Last modified: 2024-05-07 20:44:09
< 2024-05-06 2024-05-09 >First "proper" microlighting lesson today. We did exercises 2, 3, and 4.
Don't take pictures of aircraft, especially registration numbers, and post them online, because people come and steal engines. Presumed for use in military drones: https://www.avweb.com/aviation-news/u-k-probes-stolen-rotax-engines-possibly-used-in-iranian-drones/
Also don't talk about the airfield online because local people use it as ammunition, to claim they were disturbed by noise at a certain time, to try and get the airfield shut down.
Locations of controls: nose wheel steering with heels, throttle right toes, brake left toes, pitch and roll with A-frame base bar. Also a hand throttle at left hip, with choke underneath. Also ignition switches at right hip. Also trim control on right-hand vertical part of A-frame.
Only the rear wheels are braked. You want to make the nosewheel do as little work as possible because it is very weak. On a fixed-wing they say "the nosewheel is only there to stop the propeller from hitting the ground".
Front strut called a front strut.
Standard for switches is "down is off".
Always must have airspeed indicator in front of the pilot.
Wheel spats have a big aerodynamic part on them to increase the drag behind the centre of mass, so that if there is a slip angle it is corrected automatically.
Wing is quite complicated. If one side catches more wind than the other then it billows, which makes it inflate, which decreases its angle of attack relative to the other side? Not quite sure I have that right.
The wing has a varying angle of attack, I think the angle of attack is greater in the middle and shallower at the tips? Can't remember.
I asked why the trike is able to pitch at all, given that it is suspended from the wing and should always hang straight down. It is because of the thrust. If thrust exceeds drag then you're accelerating, which will increase your altitude and also pitch the trike upwards. So the increase in altitude and the increase in pitch of the trike are actually sort of separate effects, that just happen to coincide the same way they would on a 3-axis. You're not getting higher because you're pointing upwards, or vice versa. You're pointing upwards because your thrust exceeds your drag. I think that as you accelerate up to the point that your drag matches your thrust, the trike will pitch back down but you'll still be ascending.
I think if the engine were attached to the wing instead of to the trike then indeed the trike would hang pretty much level (or in fact, it would point downwards all the time, because it still has drag).
I think: Pitch up means thrust exceeds drag. Pitch down means drag exceeds thrust. Ascending means airspeed exceeds 65mph. Descending means airspeed below 65mph.
Parasitic drag: for example "form drag" caused by the shape of the plane as it hits the air.
Lift-induced drag: caused as part of generating lift (e.g. Newton's 3rd law: when you increase your angle of attack your lift vector isn't straight up, it has a component pointing backwards; also something to do with Bernoulli's principle).
The engine can rev up to 5800 rpm but in this instance it is "pitch-limited" which means it runs out of power before that point, because of the load created by the pitch of the propellor blades. The blade pitch is ground-adjustable, but you're not allowed to adjust it because it is set to a spec that is approved for noise control and changing the pitch changes the amount of noise it makes, in particular if you let it spin too fast then the tips can break the speed of sound which makes a loud noise and breaks people's windows.
Before starting you want both ignition switches off, crank it for 5 seconds. Then turn both ignition switches on, choke on (or was choke on before cranking for 5 seconds? can't remember), no throttle, and crank it until it starts.
Test both ignition systems by turning them off one by one, not allowed to drop more than 400rpm.
Can't fly until oil temperature is 50 deg. C or above.
"IMSAFE" checklist.
All of these things could affect your ability to fly, "brain can only handle 3 problems, if you are struggling with one of these then you're already starting with 1 problem".
Set altimeter to 400 feet for the runway (or whatever is appropriate for the airfield).
Before every flight you have to "book out" on the airfield log book. After every landing you have to "book in". If you fly in somewhere else and then fly out again you fill out the "book in" side after landing and then the "book out" side before you take off again.
Brad has a custom-made cart to roll the microlight on to, and then roll it sideways into the hangar, without having to derig the wing, pretty cool.
You can pitch the wing up relative to the trike by pushing the base bar forwards. You can pitch the wing down relative to the trike by pulling the base bar backwards.
You can roll the wing to the left relative to the trike by pushing the base bar to the right (lowering the left wing), and vice versa.
You can increase your airspeed by increasing the throttle ("increase power") and vice versa.
The immediate effect of increasing pitch is that you'll start to ascend and the airspeed will start to go down. The resultant steady-state effect will be that your airspeed is lower and you stop ascending. So you're just wasting more energy on drag.
The immediate effect of decreasing pitch is that you'll start to descend and the airspeed will start to go up. The resultant steady-state effect will be that your airspeed is faster and you stop descending.
The immediate effect of pushing the bar to the left is that the microlight will roll to the right, followed by slipping down and to the right, which will cause the machine to yaw to the right, which will cause a turn to the right. And vice versa for pushing the bar right. Also the nose will lower slightly.
Increasing power will initially cause an increase in airspeed, this will cause an increase in lift, which means you'll start ascending, but the torque around the point that the trike is suspended will cause the trike to pitch up, which means now your thrust is pointing more upwards and less forwards. So your airspeed will stop going up, but you'll keep ascending. And vice versa if you reduce the power.
I think I have the effects basically right, but the exact physics is maybe different to what I say. I should make a 2d flexwing simulator. Give it a control for thrust and a control for angle of attack of the wing relative to the trike, pretend the wing is Newtonian only (i.e. imagine the wing is a rigid body continuously hitting a single spherical object at the centre of lift, it can never stall, etc.), and see how it behaves.
A flexwing is "dynamically stable" in pitch, which means when you let go of the bar the bar will return to the middle (relative to the trike) and the wing will level out relative to the horizon. But it is only "statically stable" in roll, which means when you let go of the bar the bar will return to the middle but the trike will maintain its bank angle.
"I have control"/"You have control" to hand over control of the plane.
Supposed to scan the sky for other aircraft in "segments". Hold your head still and look at a segment, then move your head and look at the next segment.
I forgot to do the scanning after Brad stopped mentioning it. I also didn't get much chance to enjoy the view of the ground. I had enough to think about with handling the controls.
Practiced setting throttle to idle, wide open, and 4300 rpm. Very difficult with my clod-hopping motorbike shoes on.
When I was too abrupt with throttle changes I felt the wing move abruptly, I initially thought this was an aerodynamic effect, but it was Brad applying a pitch input because otherwise something bad could have happened, can't remember what.
Some taxiing practice on the way down to the runway. Have to coordinate use of the throttle/brake with use of the steering.
I made things difficult for myself today by wearing the motorbike shoes. They mean I have almost 0 feel for the throttle and brake.
If you make a repair to your microlight using like-for-like parts, it needs to be checked by a "competent person", which can just be another flexwing pilot. But if you make a "modification" then it needs to be checked by a proper engineer.
< 2024-05-06 2024-05-09 >