100hrs! - The perfect circuit

[bigfoot01]

I am chuffed to bits, I have now done 100hrs flying following a flight today. Following a bit of lull since September, I have spent a few pleasant hours with an instructor and have enjoyed some of the most relaxing flying of my career, where I felt I was in control and understanded what was going on. Still loads to learn, but didn't feel like a complete learner again, after not having flown for ages!

As one would expect, we did some cross wind circuits together (because it was cross wind). After the first one, my circuits were back to their old standard (!), which I am not claiming to be great.

As we were wandering around, we had a discussion about the precise way the circuits should be flown at the different phases. We also discussed the different things we had both been taught over the years, which was interesting. Next time I go up, I am going to spend some time in the circuit trying to fly much more precisely. But it got me thinking... If I am flying precisely, what are the best numbers to aim for at the different phases of the circuits. So, I thought I'd ask and see what people think and see if we can get a concensus on a perfect circuit....

(Well maybe not a concensus, but I thought it might be an interesting discusion point - please note, I did not use my GPS during the circuit!)

[BackPacker]

I did not use my GPS during the circuit!

You should. Just to record your flight path and then download it into, for instance, OziExplorer. You can see every deviation from the "perfect" circuit in great detail.

[Mad Girl]

I did not use my GPS during the circuit!

You should. Just to record your flight path and then download it into, for instance, OziExplorer. You can see every deviation from the "perfect" circuit in great detail.

Yep - I can relate to that..... especially as I'm not too good at correcting for drift

I've often taken my PDA with memory map on it to record what I've done and then "allowed" my very experienced friends, to critique my circuit flying in the club house over a cup of tea..... shows the (lack of) precision nicely.....especially when you change the map to the 250000:1 and zoom in... (also shows the speed & height profile when you download it to your PC)

I did have (just the) one, absolutely superb day where I was flying the circuit with almost metronome precision and I can't have been more than 10ft away from each track, and that was over 8-10 circuits....



Thread drift......
I remember that day especially well as it was my first solo flight after passing my test and had been feeling quite elated when I got back to the club......grin from ear to ear........and than a (fairly new) instructor pulled me over and said I'd been flying in the neighbouring airfields ATZ ... Still assuming that all instructors are sky gods and therefore always right even though I knew I'd been flying the pattern I'd been taught from day 1......I whipped my PDA out to check where I'd been (all worried... thinking "oh $%^&^l - they let me loose and I screw up!!" ) and proved that I'd not only been within OUR ATZ but followed the approved circuit path.... But he still thought he was right because that edition of the chart showed the neighbouring ATZ as curved when the join between us should have been a straight line - the chart was wrong(!)..... and had been amended.

But that whole situation totally deflated me ...

Our ex CFI heard what had happened from another instructor, and came over to look at the PDA as he hadn't seen that set up before..... He complimented me on the accuracy of my circuit flying and said that I'd been precisely where I should have been - "borrowed" the PDA to show the track to another recently qualified as an example of accuracy - and then wanted to know which instructor had tried to ruin my day!

[Lister Noble]

I hope you told him.

[bigfoot01]

To be honest, I wasn't too bothered about my ground track, I have been flying circuits round there so long, I know the bits I should have been flying over (although a couple of my turns to finals were clearly not as they should have been!!!!)

I was more interested in getting really sharp on the turns, speeds and heights, I was really taught to judge the circuits by eye, rather than fly them by numbers and my instructor noted that I wasn't really doing some bits very positively, I just wondered if anybody had views on what they should be. I have sense I am going to get a bit of flaming over this, but here's what I was up to yesterday...

So, Rotate, Best Rate of Climb to 500', 15 deg bank turn, Best Rate of Climb to circuit height, set cruise speed. 30 deg bank turn. Call Down wind. Down wind checks...

On the day, given the cross wind here's what we ended up doing. Ready to turn base; power off 30 deg bank turn 10 knots about approach speed. Stick some flap in in. 15 deg bank trun set approach speed, call finals add drag flap.

It's interesting, having given it some thought, after going solo, I haven't really done many circuits with instructors, except when they were checking I wasn't going to kill myself before going solo and during check out flights (when some have been prone to tutting a bit...!!!) so I am not surprised I am not as precise on this as should be.

Further thoughts welcomed...

[ShyTorque]

Thread drift......
I remember that day especially well as it was my first solo flight after passing my test and had been feeling quite elated when I got back to the club......grin from ear to ear........and than a (fairly new) instructor pulled me over and said I'd been flying in the neighbouring airfields ATZ ... Still assuming that all instructors are sky gods and therefore always right even though I knew I'd been flying the pattern I'd been taught from day 1......I whipped my PDA out to check where I'd been (all worried... thinking "oh $%^&^l - they let me loose and I screw up!!" ) and proved that I'd not only been within OUR ATZ but followed the approved circuit path.... But he still thought he was right because that edition of the chart showed the neighbouring ATZ as curved when the join between us should have been a straight line - the chart was wrong(!)..... and had been amended.

But that whole situation totally deflated me ...

This sort of story doesn't surprise me. A colleague of mine transitted an ATZ, on a very regular and familiar route, approximately one mile from the airfield, whilst speaking to the tower. No problems, everyone was happy. However, an aircraft not notified by ATC was seen flying close by and heading away from the airfield. Shortly after landing he had to deal with an irate instructor who complained by phone that he had seen my colleague fly close to him whilst turning long finals when teaching circuits. After some initial confusion, my colleague realised the instructor was not from the airfield whose ATZ he had transitted, but from a neighbouring airfield almost six miles away!

My colleague, who was absolutely certain of his exact track (so was his co-pilot) suggested the angry instructor filed an AIPROX so the radar tapes would be examined. Strangely, he never heard any more about it.

[T-21]

Agree with Bigfoot,circuits should be flown by eye. You have to adjust every circuit in a glider. It would be good for power pilots to do some gliding ,it would sharpen your judgment skills,and not relying on power and gizzmo's to help you.

[larssnowpharter]

You have to adjust every circuit in a glider. It would be good for power pilots to do some gliding

Agree in spades.

As I recall the USAF used to (perhaps still does?) send its sprog pilots up in gliders to teach things like secondary control effects.

Confess to being somewhat worried about basic flying skills when I read some of this stuff. What the hell are people doing with head down, looking at instruments perhaps even fiddling with GPS when they are trying to land?

[BackPacker]

So, Rotate, Best Rate of Climb to 500', 15 deg bank turn, Best Rate of Climb to circuit height, set cruise speed. 30 deg bank turn. Call Down wind. Down wind checks...

Flying the perfect circuit like that is good training. But once you've got the ticket and a bit more experience, I find it better to adapt your circuit to the circumstances. That means that no circuit will be alike.

I fly from a controlled field where we join via a "cross in the middle, join left/right downwind" procedure. Usually at 1000' or 1500'. And if the circuit is empty you get your landing clearance when crossing the runway.

So it's full flaps immediately, chop the power, carb heat on, continue perpendicular to the runway for five seconds, make a continuous descending 270 degree turn at flap limiting speed and, oh, 45 degree bank or so, join final somewhere over the threshold at 100' or so, milk out the excess speed you have above the runway and touch down.

Far from standard, but safe and the circuit/runway is clear for the next arrival/departure very quickly. Only to be done in an aircraft you are very familiar with, and a field you know very well.

And yes, we know that these kinds of instructions are possible, so the "downwind checks" are done before crossing the runway and joining the circuit.

[Flintstone]

Originally Posted by Backpacker

full flaps immediately, chop the power........45 degree bank

Really? Hmmmmm.

[youngskywalker]

That reminds me why I never sit in the back seat in light aircraft anymore, if I can't reach the controls...I'm no going!

[RatherBeFlying]

Me, it's usually carb heat on, ease power to idle, 45 degree bank, add some G to get under flap speed, then add flap and level on base at approach speed.

The bank and G get the airspeed down nicely.

[bigfoot01]

Does that mean my 15deg of bank turning finals with flap is a bit conservative then?

[Flintstone]

No. It means you're safer.

[florin_el]

circuit charts

I am getting my Garmin onboard almost at every flight. Helped me to have an ideea about precision during circuits. I was offering myself a personal debriefing after everyflight. Had ex-military instructor with eyes everywhere...

[Mark1234]

Originally Posted by flintstone

No. It means you're safer.

Not necessarily.

Here begins the debate What is a 'perfect' circuit?

I happen to know what backpacker's flying, and fly the same type. I also know he flies aeros in it (as do I). There's nothing intrinsically unsafe about a 45 degree bank. Nor is there anything wrong with using a 15 degree bank.

*Personally* I'd rather fly with someone who has some feel for the aeroplane, and can fly like that safely, than someone who's perfectly by the numbers and freaks out when they see more than 30 odd degrees of bank. My pet hate is people turning final miles out, extending full flap despite a stonking headwind, then thrashing it all the way in with power, well under glide. What if?

Yes, doing it by the numbers works, but there are many other solutions which are equally appropriate.

[BackPacker]

No. It means you're safer.

Not necessarily.

True. What matters mostly is your margin above the stall speed.

In a level, balanced turn, *any turn*, you load up the wings to some degree and thus increase your stall speed. But this effect is almost zero up to 20 degrees of bank. (At 20 degrees, the g loading increases by 6.4% and the stall speed with 3.1%) That's why, at the PPL training level, turns to final are limited to 20 degrees. So your margin above the stall is still a very healthy 27% (1.3 Vs0 minus 3%)

In a 45-degree banked turn you are pulling 1.4g. This increases the stall speed by almost 20%. But when you fly that 45-degree banked turn *at flap limiting speed* (the top of the white arc - Vfe) you still have a very healthy margin above the stall - probably more than 30% even. Depending on the exact numbers for the airframe, you can even go to 60 degrees if you need to. (Note - most airframes are limited to 2g = 60 degrees bank with flaps extended.)

The difficulty with flying your circuits like that is not in the turns. It's shedding the speed from Vfe to approx. Vs before you run out of runway. That's why you should only do this in an aircraft you're very familiar with (so you know how quickly you shed the excess speed) and a runway you're familiar with (so you know how much runway you've got left).

And to be honest, I only do this kind of stuff at my home base, where I have 2 km of tarmac with exits at the ends only. With shorter runways, or when fitting in with other circuit traffic, I typically fly a "normal" circuit. In the end it's all about adapting to the circumstances and the better you know the aircraft, the more adapting you can do.

[jamestkirk]

Load factor in a turn

Correct me if I am wrong but is'nt the load factor reduced as you are descending and not trying to maintain level flight, eg. Turning onto finals

[BackPacker]

James, it's all about acceleration. If the vertical component of lift is not equal to the weight of the aircraft (assuming drag and thrust balance each other) then the aircraft is continuously increasing its rate of descent (or climb). That's normally not what you want to achieve. So even in a descending turn you have to load up the wings, so that the vertical component of lift and drag balance the weight of the aircraft plus the vertical component of thrust.

The factor that slightly complicates this is that the increased g-loading increases drag. And the drag has a vertical component as well since we're slightly nose-down and descending.

All in all, I think that in a descending turn you don't have to load up the wings as much as in a level turn. But the exact amount is beyond me, right now. I've never been good at 3D-trigonometry.

[jamestkirk]

BP

Thanks, I have a headache now