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On eyre
27th Jun 2010, 07:01
I have always wondered why we fly a rectangular circuit and not complete an easy continuous descending 180 degree turn from a base position onto final. Probably historical - anyone any clues. Aggies do it all the time.

Trojan1981
27th Jun 2010, 07:10
? ADF fly oval circuts. You fly oval circuts in a pits too, or anything of that nature, as it is much safer considering your restricted vision.

Seagull V
27th Jun 2010, 07:15
Probably to do with cockpit visibilty from biplanes and highwing aircraft. In your average Cessna etc you cannot see the runway during the continous turning approach and you cannot see if another aircraft is inside you. Also to do with glide approaches, which was the way approaches were taught up to the 60s. Powered approaches, the Devil's work.

MakeItHappenCaptain
27th Jun 2010, 07:22
There are pros and cons for both types. You should fly whatever your school is teaching you.

IMO, square ccts are better when beginning to give the student more time to sort themselves out on each leg and to set spacing when turning downwind. They also allow for better visibility before turning each leg and better judgement of base aspect.

Rounded ccts, while taught initially with some schools, are more efficient and will come with practise. They are flown by all the airlines and (as already stated) the ADF.

There is really no 100% correct answer to this question.

ForkTailedDrKiller
27th Jun 2010, 07:42
Or you can have the best of both worlds!

A continuous climbing turn onto downwind and square base and final legs! :E

Dr :8

slamer.
27th Jun 2010, 08:29
Or the rocket like performance of C152, axe, AAIC ... etc.

Imagine where you'd end up downwind on reaching 1000agl in the ubove mentioned (and others) with a oval crosswind leg/circuit, MTOW, 25 kts headwind on takeoff.

So theres prob a bunch of good reasons to go rectangular in low performance types.

Ultralights
27th Jun 2010, 08:37
everyone knows you dont make money with Oval or tight circuits! why do 6 or 7 landings per hour when you can only do 4! and the student has t come back more often to get the required skill base up

dont you guys know anything......;)






on a more serious note, ysbk tower doesnt mind you doing ccts within the aerodrome boundary if your the only one there.

On eyre
27th Jun 2010, 08:42
I did not mean to suggest a continuous climbing turn on takeoff but rather was wondering about the turn(s) from a base position.
I take the point about visibility issues with some high wing aircraft and a similar problem exists with the visibility from some low wing aircraft on base leg.
It appears to me that it is easier to maintain and regulate a constant descending profile with a curved approach than the right angled turns we now generally carry out.

Ultralights
27th Jun 2010, 08:59
actually the closest and fastest and better circuits i have seen was from a 767 capt, bonanza owning spitfire endorsed and mustang aero routine flyer from the US, at bankstown, departed 11R, climbed straight out to 500 ft, right climbing turn 180 deg onto downwind, pretty much overhead canterbury rd, climbed to 1000, then begun descent immediately, and a 180 deg turn onto final overhead the tower, i was impressed! all in an aircraft he had just discovered existed and never flown before, the tecnam.

Wally Mk2
27th Jun 2010, 09:05
It's done purely so we are all working/flying off the same page. Structured right or wrong we have to have 'standards' as aviation grew from hapless barn storming pilots who pretty much dd their own thing in order to land with more than a couple in a particular ares for a Ldg. When all over fields where the go circuits as we know it now wouldn't make sense so now that we have 'direction' we have order:ok: Well supposed to but I all too often I see pilots who haven't got a clue about basic airmanship, something obviously not taught more often than not!:ugh:

Wmk2

sms777
27th Jun 2010, 09:22
In addition to Wally's post, we already have the technology to build "directional" runways.
What i mean is a spherical runway design where by assistance of hidden lighting we could change runway directions like a compass to ensure landing always in to wind.
Of course this would require a concrete circle of at least 3 kilometer radius. But imagine the money could be saved if all airlines contributed to construction to save circuit time because all approaches would be straight in.
Just a thought. :oh:

Ando1Bar
27th Jun 2010, 09:29
http://www.arabamericannews.com/news/images/articles/2008_03/755/u1_hookah_vmed_5p_widec.jpg

Ultralights
27th Jun 2010, 09:32
the 360 deg runway would be a great idea, coudnt imagine it being too close to built up areas though! now when i win my $50 mill tomorrow, i might just have to install the required lighting into the biggest flat paddock and create such a runway..

will the lighting be switched according by the windsock rotating, or manually, could image it would be fun to fly an approach in gusty winds with the windsock constantly changing runway headings on you. be quite a light show though.

Wally Mk2
27th Jun 2010, 09:39
What a scream "A1B" friends of yrs perhaps?:}

Wmk2

TBM-Legend
27th Jun 2010, 09:53
Navy "Charlie" pattern at 300 feet is better...:p


...or jet ops:
Landing Pattern Entry
The break is a level 180° turn made at 800 feet, descending to 600 feet when established downwind. Landing gear/flaps are lowered, and landing checks are completed. When abeam (directly aligned with) the landing area on downwind, the aircraft is 180° from the ship’s course and approximately 1˝ miles from the ship, a position known as “the 180” (because of the angled flight deck, there is actually closer to 190° of turn required at this point). The pilot begins his turn to final while simultaneously beginning a gentle descent. At “the 90” the aircraft is at 450 feet, about 1.2 nm from the ship, with 90° of turn to go. The final checkpoint for the pilot is crossing the ship’s wake, at which time the aircraft should be approaching final landing heading and at ~350 feet. At this point, the pilot acquires the Optical Landing System (OLS), which is used for the terminal portion of the landing. During this time, the pilot’s full attention is devoted to maintaining proper glideslope, lineup, and “angle of attack” until touchdown.[10]

MakeItHappenCaptain
27th Jun 2010, 10:12
i was impressed! all in an aircraft he had just discovered existed and never flown before, the tecnam.

You might have been impressed, but was he?

And carrying how much payload?
(And before you say MTOW, I'll mention that yes, they may outperform a 172, but if you want to carry more than one pax (and a light one at that) and 20Kg of baggage, forget anything RA.)

josephfeatherweight
27th Jun 2010, 10:46
"...an easy continuous descending 180 degree turn from a base position onto final."
I think you might find that conducting a continuous banked base turn is a tad more difficult than a rectangular one. I believe a student pilot finds a rectangular circuit easier to tackle initially, especially in a GAAP (or whatever it's referred to now...) environment, allowing the student to look out ahead whilst maintaining wings level, vice maintaining/correcting an angle of bank to suitably intercept an extended runway centreline.

And yes, a constant banked base turn in a high winged aircraft does restrict visibility somewhat.

My thoughts anyway...

Joe Lighty

FokkerInYour12
27th Jun 2010, 11:09
Also a square base leg makes it much easier to spot drift based upon visual ground track.

If you're on base with no offset for a headwind and you're drifting towards the runway you may have scewed up where the wind is coming from (or there's a very low windshear about to happen).

Somewhat harder to detect on oval circuits until you're familiar with the aircraft and what "feels" normal.

Biggles78
27th Jun 2010, 12:06
Or you can have the best of both worlds!

A continuous climbing turn onto downwind and square base and final legs!

And wouldn't that be a Bonanza for some. :} (Sorry Doc, really bad pun)

I have never flown a circular circuit (except my first solo) but it seems to me that if you had a circular decending approach then the "circuit" is going to be messy. I am thinking of a Rate 1 turn. The faster the speed of the aircraft, the larger the circle (and greater bank angle of course). So, unless all aircraft in the circuit have the same approach speed, they will be all over the place on the base/final curve. With a square circuit it appears to me that separation would be easier to maintain and therefore a more orderly one.

Remember I haven't flown anything except what we have now so does what I say sound reasonable (assuming I have made an iota of sense) or am I babbling from a place where the sun don't shine. :O

On eyre
27th Jun 2010, 12:15
Biggles
So what is the difference between aircraft of all sizes and speeds carrying out two 90 degree rate 1 turns or one 180 degree rate 1 turn - they will still be all over the place.
I suspect the arguments for the finite base and final turns do have merit for student or low time pilots and in busy circuit areas but for pilots more experienced and familiar with their aircraft the descending turn from base to final is more efficient - just ask the aggies.

Peter Fanelli
27th Jun 2010, 12:18
Rectangular circuits are fine, the problem is the square circuits taught by some schools.

:ugh:

A37575
27th Jun 2010, 14:01
[QUOTE][I am thinking of a Rate 1 turn./QUOTE]
Turns in the circuit are not necessarily Rate One which is 30 seconds for a 90 degree turn and is normally only applicable to instrument flying. The first climbing turn on to the first crosswind leg should be made at 30 degrees angle of bank whereas a Rate One turn with a typical 80 knot climb speed gives you around 15 degrees angle of bank. The longer you have one wing lowered in a high wing aircraft the more exposure you have to not seeing another aircraft in that blind spot.

Turning to downwind leg and depending on wind direction and speed, you may consider conducting a climbing turn to the downwind leg in order to attain the correct spacing from the runway. Do that at 30 degrees angle of bank for same reason as earlier. Turning base again for for 30-40 degrees angle of bank which is considered a medium turn. Same for turning final.

Sunfish
27th Jun 2010, 20:23
I think if I tried I could do a complete rectangular circuit at YMMB 17L in a Sportstar, including a 1000' downwind and stay within the YMMB boundary.

Ted D Bear
28th Jun 2010, 00:30
The first climbing turn on to the first crosswind leg should be made at 30 degrees angle of bank


30 degrees AOB? I don't think so! Geez, I did my ab initio in a C150 from an airfield 3,500 feet AMSL - in summer, a 30 degree banked turn on to crosswind would have been a descending turn :=

Ted

MakeItHappenCaptain
28th Jun 2010, 12:33
Agreed, Ted D Bear!

30 deg AOB in a climbing turn?

When you want to go up you need as much of your lift going as vertical as possible, not horizontally.

Basic stuff, really. (I mean it... usually covered before stalls....:ugh:)

Speaking of which....
To any students who want to do a 40 deg turn into base as normal procedure, I hope your life insurance is paid up. That's bordering on a steep turn, not medium.
Let's see if you remember what happens to stalling speed with increased AoB (read as load factor) and relate this to an wing drop/incipient spin when close to the ground.
Definitely not a standard manoeuvre now, is it?

S-turns might be taught as a way to lose a lot of height rapidly to correct an overshooting FLWOP, but the student must ALWAYS be made aware of the risks involved due to reducing IAS (due increased drag) and increased load factor.

Centaurus
28th Jun 2010, 12:40
Geez, I did my ab initio in a C150 from an airfield 3,500 feet AMSL
Of course at those density altitudes the C150 won't perform too well especially if you are using full rich mixture. Similarly on take off at that density altitude, you should lean the engine for take off otherwise the mixture is so rich as to give significant power loss. I suggest the angles of bank mentioned for the climbing turn were applicable to sea level aerodromes or at least up to 1000 ft amsl?

Centaurus
28th Jun 2010, 13:01
To any students who want to do a 40 deg turn into base as normal procedure, I hope your life insurance is paid up. That's bordering on a steep turn, not medium.
............................................................ ................................
Extract from the FAA Airplane Flying Handbook - sub heading "Basic Flying Maneuvers"

For purposes of this discussion, turns are divided into three classes: shallow turns, medium turns, and steep turns.

* Shallow turns are those in which the bank (less than approximately 20°) is so shallow that the inherent lateral stability of the airplane is acting to level the wings unless some aileron is applied to maintain the bank.

* Medium turns are those resulting from a degree of bank (approximately 20° to 45°) at which the airplane remains at a constant bank.

* Steep turns are those resulting from a degree of bank (45° or more) at which the "overbanking tendency" of an airplane overcomes stability, and the bank increases unless aileron is applied to prevent it.

MakeItHappenCaptain
29th Jun 2010, 06:13
Buggered if I will teach students to use 40 deg Aob turns as a general course of action at low level. 15 is usually fine and 30 if required to tighten up the turn onto final.
If they need more than that, then they aren't anticipating enough or haven't read the wind correctly.

I didn't say it was a steep turn, just bordering on.
Quote the CASA Flight Instructor's Manual, Turning;
MEDIUM LEVEL TURNS
Definition A medium turn is one carried out with an angle
of bank of approximately 30 degrees.
And that's the way every school I've taught at does it.

PS. None of them taught a 30deg climbing turn, either.
Again to quote the CASA Manual;
Point out that the angle of bank is restricted to only about a rate
one turn, otherwise the rate of climb is decreased markedly.

Unless you're flying at 200Kts, Rate 1 is a lot closer to 15deg than 30.

My point was that teaching a student to fly at excessive AoB's at low level in the early stages of their training might not be such a good idea.

Seagull V
29th Jun 2010, 07:58
Maybe SMS777 was onto something (other than something he ingested) with his omni directional runway idea. But it doesnt have to be as big as he desribes. What if we had assisted take off and arrested landing facilities much like those on an aircraft carrier? This would be particularly useful at city airports (formerly) GAAP as it would would release all that wasted land for the airport operators to sell off and make profits. Makes as much sense as ... helicopters.

43Inches
29th Jun 2010, 09:01
15 degrees bank angle in the climb is normal in a trainer like a 150/152, pa28 or 172. 30 degrees whilst climbing just reduces climb performance and stall margin.


The longer you have one wing lowered in a high wing aircraft the more exposure you have to not seeing another aircraft in that blind spot.



High wing aircraft need a good lookout prior to the turn. Performing a sudden eratic manuevre (like trying to turn suddenly onto crosswind or downwind) in front of another aircraft is far more dangerous. In the circuit the most important thing to remember is to be predictable. Following aircraft expect you to do a shallow climbing turn after take-off and they will manage their circuit to follow.

The rectangular circuit is much more appropriate in high density traffic environments as one can easily communicate position and visually sight other aircraft. The flow is predictable so lookout should be easier. An oval circuit requires more attention to just flying the circuit, less time available to look for traffic and more spent on alignment with the runway.

Airline manuals may depict a curved base in their manuals but inevitably most fly a square base to help judge the turn to final or separation with traffic. The curved path is more to keep the aircraft in the circling area with minimum chance of losing visual reference during such approaches.

40 degrees anywhere in the circuit is more an evasive manuevre than a normal one. Low speed with flap and a low experience pilot could easily overbank and get into trouble at low level, especially with disorientating wind conditions. If you tried this in a large aircraft it would yell at you annoyingly until the bank angle was under 35 degrees or so.

Sunfish
29th Jun 2010, 21:36
Just doing some refresher training at "another" school. Very interesting.

In the circuit, sticklers for:

15 degree bank angle.

Always with enough height and speed for a glide approach to one of the runways (actually tested, and not on the duty runway either)

Always roll wings level before applying flap (pick up asymmetry if something breaks)

Always land full flaps.

Speeds base and final in a Warrior 80 KIAS, 75 KIAS Final, bleed back to 70 kias at fence. (less for short field of course). You are going to make the runway one way or the other.

Eyes to end of runway and try and fly there taught. Always land with full back stick, ideally with stall warning indication.

Maintain full back stick while braking.


Geeze I was getting sloppy before this.....:}

Ultralights
29th Jun 2010, 22:59
Always land full flaps.

i have seen some students get into real trouble always following this "rule" scary watching a C152 on short final, full flap, with wind gusting to 20 kts and a 15 kt crosswind component..:ugh:

HarleyD
30th Jun 2010, 06:04
15 AoB climbing turn work fine and does not significantly diminish climb performance.

Other turns 30 AoB. you are very unlikely to stall from high Aob on base and final. you are much more likely to have issues if you use a shallow turn (or terrify poor luckless students that this is a maximum angle cos anything more is potentially 'dangerous').

A shallow turn, say 15 AoB, when added to a TWC on base means that the student may get pushed past the RW ECL and attempt to tighten the turn WITH RUDDER (cos more that 15 is dangerous remember). classic scenario. skid causes drag and sink, student raises nose to attempt to get picture right and treads a bit harder on the rudder, are you all following me?, there is a need to oppose the rudder with opposite aileron, so keeping low decelerating) wing up with aileron, nose starts to fall despite back pressure, low wing continues to descend despite full opposite aileron, ground getting closer, and closer faster, pull back really hard .........


15 works for oval but 30 is better for regular pattern, enabling sufficient time established with wings level to assess, adjust and confirm accurate position and approach profile.

Doing a 'derry turn' at circuit corners is fun but not for the pre solo student.

personally i like oval, but i do what is the 'normal' thing where ever i go. the "standard" pattern shape and altitude is there for a reason, not entirely sure what that is, but it does enable the instructor and student to determine if the standards specified in the instructional objectives are being met.

HD

b_sta
30th Jun 2010, 06:18
Just doing some refresher training at "another" school. Very interesting.

Are they teaching people to follow step by step instructions, or to actually fly planes? :ugh:

Capn Bloggs
30th Jun 2010, 07:29
Airline manuals may depict a curved base in their manuals but inevitably most fly a square base to help judge the turn to final
Actually, it is easier to get the onto final right by doing an oval, because if you start from a set distance out on downwind eg 1.8nm, you just fly a standard turn all the way around. Flying a square base removes a "known" because you have to judge the distance to the ECL for the turn onto Final.

Also, any square basing that goes on will also make the circuit bigger/wider, as well as annoying the pax by 2 x 90° turns instead of one continuous one.

BurntheBlue
30th Jun 2010, 08:40
Hi PPRuNe, im new to this but not to flying. Im really pleased to find another site worth visiting and particularly enjoying the Downunder threads.

What if we had assisted take off and arrested landing facilities
Wouldn't that be a scream, i can imagine the punters now, loves it.

are you all following me?
C'mon HarleyD, we get it but must you be such a douche about it?

What i mean is a spherical runway design
How would an IFR approach work into a circular runway? Perhaps ILS on a swivel. Maybe if RWY lights and approach directions are designated manually by someone qualified on the aerodrome (obvious answer for zones is the tower) Regulated kind of like a change of circuit direction. Brings up all sorts of issues doesn't it.
On the side, i assume that was a circular, not "spherical" runway sms777. Maybe in that case aircraft should orbit at various distances from the landing globe slowly making their way closer to landing... or do they just fly into the globe?

Food for thought: I once belonged to an outfit whos CFI insisted on students turning through 110 at the end of the downwind to make the resultant 70deg turn onto final easier to judge. I trialled it for a while and students really did get the hang of things quicker.

And finally, **NO** to >30 AOB in the circuit. Especially if you're instructing ab-initio. Thats playing with fire.

ForkTailedDrKiller
30th Jun 2010, 09:47
Im really pleased to find another site worth visiting

Huh?

Where? :E

Dr :8

poteroo
30th Jun 2010, 12:15
Reckon it requires greater skill & judgement to make the climbing 180 and descending 180 turns..... so,

Square for ab initio - thru solo - up to precautionary

Oval x low level circuits - before & as an aid to precautionary exercise. Also useful for teaching bad wx/low vis arrivals.

happy days

Super Cecil
30th Jun 2010, 23:35
Typical prune, two pages of total drivel :}

HarleyD
1st Jul 2010, 01:37
Reckon it requires greater skill & judgement to make the climbing 180 and descending 180 turns.....


potaroo: I recon you are spot on. "square" works for setting the fundamentals and the curved approaches are for when judjement is able to be used - totally agree.

In real life i have done many thousands more curved approached and departures than square cornered ones, so a it is am important skill that needs to be learned regardless of what type of flying the student will be doing later.

HD