Gyroplane Stability and Aerodynamics - Glasgow University
Posted: Mon Feb 03, 2014 8:47 pm
Gyroplane Stability and Aerodynamics - Glasgow University:
Hi all, some time ago it was mentioned that Glasgow University did testing on gyroplanes to investigate stability issues. It was also mentioned that Glasgow and Dr Huston said that Horizontal Stabilizers were the holy grail of gyro planes and that adding a horizontal Stabilizer would significantly improve a gyroplanes longitudinal dynamic stability........
The report is 350 pages long, I read through all of it and thought that it would be a good thing to post some of this reports findings for you all to read.
Download the report and findings here: http://www.caa.co.uk/docs/33/Paper2009_02red.pdf .
I find it very interesting that the report found just the opposite to what was posted on this forum.
Foreword
Five fatal accidents to Air Command Gyroplanes between April 1989 and March 1991 resulted in CAA requesting that AAIB undertake an Airworthiness review of the Air Command. AAIB produced report EW/101/06 Airworthiness Review of Air Command Gyroplanes dated 12 September 1991. Recommendation 4 of the report (see 2.0 below) was the driver that led to the initial research contract with Glasgow University, requesting CAA to explore the possibility of assisting the gyroplane fraternity in a research programme on aerodynamic and airworthiness characteristics of gyroplanes.
This comprehensive report represents a significant step forward in the understanding of the aerodynamics of gyroplanes. The conclusions presented are the scientific results of the tests and studies carried out on a limited number of gyroplane designs. The report does not cover all configurations of gyroplane designs and therefore the conclusions may not be directly appropriate to gyroplanes not specifically addressed by the report. It is important to appreciate that it represents the scientific findings of the areas addressed and does not attempt to extrapolate beyond those boundaries as this would be speculation and not appropriate for a scientific research report. Various conclusions have been made in the report and are noted below:
1. CG / Thrust line offset. The recommendation that the vertical location of the centre of mass is within 2 inches of the propeller thrust line is a result of the study and therefore is reported as such. CAA accepts that closer alignment of the CG and the thrustline is a sensible design aim to achieve pitch dynamic stability (phugoid mode) but also has flight test experience of a gyroplane design that achieves good stability but is well outside of the 2 inch criteria. CAA Flight Test Specialist qualitative assessment implies that pitch dynamic stability may not be solely a function of CG/Propeller Thrust alignment for all types of Gyroplane. It is appreciated that in paragraph 8.3.1 (page 152) of the report it is stated that other factors can affect the phugoid mode.
MPD 2005-08 was issued 24 August 2005 mandating, in part, restrictions on pilot experience, VNE and wind/gust speeds for single seat a/c. These could be removed if acceptable evidence was presented to show that the CG/thrustline offset was within ± 2 inches. However other restrictions noted in the MPD would still apply.
Advisory material to BCAR Section T.23 now includes ± 2" criteria.
2. Effect of tail planes.
The report also concludes that horizontal tailplanes are largely ineffective in improving the long term response of pitch dynamic stability (phugoid mode).
The Horizontal Tail
The configuration of the tail sections of the VPM M14 and M16 aircraft are quite unusual in terms of the large endplates on the horizontal tail surfaces. It has already been established that these endplates are beneficial for lateral stability but it was unclear what effect, if any, they would have on the lifting effectiveness of the tailplane. To investigate this, a single test was carried out with the cowling on, tail on configuration but without the endplates. The measured normal force and pitching moment coefficient curves are compared with those from the corresponding test with the endplates on in Figure 3.27.
By preventing the flow of air around the tips of the horizontal tail, the end plates restrict the flow over the horizontal tail to an almost two-dimensional state. This should allow the tail to develop higher lift than a conventional tail at moderate incidence but will result in a sharper stall. This is illustrated in Figure 3.27 where the loss of normal force due to tail stall is apparent at around twenty degrees when the endplates are on but there is a much more gradual loss when the endplates are removed. There is no clear indication in the CZ curve of any increase in lift at moderate incidence but the gradient of the CM curve is obviously greater between -20 and +20 degrees when the endplates are on. This is indicative of increased tailplane effectiveness.
The effect of increasing the length of the tail boom by approximately 0.3m (on the full scale vehicle) was also examined. The results of this study are presented in Figure 3.28 and were very much as expected with almost no change in the normal force coefficient curve, but a substantial change in the gradient of the pitching moment coefficient curve. This is simply due to the increased offset of the tail from the fuselage reference point. It also appears, however, that the stall angle of the tail at positive incidence is reduced with movement away from the gyroplane forebody. This is undoubtedly a result of a change in the effective angle of attack experienced by the tail due to reduced interference between the tail and the forebody.
Perhaps the most significant observation associated with the tailplane is the lift-curve slope. This is a measure of efficiency and also an indicator of its likely impact on the complete aircraft and it can be extracted from these data readily. For example Figure 3.7 compares Z-force coefficient with tail on and off; analysis shows that the lift-curve slope is 2. A typical value for a blade is 5.7; for a helicopter horizontal tailplane 3.7; and the theoretical maximum for a finite wing is 2π.
When combined with the short moment arm of the typical pusher configuration it can be seen that tailplane effectiveness is likely to be limited at anything other than high speed. Note that with power on, where even the low-set tailplane might be expected to experience some slipstream benefit, the lift-curve slope increases only by a relatively small amount to a value of 2.7 - still well below even helicopter values.
I will post some more shortly..
Regards
Hi all, some time ago it was mentioned that Glasgow University did testing on gyroplanes to investigate stability issues. It was also mentioned that Glasgow and Dr Huston said that Horizontal Stabilizers were the holy grail of gyro planes and that adding a horizontal Stabilizer would significantly improve a gyroplanes longitudinal dynamic stability........
The report is 350 pages long, I read through all of it and thought that it would be a good thing to post some of this reports findings for you all to read.
Download the report and findings here: http://www.caa.co.uk/docs/33/Paper2009_02red.pdf .
I find it very interesting that the report found just the opposite to what was posted on this forum.
Foreword
Five fatal accidents to Air Command Gyroplanes between April 1989 and March 1991 resulted in CAA requesting that AAIB undertake an Airworthiness review of the Air Command. AAIB produced report EW/101/06 Airworthiness Review of Air Command Gyroplanes dated 12 September 1991. Recommendation 4 of the report (see 2.0 below) was the driver that led to the initial research contract with Glasgow University, requesting CAA to explore the possibility of assisting the gyroplane fraternity in a research programme on aerodynamic and airworthiness characteristics of gyroplanes.
This comprehensive report represents a significant step forward in the understanding of the aerodynamics of gyroplanes. The conclusions presented are the scientific results of the tests and studies carried out on a limited number of gyroplane designs. The report does not cover all configurations of gyroplane designs and therefore the conclusions may not be directly appropriate to gyroplanes not specifically addressed by the report. It is important to appreciate that it represents the scientific findings of the areas addressed and does not attempt to extrapolate beyond those boundaries as this would be speculation and not appropriate for a scientific research report. Various conclusions have been made in the report and are noted below:
1. CG / Thrust line offset. The recommendation that the vertical location of the centre of mass is within 2 inches of the propeller thrust line is a result of the study and therefore is reported as such. CAA accepts that closer alignment of the CG and the thrustline is a sensible design aim to achieve pitch dynamic stability (phugoid mode) but also has flight test experience of a gyroplane design that achieves good stability but is well outside of the 2 inch criteria. CAA Flight Test Specialist qualitative assessment implies that pitch dynamic stability may not be solely a function of CG/Propeller Thrust alignment for all types of Gyroplane. It is appreciated that in paragraph 8.3.1 (page 152) of the report it is stated that other factors can affect the phugoid mode.
MPD 2005-08 was issued 24 August 2005 mandating, in part, restrictions on pilot experience, VNE and wind/gust speeds for single seat a/c. These could be removed if acceptable evidence was presented to show that the CG/thrustline offset was within ± 2 inches. However other restrictions noted in the MPD would still apply.
Advisory material to BCAR Section T.23 now includes ± 2" criteria.
2. Effect of tail planes.
The report also concludes that horizontal tailplanes are largely ineffective in improving the long term response of pitch dynamic stability (phugoid mode).
The Horizontal Tail
The configuration of the tail sections of the VPM M14 and M16 aircraft are quite unusual in terms of the large endplates on the horizontal tail surfaces. It has already been established that these endplates are beneficial for lateral stability but it was unclear what effect, if any, they would have on the lifting effectiveness of the tailplane. To investigate this, a single test was carried out with the cowling on, tail on configuration but without the endplates. The measured normal force and pitching moment coefficient curves are compared with those from the corresponding test with the endplates on in Figure 3.27.
By preventing the flow of air around the tips of the horizontal tail, the end plates restrict the flow over the horizontal tail to an almost two-dimensional state. This should allow the tail to develop higher lift than a conventional tail at moderate incidence but will result in a sharper stall. This is illustrated in Figure 3.27 where the loss of normal force due to tail stall is apparent at around twenty degrees when the endplates are on but there is a much more gradual loss when the endplates are removed. There is no clear indication in the CZ curve of any increase in lift at moderate incidence but the gradient of the CM curve is obviously greater between -20 and +20 degrees when the endplates are on. This is indicative of increased tailplane effectiveness.
The effect of increasing the length of the tail boom by approximately 0.3m (on the full scale vehicle) was also examined. The results of this study are presented in Figure 3.28 and were very much as expected with almost no change in the normal force coefficient curve, but a substantial change in the gradient of the pitching moment coefficient curve. This is simply due to the increased offset of the tail from the fuselage reference point. It also appears, however, that the stall angle of the tail at positive incidence is reduced with movement away from the gyroplane forebody. This is undoubtedly a result of a change in the effective angle of attack experienced by the tail due to reduced interference between the tail and the forebody.
Perhaps the most significant observation associated with the tailplane is the lift-curve slope. This is a measure of efficiency and also an indicator of its likely impact on the complete aircraft and it can be extracted from these data readily. For example Figure 3.7 compares Z-force coefficient with tail on and off; analysis shows that the lift-curve slope is 2. A typical value for a blade is 5.7; for a helicopter horizontal tailplane 3.7; and the theoretical maximum for a finite wing is 2π.
When combined with the short moment arm of the typical pusher configuration it can be seen that tailplane effectiveness is likely to be limited at anything other than high speed. Note that with power on, where even the low-set tailplane might be expected to experience some slipstream benefit, the lift-curve slope increases only by a relatively small amount to a value of 2.7 - still well below even helicopter values.
I will post some more shortly..
Regards
