UTIAS visit – Variable Stability and Upset Recoveries

utias

A visit at University of Toronto – Institute for Aerospace Studies was arranged in order to expose some TPS students to the Variable Stability concepts in a moving base simulator. Beside this, we had the chance to experience some Upset Recovery training as modeled for a current Part 25 airplane, going through stick shaker, stick pusher and eventually variable intensity roll-offs depending on the configuration and the entry deceleration rate.

utias_sim_external

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Developing HELIWASP™

The HELIcopter Weapons and Avionics Simulation Platform (HELIWASP™) is currently under development as a flexible Helicopter simulation platform focused on weapons and avionics testing. Setup is primarily composed of OTS hardware components which are integrated though a number of programming tools. Compared with other similar solutions being in the 6digit price range, HELIWASP™ has only a fraction of the cost and could also be considered a more flexible platform serving as a base for further development. Still work on external visuals and mounting systems has to be done, but the proof of concept was been already demonstrated and the remaining work should be a matter of time and a relatively small budget.

heliwasp_seats

heliwasp_initial_displays

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Reviewing AVIATION 2017 abstracts

aviation2017

I was assigned the review of a number of abstracts for AVIATION 2017 being currently a member of the Flight Test Technical Committee. Definitely a responsibility to evaluate and decide on work of colleagues. Currently subjects or other details cannot be released, but it was a constructive experience cooperating with other reviewers mostly from the US and forming a correct mindset on what a good paper/abstract should look like.

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Night flying under a cloudy full moon

Night rating flights are currently taking place. Quite an experience navigating in a night VFR environment though city lights and full moon light.

full_moon_flying

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November Remembrance

Remembrance Day is a memorial day observed in Commonwealth of Nations member states since the end of the First World War to remember the members of their armed forces who have died in the line of duty (ref. Wiki). November the 11th is generally assigned as the Remembrance day and a poppy flower has been a familiar emblem of it.

This year I will replace the poppy with a cyclamen.  Moving forward, lest we forget.

kyklamino

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IFR training sim setup

Instrument Flying Rules flying is not considered the most exciting or easiest form of flying and that is why many pilots skip it. However those who are IFR rated will admit that this is a new world of flying where you really understand some flying principles about precision flying. The procedures involved also upgrade dramatically the pilot’s understanding about flight operations, airspace and navigational aids. Towards the developing of instrument flying skills and procedures understanding, the use of a desktop flight simulator can be of significant aid. Below my setup being currently in the mod of my IFR training.

ifr_sim_office

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Yaw due to roll rate derivative

Preparing a series of lectures on Aerodynamic Derivatives, I came through one of the less common and maybe less well understood stability derivatives, the yaw due to roll rate C_{n_p}.

mig29_rollDifferent textbooks provide different explanations on the physical origins of this derivative, the main which are the following:

  1. Wing drag increase (+). This actually refers to the profile drag increase due to the angle of attack increase in the down-moving wing while a reduction takes place in the up-moving side. The sign of this contribution is positive, considering that a right roll rate gives a right yaw tendency. This effect should not be confused with C_{n_{\delta_\alpha}} which is the yaw moment due to aileron deflection (aileron adverse yaw) and is attributed to the increase in profile drag due to the deflected control surfaces.
  2. Leading edge suction or wing lift vector tilting (-). The down-moving wing seeing an increased angle of attack, experiences a forward tilting of the lift vector, while the opposite happens for the up-moving wing. It is encountered in subsonic leading edges only and the result is a negative (left) yaw contribution from a right roll.
    cnp1
  3. Wing tip suction (-/+). This effect is encountered when a lift generated wing experiences roll, where a side force appears due to the asymmetry of the lift distribution and the  resulting asymmetry of the tip vortexes and tip side pressures. It is mostly evident in low aspect ratio, thick tip wings and its contribution can be either negative or positive based on the relationship between the tip side force center and center of gravity – if CoG is forward than the tip suction center the yawing contribution is negative.
    cnp2
  4. Tail contribution, C_{n_{p_{v}}} (+). In a right roll, the vertical tail of a conventional airplane experiences an increase in its angle of attack which generates a negative side-force on the tail surface, resulting in a positive yawing moment around the airplane’s CoG.

Correct prediction of the C_{n_p} is difficult and many times even the sign of the derivative is miscalculated and generally wind tunnel tests will be need to run to get a valid estimate. However, the effect of C_{n_p} in the airplane’s stability is frequently weak and its accurate prediction is not a critical item.

References

  1. US Air Force Flight Test Center, Flying Qualities Testing-Stability Derivatives.
  2. Bernard Etkin and Lloyd Duff Reid, “Dynamics of Flight, Stability and Control”.
  3. Ian Roskam, “Airplane Flight Dynamics and Automatic Flight Controls –Part I”.
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