Turns at low IAS

[spacesailor]

They ( boffins ) designed lots ( books of them ).

You can design your own, not too hard, just have to know exactly what the final wing will be used for.

The new designs are all a composite,s of bits to do things a single wing can,t, flaps , extensions both leading & trailing.

Sailplanes have the most efficient airfoil, not much good on the high-lift slow, low powered planes, in 95-10 caturgury. 

BUT

Why try to make a new WHEEL .

spacesailor

 

[Tigershark21]

Generally I believe Low ALT and low IAS, turning cross to downwind. A drop in airspeed and increase in ground speed whilst also factoring in a further decrease in lift because of angle of bank and shift in the total reaction of the wing thereby increasing the stall speed at the same time airspeed is dropping. A double edged sword!

 

Aggravating issues of sink rate and stall onto the downwind leg if inducing more drag by a higher degree of maneuvering on a high performance, less forgiving wing at low speed. Especially a downwind turn of higher AOB. Complicating with a climbing downwind turn 🤪

Enhancing factors of sink rate and stall to be aware of in unfamiliar locations: Density altitude at location, weather/wind shear (speed and direction), temp. But also be aware of wing loading, wing/aerofoil design purpose limitations.

 

Wing design is a tade-off to compliment a particular flight envelope it must excel at. The trade-off is that it may be good at a certain job (training or flying fast, or high altitudes etc etc), but worse at another envelope of its flight. Some people refer to these as 'vices' and they'll say "it will bite you" but actually, these are pilots flying the wing outside its designed parameters and must get familiar with the operator's manual because they are flying a different type of wing than what they are used to which may once again excel at a different envelope of flight. Stability issues and tight parameters can catch people out. Not all wings fly equally. Some aerodynamic devices may be employed to alleviate undesirable effects somewhat and minimise the negative 'trade-offs' but good operating procedure is paramount.

 

The aircraft's design performance specifications is the first step in wing design by knowing these initial requirements. These will determine at a basic level:

 

Aerodynamic characteristics of given aerofoils for certain jobs (wing air displacement)

Wing's stall pattern

Geometric characteristics of an aerofoil and the effects of these geometric parameters

Reynolds number and the roughness on aerodynamic characteristics of aerofoils

The Aerofoil camber

Aerofoil thickness ratio

Aspect ratio

Wing sweep

Wing taper ratio

Twist / or washout

Angle of Incidence

Dihedral type if any

Wing location

Flaps & Aileron design, area and position.

Other requirements such as lift or spoil devices

Wing tip/root design

 

 

 

Edited January 8, 2021 by Tigershark21

[old man emu]

I'm puzzled. Let's say that we are flying a plane with a cruise speed of 80 kts and a stall speed of 30 kts IN NO WIND. Just after the turn from crosswind to downwind, the plane gets to 80 kts at cruise power for the downwind trip. At the end of downwind you make a co-ordinated descending 90 degree turn and reduce power, but maintain pitch with the elevators until you are 500' AGL. Then make another 90 degree descending turn onto Final, while maintaining the elevators in a constant position to achieve a flight line to the aiming point. If the aircraft drops below the desired flight line, then add power to stop the descent until the aircraft flies into the desired flight line. Pull power if above the flight line. At all times the position of the elevators remains constant. At the aiming point, the power comes right back and the Flare is initiated.

 

If my technique is correct, and I'm open to correction, how can this description of the way a student has been taught to land a PA-28 be correct?

 

Holding steady at 70kts down final on an even profile with the plane trimmed sets us up in the correct configuration without having to fiddle with power changes too much. But reaching the point where we need to start slowing down to get back to 66kts over the threshold is where it gets busy as I pull back on the power and simultaneously increase back pressure to maintain a straight approach path.

 

Am I wrong in thinking that one sets the pitch angle to a desired flight line with the elevators and maintains the flight line with thrust?

[Jabiru7252]

One feels very satisfied when one trims the plane on final and it just follows the 'glide slope' without any changes to pitch or power. However, minor changes to both even in calm conditions is normal and larger changes to both in windy and/or rough conditions is expected. I have (somewhere on my computer) some video where I'm hands off until about 50 feet AGL in one of those really smooth times just before sunset. Better than ice cream. You're doing what I did when I flew PA28s.

[facthunter]

OME If you are maintaining a glide path at 70knts (stabilised) and you reduce power to slow a bit you have less lift at the slower speed and will drop below the path if you don't keep the lift the same (equal to the weight) by increasing the  angle of attack as you do throughout the flare. At the beginning of the flare you need a bit more lift to arrest the sink rate. Some times ground effect will achieve that for you, but don't count on it if it's your first try on that particular plane. Nev

[old man emu]

1 hour ago, facthunter said:

If you are maintaining a glide path at 70knts (stabilised) and you reduce power to slow a bit you have less lift at the slower speed and will drop below the path

I fully agree with that statement as it stands. However, if the glide path has been established at a determined speed and with a certain engine RPM, if, due to some mistake in setting up the glide path, or an unexpected upsetting force (gust, shear) and the aircraft goes either above or below the desired glide path, then the glide path can be regained closer by the manipulation of THRUST.

 

Look at this side-on circuit depiction. The final leg,, or glide path to runway, can be described as the hypotenuse of a right triangle.

 

http://1.bp.blogspot.com/-_FDfiTi7M_8/VBcwypahL-I/AAAAAAAAAEY/e4AfvWBh3kk/s1600/basic_circuit_profile.gif

 

Here's a depiction of a plane flying that glidepath to the runway.

The green dots represent the aircraft at points along the desired glidepath, with attitude and power set. The orange dot represents the aircraft a little closer to the runway, but it has gone below the desired glidepath for some reason. To stop making matters worse, the pilot increases THRUST which stops the descent until the actual flight path intersects the desired glidepath at the lower green dot. Then the extra THRUST is removed and flight on the desired glide path continues. 

 

The Blue dot represents the aircraft that has risen above the desired glidepath for some reason. The aircraft can be returned to the desired glidepath by increasing the rate of descent by reducing THRUST until the actual flight path intersects the glidepath at the lower green got. Then the THRUST is returned to the level it was at the first green dot.

 

In other words, instead of pushing and pulling on the elevator controls, they are left untouched, but the throttle is the control that is pushed and pulled, until it comes time to flare, when it's pull back on both.

 

Yes. I know I am describing the "normal" landing approach where THRUST is available. I fully agree that a deadstick landing would be conducted using the elevators.

 

[Student Pilot]

This stuff hurts my head.......................I don't understand the theory, does that make me a bad pilot? I know if you get too slow you get in trouble, I know how to turn low and slow is that enough? 

Protons and neutrons have approximately the same mass, about 1.67 × 10-24 grams, which scientists define as one atomic mass unit (amu) or one Dalton, Positively charged subatomic particle forming part of the nucleus of an atom and determining the atomic number of an element. It weighs 1 amu.

Discuss....................

[Tigershark21]

5 hours ago, old man emu said:

I'm puzzled. Let's say that we are flying a plane with a cruise speed of 80 kts and a stall speed of 30 kts IN NO WIND. Just after the turn from crosswind to downwind, the plane gets to 80 kts at cruise power for the downwind trip. At the end of downwind you make a co-ordinated descending 90 degree turn and reduce power, but maintain pitch with the elevators until you are 500' AGL. Then make another 90 degree descending turn onto Final, while maintaining the elevators in a constant position to achieve a flight line to the aiming point. If the aircraft drops below the desired flight line, then add power to stop the descent until the aircraft flies into the desired flight line. Pull power if above the flight line. At all times the position of the elevators remains constant. At the aiming point, the power comes right back and the Flare is initiated.

 

If my technique is correct, and I'm open to correction, how can this description of the way a student has been taught to land a PA-28 be correct?

 

Holding steady at 70kts down final on an even profile with the plane trimmed sets us up in the correct configuration without having to fiddle with power changes too much. But reaching the point where we need to start slowing down to get back to 66kts over the threshold is where it gets busy as I pull back on the power and simultaneously increase back pressure to maintain a straight approach path.

 

Am I wrong in thinking that one sets the pitch angle to a desired flight line with the elevators and maintains the flight line with thrust?

You're correct Emu,

Here, thrust is your true elevator, and your elevator (and trim) is your speed control which is maintained by varying the wing's angle of attack at a given thrust in order to hold a given attitude at a given speed in either a climb, level flight or a descent unless the critical angle is reached.  

[facthunter]

There were 2 different situations there so why discuss both at the same time?  Of course if you fall below the glide path you need extra power to regain it UNLESS you are also too FAST where you can use that energy instead.. I can't see why all this has to be so difficult.  Gaining height  requires energy be added (all other things being equal)   You can't obtain potential energy( Height,) without contributing another form of energy to the situation. In this case power from the engine, but power changes can produce different pitching forces as does a change of airspeed so that has to be managed as well.  IF the power applied just increased the  airspeed you don't necessarily regain the glide path just by opening the throttle.. You would just be going faster That's the "all other things being equal" bit. Nev

Edited January 9, 2021 by facthunter

[old man emu]

1 hour ago, Student Pilot said:

.I don't understand the theory, does that make me a bad pilot?

I wonder why no one has shot back at me, "Those who can, do. Those who can't, teach."

 

33 minutes ago, facthunter said:

IF the power applied just increased the  airspeed you don't necessarily regain the glide path just by opening the throttle.

In this case, the aircraft was happily coming down the glidepath at the desired speed, not too fast, not too slow, just right. You know, Newton's First. Then something happened to knock it off the desired path. Newton's Third. What I'm saying that you don't shove the throttle knob to the wall and get the aircraft speeding up. You give it a nudge to halt the descent until, by flying parallel to the original track over the ground, you intersect the desired glidepath and re-establish the desired airspeed by un-nudging the throttle.

 

A side issue that has struck me in this discussion is that there does not seem to be a method taught by all instructors for carrying out flight down the glidepath that is consistent with all. From responses here, some have been taught to control descent with elevators and some have been taught to use the throttle. Is it any wonder that discussions reach no end?

[Jabiru7252]

As a LSA pilot (and private pilot for that matter), knowing the theory of flight to the tenth degree is not going to make you better or safer, just like knowing the weight of electrons, protons and neutrons never made me a better electronics technician. Study what you need, get a basic understanding, pass the exams and you'll be good. Anyway, you're not going to give a toss about the physics of flight when the ground comes rushing up at you because you've pulled the wings off your plane doing something stupid.

[Garfly]

I think, this much, everyone is in passionate, furious agreement with; even OME (at times 😉

[facthunter]

 You are flying along maintaining a certain level. What do you control airspeed with? Power of course. You are descending on a fixed glidepath. The same applies. So in those instances speed is NOT controlled with elevators. IF you are gliding, Power is not in the equation so you control it with rate of descent. If you are in a steep turn with full power on and the speed is too low all you have left is to commence a descent at a high enough rate to get the Airspeed you NEED ie use pitch change causing a higher RoD to increase airspeed. OR reduce the bank angle and reduce drag. and lower your safety speed required too.  This is all about flying your plane properly and not thinking "is speed controlled with elevators or Power? Well,  it really DEPENDS on the particular situation you are in Doesn't it  so you use what you have to WHEN you need it. So it's a silly question, in my view. I've mentioned many times the concept of considering energy in all this. It's not something new, but I must be writing in invisible ink sometimes. .NEVER been one question about it. You are climbing out in your lead slug Mk1 and it's a warm day and you notice the airspeed is a bit low. You check you have full throttle and maybe that both switches are on Carb heat off. flaps UP and its still slow and you've stopped climbing. Then you have only one thing, lower the nose carefully till you have a safe speed THEN see what you can do next if climbing is out of the question.. Nev

[Jase T]

Nev dont make me hit you over the head with my Trevor Thom BAK manual from 1985... P+A will ALWAYS = P

 

Power - not throttle position but the power your engine is capable of producing at that instant in time all things considered (including DA, age, set up etc etc etc) 

plus

Attitude - the one you have set or just adjusted to

 

Equals

Performance - a combination of IAS and rate of climb / decent. You may need a specific one to avoid a stall or to climb out before an obstacle or to meet a touchdown point. 

 

If you are not getting the performance you want you need to change one or both to get it... If you have no more P you need to use A to give you the best you can get. 

 

If you want S&L and a different IAS you need a completely different P and a completely different A you cant just increase power.... as an ab initio  pilot you learned "Change, Check, Hold, Adjust, Trim" or something similar when changing something but as your experience improved you "sort of do them all at the same time" but the P+A=P rule still applies.  It applies in a climb, in a descent, in a turn, in a steep turn and on approach....

 

[Student Pilot]

PP

[bull]

3 hours ago, old man emu said:

I wonder why no one has shot back at me, "Those who can, do. Those who can't, teach."

 

In this case, the aircraft was happily coming down the glidepath at the desired speed, not too fast, not too slow, just right. You know, Newton's First. Then something happened to knock it off the desired path. Newton's Third. What I'm saying that you don't shove the throttle knob to the wall and get the aircraft speeding up. You give it a nudge to halt the descent until, by flying parallel to the original track over the ground, you intersect the desired glidepath and re-establish the desired airspeed by un-nudging the throttle.

 

A side issue that has struck me in this discussion is that there does not seem to be a method taught by all instructors for carrying out flight down the glidepath that is consistent with all. From responses here, some have been taught to control descent with elevators and some have been taught to use the throttle. Is it any wonder that discussions reach no end?

I,m an old AUFmember and was taught by an instructer in one  of the first produced 2 seat thruster gemini,,,,,,And the procedure we where taught was ALL landings and circuits are set up on late downwind as if the fan had stopped,,,,,,ie:All landings where set up for deadstick /failed engine,,,,,So when it happened you would always have speed and height to land the plane ...........................

[bull]

As an aside from that as well ,we where taught to EXPECT the fan to stop at at any time and to always Look outside and down ,Oh there,s a an oval to the left ,a road to the right .  Like sizing up landing sites that don't involve any injury hopefullyall the time ,not hiding inside watching a screen on the dash................cause of the regular and expected erratic running and failure for a variety of reasons of two stroke engines in the 1986,to 87 region lol

Edited January 9, 2021 by bull

[facthunter]

Jase I don't believe you've read what I  said carefully. Don't accuse me of saying what I didn't . I also didn't come down in yesterdays shower and know most of the people that wrote those manuals. Some were close friends. Today Precision approaches are flown on autopilot .Prior to that we HAD to fly them by hand on every check so if I didn't know the essentials of this, how come I didn't fail a check or crash?. Nev

[old man emu]

16 hours ago, bull said:

we where taught to EXPECT the fan to stop at at any time

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.

 

A NASA study done in the late 1970s proved that the average altitude loss in spins done with a Grumman American AA-1 (Yankee) and a Piper PA-28R (Arrow), two popular single-engine aircraft, was nearly 1,200 feet. (It should be noted that neither aircraft is approved for spins, but NASA was testing them for possible improvements in spin handling characteristics.) I know that these are heavier aircraft than RAAus types, but also factor-in that the pilots were test pilots who expected the stall/spin and who knew how to recover from it.

 

In the Yankee, it took an average of 210 feet for entry, 340 feet for stopping the turn, and another 550 feet for recovery, for a total of 1100 feet. In the Arrow, the figures were 140 feet for entry, 400 feet for stopping the rotation, and 620 for recovery, for a total of 1160 feet. In short, the average vertical recovery distance was just short of 1200 feet. Pilots allowing a spin to develop at or below traffic pattern altitude are nearly certain to crash, no matter how quick their reflexes or skillful their recovery.

 

Getting back to controlling the glidepath, no one has mentioned making small changes to attitude by the use of the elevator trim control. Surely that control can be used for more delicate alterations to trim than pushing and pulling the control column and getting coarse adjustments.

 

.

[facthunter]

Trim is supposed to be used to relieve control pressure. Not my idea . It's a universal rule  You place the control where you want it and the last  thing you do when stabilised is relieve the pressure (IF you want to)  In turns as an example. You don't usual trim to a turn and some don't fully trim the back pressure prior to the flare.  IF your primary pitch control fails some trim systems are a separate means of pitch control, but usually it's done with some difficulty and you would need to be practiced to carry if off successfully. Nev

[old man emu]

8 minutes ago, facthunter said:

Trim is supposed to be used to relieve control pressure. Not my idea . It's a universal rule

My legs are a bit sore for me to stand, so this time, do you mind if I just "sit corrected".

[facthunter]

SOME procedures are basic even over time. It's NOT emphasised enough. Some autopilots can be holding  largish out of trim forces and should be checked occasionally or  it may disconnect  and suddenly you are hurtling up or down with passengers in the air... Some people get in a lot of strife with trim particularly aileron and rudder trim which is rarely fitted to U/L's. Remember the order.. Reach your level,   lower nose  to achieve speed at that level , reduce power and trim out stick forces while holding a fixed attitude during the process. .The last takes a bit of doing as it has to be right on and the pitch changes are subtle  Some aircraft have large trim changes with airspeed change. Others like flying boats or underslung Jets  react to Power changes. Nev

  

[Yenn]

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.

[facthunter]

And LOW flying can't be taught for the majority of RAAus pilots. I've always thought that is WRONG.. Landing, taking off and going around is LOW flying and subject to well know illusions. OUR stall training is minimal and not related to REAL situations, either.  Nev

[Jase T]

4 hours ago, facthunter said:

Jase I don't believe you've read what I  said carefully. Don't accuse me of saying what I didn't . I also didn't come down in yesterdays shower and know most of the people that wrote those manuals. Some were close friends. Today Precision approaches are flown on autopilot .Prior to that we HAD to fly them by hand on every check so if I didn't know the essentials of this, how come I didn't fail a check or crash?. Nev

Nev

 

I sincerely apologise if you felt any offence it was never my intent. My reply was simply to the "change power to change speed" concept. I did not mean to say you were in error or to belittle your knowledge or experience. Interesting that you knew these guys, I purchased my original BAK book from Mr Thom himself some time in the 80's still have his Nav, Wx and Instrument books on the shelf and use them as as a reference. I like the way he simplifies things when i cant find the words to explain a concept. . I am sure we must have moved in the same circles at some stage and must have crossed paths. Only Nev I knew was a very experienced ex airline (piston engine airline) instructor. Did my initial instrument flying with him in 1989. I think he went on to import the very first Glassair in the country. 

 

Anyway I do sincerely apologise and will refrain from replying to comments that may offend in the future.