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Lesson 2: Power, Trim and Flaps

by Stewart NWFT on 17th August 2016 No comments

My second lesson was to continue the focus on the effects of controls, today incorporating throttle, trim and flaps. My previous instructor Andrew Raven wasn’t available today, so I was introduced to Tim Senior, another one of North Weald’s experienced flight instructors.

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I was incredibly pleased to find out that we would be flying in G-LOMN once again today, the same aircraft I flew in my first lesson only two weeks previous.I guess you could say I’ve already become some-what attached after getting my first flying hours with her. She hadn’t been flown today, so myself and Tim went through the full checks to ensure she was in good working order.

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I picked up a Pooley’s 152 checklist from the North Weald shop last time for £6.50, so this process was a simple yet thorough one. It’s important to get in to good habits early, so I make sure I go through it all in detail and also study it every night before I go to bed (takes about 5 minutes).

Pre start-up checks done, GoPro attached, instructor Tim safely inside and ready… We fired her up. Initially, to continue with my taxying training from the last lesson, we made our way to the tarmac crossing in order to practice.

Taxying:

Now this is actually a lot trickier than you may think. It’s almost the complete opposite of everything you have learnt and been taught about driving… Firstly, the steering is done with your feet and not your hands. Secondly, to turn right, you have to press on the right pedal. Essentially pushing against the turn rather than with it. Thirdly, the speed is controlled by the throttle which is increased/decreased using your right hand (when sat in the captains seat). Confused yet? It’s about to get even worse! Each rudder pedal then has the brakes for each side on the top of the pedals. You brake by rolling your feet forward. The brakes can then be used to make sharper turns too. For example, sharp right turn would require right pedal plus right brake.

It’s something that is going to be mastered simply by lots of practice. Through force of habit, my hands wanted to do all the steering! I’m sure with some taxying practice every lesson, it’s a skill that i’ll soon get the hang of.

As we continued our taxy towards the active runway, today runway 02 with left circuit, we made our intentions clear ‘G-LOMN ready for departure’. ‘G-LOMN cleared for take off runway 02’. ‘Cleared for take-off G-LOMN’. Throttle at full, we raced down the runway for a departure to the north.

The effects of POWER:

This exercise was to demonstrate the affect increasing and decreasing the power (rpm) has on the aircraft, the secondary effects felt and how we counteract these. Firstly, Tim pushed the throttle in which increased the power delivered to the engine. This caused the nose of the aircraft to pitch up. This is because increasing the power increases the airspeed. Increasing the airspeed increases the flow of air over (and under) the wing. The wings generate more lift with more airspeed. Therefore, the aircraft goes up. Or technically speaking, pitches up. This then has a secondary effect… An increase in RPM creates a stronger slipstream generated by an aircraft with a clockwise propeller motion. This slip stream then hits the left (port) side of the vertical stabiliser (fin), pushing it to the right and therefore ‘YAWING’ the aircraft to the left. Please get in touch if this needs a little more explanation! To counteract this pitch up and left yaw, we push (away from you) on the yoke to bring the nose down and push on the right rudder to counteract the left yaw. Simple, right? Naturally, bringing the aircraft in to level flight with increased power then increases the airspeed.

Next, Tim reduced the power by pulling out the throttle control. This reduces the airflow over the wings and therefore the speed decreases. This then reduces the lift generated by the wings of the aircraft and the nose pitches down. This was counteracted by pulling (towards you) on the yoke to bring the nose up. Bringing the aircraft in to level flight with reduced power then reduces the airspeed further.

TRIM:

Having to constantly counteract the effects of increasing and decreasing the power can be very tiring work. Luckily, the aircraft has a system in place to reduce this workload, but it’s [apparently] a serious sticking point for many aspiring pilots. This is called the ‘TRIM’. The trim is a small tab found on the elevator of your fins. There are a couple different designs depending on the aircraft, but they essentially accomplish the same thing. When you push on the yoke (away from you) what this actually does is moves the tail-end of the elevator downwards. The downward pointing elevator then generates more lift at the rear of the plane and the tail moves up in relation to the body of the aircraft. This therefore pitches the nose down! Make sense?

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So, how does the trim help us? Well, if you increase the power and your nose pitches up, you have to push on the yoke to counteract this. By rolling the trim wheel forwards this actually brings the trim tab downwards and does the job you are currently doing manually with the yoke. Once you can feel that you are no longer having to push on the yoke to counteract your increased power, and the aircraft is remaining in level flight, you have successfully trimmed the aircraft!

Similarly, if you decrease the power and the nose pitches down, you need to pull on the yoke to bring the nose back up in to level flight. By rolling the trim wheel backwards, this points the trim tab on your elevator upwards, reducing the lift generated by the tail of your aircraft. Once you are no longer having to pull on the yoke in order to remain in level flight, your aircraft is once again trimmed!

This one needs practice. Luckily, I got the hang of it pretty quickly but it will be something I need to practice in almost every lesson. I’ve been told by a couple instructors that this can be many aspiring pilot’s achilles heel!

FLAPS:

Our final point to today’s lesson was to monitor the effects of using each stage of flaps. The flaps can be found on the inside of each wing on the tail-end. These, like the trim, are designed to assist with your flying.

This particular aircraft (Cessna 152) has three stages of flaps; 10, 20 and 30. The flaps only move in a downward motion in regards to the angle of the wing. I.e. the flaps cannot move upwards from their starting point (0) when level with the wing. You can move upwards from 30 to 20 for example, but you can never go upwards from 0. This is obviously different from the trim tab as that can be moved upwards in order to reduce the lift generated by the elevators. So what does that actually mean?

This means that the only function of the flaps is to generate increased LIFT. Remember, when your ailerons, elevator or trim tab points downwards, this generates lift. And the same applies for the flaps. Each degree of flaps produces more lift for the wings. 10 being a small increase in lift generated (at a constant speed) and 30 being a big increase in lift generated. So why do we need them?

Flaps have a couple of useful functions. The first being that having some stage of flaps allows us to take-off at lower airspeeds. Because moving the flaps down increases the lift generated by the wings, we can get airborne quicker. The second being that we can have a slower approach which makes landing safer. As we are able to generate lift at slower airspeeds, we can make a nice and controlled approach on to the runway.

To demonstrate these effects, Tim brought the aircraft to below 85 knots. This is because the flaps cannot be operated at speeds greater than that. This is highlighted on the Airspeed Indicator by a bold white line around the dial. The effects were as follows when starting from level flight at constant power:

0 flaps > 10 flaps = Small pitch up, airspeed drops slightly

10 flaps > 20 flaps = Big pitch up, large drop in airspeed

20 flaps > 30 flaps = Small pitch up, small drop in airspeed

30 flaps > 20 flaps = Small pitch down, slight increase in airspeed

20 flaps > 10 flaps = Big pitch down, large increase in airspeed

10 flaps > 0 flaps = Small pitch down, small increase in airspeed

And that completed today’s lesson. We made our way back to North Weald where I was able to taxy back in to park. And that was my first flight with Tim!

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If anyone has any questions about anything in this blog, I realise it was a technical one today, please do not hesitate to get in touch. I’m hoping to upload and attach some videos from this lesson demonstrating each of these exercises, so watch this space.

Until next time…

Stewart NWFTLesson 2: Power, Trim and Flaps

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