Circuit shape
 

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.

? 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.

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.

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.

Or you can have the best of both worlds!

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

Dr :8

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.

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.

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.

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.

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

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:

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.

What a scream "A1B" friends of yrs perhaps?:}

Wmk2

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 1½ 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]

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.)

"...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

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.

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

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.