Gyroplane Stability and Aerodynamics - Glasgow University

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Gyroplane Stability and Aerodynamics - Glasgow University

Postby saraf » 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
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Re: Gyroplane Stability and Aerodynamics - Glasgow Universit

Postby saraf » Mon Feb 03, 2014 9:43 pm

Quote from report:

Wind tunnel tests have shown that the aerodynamic properties of gyroplanes are relatively insensitive to configurational changes. Even at the high speed end of the range, the aerodynamic properties of the vehicle pod and tailplane have little influence.
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Re: Gyroplane Stability and Aerodynamics - Glasgow Universit

Postby saraf » Mon Feb 03, 2014 9:44 pm

Some more from report:

CAA Comment

CAA accepts that closer alignment of the CG and the thrustline is a sensible design aim to achieve pitch dynamic stability (phugoid mode) and whilst conclusive Flight Test evidence has supported this and directly led to the issue of MPD 2005-08 for single seat gyroplanes, other flight tests provide evidence of a gyroplane design that achieves good stability whilst being 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.

The report also concludes that horizontal tailplanes are largely ineffective in improving the long term response of pitch dynamic stability (phugoid mode).
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Re: Gyroplane Stability and Aerodynamics - Glasgow Universit

Postby TheBladeRunner » Mon Feb 03, 2014 9:46 pm

Glasgow University found these findings...????? (**)

Make sure you gentlemen pack your umbrellas for this one!
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Re: Gyroplane Stability and Aerodynamics - Glasgow Universit

Postby saraf » Mon Feb 03, 2014 9:47 pm

Some more interesting facts:

The tailplane effect on Section T compliance, by comparison, is limited. It fails to change the frequency of the phugoid across the speed range; improves the damping only with speed; but has a gross effect on the short-period mode (Figure 7.20 a)). The Section T compliance mode is therefore negligibly affected by a horizontal tailplane at low speeds (consistent with the poor aerodynamic efficiency identified in tunnel test), whereas propeller thrust line location has an impact across the speed range. Heresay evidence from the gyroplane community however is that tailplanes are significant components for the improvement in gyroplane stability. This perception is probably associated with their impact on the short-period mode seen in Figure 7.20 a) – the short-period mode is not an issue for compliance demonstration, but it is the mode that pilots excite to manoeuvre their aircraft and hence the mode that determines how handling qualities are perceived.
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Re: Gyroplane Stability and Aerodynamics - Glasgow Universit

Postby saraf » Mon Feb 03, 2014 9:50 pm

Pod and Tailplane On/Off Figures 7.22–7.24)

Simulation of pod and tailplane removed shows little difference in the trim variables relative to the standard aircraft (Figure 7.22) or in the phugoid mode, and hence compliance with Section T is not influenced by airframe aerodynamics.
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Re: Gyroplane Stability and Aerodynamics - Glasgow Universit

Postby saraf » Mon Feb 03, 2014 9:54 pm

It is worth noting that the modification proposed to solve the stability problems which led to the grounding of the Air Command gyroplane type comprised principally, in aerodynamic terms, of the addition of a pod and a tailplane. These tests suggest that this modification would not be very effective and, indeed, this proved to be the case.
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Re: Gyroplane Stability and Aerodynamics - Glasgow Universit

Postby Rocket » Tue Feb 04, 2014 9:57 am

This was "heavy reading" i was interested to see the max teeter angle (8 degrees) even today a M16 on full aft stick somehow seems to exceed 8 degrees? (i speak under correction) but when we refer to the diagrams presented in this comprehensive report it seems the aircommand still had a issue of blade contacting with the propeller? is this correct?

The other significant point that came through in the report was what i can make out was on the vpm the vertical fins on the horizontal stab in fact aid aerodynamic lift at certain angles of incidence? or am i mistaken?

As i say a very detailed report written by some serious flight test engineers. not sure to many Gyro pilots in this forum can argue the credentials of the men who were involved in this test

Thanks for posting

best i get a licence or some flying time so i can comment?
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Re: Gyroplane Stability and Aerodynamics - Glasgow Universit

Postby t-bird » Wed Feb 05, 2014 3:20 am

Hi Eben

Here is my take on it

You guys are doing a great job in teaching pilots to fly the RAF safely. You have proofed that it can be done but it takes longer than other gyros to learn to fly.

I have tried the stock standard RAF in South Africa and could not fly it after 300 hours on other gyros and 150 on fixed wings.

All RAF’s in Australia have stabs that is per the regulations, here are one https://www.youtube.com/watch?v=uAk_cQV ... ata_player

I went for a flip in a modified Raf with a tall tail and dropped keel. What a surprise I could fly it from the word go. Take off circuits landings etc.

The modified Raf is used for training and pilots train in it and then fly a single seater solo without a problem. The guys are usually solo at less than 20 hours.

This modified Raf out climb all the Gyros than includes an ELA and MTO 03.

No maths behind it like you report just experience
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Re: Gyroplane Stability and Aerodynamics - Glasgow Universit

Postby saraf » Wed Feb 05, 2014 6:40 am

Hi t bird

This is not about the RAF. This is what is said in the repot by the profs.

If you wanna fit a tail to your RAF you are more than welcome to do so....

Regards
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Re: Gyroplane Stability and Aerodynamics - Glasgow Universit

Postby t-bird » Wed Feb 05, 2014 8:47 am

Then these Proffies of yours have not flown a raf in both configurations if they came to the conclusion that a gyro is insensitive to changes in the tail plane.

Sell me a Raf kit with a tail and I will buy it. It is too expensive buying a std raf and modifying it.
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Re: Gyroplane Stability and Aerodynamics - Glasgow Universit

Postby saraf » Wed Feb 05, 2014 9:41 am

What is your email.

Tbird , you need to remember that the testing was done on 5 differant aircraft as well as the vpm/magni. And this was foun to be the same on all of them.

Anyway just some info i found on testing done by Glasgow. Who apparently is the best in doing the testing.......
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Re: Gyroplane Stability and Aerodynamics - Glasgow Universit

Postby Learjet » Wed Feb 05, 2014 10:13 am

Seems that (on the Magni M16 at least) the Helsinki University came to an altogether different conclusion...

EFFECT OF HORIZONTAL TAIL ON THE STABILITY OF THE VPM M16 AUTOGYRO
Report AALTO-AM-18
Seppo Laine
Emeritus Professor of Aeronautical Engineering

Aalto University School of Science and Technology
Faculty of Engineering and Architecture
Department of Applied Mechanics

http://www.aero.hut.fi/pubs/reports/AAL ... io-2_1.pdf
Abstract
The aim of the present work is to study the importance of the horizontal tail on the longitudinal
stability of the VPM M16 autogyro in horizontal flight. The stability analysis is carried
out by utilizing stability derivatives obtained with the aid of flight trials and by employing
wind tunnel test results to evaluate the effect of the tailplane on the stability derivatives. The
test data, produced by the University of Glasgow, is utilized in this report. The stability analysis
is performed employing four equations of motion: two force equations, the pitching
moment equation, and the rotor torque equation. The study shows that the tailplane of the
VPM M16 is necessary to ensure longitudinal stability stick fixed at an airspeed of 63 mph.

Conclusion
Based on the published data of the stability derivatives and the aerodynamic characteristics
of the VPM M16 autogyro, the stability analysis shows that the horizontal tail of this autogyro
is necessary for its longitudinal stability stick fixed in horizontal flight. Without a horizontal
tail this autogyro would have an unstable short period motion.
Dave Lehr
Magni Gyro M22 ZU-EPZ
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Re: Gyroplane Stability and Aerodynamics - Glasgow Universit

Postby saraf » Wed Feb 05, 2014 11:26 am

Hi dave, yes the vpm needs one according to the report , but the report does not say that all gyros do,like it is claimed.....


Anyway did not want to start a debate again. Ony posted info i was told to go and check out. People will anyway believe what they want to believe.....

Regards eben jnr.
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Re: Gyroplane Stability and Aerodynamics - Glasgow Universit

Postby TheBladeRunner » Wed Feb 05, 2014 5:42 pm

So the conclusion is that the report that best floats your boat is the right one???

So who is right???

Glasgow.... The holy grail of gyros testing
Or
Helsinki....???
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