RPM or IAS?
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RPM or IAS?
PLEASE...don't construe this (as ppruners normally do) as an attack in the "our way - your way" genre.
I am going to ask for your individual preference - with an explanation.
I recently became involved in a conversation between numerous flying instructors...some CAA, some FAA.
A difference had been spotted in the teaching of "straight and level".
Many of the FAA guys said "set a particular RPM - as written in the flight manual. This will give a particular %age power and a predetermined fuel burn, performance, time/distance calculation etc - but the IAS will vary from trip to trip."
Many of the CAA guys said "decide on a required indicated air speed and set sufficient power to achieve it - this will give an accurate IAS, which can be corrected for temperature and altitude to give an accurate TAS, which can then be entered onto the whizz wheel to get an accurate ground speed to get an accurate leg time for the trip"
Both of these seemed to make sense....but you can't do both at the same time.
Anybody prepared to say which is better....and why?
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Support the right to arm Bears!!
I am going to ask for your individual preference - with an explanation.
I recently became involved in a conversation between numerous flying instructors...some CAA, some FAA.
A difference had been spotted in the teaching of "straight and level".
Many of the FAA guys said "set a particular RPM - as written in the flight manual. This will give a particular %age power and a predetermined fuel burn, performance, time/distance calculation etc - but the IAS will vary from trip to trip."
Many of the CAA guys said "decide on a required indicated air speed and set sufficient power to achieve it - this will give an accurate IAS, which can be corrected for temperature and altitude to give an accurate TAS, which can then be entered onto the whizz wheel to get an accurate ground speed to get an accurate leg time for the trip"
Both of these seemed to make sense....but you can't do both at the same time.
Anybody prepared to say which is better....and why?
------------------
Hunting is bad!!
Support the right to arm Bears!!
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RPM. If you try and get a student to fly at a particular airspeed in the early stages they will fixate on the gauges and piss about for ages trying to adjust the RPM precisely. Additionally if you go through rising or falling air your airspeed will fluctuate and there's little point in trying to keep it at the same value while that's going on. Basically in a C152 I get them to set 22-2300 and assume 90 kts, job done. Mind you in a Katana you can set an RPM and get a whole range of airspeeds. Funny little buggers, them.
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When teaching some one to "fly" in the aircraft initaly just set an RPM that will give a known airspeed as height and heading holding are the important things to master.
When it comes to the navigation the whole range of power settings should be explored to get the best setting for that nav ex and the 20% extra fuel burn if the mixture is not leaned should be stressed.
When it comes to the navigation the whole range of power settings should be explored to get the best setting for that nav ex and the 20% extra fuel burn if the mixture is not leaned should be stressed.
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Surely this is why the normal teaching is S&L 1 AND 2, S&L 1 teaching the basic at a set RPM, then S&L 2 to practice flying at set speeds, once this lesson is covered the emphasis should be on a particular speed rather than a set RPM asthis is required for accurate Nav.
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Bear Cub
Your question is very curious. You refer to teaching Straight and Level yet the essence of the question is about cruise technique which is not part of teaching Straight and Level.
The aim of the Exercise is to teach the student to fly at a constant altitude in a constant direction. Initially, this is achieved by setting a constant RPM to limit the number of variables.
In part 2 of the exercise, the student learns to fly Straight and Level with different power settings (Changing RPM and IAS) and various flap settings. In other words, to practice the techniques learned in Part 1 with more variables.
Quite where fuel flow %power, IAS, and Wizz Wheels come into this exercise I cannot imagine. The average FAA instructor does seem to have a desire to sit in the right hand seat and deliver lectures whilst the poor student is trying to fly the aeroplane. Not a good technique; neither is teaching cruise technique at that stage of training.
Your question is very curious. You refer to teaching Straight and Level yet the essence of the question is about cruise technique which is not part of teaching Straight and Level.
The aim of the Exercise is to teach the student to fly at a constant altitude in a constant direction. Initially, this is achieved by setting a constant RPM to limit the number of variables.
In part 2 of the exercise, the student learns to fly Straight and Level with different power settings (Changing RPM and IAS) and various flap settings. In other words, to practice the techniques learned in Part 1 with more variables.
Quite where fuel flow %power, IAS, and Wizz Wheels come into this exercise I cannot imagine. The average FAA instructor does seem to have a desire to sit in the right hand seat and deliver lectures whilst the poor student is trying to fly the aeroplane. Not a good technique; neither is teaching cruise technique at that stage of training.
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Noggin...not being a wordsmith, I find I cannot write a simplified message that covers every individual eventuality of how readers will construe what I've written.
If someone tries to cover every potential variation then it is classed as "legalese" and is often very difficult to understand.
I was under the impresssion that a well flown navigation trip would involve a good percentage of straight and level - where the aircraft is at a constant altitude, on a constant heading, flying at a constant airspeed and in balance....and some would also add "with the mixture leaned".
As the all American "Law of Primacy" (what the student first sees, is what he tends to do for the rest of his flying career) is so relevant, I do not think it particularly unreasonable to point out to said student that the reason he is being shown "straight and level" is that he will need to do it - a lot - once he has the licence and is buggering off on his own.
I have seen many many pre-flight briefs (for exercise 4 pt 1 and 2) that include the comment "check mixture rich before applying full power for a climb" but very very few that say "stabilise aircraft then lean mixture correctly at top of climb"...so not many do it.
If an instructor explains the reason for doing something rather than just how to do it.....
If someone tries to cover every potential variation then it is classed as "legalese" and is often very difficult to understand.
I was under the impresssion that a well flown navigation trip would involve a good percentage of straight and level - where the aircraft is at a constant altitude, on a constant heading, flying at a constant airspeed and in balance....and some would also add "with the mixture leaned".
As the all American "Law of Primacy" (what the student first sees, is what he tends to do for the rest of his flying career) is so relevant, I do not think it particularly unreasonable to point out to said student that the reason he is being shown "straight and level" is that he will need to do it - a lot - once he has the licence and is buggering off on his own.
I have seen many many pre-flight briefs (for exercise 4 pt 1 and 2) that include the comment "check mixture rich before applying full power for a climb" but very very few that say "stabilise aircraft then lean mixture correctly at top of climb"...so not many do it.
If an instructor explains the reason for doing something rather than just how to do it.....
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When teaching Straight & level:
POWER + ATTITUDE = Performance.
When teaching navigation, having initially set the performance equation above, the student can then do the numbers to work out the IAS required to achieve the planned TAS and adjust power accordingly. At least that is one way to do it. (And, yes they must also learn about correct mixture setting).
POWER + ATTITUDE = Performance.
When teaching navigation, having initially set the performance equation above, the student can then do the numbers to work out the IAS required to achieve the planned TAS and adjust power accordingly. At least that is one way to do it. (And, yes they must also learn about correct mixture setting).
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As you say, what the student first sees tends to stick, is quite true, this is why it is quite important to teach the basics of straight and level before introducing cruise technique, which should be left until the navigation phase Ex 18.
Most light trainers with a fixed pitch prop do not leave much room for manoeuvre. The manufacturers recommended cruise speed is based upon the best speed/drag ratio, which can be determined by drawing a tangent to the total drag curve from the origin. Using this graph, you can also teach the student that there are different speeds for range and endurance. Hopefully, the prop pitch will have been optimised for maximum efficiency at or close to that speed. Therefore, by setting the recommended rpm you achieve the stated IAS.
With regard to leaning, most training aircraft do not have a CHT guage or a fuel flow meter by which to set it. Running an engine rich will do it no harm, but running an engine too lean will damage the engine, by raising the cylinder head temperature and leaving deposits in the engine. I seem to recall that Lycoming do not recommend leaning much below 5000 ft. In the UK most PPLs fly below 3000 ft so leaning may not be as common as in the US where the average ground elevation is above 3000 ft.
The maximum scope for cruise technique does not accur until the student encounters a more powerful aircraft with a VP prop. If you are flying high speed cruise, fuel consumption will be high and whether you fly for the recommended rpm/MP or IAS does not really make a lot of difference. When flying for range, IAS is more important as you will not achieve the optimum range at a lower IAS than recommended.
It is probably fair to say that PPLs will fly further and higher in the US than the UK, consequently more consideration may be given to obtaining optimum performance. In the main very little is taught to ab-initio PPL students in the UK regarding cruise performance, if it was, they would probably fly higher.
Most light trainers with a fixed pitch prop do not leave much room for manoeuvre. The manufacturers recommended cruise speed is based upon the best speed/drag ratio, which can be determined by drawing a tangent to the total drag curve from the origin. Using this graph, you can also teach the student that there are different speeds for range and endurance. Hopefully, the prop pitch will have been optimised for maximum efficiency at or close to that speed. Therefore, by setting the recommended rpm you achieve the stated IAS.
With regard to leaning, most training aircraft do not have a CHT guage or a fuel flow meter by which to set it. Running an engine rich will do it no harm, but running an engine too lean will damage the engine, by raising the cylinder head temperature and leaving deposits in the engine. I seem to recall that Lycoming do not recommend leaning much below 5000 ft. In the UK most PPLs fly below 3000 ft so leaning may not be as common as in the US where the average ground elevation is above 3000 ft.
The maximum scope for cruise technique does not accur until the student encounters a more powerful aircraft with a VP prop. If you are flying high speed cruise, fuel consumption will be high and whether you fly for the recommended rpm/MP or IAS does not really make a lot of difference. When flying for range, IAS is more important as you will not achieve the optimum range at a lower IAS than recommended.
It is probably fair to say that PPLs will fly further and higher in the US than the UK, consequently more consideration may be given to obtaining optimum performance. In the main very little is taught to ab-initio PPL students in the UK regarding cruise performance, if it was, they would probably fly higher.
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We teach "set an RPM, take what you get" for the S+L lesson, because the student can hear it and they don't have to look inside to set it initially (although they do, trying to find the tacho...)
We're not tryin to teach cruising at this stage, just trying to give them the skills to fly the circuit well so they can practice the landings which are after all the really important bit. This is why my way is better
)
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Confident, cocky, lazy, dead.
We're not tryin to teach cruising at this stage, just trying to give them the skills to fly the circuit well so they can practice the landings which are after all the really important bit. This is why my way is better
)------------------
Confident, cocky, lazy, dead.
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Well....the assumption seems to be that S + L in leanring is different from S + L in real flying...so dare I rephrase the questiond and ask.....
When teaching navigation in a simple, fixed pitch, training aircraft would you suggest to student to set an RPM and accept whatever speed - but rely on the performance, fuel burn and other figures in the manual (which are always refered to as suspect when discussing take off distances and climb performance) - or would you teach nominate an airspeed, thereby gaining an accurate groundspeed.
Could I ask you one more favour...admit to which instructor rating you are using - UK, USA, Oz..or any other.
I'm just researching to see if there is a pattern to all this. I simply don't understand how there can be differences....but there are.
When teaching navigation in a simple, fixed pitch, training aircraft would you suggest to student to set an RPM and accept whatever speed - but rely on the performance, fuel burn and other figures in the manual (which are always refered to as suspect when discussing take off distances and climb performance) - or would you teach nominate an airspeed, thereby gaining an accurate groundspeed.
Could I ask you one more favour...admit to which instructor rating you are using - UK, USA, Oz..or any other.
I'm just researching to see if there is a pattern to all this. I simply don't understand how there can be differences....but there are.
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First in first served!, my answer remains as above. Our four C152s all have slightly different cruise speeds at the same RPM, and the Aerobat with its climb prop is the best hour builder by 10 knots! We find where we are (central NZ) that we hardly ever get to do S+L for long enough to make it worthwhile worrying about the 2 knot difference (diversions and stuff) though.
Setting RPM works out correctly to the minute after a half hour leg so I suppose setting airspeed would too. Does it really matter? You're not going to miss the last fuel stop for an hour and a half without topping up anyway, at least not in a C152 in this country. A-B-C trips are usually OK, but A-B-C-D trips are pushing it.
Instructing in New Zullund by the way luvvly jubbly
Setting RPM works out correctly to the minute after a half hour leg so I suppose setting airspeed would too. Does it really matter? You're not going to miss the last fuel stop for an hour and a half without topping up anyway, at least not in a C152 in this country. A-B-C trips are usually OK, but A-B-C-D trips are pushing it.
Instructing in New Zullund by the way
luvvly jubbly
