Turns at low IAS

[kasper]

On 08/01/2021 at 8:39 PM, pmccarthy said:

Who can tell us about wing designs? I know little about them, except most wing cross sections were designed in the early 1930s and we just choose one of them. It must be more complicated.

Well that’s a whole forum on its own. The starting point if you are selecting for a performance optimised point  is state that design point and what the allowable edges of that performance envelope is going to be allowed. Then you have to work through all the compromised that go with turning that into an airframe.  
 

or you chose a section from any reputable book that’s been used before put that into something that’s pleasing to your eye and discover the performance envelope when you’re finished.  

[skippydiesel]

12 hours ago, aro said:

A standard circuit is pretty clearly defined in AIP. If you're looking for a particular person, I don't know. I suspect it predates WWII.

At a guess, I would suggest the concept of a recognised/defined/standard circuit pattern, to have arisen with the advent of the runway. Prior to the runway a pilot landed/took off, into wind, on a designated field/paddock.

 

Further guesswork - the development of the runway came about at roughly the latter part of the period between the two Great Wars, as a response to the need for all weather operations (civil & military)and the dangers, to ground activity & conflicting aircraft,  of aircraft landing/TO from any direction (as determined by pilot/wind) became evident .

 

Coinciding with the development of a defined runway, would have been the safety concept to having arriving/departing aircraft (greater air congestion) operating within a recognised air corridor/pattern -  hight, arrival points & circuits.

[old man emu]

47 minutes ago, skippydiesel said:

Further guesswork - the development of the runway came about at roughly the latter part of the period between the two Great Wars,

I'd say it was post-WWII. Prior to the arrival of those really heavy bombers, operations were mostly carried out from all-over fields. Just look at footage of operations by both the RAF and Luftwaffe up to about 1942. After that heavier aircraft required reinforced ground (runways) for efficient gaining of takeoff speed. In the Pacific, engineers had to deal with uncompacted soils with a lot of vegetable content, and the need to construct operational airfields as fast as possible. It as easier to drive bulldozers and graders along a single straight line, then lay down steel matting to create a firm surface.

 

After WWII there were lots of these new runways all over the place; commercial aircraft had become bigger, and those original all-over fields had had runways installed.

[Old Koreelah]

4 minutes ago, old man emu said:

After WWII there were lots of these new runways all over the place; commercial aircraft had become bigger, and those original all-over fields had had runways installed.

Is this a major factor in the expansion of fin/rudder area? 

Compare the small tails on early wartime fighters with modern planes, which are more likely to land in crosswinds.

[old man emu]

Wouldn't small tails make lessen the aircraft's stability around the yawing axis, which would give better maneuverability is combat? 

 

Here's a quote from this research paper: https://www.fzt.haw-hamburg.de/pers/Scholz/Aero/AERO_TN_TailSizing_13-04-15.pdf

 

[kasper]

3 minutes ago, old man emu said:

Wouldn't small tails make lessen the aircraft's stability around the yawing axis, which would give better maneuverability is combat? 

Beat me to it.

 

Civil aircraft after WWII had to be - to get past certification - benign in handling. 

This meant that

1. design stability increased (larger fixed area of control surfaces)

2. control authority decreased (smaller deflections and/or smaller control surfaces)

3. cointrol force through cockpit controls had required force gradients (more deflection = more force required)

 

All of that leads to larger tails and arguably boring aircraft (try flying a Pitts when you are only used to a cessna 172 ...)

 

All of this design requirements feeds into other aspects of modern flying 

- you cannot use full deflection on controls over your ref speed or you risk tearing the aircraft apart

- you have over a drink discussions (or forum chat) on the perils of former military pilots flying civil aircraft where in an emergency they may revert to trained behaviours of full deflection which is possible and trained for in miltary but can tear your plane apart in civil flight

 

 

[old man emu]

Compare fin sizes:

WWII training aircraft

 

WWll fighter

 

 

 

[APenNameAndThatA]

3 hours ago, old man emu said:

Wouldn't small tails make lessen the aircraft's stability around the yawing axis, which would give better maneuverability is combat? 

 

Here's a quote from this research paper: https://www.fzt.haw-hamburg.de/pers/Scholz/Aero/AERO_TN_TailSizing_13-04-15.pdf

 

In the case of the tail, decreased stability would not help in maneuverability. It would decease ability to maintain co-ordinated flight with rapid turns. When maneuvering aircraft vigorously, rudder input is *increased*, so you need an effective rudder. It would not make adverse roll and Dutch roll worse. It would make the aircraft less stable, which would make it less useful as a gun platform.

 

This issue is different with dihedral, where stability acts against the ability to roll the aircraft.

[skippydiesel]

All control surfaces, working together, & their impact on the relative wind flow,  effects maneuverability, however I understand, perhaps incorrectly, that wing length (span) is the single largest degerminator of role rate (maneuverability). Most competition level aerobatic aircraft have relativly short wingspans, for this very reason.

[old man emu]

It stands to reason that if you stick a long, broad planks on the sides of a fuselage, it's going to take a lot of effort to push them over the top of the fuselage, so a slower roll rate. If you simply want to prevent too much roll if the aircraft is upset, then dihedral is the easiest thing to build in.

 

Wouldn't it be more useful in a fighter to have it somewhat unstable in the roll axis so that the aircraft would enter the manoeuvre a lot quicker? Trade off , trade off trade off.

[APenNameAndThatA]

On 10/01/2021 at 11:39 AM, old man emu said:

That's 1920s - 30s expectation, when all engines - aircraft, motor vehicle and marine - were not as accurately made as they are now. The materials were not as good. The oils were not as good. the petrol was not as good and the ignition systems were not as good. And engines failed. Nowadays an engine failure still remains a 100% possability, but the probability could be thought to be well below 5%. Telling a student pilot to EXPECT and engine failure is scaremongering. Advise them that it could happen, but not that it must happen.The same goes for most things students are told will kill them - stall/spins at below 2000' AGL excepted.

The above conflates expectation with respect to preparation with expectation with respect to probability. The reason that it is important to expect an engine failure is as follows. It takes about three seconds for someone to respond to an engine failure on takeoff. During that time, the aircraft can go from Vy to below the stall speed. In addition, there is a temptation to pull the stick back. That means that the pilot needs to be ready to push the stick forward quickly.

 

About the probability of an engine failure being "well below 5%". Rotax engines have a failure rate of 15 per 100 000 hours. If you assume that flights are one hour long, and that *all* the failures are at takeoff, the probability of engine loss at takeoff is 0.015%.

 

I got some push back on this forum a while ago when I suggested that RA-Aus flying seemed to be safer motorcycle riding but more dangerous than driving. According to FlightSafety magazine, the former chief commissioner of the ATSB said that private pilots were dying at the same rate as motorcyclists. That means that RA-Aus flying is not a low-risk activity by normal measures.

 

All this means that there is genuine utility in pilots both expecting and engine failure on takeoff, and, at the same time, the same pilots knowing that an engine failure on takeoff is very unlikely.

Edited January 12, 2021 by APenNameAndThatA
accidentally posted early.

[APenNameAndThatA]

On 11/01/2021 at 12:33 PM, old man emu said:

T

 

Units should not be stated as part of formulas.

[APenNameAndThatA]

31 minutes ago, old man emu said:

It stands to reason that if you stick a long, broad planks on the sides of a fuselage, it's going to take a lot of effort to push them over the top of the fuselage, so a slower roll rate. If you simply want to prevent too much roll if the aircraft is upset, then dihedral is the easiest thing to build in.

 

Wouldn't it be more useful in a fighter to have it somewhat unstable in the roll axis so that the aircraft would enter the manoeuvre a lot quicker? Trade off , trade off trade off.

Yes.

[Garfly]

8 minutes ago, APenNameAndThatA said:

Units should not be stated as part of formulas.

Whoaaa ... more scientism here than you could poke a joy-stick at.

[old man emu]

21 hours ago, APenNameAndThatA said:

Units should not be stated as part of formulas.

 

the entry where I got it from. https://en.wikipedia.org/wiki/Standard_rate_turn  (edited...mod)

[spacesailor]

  I would expect.

Aileron's further out towards the Tip, would roll quicker than the same Wing, with inboard ailerons, !.

ALSO the size/percentage of ailerons to that same wing span would also change the roll rate.

I'm just an Old balsa & tissue modeler.

spacesailor

[lee-wave]

On 10/01/2021 at 2:40 AM, Yenn said:

Two things stand out from this discussion. We seem to be unaware that no single control works the way it seems. By that I mean that the ailerons do not cause a turn and the application of power does not cause a climb. There has to be some other control input at the same time, except maybe when we have no power.

The other thing is that the "downwind turn" or whatever you like to call it is still alive and well. When we fly, we are flying in a parcel of air that is probably moving. All our inputs affect the planes location in that parcel of air. One of the big problems which causes the stall spin in base turn is that we are no longer flying in that parcel of air, but are using the stationary ground as a reference. That is stuffing up our interpretation of what the plane is doing.

If you low fly you have to fly the plane in the parcel of air, plus you have to be aware of how that parcel of air is travelling across the ground. Not having that knowledge and being able to use it is what causes the problems.

As far as I can read Yenns is the only reply that addresses omes original question.  The most dangerous part of a circuit is the turn from base to final where the pilot has to contend with a visual illusion..... 

If the wind is of any strength straight down the runway then visually, despite the pilot making an accurate coordinated turn, he would think that the aircraft is skidding and subconsciously apply more rudder.  If you add to the equation the lower airspeed and the reluctance of many pilots to bank steeply near the ground then the result is a perfect set up for an entry into a spin....

I remember, quite clearly, after glider tow #21 in a Cub or Pawnee, tired and probably dehydrated, shouting out to myself 'feet off the rudder pedals'...  better a slipping turn then skid... that is also how I taught hundreds of glider pilots...

[pmccarthy]

I remember being told when established on final to leave the stick alone and fly with throttle and rudder only.

[Thruster88]

54 minutes ago, pmccarthy said:

I remember being told when established on final to leave the stick alone and fly with throttle and rudder only.

I would say that is very poor advice.  

[RFguy]

that would leave no sensible options for maintaining centreline  in a crosswind....

or producing a slip (turn or forward slip) if needed

nor situations requiring recovery from a hot sink where along with power some stick is required  to overcome the sink rate .

 

Sure, in absolutely zero Xwind condix, no thermal activity, and starting from a suitable distance, and having a nice long runway, -  maintaining approach slope  can be done with just throttle  and nothing else, I agree . 

[Garfly]

Maybe the advice given was to avoid steering with ailerons on final rather than leaving the stick alone ... as in:

 

 

[old man emu]

7 minutes ago, RFguy said:

Sure, in absolutely zero Xwind condix, no thermal activity, and starting from a suitable distance, and having a nice long runway, -

When I set up the main factor for a discussion, I like to consider that all other factors, as RFguy says here, are at their optimum.  This does mean that the discussion necessarily is theoretical, but that I am aware of the reality that it is probably only at 'Tiger time' that reality and optimum are the same. Unfortunately, people seem to have the need to go into worse case scenarios before the theoretical basis has been clarified. 

 

On 08/01/2021 at 6:12 PM, Garfly said:

OME, in my humble opinion, you sell your research efforts short if, finally, you settle for 'because they do'

Because the original point was, "Why are students made to learn Lift theory to engineering levels to answer the question 'How is Lift created?'"?"  As can be seen from that thread, the discussion is soon reductio ad absurdum. Therefore, it is sufficient to tell the student, "Because it is", and then let the student experience the effects of low speed, pitched up nose and then the two together. At the ab initio stages of learning to fly, a student is not going to be put into situations conducive to high speed stalls, or stalls at high angles of bank.

 

[old man emu]

19 minutes ago, Garfly said:

Maybe the advice given was to avoid steering with ailerons on final rather than leaving the stick alone ..

The only thing that sticks in my mind about landing from my student pilot days was when I was trying to master X-wind landings. Couldn't do it with my junior instructor, so the CFI took me up in the C-150 (which had a yoke control). as we were coming downwind he said, "You can drive a car, can't you? Well, when we get onto finals, use the rudder to keep us lined up with the runway, and steer with the yoke if we move away." Nailed it first go.

 

Now, was this advice peculiar to tricycle u/c aircraft, or was I being told in different words to side slip?

[RFguy]

On final I use roll to hold centreline ,  rudder coordinated (no slip) - so my nose is pointed out somewhere  else..... , until the flare where then I bring the aircraft aligned with runway with rudder - THAT is the slip  ....and usually accompanies some extra roll input  to get windward wing down.

 

Of course, you could , on final, use roll and rudder and  fly uncoordinated  in a slip to hold yourself  pointing straight- but that is a high drag configuration, which I guess u might want to use if you want to lose a little extra height, or slow things down a bit (with the drag) .....

 

[facthunter]

Tricycle or tailwheel fly much the same till you bring the ground into it. In really rough air you will certainly be very active on the controls on late final. As in many of these  It isn't strictly one or the other and that's not avoiding the question either.  Don't be too unbalanced at speeds without a fair control margin especially if you are pulling any"G" whatever. Don't over control and maintain coordination or you make more work for your self. Nev