Learning to fly, or thinking of learning? Post your questions, comments and experiences here

Moderator: AndyR

#1910031
My last but most memorable lesson for a bit, whilst I jump through the hoops trying to get my medical sorted. My AME predicts using her experience my case will take approximately two months. As hugely frustrating as the time frame and uncertainty is, I'm told I ought to count my blessings compared to the time frames of some other cases.

This lesson started out as an experience flight where we would land at another airfield. But due to weather, it changed to a normal discovery flight. That's how I've had my two or three lessons so far- they're trial lessons until I can dedicate myself properly after my medical is sorted.

This flight was in the Piper: I don't normally fly something with four seats, so I was able to invite my friend to come along this time! He got some great shots I wouldn't normally be able to.

The lesson focussed on straight and level flight/attitudes. I struggled to distinguish which was which a couple of times between "straight" and "level", but eventually nailed it down by equating "straight" to the horizontal plane (roll and yaw), and "level" to vertical (nose attitude).

We also covered why you should use the window as a primary means, and the instruments secondarily. My instructor also broke down the reasons as to why steam instruments might have significant delays to their display (I don't know if electronic avionics have the same delay(?) )

Finally, I learned something quite revealing about the trim- Turns out it's not the delicate feather of a tool I thought it was. I had no idea you could move it so much so quickly, I thought it was just for gentle fine-tuning. I only learned this after my instructor became confused as to why I was being so reserved with it as we flew through turbulence.

Flyin'Dutch', tr7v8, A le Ron and 1 others liked this
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By NDB_hold
#1910104
Trim: this does vary between different aeroplanes. The Pipers generally have a spring bias system which just pulls on the (all moving) tailplane with a spring, so you need quite a bit of movement of the wheel to do anything. Aircraft with a traditional trim tab (e.g. Slingsby Firefly, which we use at our club for training, or the Grob Tutor used for air cadet flying) need a much smaller movement.

You’ll always get a delay with the Vertical Speed Indicator, because the way it works is literally to compare the pressure now with the pressure a few seconds ago. That’s still true even with electronic displays in most cases (though there is such a thing as an IVSI, Instantaneous VSI - bit of reading here: https://www.mcico.com/resources/flight- ... t-lag-time)
#1910109
NDB_hold wrote:
>
> You’ll always get a delay with the Vertical Speed Indicator, because the
> way it works is literally to compare the pressure now with the pressure a
> few seconds ago.

No it doesn't. Not exactly. Go back to the books. It's worth understanding how the pressure instruments work so you know what's going on when they don't work properly. The theory learning for the ppl covers this and there will be exam questions.
#1910121
Well, that’s pretty much exactly the explanation given here: https://skybrary.aero/articles/vertical-speed-indicator

‘ The capsule is fed with static pressure from the pitot-static system, while the case is also connected to that system through a calibrated nozzle. The nozzle restricts the passage of air so that there is a time delay between a change in static pressure and that pressure being experienced within the case.’

To measure a rate of change, you have to measure the quantity at different times and compare them. That can only be done by comparing the value now with the value in the past, because we lack the ability to measure the future…
By TopCat
FLYER Club Member  FLYER Club Member
#1910137
NDB_hold wrote:

> To measure a rate of change, you have to measure the quantity at different
> times and compare them. That can only be done by comparing the value now
> with the value in the past, because we lack the ability to measure the
> future…

No. The VSI readout is based on an instantaneous pressure difference between the static pressure outside the capsule, and the static pressure inside the capsule.

The capsule is a sealed expanding case inside the instrument, connected directly to the static pressure outside. Outside the capsule but inside the instrument, changes in static pressure equalise only slowly.

This means that that if you stop climbing or descending, that pressure difference gradually becomes zero.

This article explains it quite well:

http://www.pilotfriend.com/training/fli ... ng/vsi.htm
By TopCat
FLYER Club Member  FLYER Club Member
#1910181
NDB_hold wrote:
> But surely the 'trapped static pressure inside the case' is nothing more
> than the static pressure outside the case a few seconds previously?

Of course, but IMHO that's not a helpful way of explaining what's really going on.

When you said

> To measure a rate of change, you have to measure the quantity at different
> times and compare them.

I'd humbly contend that as an explanation, it implies measuring the same thing at intervals, which is absolutely not how the VSI works at all.
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By Paul_Sengupta
FLYER Club Member  FLYER Club Member
#1910240
NDB_hold wrote:
> Trim: this does vary between different aeroplanes. The Pipers generally
> have a spring bias system which just pulls on the (all moving) tailplane
> with a spring, so you need quite a bit of movement of the wheel to do
> anything.

It's the PA-38 which has the springs. The PA-28 has a big traditional tab.
#1910367
After flying PA28,s Roy kindly handed me the controls of the Pup. I wanted to make a slight nose down adjustment so put in a PA28 sized chunk of trim.

Not quite a Vne dive, but certainly heading that way.

And as Paul didn't use it, I'll add the standard student response for when the instructor talks about 'Straight and Level."

"Which one do you want first?"
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