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Trim 2

So after seeing what Trim was for, I jumped into the plane to try it out. (I wrote about that flight in a previous post “A Short Flight”). Then I went back and studied the section further. Being able to test it out in a simulator certainly made it a little easier to understand.

I had to re-trim a couple of times after adjusting the power level. The Air Pilots Manual encourages a lot of Trim use, in a natural way, but also emphasises when it should not be used. Trim shouldn’t be used to change the attitude of the plane – it should be changed by using the yoke and then the force used is trimmed off. It also shouldn’t be used in transient manoeuvres like turns.

Trim is an art, or so I read, but with the limitations of FSX I personally found it to be a bit clumsy. Once it’s trimmed correctly my Cessna 152 flew like a dream, straight and level, but it wasn’t so much of a smooth process to get there. In real life it’d be smooth as you could feel the pressures on the yoke being relieved.

I went through the air exercises laid out in the book – number 2 was specially interesting. It was to see the effects of an incorrectly trimmed aircraft. At 3000 feet and level, I moved the trim wheel forward. It became increasingly difficult to keep level and in the end I lost about 500 feet. Almost impossible to fly, and a good lesson learned in the correct use of my new best friend, Trim.

Apologies because it was a while since my last post – a sick 23 month old daughter and an 8 months pregnant wife took all my time up and if I have no time for Flight Sim, I have no time to blog either!

Feed

A quick post because I wanted people to know I have set up a feedburner feed for FS Ground School. I don’t know if I can put a widget on my word-press blog, so here it is in text for those of you who want can copy it into your favourite RSS subscriber.

I’ve already started work on my very own domain where I won’t be restricted as I am with this one. I’ve heard some people say the RSS doesn’t work right. Maybe this will help in the meantime. Thanks for all your support.

http://feeds.feedburner.com/FsGroundSchoolBlog

Trim

Here’s something I had heard bits of before but never really paid much attention to it. I think part of why I ended up using the auto-pilot in flight sim previously rather than hand flying was because of that mistake. Trim is essential, I see now, and after a few flights utilizing it I could never go back.

It might sound silly to you veteran pilots out there or those of you who knew the trim wheel from the first flight sim experience but there must be many who overlooked this, and quite possibly put many off flight sim completely.

Trim is used to relieve control pressures during steady conditions of flight (climb, straight and level, descent). No more holding back the yoke manually for ten thousand feet. So how does it work?

On the trailing edge of the plane is a small trim tab that is operated by a wheel or handle in the cockpit. It’s job is to hold the elevator displaced by aerodynamic force rather than control pressure and it does that by effecting the airflow. When the trim tab is deflected down, for example, the airflow over the upper surface of the elevator increases speed and as I learned previously, reduces the static pressure. Voila, no need to hold that yoke in place and get tired.

The problem with flight sim is that Trim doesn’t seem easy – at least not to me. On one of my last flights (see my last post here) I tried using Trim but I found it rather difficult. Maybe it’s because I can’t feel the pressure on the yoke, but it was hard to tell when I could release the yoke (or joystick in my case). That meant a lot of bobbing up and down as I released the yoke, saw my nose dropping and would pull back again and trim some more. I don’t know what it is like in real life, or if there’s a better way to do it in flight sim – I encourage you to comment below and give me your thoughts or even corrections if I got something wrong.

There’s still some more to be said for trimming, but I’ll save that for the next post. In the meantime I’d like to thank everyone who gave a shout out for FS Ground School lately – I appreciate it as I try to become part of the flight sim community.

A Short Flight

The beauty of FSX is that there’s no need to worry about making mistakes because there are no consequences. While learning the PPL through FSX this is a vital tool because it means that rather than get bogged down with a lot of theory I can get out there and put it into practice. That’s exactly what I decided to do!

After departing from YSTH St Helens in Tasmania, Australia, I headed up the coast. I read a little bit about Trim (the next post will go into it more) so on my climb-out I tried to use it to ease the strain of holding back on the yoke. I found it very difficult to feel when it was properly calibrated but I eventually got the plane climbing at a steady 70 knots.

It felt very good to level the plane off and reduce the throttle at 2000 feet. Having a complete hands-on approach is new to me and it was very fulfilling when I didn’t bust my chosen altitude by more than 20 feet or so. Being VFR I had a general flight plan – follow the coast all the way around until I see the mouth of the Tamar River and then look out for Devonport Airfield.

The Cessna settled into a 95 knot flight. I was using FS Flying School for the first time, to get some idea of how I am doing. I had to laugh out loud when the instructor told me that something smelt in the cabin. I don’t know what it was, but I cracked the window open and turned on the cabin air.

The mouth of the river Tamar and time to focus on finding the airfield. I found that the C152 tended to roll ever so slightly to the left throughout the entire flight (no winds) and I am left wondering if having to compensate slightly and constantly is a quirk of the aircraft or if I am doing something wrong. If someone can comment and help me out with that I’d be most grateful. It was hardly noticeable, but then I’d end up a few degrees off my chosen heading.

When landing I found I was about ten knots too fast and a little low but I touched down smoothly enough albeit not on the centre-line. When I shut down the engine I felt great. It was very rewarding flight and seeing my report was even better:

Flight commended in the following areas:

• Smooth turns.
• Nice banking.
• Correct matching of flaps to speeds.
• Comfortable G forces.
• Smooth pitch control.
• Flown within aircraft’s maximum speed limit.
• Gentle taxi turns.
• Good take off steering.
• Appropriate position of flaps during taxi.
• Safe taxi speed.
• Smooth braking during taxi.
• Smooth climb during takeoff.
• Wings level near ground.
• Well coordinated turns.
• No stalls.
• No flying dangerously close to stall speed.
• Smooth comfortable descent rate.
• Pitch not too high.
• Pitch not too low.
• Approach speed not too fast.
• Low altitude speeds not too fast.
• Good clearance of obstacles.

The previous weeks I have been focusing a lot on the flight controls and keeping them all co-ordinated so seeing a report like this (taken from FS Flying School) was very fulfilling. Also a few things for me to work on (late rotation, poorly trimmed aircraft because I took a long time to get it right), but not bad all in all for my first proper flight in the C152.

Further Effects of the Main Flight Controls (Part 2)

Following on from the previous post about Yaw and Roll being linked, likewise Pitch and Airspeed is also linked. To put it simply – a basic fact that everyone probably already knows – if you dive in a plane the airpeed increases and if you point the nose up it will slow down. But what is the science behind it? Having a full understanding should come in useful while flying around.

Well, as I understand it with the aid of the Air Pilots Manual, when the pitch is changed it effects the airflow. When the nose is raised the airflow strikes the wings at a greater angle of attack and cause drag. That will obviously lead to a loss of airspeed.

On the other hand if the plane is pointed down, the angle of attack is reduced which means less drag and more speed. Its a very critical part of flying, from take-off speeds, maintaining level flight and descending among others.

I climbed into the air to try it out and to get a feel for how the aircraft responded. On the climb out of the airport I varied my climb angle to see how the speed would be effected. Just by pitching the aircraft to different degrees I was able to quite concisely control the airspeed without needing to touch the throttles.

The next part of the book covers Trimming but first I want to get into the air to see what I have learned so far.

Further Effects of the Main Flight Controls (Part 1)

Now that we’ve got the idea of how each of the main flight controls work, it’s time to see the secondary effects each one has and how they influence each other.

The whole point of this blog is to share my experiences with following the Air Pilots and Manuals for a PPL in FSX and hopefully helping a few others along the way (and hopefully getting some help too), and while the basics make sense on paper, it took me a while to start co-ordinating them all. I’m not new to Flight Simulator but I was a huge fan of the auto-pilot. That grew old rather quickly so now it’s time to buckle down for the hands on approach.

Roll Causes Yaw – When you bank the aeroplane the lift force generated by the wings is tilted. Because there now exists a sideways component of the lift force the plane slips towards the lower wing. When the plane is in this configuration the large surfaces on the plane like the fin and fuselage behind the centre of gravity get struck by the airflow and causes yaw. The nose will drop and a spiral descent will begin.

Yaw causes Roll – When rudder is applied it will yaw the nose of the plane (the same direction as the pedal you are pushing). Yaw tends to make the outer wing rise for two main reasons. Firstly the outer wing is moving faster and that means it generates more lift and secondly due to inertia – the plane will continue to move in the original direction causing the outer wing to be presented to the airflow at a greater angle of attack – if it has a dihedral.

Dihedral!? I had to look it up, I’m not ashamed to say. Dihedral simply describes a wing that is angled up towards the wing-tip.

The inner wing becomes a little more shielded from the airflow due to the fuselage and loses lift.

Next time I’ll be taking a look at Pitch and Airspeed and how they effect each other.

Main Flight Controls (Part 3)

The third main flight control controls yaw. It’s the rudder, and it is controlled by pedals in the cockpit (which are interconnected so when one pedal moves forward, the other moves back). So how does it work?

When the pedal is pushed forward (let’s say the left one), the rudder deflects to the left. By doing that, the speed of the airflow on the right side of the plane increases and the static pressure is reduced. That creates an aerodynamic force to the right. Because the plane rotates about it’s centre of gravity, the nose yaws left.

I have found using rudder accurately is a challenge at the beginning. It can be hard to keep a turn co-ordinated, but I have heard that eventually it becomes natural (much like balancing the clutch when learning to drive) so practice is the key – and it sure is fun. Using rudder pedals on your flight sim set-up is a sure way to increase realism.

Because drag increases, yawing the plane can (in real life) be uncomfortable and it’s quite inefficient. The rudder then is primarily for preventing unwanted yaw (although it is used for other functions). More on this on a future post when we get to the flight instruments. In the next post we’ll take a look at the secondary effects of each main flight control.

Main Flight Controls (Part 2)

Time for another basic, but necessary, lesson. Last time I learned about the elevators – I always knew that pulling back on the yoke made the plane climb but now I know why, and that’s one of the benefits of going through the PPL manuals in FSX.

The second of the main flight controls are the ailerons.

They are hinged control surfaces on the trailing edge of each wing. When an aileron is moved down it increases the life generated by that wing. The other aileron goes up and reduces the lift on its wing and hence the plane rolls. So turning the yoke to the right raises the right aileron, lowers the left and the plane rolls to the right.

The related exercise included several turns and seeing the effect of turning the yoke further to increase bank angle, centralising the column to maintain a steady bank angle and how to roll out of a turn.

It will take a bit of practice for me to start rolling out on specific headings, and to maintain an altitude – turning without compensating with back-pressure on the yoke will result in an altitude loss. Also, the turns weren’t very co-ordinated but that’s where rudder comes into play and will be dealt with in the next part.

Main Flight Controls (Part 1)

Here’s the first ‘real’ lesson in the PPL (learning through FSX) Air Pilot’s Manual –  the primary effect of each main flight control. It’s quite simple to learn in theory, but what was it actually like in the aircraft? The three main controls are the elevators, ailerons and the rudder.

– the elevator controls pitch

– the ailerons control roll

– the rudder controls yaw

Pushing the yoke/joystick forward makes the aircraft pitch down, and pulling it back does the opposite. The way it works is that the airflow around the tailplane is altered thus changing the aerodynamic force generated by it. If the elevators go up (pulling back on the yoke) there is an increased speed of flow beneath the tailplane and a reduction of static pressure in that area. The downward aerodynamic force on the tailplane causes the aeroplane to rotate on its centre of gravity and the nose goes up.

That’s really easy to understand, so it was up into the air to try it out. After establishing the aircraft in straight and level flight, I tried various climbs and dives at different rates.  It’s important to note that the airspeed changes during this manoeuvre – the more I pitched up, the faster I lost speed and the more I pitched down the faster I got.  At this point nothing is rocket science and I haven’t learned very much except for how to explain it a little better that before.  That said, everyone has to start somewhere and it’s nice to fill in gaps in my knowledge along the way as I work through the chapters of the book.

Please leave comments, add details or mention something I missed regarding the elevators that perhaps isn’t mentioned at this basic level. Being as I have never been in a GA plane in the real world, how good a job does FSX do in modelling this?

In part 2, I have some exercises with the ailerons to complete, and also don’t forget Angle of Attack’s great video series. Episode 3 talks about the flight controls.