Weight-Shift Control Trike Aerodynamics- Wing tip angle of attack (AOA) in turns test demonstration Part 2

Published by: Paul Hamilton on 16th Feb 2017 | View all blogs by Paul Hamilton

 

There has been a question about the basics of angle of attack of the tip in a turn for the weight-shift control trike wing considering wing twist and roll dampening. Here is a simple test with airflow and angle of attack clearly shown for a turn.

 

We saw in the last video that the twist in the wing tip could vary as much as 6 to 9 degrees up and down from neutral in extreme turns side to side in the Revo Rival S trike. This was a simple test, but the measurements were simple, reliable and repeatable with error bands providing a reliable 6 to 8 degrees twist change. We calculated the roll dampening factor. Here we are actually able to look and see it.

 

Here, with this visualization of actual airflow and wing twist in relation to the airflow, we are able to see the angle of attack of the tips for the phases for a turn. We went 60 degrees to 60 degrees bank to be able to detect the airflow and angle of attack of the wing. Any smaller is just too hard to see a significant enough change to provide reliable conclusions.

 

http://www.trikepilot.com/videos/view/_25207

 

So based on our visualization of this video, we will break the side to side (60 degrees left to 60 degrees right) turn down into six distinct phases. We have not considered the adverse yaw which is a completely different topic. Phases of the turn:

 

Phase 1 Initial weight shift/billow shift, washout/twist change.

 

This is where the weight is shifted, side pressure applied and the tip twists to reduce lift to start the roll.

 

Phase 2 Start of the roll.

 

This is where the wing starts dropping and starting the rolling momentum of the heavy wing above. The wing is just starting to accelerate down. Side control pressure is present to provide maximum twist in the wing to continue to roll/accelerate the wing down. Here we have a significant reduction in angle of attack of the wing from the billow shift/washout/twist change to provide enough tip roll moments to roll the wing.

 

Phase 3 Mid roll acceleration.

 

This is where the wing has gained some roll momentum, shown here as the “wing level” rolling side to side, and still gaining roll momentum. Here we see the angle of attack on the wing start to increase as the roll dampening (change of airflow to the wing as the wing drops increasing the angle of attack of the wing). Here we see the roll dampening start to increase. Here roll pressure is still applied to provide as low as angle of attack on the tip as possible to continue the roll.

 

 

 

Phase 4 Max roll acceleration.

 

This is where the roll momentum has built and the wing is dropping at the maximum roll velocity. Here the roll dampening is at its greatest and the angle of attack on the tip is the greatest because of the roll dampening. Here we are past level and the turn is initiating in the other direction. This is where adverse yaw is probable the greatest and trying to catch up with the turn.

 

Phase 5 Roll deceleration.

 

Now we have some centrifugal force and we can release the control pressure to let the centrifugal force bring the undercarriage out directly under the wing and stabilize the turn in the opposite direction.

 

Phase 6 Stabilized turn.

 

Once the control pressure is released we are in a stabilized turn and the angle of attack on the tips is equal as in level flight except we have greater g loading in the higher banked turn.

 

It should be noted that in a WSC roll the weight of the undercarriage provides substantial rolling moment. However, the percentage of actual weight shift verses aerodynamic billow shift/washout/twist change  rolling moments is largely dependent on the specific trike design and the ability of it to provide the twist change from the weight shift, wristed keel or roll assist (which is used with the P&M STARS system). Based on calculations, I estimate the percentage of weight shift rolling moment to twist change aerodynamic rolling moments to range between 25 to 75 percent of the total rolling moment for the trike depending on the specific design.

 

 We have a large range of trike designs out there with different design characteristics…

 

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