintain directional control.
Total airborne time:- approx 1min.
First flight
At no time did the drag rudders give any sort of useful directional control.
In the slight cross-wind present on the day, the aircraft immediately yawed into wind at lift-off and continued tracking down the runway.
The elevons gave good roll control and although adverse yaw was always present the aircraft quickly established itself in a balanced turn to suit the bank angle selected. It was very noticeable that when ever the aircraft was in steady flight, either straight & level or in a turn, the yaw string was straight down the centre line without any help being needed from the drag rudders. In this respect it behaved like a weight-shift aircraft.
Medium rate turns were carried out by gradually increasing the turn rate from a low initial start value in order to minimise the adverse yaw tendency. These felt comfortable and a tendency for the nose to drop was easily corrected with back stick.
There was no sign of dutch roll which was a relief as there seems to be a history of this in other plank type aircraft at low speeds.
The max speed reached during the flight was 84mph IAS.
There was no conventional stall pitch break, just a developing mush with a high sink rate. This seemed to happen suddenly to the extent that a vertically downwards acceleration could be felt, as in a lift.
“Stalls” were tried from steady nose up climb attitudes. These ended up with a fairly rapid nose drop to an attitude which seemed to mirror the attitude of the initiating climb, I.e., the steeper the initial climb attitude, the steeper the resulting nose down attitude. There was nothing scary about the aircrafts behaviour during these manoeuvres, i.e., no signs of tuck or tumble.
The first landing was from a fairly long final approach. This brought home the difficulty of keeping aligned with the runway centre line in an aircraft without effective rudder control and with a tendency for adverse yaw. It was quickly found that small roll inputs and care to avoid over control was the way to go.
The next thing noticed on the approach was that the decent rate was very slow. There are no drag devices fitted and no recourse to side slip. Putting the nose down merely swopped a too high condition for a too fast condition. The aircraft came over the hedge with a bit of both but thanks to the 700m runway at Shotts all was well. It was noticeable that pitch control in a flair starting at 70IAS was much more sensitive than one starting at slower speeds.
Immediately following this first circuit another was carried out in an attempt to get a shorter landing run, it was a bit shorter this time but there is still much room for improvement.
These first flights were all about assessing the aircrafts qualitative behaviour and the findings were highly encouraging. We now look forward to continuing the testing with the focus on gathering quantitive data. At this stage we don’t even know if the aircraft has a trim speed, hands off. (There is no trimmer fitted).
Flight details:- 20mins, 2 landings.
Engine behaviour
The engine fitted to G-CKAA is a single cylinder 2-stroke of about 30hp with belt reduction and a diaphragm pumper carburettor. Earlier hops carried out by Mike himself had been done with the carb “H” screw 2 turns out, (recommended range; ! !/2 to 2 turns out}. This setting was known to be a bit too rich but it had been good for the hops so it was retained for the first flight in the interests of engine cooling. The “L” screw was also left at the same setting as for the earlier hops. This gave a reliable idle, all-be-it a bit lumpy.
During taxing tests up and down the strip it was found that at full throttle the engine appeared to be over rich. Throttling back to about 3/4 throttle smoothed it out. At this throttle setting the engine ran strongly and sweetly and gave the aircraft a comforting acceleration on the ground. For all subsequent take-offs, both for hops and for actual flights, the throttle was pulled slightly back from the full throttle stop until the engine ran sweetly.
Mike’s incident
Following the successful first flight Mike was encouraged to have a go himself. His plan was to try a hop and then, if he was happy, perhaps to do a circuit. Unfortunately, I had forgotten to tell him about my findings in relation to the best throttle setting for take-off.
We stood at the runway threshold and watched Mike go. The engine sounded a bit rough and didn’t seem to be giving of its best; this can be heard in several video clips taken at the time. The aircraft was seen to take off for the hop but as he throttled back it seemed to come down steeply and bounced. This was the first of a sequence of bounces, possibly further provoked by PIO, which ended with a bent nose leg and a tow back to the hangar.
My view is that, with the engine not running at its best, acceleration down the runway was lower than he had been used to during his previous six very successful hops. This probably led to him leaving the ground at a lower speed than before and maybe in the aircrafts high drag zone where deceleration would be higher on throttling back. A rapid sink rate and bounce could then result.
It might have been better to open the throttle after the first bounce but with the aircraft half way down the strip already this option would not have seemed attractive. If he had managed to get well up in the air with an engine below par the consequences could have been far worse than a bent nose leg.
Eddie Clapham
7-10-19
Second test flight report
On 17-18 Sept 2020
Introduction
The Plank’s first flight, (as opposed to the very successful hops carried out by Mike earlier), took
place at Shotteswell on 5 10 19. This flight showed that while the basic handling was satisfactory
there was litt le or no yaw control from the drag rudders and, with no flaps and no ability to
sideslip, getting the approach right was quite difficult. Another problem had been that the engine
was running too rich at full throttle meaning that max power had not been ava ilable. (The “H”
screw had been set to 2 turns out).
During last winter the drag rudder control system was altered to give approx 80deg full
deflection. Compression springs had also been introduced between the rudder pedals and the
nose wheel steering arm s so that both rudder pedals could be pressed to full deflection at the
same time. This allowed normal steering on the ground while the springs were uncompressed and
full deflection of both drag rudders when both pedals were pressed to full deflection toge ther.
Thus both 1 st flight control issues should at least be alleviated.
In this difficult year it was not until 17-18 Sept 2020 that all the requirements for flight testing
came together. Luckily, this date also fitted in with Dan Griffiths’ schedule. Dan had expressed an
interest in flying the Plank some time ago and he was able to call in at Mt Airey in his Mooney on
the way home from Doncaster to order to try out the Plank. Needless to say, Mike and his team
were delighted that this could h appen and we greatly appreciated Dan’s efforts and our interaction
with him.
Ground Handling
The introduction of compression springs into the nose wheel steering circuit made steering
slightly less positive but this was not a problem on the day when it wa s easy to keep the aircraft
straight during the take off run. It might be more of an issue in a strong cross wind or on a strip
with a side slope. The turning circle seemed unaffected.
Flight testing
Weather conditions
CAVOK with an approx 12mph
gusty wind roughly down Mt Airey’s 07 runway throughout the
two days of testing.
Instrumentation & Limits
Aircraft:
ASI (mph) 84max, Altimeter, Compass, “G” meter. No slip ball is fitted but there is a
yaw string.
Engine:
Tacho & Hrs (7600max rpm)*, Co mbined CHT( 200degC max) & EGT (640degC max)
*This is the aircrafts placard limit. The Bull Max 250 Manual shows max rpm
as 7800 with max power rpm variously quoted as 7400 & 7600.
No attempt was made to calibrate the ASI with a GPS because the gusty
conditions made flying at
a constant IAS difficult.
All EFC flights were carried out with an i
pad mini running SkyDemon. The data recorded
proved to be very useful for post flight analysis.
Flights
The Plank did three flights on the 1st day and two on the 2nd day as below, (SkyDemon times are day as below, (SkyDemon times are wheels-off to wheels-on):-
1 EFC/75kg 17 4lbs as before 1.875 out
2 EFC 21 2lbs as before 1.75 out
3 EFC 20 none 20deg down 1.75 out intake air box*
4 EFC 77 none 40deg down 1.6 out intake air box
5 DG/80kg 15(est) none 40deg down 1.6 out intake air box
Immediately after take off the pilot is aware of carrying a rearward stick force of about 3lbs. This
remained throughout the testing in spite o f, our efforts to reduce it by removing nose weights and
setting the fixed elevon trim tabs down. During fly bys, ground observers commented that the
elevons seemed to be reasonably in line with the wing TE. If the stick was released in level flight
there was an immediate nose down pitch response but the rate of change of attitude was fairly
slow and not alarming, however I did stop at about 30deg nose down by applying back stick.
deflection. Alternating left and right stick produces clear alternating adverse yaw but I forgot to
see if this could be reduced by use of the drag rudders. Dan did comment that opposite rudder
tended to make a steady turn feel nicer. L ast year I had difficulty holding the runway centre line
during the approach which I put down to lack of a yaw control. This time I had no such difficulty
even though I wasn’t using the drag rudders. This I put down to my greater familiarity with the
aircr aft and its response rates.
that pitch and roll rates increase linearly with stick displacement. There was no indication of an
over quick response to pitch inputs. The handling in this respect feels very normal and quickly
inspires confidence. That this was the case for me can be seen in the SkyDemon track records
which show a considerable amount of manoeuvring in all my flights, (medium rate turns & ge ntle
wing overs).
was noticed that airspeed seemed to increase rapidly when the nose was dropped.
The drag rudders used together produced a nose down pitch change and an increase in rate of
decent. This was not measured.
I was quite surprised to find such apparently normal handling in such a radically different aircraft.
Shortly after returning from the Plank testing I flew my Eurostar solo for comparison. I found
that, if I locked the rudder pedals with my feet in the straight ahead position and set the throttle
for 80mph S&L, I could repeat my Plank manoeuvrings with equal ease and with the slip
indicator rarely more than 1/2 a ball out once things had sett led down. In other words, there is not
a lot of difference between the feel of a Eurostar and the feel of the Plank over the flight regime
evaluated.
at about 50mph IAS. This state is reached with the stick well back and doesn’t seem to change much
when the stick is pulled fully back against the back stop. This applies to a stall approached from
level flight. Stalls from a more nose up attitude led to a nose drop followed by an automatic
recovery to the nodding mode with the stick held hard back throughout. Accelerated stalls and
turning stalls were not tried.
Take of & climb figures will be effected by the fact that at times the engine was not running at its
best. By flight 4 we think we had got the full throttle mixture adjustment about right so the values
for this flight are likely to be the most accurate.
Take Off Distance (R/W threshold to Lift Off from SkyDemon log)
Flight Number 1 2 3 4
ROC (ft/min) 372 261 367 406
The following data was noted in S&L flight:
IAS (mph) RPM CHT (deg C) EGT (deg C)
70 7000 210 575
80 7400 200 600
I ran out of fuel on Flight 2. Altitude and distance up-wind at the time made a landing back on the
field both possible and easy. The resulting 2 minute glide and the SkyDemon log enabled an
accurate determination of the ROD and glide angle with the engine stopped. During the Eurostar
flight already mentioned I took the opportunity of obtaining e ngine stopped data for comparison.
The two aircraft were found to be quite similar.
Plank 60-70 862 (av. over 2mins) 6.6:1
Eurostar 60 650 (av. over 1min) 8.1:1
Eurostar 70 853 (av. over 1min) 7.2:1
The engine is a Ciscomotors 2-stroke Bull Max 250 pull start (not accessible to the pilot). It is a
single cylinder, single ignition engine producing 30 33 HP and is used in some of the bigger
Powered Paragliders. These are pushers as i s the Plank. It has a balance shaft to reduce engine
vibration, a poly V belt reduction drive to the propeller and a pumper diaphragm carburettor.
This type of carburettor has two diaphragms which pulsate under the influence of varying
crankcase pressure. One acts as a pump lifting fuel from the tank and supplying it to the other
diaphragm which operates a needle valve metering fuel to the engine in proportion to the intake air flow.
starting. The Plank has a manually operated squeeze type primer bulb between tank and carb
which has to be operated in conjunction with pressing the second diaphragm to get fuel into the
engine. Care has to be taken not to over fuel the engine during this procedure. The engine manual
says that if this happens the throttle should be fully opened for repeated start attempts. I had to
use this technique for most starts during the testing period. The trouble is that you can’t see how
much fuel is being delivered to the engine and one’s first thought, if it doesn't start, is that it needs
more fuel which may only add to the problem. We must give further thought to the starting issue
and come up with a reliable procedure requiring less pulling on the starter chord.
rpm range and the other with a “T” bar for the High rpm r ange. The initial settings for the L screw
and the throttle idle stop gave a reliable idle on the ground and in the air. Throughout the test
period these were not changed from the initial setting. The engine manual states that the H screw
should be set bet ween 1.5 & 2.0 turns open from the fully in position. 2 stroke engines are very
sensitive to air/fuel ratio; too rich and they run unevenly and fail to reach max power rpm at full
throttle, too weak and they run too hot and may seize up. Last year we had t he H screw 2 turns
out and only got acceptable running by throttling back until the engine ran evenly, all be it at less
than max rpm. This year we started with the H screw 45deg further in, i.e. at 1.875 turns out. It
was still a bit uneven at full thrott le with rpm fluctuating between 7300 & 7600. Further changes,
ending up with1.6 turns out and the standard intake airbox fitted. This combination gave steady
running at 7500-7600rpm during a 20sec ground check at full throttle. Engine temps stayed
withi n limits. These were the settings for Dan’s flight and he reported steady running between
6000-7600rpm.
shrieking noise and the engine racing. Throttling back s orted it and belt tension was reset after
landing.
Vibration level was very low and noise levels in the cock were acceptable even without a headset.
A brief guide for new MW9 Plank pilots
Engine Ground Check
Warm up to 100deg CHT
Go to full throttle watching rpm (limit 7600). rpm should reach 7500. The engine should sound
smooth and even.
Run at full throttle for about 20secs. Temps should stay within limits during this check.
Taxi to threshold checking out the feel of the rudder pedals and steering as you go.
Line up, full throttle, keep straight.
Lift nose wheel a little at 45-50mph.
Lift off 50-55mph.
Accelerate to 65mph staying low, keep straight using stick.
Climb away at 65mph, check rpm, throttle back to 7500 if necessary.
Climb to 2000ft, throttle back to 7000rpm/70mph.
Check control responses in gentle manoeuvres to gain confidence, you will probably be surprised
at how normal it feels.
Practice keeping straight for the landing and check out the aircraft feel in the glide 4.
Approach at 65mph; at this speed the aircraft feels nice in pitch and has enough energy available
for the round out and hold off with the engine at idle.
some way out with enough power to give an appropriate decent rate down to runway level.
Needless to say, his round out, hold off and touchdown were immaculate at the first a ttempt.
26-9-2020