Steering on final with rudder

[Oscar]

I reckon the usual stall margins applied to actual weight are about right. If it's bumpy or there are obstacles affecting the wind flow (Mechanical turbulence) a bit extra is normal. You may need to get as slow as possible because of runway length so I suggest a slower lower (has to be) powered approach but why get real slow too early. Flying really slow is not something you do without giving it your total attention. You deliberately sacrifice some safety margins in special circumstances. Nev

Nev, I've had some trouble adapting to power flying. As a glider pilot, I craved the kinetic energy equation - speed or height = safety - and Polo Flat was in unforgiving terrain. Fly the circuit high, turn final high, pull brakes and sideslip, keep the speed up and only let it wash off from about the last ten - twenty feet or so to touchdown, play the brakes. That's energy management that doesn't quite translate to power flying as I have discovered. I don't trust the noisy thing out the front...

 

 

[facthunter]

I have no doubt with a glider spin recovery should be taught before solo and the comparison between the characteristics of the two types should not be taken too far, because a lot of it is to do with the large wingspan as I see it. I just looked at my original log book and it WAS done before solo too. That was 1960 when spin competent trainers were about. My initial trainer was a Chipmunk. Probably an excellent choice in retrospect.

 

A flew a kookaburra? for a bit but it didn't make an impression on me and some years later a Blanik which I reckon I took to OK. I was an engine nut back then. They are ALL aeroplanes IF you have a good look at what you are actually flying before you get in, you can pretty much know how it will fly That's why I would allow myself a few hours on a Pitts till someone else was happy..Nev

 

 

[motzartmerv]

I don't trust the noisy thing out the front...

That's a good idea;)

 

 

[Oscar]

That's a good idea;)

No matter who manufactured it.

 

 

[djpacro]

..... That's why I would allow myself a few hours on a Pitts till someone else was happy..Nev

Few people need the capability of the Pitts to get up to speed on that subject.Anyway, some people won't be happy because the Pitts generally sideslips down final to enable the pilot to see the runway so one has to steer with rudder, no co-ordinated turns on a straight final approach here.

 

 

[Oscar]

I have no doubt with a glider spin recovery should be taught before solo and the comparison between the characteristics of the two types should not be taken too far, because a lot of it is to do with the large wingspan as I see it. I just looked at my original log book and it WAS done before solo too. That was 1960 when spin competent trainers were about. My initial trainer was a Chipmunk. Probably an excellent choice in retrospect.A flew a kookaburra? for a bit but it didn't make an impression on me and some years later a Blanik which I reckon I took to OK. I was an engine nut back then. They are ALL aeroplanes IF you have a good look at what you are actually flying before you get in, you can pretty much know how it will fly That's why I would allow myself a few hours on a Pitts till someone else was happy..Nev

A Shortwing Kooka I flew, it was a barge. Nothing reminded me of it so much as driving a Centurion Tank years later. First single-seater an Arrow, thence a Pilatus B4 and a Boomerang (which was the nicest thing EVER to sideslip in, it would hold about 30 degrees nose off track. Blaniks are really dignified gentlemen of the air, not the best at most anything but impeccably behaved in any circumstance. Lexus behaviour; for a Mercedes 6.3 AMG ride, try a Janus with full water. First solo flight - a Motor-Falke (and that was the barge you have when you are tired of the frisky antics of barges.)

 

 

[pmccarthy]

Aahh the Blanik! An hours drive to the field then half a days wait in the hot sun for my turn at a twenty minute dual. Lots of students and only one glider. Never did solo, went power flying instead. Five minutes from home, time for lesson pre- booked, and the aeroplane would stay up for a full hour. But I do remember that gliding was fun.

 

 

[Oscar]

But after you've done that and solo'd, you get to use single seaters... a 300k around a nominated triangle is lots of fun, even missing out on completing a 500k because you were gazumped by a cold front which you were on top of but had to outrun to get home is good; chasing a few mates around the sky for five or six hours and ending up flying home in formation in the velvet air of last light. Just buggering around and chasing clouds for lift for the hell of it.

 

Sitting in a thermal and watching a wedgetail eagle riding the lift off the top of your wing like a porpoise surfing your bow wave slide in to a couple of metres of the cockpit, give you a beady, unblinking black eye, and then lazily peel away because he/she knows a better thermal.

 

Staying up for free instead of using 14 litres/hour.

 

 

[Bob Llewellyn]

Continuity applies along streamlines not across the boundary layer. I suggest that you revisit the definition of boundary layer displacement thickness.

The boundary layer is the region in which the continuity, as expressed by Bernoulli's total energy equation, no longer holds due to viscous transfer into the skin. Look up a textbook yourself, buddy. Now, if an icthyoid body of fineness ratio 5 did not have a boundary layer, the pressure recovery - suction back to the point of maximum cross-section, increasing pressure thereafter - would give no net drag. At the outer edge of the boundary layer - by definition - the local static pressure is changed by total energy effects, and the local static pressure is not the free atmospheric true value.

At the inner edge of the boundary layer - the laminar sub-layer, look it up - the local static is indeed very close to the true static. At the outer edge, it is totally at the mercy of the free stream velocity depressing the local static to compensate for the dynamic pressure, which is an expression of conservation of energy, or more accurately - wait for it - CONSERVATION OF MOMENTUM!

 

look it all up.

 

Hoerner, "Fluid Dynamic Lift"; "Fluid Dynamic Drag: Theodore Theodsen, "Thin Airfoil Theory"; Lanchester, "Aerodynamics"; any university course on Thermofluids

 

 

[motzartmerv]

Perhaps you guys should start a separate thread? Its very informative but getting off track a bit..

 

 

[djpacro]

The boundary layer is the region in which the continuity, as expressed by Bernoulli's total energy equation, no longer holds due to viscous transfer into the skin. Look up a textbook yourself, buddy.

Nope, I am definitely not your buddy! And, continuity is the equation for conservation of mass.I am sure that others appreciate your list of very fine references.

 

 

[Bob Llewellyn]

Nope, I am definitely not your buddy! And, continuity is the equation for conservation of mass.I am sure that others appreciate your list of very fine references.

Continuity is the property of continuum mechanics, as used by Newton in the theorem that the transverse viscosity is proportional to the strain rate. Conservation of mass per se is not a principle of physics; conservation of momentum, and conservation of energy, are. An implication of continuum mechanics is the constant mass flow of an incompressible fluid through a tube of varying cross-section; but I assumed we were talking about air, a compressible fluid, in a free state - the atmosphere - rather than within a garden hose. Clearly we are talking at cross-purposes.

 

 

[djpacro]

.... any university course on Thermofluids

such as http://soliton.ae.gatech.edu/classes/ae3051/AE3051Labpres_flowvis.pdf has statements such as

Using boundary layer theory* one may show that the static pressure is constant through the boundary layer in a direction normal to the surface

and I will stick with the classic definition of continuity used in aerodynamics.Now I shall get back to the thread topic ...................

 

 

[Bob Llewellyn]

such as http://soliton.ae.gatech.edu/classes/ae3051/AE3051Labpres_flowvis.pdf has statements such asand I will stick with the classic definition of continuity used in aerodynamics.

Now I shall get back to the thread topic ...................

"...and that the boundary layer is a region of rotational flow so that the stagnation pressure is not constant everywhere..." from the same page. So you use selective quotes instead of understanding the subject? Which boundary Layer Theory, by the way? You said "Static pressure outside the boundary layer is the same, typically, as on the surface." Now you are saying that static pressure inside the boundary layer is constant, by selective editing. Which definition are you sticking by? They can't both be right...

Please don't feel that you need to reply; your insistence that your criticisms MUST be correct, even if you have to contradict yourself to prove them, demonstrates that this debate is, essentially, futile.

 

 

[djpacro]

"...and that the boundary layer is a region of rotational flow so that the stagnation pressure is not constant everywhere..." from the same page. So you use selective quotes instead of understanding the subject? Which boundary Layer Theory, by the way? You said "Static pressure outside the boundary layer is the same, typically, as on the surface." Now you are saying that static pressure inside the boundary layer is constant, by selective editing. Which definition are you sticking by?..

No inconsistencies there at all. My prior post quoting the Uni on constant static pressure profile within the boundary layer is consistent with my comment that static pressure at the surface is the same as at the edge of the boundary layer. Stagnation pressure has nought to do with this point.

[Keenaviator]

When I was a youg lad at school the toilets were outside and had no roof; I could actually p1ss over the wall. Those were the days!

 

 

[Bob Llewellyn]

When I was a youg lad at school the toilets were outside and had no roof; I could actually p1ss over the wall. Those were the days!

We had a roof. When I venture a technical opinion, I expect to either be able to substantiate it, or willing to withdraw it. So far Mr Acro has given three cases of "you're wrong because I disagree with you", without substantiation. It is his right to disagree with me; but if it's only an opinion (it keeps changeing, except for my wrongness?), why doesn't he have the grace to say so? If it's sustainable, why does he reject all of my references, and supply a selective generalised quote?

I have no objection to him having an unsustainable opinion which differs from my understanding of the facts, such as they are; I do object to him claiming a superiority of opinion based upon nothing.

 

I can piss right over the toilet these days...

 

 

[farri]

......And now folks! Try to remember! " It`s not who`s right, it`s who`s left!"

 

Frank.

 

 

[rgmwa]

......And now folks! Try to remember! " It`s not who`s right, it`s who`s left!"Frank.

Now I'm confused. Is that "who's left the field" or "who's left standing"?

 

rgmwa

 

 

[farri]

Which ever you prefer rgmwa. In either case you still need to be around.......

 

Frank.

 

 

[djpacro]

We had a roof. When I venture a technical opinion, I expect to either be able to substantiate it, or willing to withdraw it. So far Mr Acro has given three cases of "you're wrong because I disagree with you", without substantiation.

Which are the three - from the six below, I guess? Likewise, I can substantiate and happy to withdraw any of the three if wrong.1. "Another option is pitot-static boom as used on the Pitts - very small pressure error (location of static behind the collar is critical)".

2. "Static and dynamic change but not total."

 

3. "Full chord ahead or whatever is good for a prototype but not required for production examples."

 

4. "Trouble with the side if the fuselage is that it usually is in the prop slipstream so static pressure error increases with high power and low airspeed."

 

5. "Static vents are often on forward fuse or mid fuse not near the tail."

 

6. "Static pressure outside the boundary layer is the same, typically, as on the surface."

 

Which three do you seek substantiation for?

 

.. but if it's only an opinion (it keeps changeing, except for my wrongness?), why doesn't he have the grace to say so? ..

No change anywhere in my statements.

 

.... why does he reject all of my references ...

I did not reject your references. It would help if you were quite specific as to which page of which reference substantiates any of your views which differ from mine.

 

.... supply a selective generalised quote? ...

because it was one which specifically addressed my point. It was a generalised quote because the Uni decided they could make such a generalised quote - take it up with them if you disagree. I provided one Uni report which supported my view, there are others including reports with test data.

 

I do object to him claiming a superiority of opinion based upon nothing. ...

Now, where did I make such a claim?

 

When I venture a technical opinion, I expect to either be able to substantiate it, or willing to withdraw it. ...I do object to him ..

You have not provided substantiation of your opinions (just an observation) yet you are insulting of mine. I look forward to the hearing of your objection by the mods.

[motzartmerv]

........

[motzartmerv]

the Pitts generally sideslips down final to enable the pilot to see the runway so one has to steer with rudder, no co-ordinated turns on a straight final approach here.

Not to be picky dave, but are you saying that the pilot in a sidelsip only uses rudder to steer? Or do they still use rudder and aileron together, all beit in a crossed fashion. If you tell me that a pitts pilot locks aileron solid and uses his feet to steer down final ALONE...I will come to Melbourne and eat the aeroplane..!!..

 

 

[Dafydd Llewellyn]

Just curious oscar, why would you need to use rudder to stay level when being tugged too fast.?

Whilst I hesitate to add more fuel to this fire, the above question begs an answer, which may help clarify things:

A test-pilot's approach to stall behaviour requires that one brings the aircraft to the stall, and then sit there and observe what happens - but catch it before it goes into a spin. In the pre-certification flight testing of the CA21 skyfox, the original Jabiru, and the Seabird Seeker, I spent a lot of time investigating stalling the aircraft at its extreme CG positions, in every configuration, straight and in turns, at all power levels. They all showed the same basic characteristic, i.e. they became very vague in their aileron response, and would undergo a mild wing drop, which would recover itself and maybe go the other way. In the case of the CA 21, that would repeat, getting a bit more severe each time, until after two or three cycles the airoplane would spear off into an incipient spin. In the case of the Jabiru, the wing-rock would continue more or less indefinitely, and the Seeker would damp out after one or two cycles - mostly. Whilst in this phase, one could (sometimes) pick-up a small wing drop with rudder whilst holding the stick back, but the ailerons were ineffective at best - but essentially they all went out of control laterally, before there was any G-break (nose drop) - which meant they were fundamentally non-compliant. Finding a fix for this meant I got more practice in stall recovery and post-stall behaviour than I really needed.

 

All three of them used a rectangular wing planform - which is known to be a feature that promotes initial stalling in the centre of the wing; two of them has washout; and all three used a wing airfoil that stalled by progressive separation from its trailing edge - i.e. a so-called "docile stall" airfoil; this could be seen by the behaviour of a wool tuft at the wing trailing edge - at 5 kts above the stall, it was laying on the top of the wing, pointing forward. They were also all high-wing aircraft.

 

What the textbooks on wing design do NOT point out, is that an aft-stalling airfoil gets reverse-flow on the top surface as it approaches the stall; and this extends further and further as you slow down. It eventually reaches the aileron hinge line, and by that time, the ailerons are definitely NOT working the way they are supposed to.

 

Now, I have only theoretical reasoning based on these observations to go on, but what I think happens is that these aircraft all develop a patch of separated flow on the top of the wing, starting at the trailing edge close to the fuselage, just as the textbooks say they should. However it may start on either wing first; and if it does, that wing will drop a bit. That causes sideslip which "blows" the separated patch across to the opposite wing, so the wing-drop reverses - etceters ad nauseum. This is the mechanism of the "falling leaf" manoeuvre, and the original Markey Ultrabat (VH-ANT) exhibited exactly that when I test-flew it, so the behaviour is not confined to high-wing aircraft.

 

It followed that wing modification that managed to contain the separation bubble, should correct this behaviour - and indeed they did, on the Seeker.

 

However, if you have an aircraft that behaves this way, it is quite possible to "correct" a mild wing-drop with rudder - though in many cases the aircraft will do that itself, but rather more slowly and somewhat erratically. Most aircraft are elevator-limited at the stall, at least at forward CG, and will only get to the beginnings of wing stall - so if you happen to be flying one of these, and the CG happens to be in the right place, you can sit there with the stick hard back and pedal it all day; but don't project that behaviour to all aircraft, or the same aircraft at full aft CG, or you may get a really big surprise.

 

Once I had modified the Seeker to contain the stall bubble, it stopped exhibiting the rock & roll behaviour - but it then became obvious that the aileron response was reversed from about 5 kts above the stall down. So it then got VGs across the full span - and in that configuration, the stall speed went down about eight knots - and the stall was then so violent it put the aircraft on its back & took 600 feet to recover despite my being ready for it. It took several further iterations to get it where it is to-day - i.e. almost impossible to stall or induce a wing drop. That's another story, and proprietory information; but I do speak from practical experience. I think few of the contributors to this thread would have gone to the trouble of weighing their aircraft with the pilot aboard before & after the flight, to make sure the test was done at precisely the aft CG limit - and therefore they have experienced only a limited sample of what their aircraft can actually do. It is dangerous to draw conclusions on such limited experience.

 

 

[motzartmerv]

Thanks dafydd. Thats great information. Having tested several homebuilts I do have an Idea of what your saying. However my original question was about steering with the rudder 'only' when too fast, which Oscar later corrected and said he was too slow.

 

We have done lots of 'ribbon testing' on our aircraft to observe the airflow approaching and during the stall. Almost all have indicated this reverse flow you speak of and is a curious factor that i like to demonstrate, particularly with aifoils that promote :"grabbing" of the aileron at the point of stall. Aircraft like the foxbat, which has a very strong Aileron grab tendency (my term) which bangs the stick hard over at the break. Also the piper sports, which has a very rear cof g at the best of times (33% MAC i think) is another aircraft that tended to misbehave in this fashion. Approaching the stall when the separation point would move forward past the aileron there was a strong pull on the ailerons. The interesting thing is it didn't always pull the same way..Its a feature of that particular aeroplane that I dont like, when you increase the AofA the aileron feedback changes significantly, and you even feel forced feedback (again, not a technical term, my description) which feels like someone else on the controls pulling the aileron into the turn direction..Not nice, I dont like having a ghost on the controls with me..

 

Ps. Please note, im only a pilot not an engineer so i can only relate what i feel to my limited knowledge of the mechanics.

 

Cheers