FLIGHT REPORT by Dave Welles
Marske Pioneer 2D @ Marion OH, on 6/22/04

CHANGES
Since I last flew this aircraft (See 9/28/03 Report) a number of changes and improvements have been made:
1.The main wheel has been replaced with a larger diameter wheel (with a drum brake) to improve rough field operations capability. The nose skid was replaced with a nose wheel. Both wheels are faired to the fuselage with fairing skirts. Appearance-wise this gives the aircraft forward fuselage a ‘PW-5 look’.
2.A ‘moveable weight’ trim system has been added that is controlled by a small crank / cable drum arrangement located on the L/H side of the cockpit below the spoiler handle. This mechanism has a cover that is slotted to accommodate the trim position indicator. A very tidy, functional arrangement.
3.The old ‘removable’ canopy has been replaced with a ‘forward hinging’ version. It contains an emergency release that is activated by a ‘T’-handle located on top of the glare shield.
4.The fillet between the wing and fuselage was reshaped to correct an apparent wing root (airflow) separation problem. Additionally, a fence was installed at the inboard end of the ‘elevator’ for the same reason.
5.Mylar seals were added to the wing / aileron gap, top surface.

The aircraft empty weight is now 432 lbs.

TEST OBJECTIVES
In the two days available the consensus was to come up with a plan to improve the handling qualities (read improve roll rates and turning ability). This puts the focus on the lateral – directional qualities of this aircraft, as the longitudinal stability / controllability is really quite good.
The tests and objectives are as follows:
a.Determine if the aileron differential is optimum. The original design called for a 3:1 ratio (30 o up / 10 o down, I think, at maximum stick deflection); this had been changed to 3:2 (approx.) to improve roll authority and fix a perceived ‘proverse yaw’ problem. The plan was to fly the current set-up then put the aileron rigging back to ‘standard’ and refly the tests (Roll rates and Dutch roll characteristics)
b.Evaluate the turning qualities by looking at the ‘Spiral Stability’. This was to be measured by placing the aircraft in a coordinated turn (30 o degrees to be documented) than releasing the controls (stick and rudder) and timing the interval until the bank had reached either 50oor 10 o; or, record the bank angle after 30 seconds.
c.Evaluate differential spoilers for roll control. This was to be done by disconnecting a spoiler and quantifying what the roll (and yaw) responses are with single spoiler operation.
d.Conduct a ‘tuft study’ with both wings tufted; and for air-to-air videoing, the wing root, aft fuselage, and rudder.
TEST INSTRUMENTATION AND SET-UP

WEIGHT & BAL: 5 lbs. fixed ballast was added at the rear anchor point of the ‘moveable weight trim system’ (Sta. not available) to yield a (almost) 10 inch balance dimension (Marske system) with the trim weight cranked fully aft. The flying weight was 620 pounds. Because of decreased cockpit space (the larger main wheel and the tube for the trim system (sliding weight) along the bottom of the aircraft) I no longer fit with a parachute. Because of the ‘low risk’ nature of the proposed testing the decision was made to fly W/O a chute.

Reference marks were made on the lower edge of the instrument panel to indicate aileron stick positions of ‘neutral’, ½, and full stick throws (left and right).

For bank angle(s) marks were added to the canopy sides that, when aligned with the yaw string tape (parallel with the horizon), yielded a 30 degree bank (left or right).

The tuft pattern, applied to the wings, was spaced at (about) 2.5 feet apart along the 60% chord with another line of tufts (mid spaced with the above pattern) at the 90% chord line. For the ‘air-to-air’ flight, additional tufts were added to the wing root (in the area that was unobservable from the cockpit) continuing the described pattern inboard and including the fuselage, and fin and rudder (right side only).

Marks were made (using a protractor) to indicate yaw string positions of neutral, and 15 degrees left and right.

RESULTS

The first flight was made on 6/22/04 from a 3000’ AGL tow in moderate soaring conditions. The first half of the flight was in air too turbulent to get much meaningful data. Eventually things smoothed out with thermals still good until well after 7:00 PM.
The first impressions / comparisons with the September 03 flight were that at slow / minimum airspeeds the wing behaved differently. Its propensity to slice (yaw) to the left, or if turning, in the direction of turn, were largely gone. The tuft pattern on the wing showed no separation inboard as was previously observed; but the R/H wingtip was separating (stalling) before the left. (Later measurements showed the L/H tip as having about 1.9 degrees of incident less than the R/H side)
The moveable trim system worked very well. The minimum trimable airspeed was an indicated 40 - 42 mph (trim weight full aft) and, with the weight forward, the trim speed was 65 IAS. The T/O and landing were made with the trim in a ¾ aft position. On tow the weight was moved to approximately the middle, to trim out the forces and ‘zero’ the elevator position. (Zero = the trailing edges of the wing and elevator are ‘even’.)
The minimum flight speeds / stall: with the weight aft was 32 IAS, and weight forward, about 1.5 MPH greater. With the trim weight fully aft (worst case) the static longitudinal stability was positive over the speed range of ‘minimum’ to 80 MPH IAS.

SPIRAL STABILITY(See data sheet below)
The tests were done with the controls completely released after the aircraft was established in a coordinated turn at the target airspeed. This aircraft exhibited excellent turning stability. Three of the points showed the bank unchanged after :30 seconds and only one, (60 mph / L.turn) showing an inclination to spiral dive with an airspeed of 70 mph (at the 50 degree/:25 second point) with an increasing bank. The warp (wash out) in the outboard portion of the L/H wing panel is, no doub,t a factor as was the random turbulence.
This aircraft can be very easily thermalled hands off with rudder imputes only. The only area where one wished for more (vertical) tail volume is in rough air to damp out the associated (uncommanded) yawing. The yaw string should definitely be on the ‘required equipment list’ for this aircraft.

ROLL RATES(See data sheet below)
The roll rates were measured from a 30 degree coordinated turn in one direction to (passing thru) 30 degrees bank in the opposite direction. The reference marks to gage the 30o points worked very well. The realistic minimum speed (at 30 deg.) was 38 IAS; slower speeds could result in the wing tip (the tip moving downward) stalling with the commencement of the roll. This accounts for the first (L-R / 3 sec.) point. The tip stall also gives the impression of aileron ‘proverse’ yaw and makes stopping the roll and controlling the opposite turn problematic until the flow at the tip reattaches. The tuft pattern on the wings was invaluable in sorting things out.
For all of these points an effort was made to coordinate the rudder with the aileron input. At the lower speeds the rudder was insufficient to balance the adverse yaw generated by the ailerons; but improved as the speeds increased. For the ½ aileron inputs at lower speeds there was not a whole lot of aileron left over from that (the opposite aileron) required to coordinate the initial (set-up) turn, hence the slow times.
It should be noted that one of the more significant differences, in thermalling, between last year and this, was the balance of the controls – last year the aircraft required significantly less (opposite) aileron to coordinate the turn. Now, at minimum speeds, it takes almost ½ opposite aileron; with the amount of (bottom) rudder is unchanged. The probable cause being a change (improvement) in the wing root separation problems.
Another characteristic, noticed while doing the ‘full aileron’ roll rates, was a change in the longitudinal trim (while rolling) that required significant forward stick (movement) to counteract. In other words, for the same airspeed and trim weight position, the elevator position in ‘wings level’ flight is farther aft than the elevator position required (to maintain a constant pitch attitude) when rolling through ‘level’.
I suspect this characteristic is a function of ‘aileron differential’ and becomes more noticeable as the differential is increased. This characteristic did seem more pronounced when rolling to the right.
AILERON RIGGING
(full stick travel – measured 6/23/04)

Stick Position L/H Aileron R/H Aileron Differential (up/dn)
Left 24o UP 16 o DOWN 3/2
Right 16 o DOWN 28 o UP 3.5/2

It should be mentioned that the above-described characteristic was not apparent with ‘partial aileron rolling’ or at the onset of the ‘full aileron rolling’.

DUTCH ROLL(See data sheet below)

Aileron inputs / rudder fixed: These were done by finding an aileron input (magnitude and frequency) that resulted in repeatable oscillations of roll and yaw. Typically this was with (about) 2/3 available aileron travels (both directions) at 2 seconds per cycle. Too large an aileron input resulted in yaw excursions that blanketed the elevator; introducing unwanted pitch changes into the picture.
By observing the elliptical path the wing tip is tracing, during the above-described oscillations, one can readily see the ratio of roll to yaw. Our intent was to compare this ratio to what the ‘rigged-back-to-standard’ aileron configuration would yield.
The second, and for us less important, part of this check is to release the controls and observe how the oscillations damp out. These results were ‘deadbeat’ (immediate cessation) to maybe 5 o of continued roll.

Rudder inputs / Aileron fixed: This is another way to excite any ‘Dutch roll’ tendencies the aircraft may have. The control inputs used (rudder doublets) were limited to keep the elevator ‘unblanketed’, with yaw excursions of about +- 10 o.
The path the wing tip traced was a straight line angled to the horizon (the tip moving ‘forward and up’, ‘aft and down’). The ratio of yaw-to-roll becomes the horizontal and vertical legs of the triangle with the wing tip path serving as the hypotenuse. For aircraft with more ‘effective dihedral’ the wing tip path (usually) will trace a more elliptical path; the thinness (fatness) also being a measure of the ‘effective dihedral'.
The conclusions that can be drawn from this are:
1.Even at the ‘minimum speed’, there is still adequate rudder authority; and the effective dihedral does not decrease with increased angle-of-attack (contrary to conventional theory for a forward swept wing plan form).
2.For our proposed comparison with the rerigged ailerons this portion (aileron fixed) need not be repeated.

STEADY HEADING SIDE SLIPS(No recorded data)
The aircraft can be very readily slipped. Which is good, because of the relatively ineffective spoilers and, faced with landing over an obstacle into a short field, this becomes a required maneuver. In entering the slip there is a decided discontinuity in pitch authority when the elevator (one side only) gets (partially) blanketed. The nose pitches down, changing about five degrees, but the slip can be continued with a ‘new’ stick (elevator) position. Not unlike the pitch / stick position change that occurs when cracking the spoilers open. (See ‘Spoiler Evaluation’)
Once the slip is established it takes significant aileron, into the slip, to maintain the low wing (down) position. This is another measure of ‘effective dihedral’ and from a ‘slipping’ standpoint I would not want it any stronger.
The speeds looked at were only in the 45 to 55 IAS range. The minimum speed (at which a controllable full slip is possible) should have been looked at as well, but wasn’t.

DATA CARD

ROLL RATES
(30 – 30)
Full Aileron ½ Aileron
SPEED L -R R –L L – R R - L
Minimum 3 sec/36 mph 6 /38 10 / 38 7 / 38
45 5 4 - 8
60 3 3 - 11
80 2.6
RUDDER FIXED (note max slip / yaw string)

Minimum
45
60
80
SPIRAL STABILITY
(From 30 degrees, time to 50 degrees or 10 degrees)
SPEED (mph) L / H R / H
Minimum (38) :30 sec / 10 deg :30 sec / 30 deg
45 :30 sec / 30 deg :30 sec / 50 deg
60 :25 sec / 50 deg :30 sec / 30 deg
80 - -
DUTCH ROLL
(Excite W/ Ailerons, Rudder Fixed)
SPEED ROLL : YAW PERIOD DAMPING
Min. (38 mph) 3 : 1 2 sec / cycle Dead beat
45 4 : 1 “ “
60 5 ; 1 “ “
80
Excite W/ Rudder, Ailerons Fixed
SPEED YAW / ROLL PERIOD DAMPING
Min. (38 mph) 4 : 1
45 8 : 1
60

NOTES:
Roll rates – indicate any points where the rudder is inadequate. With “rudder fixed” note amount of induced slip. (from yaw string)

Dutch Roll Checks – note amount of input used to excite; try different amounts.

Steady Heading Side Slips – Evaluate at 15 degrees (yaw string) and full slip. For speeds of min+ 5, and min+15.

SPOILER EVALUATION
The pitch changes that occur with spoiler usage are not unlike those of the early model SGS 1-26’s (before dive brakes replaced the spoilers). What makes this an insidious problem for the Pioneer (and not the 1-26) is its lower mass moment of inertia about the pitch axis resulting in very sudden pitch changes (excursions) that are beyond the ability of most (myself included) to anticipate and react to in a timely manor. (A ‘must do’ situation if close to the ground to prevent hitting ‘nose first’)
Where this is most serious is the region (of spoiler travel) between ‘closed’ and ‘cracked’; a range of spoiler handle travel of only about ½ inch. Once the spoiler doors have broken through the boundary layer, additional opening of the spoilers (beyond ‘cracked’) results in pitch changes that are very linear and completely controllable.
This discontinuity works in both directions; going from ‘open’ to ‘closed’ will result in a sudden uncommanded pitch UP, as the spoilers reach the ‘closed’ position and the boundary layer reattaches, requiring a repositioning of the stick about (seems like) two inches forward from that required for the ‘cracked’ position.
Conversely, when transitioning this region, (‘closed’ to ‘cracked’) the stick repositioning is about two inches of aft travel (to arrest the nose down pitching). To avoid this ‘squirrellyness’ close to the ground, the spoilers (on approach to landing) should not be closed completely, but instead, should be kept ‘cracked’ at a minimum (instead of ‘closed’).
This is not to say that the landings should be made with the spoilers ‘cracked’ – anywhere from ‘cracked’ to ‘full’, as the situation dictates, is fine. Just stay away from that non-linear region that exists between ‘closed’ and ‘cracked’ when close to the ground.

SINGLE SPOILER / ROLL EVALUATION(Not done)
From the above observations and conclusions (see ‘spoiler evaluation) I would recommend not doing the proposed test for the following reasons:
1.Not only would there be ‘yaw’ responses but ‘pitch’ responses as well – both of which, probably, would generate more problems than they solve. The basic improvement we are seeking is in ‘roll’ (only), unencumbered by other (axis) angular accelerations.
2.In the process of improving / solving the (normal) spoiler usage problems a lower spoiler door (was standard) may want to be reinstalled. (see ‘recommendations’)
3.The ‘discontinuous’ (non-linear) characteristics of the spoiler response when ‘breaking’ the boundary layer only adds to the unattractiveness of the idea.

See NACA Report #494, by Fred Weick & ? for a comprehensive study (advantages and short-comings) of some ‘roll spoiler’ configurations.)

‘RIGGED-TO- STANDARD’ AILERON COMPARISON(Not done)
When we were documenting the aileron travels flown (the first half of the planned comparison) we discovered that the ‘aileron jamming’ problem, (See 9/28/03 Report) caused by the “C” section of the wiper seal / aileron shape catching on the lower wing skin, would (potentially) reappear with the increased aileron travels required to reset aileron travels back to ‘standard’.
Without control stops at the ailerons (to positively insure against an over travel / jamming situation) the decision was made to abandon this comparison, and instead, concentrate on the air-to-air / tuft study video flight.
In hindsight, I’m not sure that this comparison would have been of much benefit (read “step-in-the-wrong-direction”) because of the ancillary uncommanded pitch changes associated the increased ‘aileron differential’. (See ‘Roll Rates’, above)

AIR-TO-AIR (TUFT) VIDEO (Flown 6/23/04)
The Pioneer was flown by Mat; Mike (PIC) and myself (rear seat) flew the Grob 103 video plane. Additional, tufts had been added to the wing root, fin /aft fuselage, and rudder.
The conditions cooperated in that we were able to join up with Mat, who launched first, and we worked a number of good thermals together, with ample opportunity to get the video we wanted. In hindsight, we were to narrowly focused on getting the stall / tuft pattern on the R/H side and failed to get such things as the tuft / separation pattern associated with yaw excursions (how the elevator gets blanketed). Etc.
From my ‘rear seat’ perspective the general tuft pattern on the wing root / fuselage /fin & rudder looked really solid (no sign of separation). The pattern on the R/H wing tip / stall was better seen from the cockpit of the Pioneer. Our camera technique was not real great with the associated unsteadiness obscuring the detail we wanted.
In doing the ‘ minimum speeds / stalls’ (the Grob being above and behind, 5 - 4 O’clock) the minimum speed of the Pioneer seemed about (estimated) 2 knots slower than the Grob. Thermalling, the Pioneer could easily out climb the Grob.
Results aside, this flight was ‘fun’ – observing the Pioneer in flight (has a ‘unique’ look to go with its ‘unique’ characteristics) and flying with Mike – an excellent sailplane pilot with lots of enthusiasm – made for a good ending to a good trip.

RECOMMENDATIONS
SAFETY-OF-FLIGHT– The following (first three items) should be addressed ASAP:
1.Replace the “VNE=130 MPH” Placard with an airspeed indicator ‘red-line’ (piece of red tape) appropriate to the ‘operational’ never exceed IAS.
2.Modify the spoiler system to allow safe opening / closing (with controllable pitch changes) close to the ground. Maybe reinstalling a ‘smaller’ lower spoiler door (or adding big holes to the ‘original’ lower door) is the easiest way to go.
3.Change the Aileron leading edge / wiper seal from an open “C” section to a closed “O” or “D” section to preclude the previously described ‘jamming’ problem. (See 9/28/03 Report). And / or add aileron stops (wing) to insure that no ‘over-travel’ / jamming can occur.

(Recommendations, continued)
IMPROVEMENTS (General)
1.Replace the nose wheel with a semi-retractable nose skid that would give the higher (nose up) attitude desirable for the take-off; and for landing, be in the retracted position to allow for greater ground clearance to minimize premature nose / ground contact.
2.Add an ‘UP-Aileron only’ segment to the wing tip section. To be ‘lifted’ (driven) by the UP motion of the existing aileron. Depending on results, an inboard portion of the existing aileron(s) could be removed to lighten aileron forces. These segments could also serve as tabs to trim out, or minimize, the effects of the warped L/H wing.
3.Redesign the aileron bell cranks (in the wings) to optimize them for the (existing) 3/2 differential, and, in rigging, ‘even up’ the aileron travels. The redesign should include a “rig-pinning” feature and, “aileron stops”.
4.Recommended testing: To measure the Pioneer against other sailplanes, ridge running would be an efficient, fun way to go. The sailplane should be cleared to airspeeds of, at least, 120 MPH IAS* first (with mass balanced ailerons). The test comparison is to go with other sailplanes (one at a time) at a series of speeds , with the sailplane with more performance flying higher (in weaker lift) as required to maintain equal speeds. This altitude delta becomes a measure of the performance difference between the sailplanes, at that speed. The other measure would be for each sailplane to carry a recording ‘g’ meter and compare the max. reading / run for each sailplane. The ability of the Pioneer to ‘unload’ the vertical gusts quicker (because of the much lower mass moment of inertia / pitch axis) the smoothness of the ride, as measured by the max. ‘g’ recorded, should be equivalent to sailplanes with much higher wing loadings. Here again, maintaining the same speed / run is critical for comparison purposes. *At Harris Hill, in good ridge lift, a 2-33 can maintain 80 MPH.

CONCLUSIONS (Not set in concrete)
The Pioneer is a much-improved sailplane from what I flew a year ago - except in two areas- the nose wheel (replace W/ a skid) and, poorer fit (for my 6’-3” frame). The hinged canopy and the trim system, from an operational standpoint, are welcome additions.
We probably won’t ever know just how big an improvement the new wing root fillet is, but based on the observed tuft patterns and changes in handling qualities (from last year), I think its contribution is large.
I think an improvement in roll-rate / maneuvering capability can be easily accomplished by a rework of the aileron system. I would wait until after modifying and mass balancing the ailerons to fine-tune aileron travels and differentials. I don’t think the ‘anti-servo tab’, installed on the outboard end of the aileron (ala. Monarch) is as good a direction to go, compared to the additional (recommended) ‘tip’ aileron segment; for the following reasons:
1.Harder to mass balance and may (possibly) contribute to aileron flutter.
2.Does nothing to keep the airflow attached, on the wing tip segment, during rolling. The ‘tip’ aileron segment, deflected UP, would. (See ‘Roll Rates’ for problem description)
3.May create a ‘proverse yaw’ prone aileron system – Of the two I will take the ‘adverse yaw’ first. (Either system will require some tuning – less so I think for the ‘tip aileron’ concept.)