Question about variable-pitch propeller aircraft & slow flight
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Question about variable-pitch propeller aircraft & slow flight
This question is specific for a normally aspirated Cessna 172RG with variable-pitch prop.
First & foremost I know the aircraft flight manual will shed some light on this but I wont get a chance to have a good read of it until next week, so I'm just after a generalized answer until then.
Say I have pax on board & we are sight seeing over a small city. I want to fly at a slow speed suitable for this situation, I would even put on a stage of flap.
What is better? Reducing the manifold pressure then bringing the pitch control to full fine (Just like a finals configuration) & hence treat the aircraft as fixed pitch (throttle controls RPM etc) OR find the MP/RPM configuration suitable for the purpose of sightseeing at slow speed given the aircraft weight etc, for example 20"/2050RPM or 2100"/2150RPM etc etc.
The first option I think would be more suitable, especially if the turns are steep enough to require more power in the bank. Imagine doing a 45 degree turn with the second option, I'd need to increase the RPM then increase the MP & vice versa once I've leveled off, so much work compared to the first option!
First & foremost I know the aircraft flight manual will shed some light on this but I wont get a chance to have a good read of it until next week, so I'm just after a generalized answer until then.
Say I have pax on board & we are sight seeing over a small city. I want to fly at a slow speed suitable for this situation, I would even put on a stage of flap.
What is better? Reducing the manifold pressure then bringing the pitch control to full fine (Just like a finals configuration) & hence treat the aircraft as fixed pitch (throttle controls RPM etc) OR find the MP/RPM configuration suitable for the purpose of sightseeing at slow speed given the aircraft weight etc, for example 20"/2050RPM or 2100"/2150RPM etc etc.
The first option I think would be more suitable, especially if the turns are steep enough to require more power in the bank. Imagine doing a 45 degree turn with the second option, I'd need to increase the RPM then increase the MP & vice versa once I've leveled off, so much work compared to the first option!
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first, if you're low and slow, don't be doing too many steep turns. will be uncomfortable for your sightseeing pax (is a very quick way to make them feel queasy), and there's not enough fat in the airspeed/stall equation, especially as you're obviously not overly experienced in the aircraft. very easy to get into a stall in the turn situation. personally i'd be setting 2200rpm, whatever MAP it takes to maintain 85-90kts, maybe even 10 deg flap if you're that way inclined (will give better forward vision at least) and keep the bank angle down to 30deg max.
my 2c........
my 2c........
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Thanks for the replies VK2TVK & toolowtoofast. I agree about the not getting too stressed about the RPM in this context, that compliments what I've learned so far more or less.
Yes more than one or two 45 degree turns would be pushing it pax comfort wise so I wouldn't get too carried away with those. I would be flying 1500 feet above sea level so worst case scenario I would be a safe height to recover from the onset of a stall.
Yes more than one or two 45 degree turns would be pushing it pax comfort wise so I wouldn't get too carried away with those. I would be flying 1500 feet above sea level so worst case scenario I would be a safe height to recover from the onset of a stall.
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Looking at the Arrow POH, at 2000' P/A, you'll get 110 hp (55% rated) with either of these settings:
2100 rpm / 22.4" MAP
2400 rpm / 20.0" MAP
I've even seen guys do 2200 rpm / 19" MAP but that's just as fine.
I agree that you should avoid steep turns (includes 45 degrees AoB). Even with a low wing on a scenic flight (plank obstructing views), you should not bank any more than 15 degrees AoB in slow flight. You don't want to stall as you are likely to experience wingdrop - how current are your spin techniques ? You will appreciate why we practice HASELL checks and terminate practice recoveries at minimum of 3000' AGL.
2100 rpm / 22.4" MAP
2400 rpm / 20.0" MAP
I've even seen guys do 2200 rpm / 19" MAP but that's just as fine.
I agree that you should avoid steep turns (includes 45 degrees AoB). Even with a low wing on a scenic flight (plank obstructing views), you should not bank any more than 15 degrees AoB in slow flight. You don't want to stall as you are likely to experience wingdrop - how current are your spin techniques ? You will appreciate why we practice HASELL checks and terminate practice recoveries at minimum of 3000' AGL.
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Have you ever stalled out of a turn before? 
You might find you would have preferred a bit more than 1,500ft... When you did your stalling lessons you would have/should have been over twice that high.
I think you will find that with a variable pitch prop, people usually leave the RPM set at the cruise setting and then just adjust MP accordingly to achieve the speed/performance required (adding power through a turn usually not a problem).
If you are hiring from a Flying School, have a chat to the instructors/CFI on the preferred methods of operation for their aircraft and of course as you have said, the Operating handbook is the bible document. Be careful to abide by any special requirements such as time limits associated with certain RPM ranges (some aircraft have such limitations - for example a small range where long term operation in that range can have damaging vibration consequences).
You might find you would have preferred a bit more than 1,500ft... When you did your stalling lessons you would have/should have been over twice that high.I think you will find that with a variable pitch prop, people usually leave the RPM set at the cruise setting and then just adjust MP accordingly to achieve the speed/performance required (adding power through a turn usually not a problem).
If you are hiring from a Flying School, have a chat to the instructors/CFI on the preferred methods of operation for their aircraft and of course as you have said, the Operating handbook is the bible document. Be careful to abide by any special requirements such as time limits associated with certain RPM ranges (some aircraft have such limitations - for example a small range where long term operation in that range can have damaging vibration consequences).
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On the very few occasions I have done a 45 degree banking turn on a sight seeing flight at 1500 feet it hasn't been a 360 degree bank more like a 100 degree turn & at full power. That to me isn't reckless & if peoples safely margins are such that they see it as dangerous then I'm surprised they can even get out of bed in the morning & face the danger's of day to day living.
Years ago my instructor made a sharp bank over his friends house when he spotted it, I can't recall what angle of bank it was but close enough to 45 degrees & around 1500 feet. With stall practice I've always known I need to recover by 2500 feet & not to perform stalls over built up areas etc, same deal with max rate turns etc. I can't recall ever being told to take the same precautions with 45 degree banks.
I've just never looked at them as being potentially dangerous maneuvers like stall practice, max rates etc.
Years ago my instructor made a sharp bank over his friends house when he spotted it, I can't recall what angle of bank it was but close enough to 45 degrees & around 1500 feet. With stall practice I've always known I need to recover by 2500 feet & not to perform stalls over built up areas etc, same deal with max rate turns etc. I can't recall ever being told to take the same precautions with 45 degree banks.
I've just never looked at them as being potentially dangerous maneuvers like stall practice, max rates etc.
What are you going to achieve by banking at 45deg instead of limiting your turns to 30deg or less?
You are in a high-wing aircraft on a sight-seeing flight (ie. the view will be fine).
Why would you reduce your margins?
Low speed, low altitude, low experience level, steep turn...
Must be a bloody small city if you need to bank at 45deg to stay over it!!
You are in a high-wing aircraft on a sight-seeing flight (ie. the view will be fine).
Why would you reduce your margins?
Low speed, low altitude, low experience level, steep turn...
Must be a bloody small city if you need to bank at 45deg to stay over it!!
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"Do you guy's think a 45 degree bank at full power & at 1500 feet AMSL with pax briefed about the turn is reckless?"
IMHO - no, not reckless.
What about a 40+ deg AOB, 360 deg turn (any where between 5 - 10 consecutive times) at 500ft.... is that reckless? I'd still have to say no.
However this is all dependent on level of pilot experience.
Knox.
IMHO - no, not reckless.
What about a 40+ deg AOB, 360 deg turn (any where between 5 - 10 consecutive times) at 500ft.... is that reckless? I'd still have to say no.
However this is all dependent on level of pilot experience.
Knox.
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Don't get me wrong I don't make a habit of performing 45 degree turns at any stage of or on any type of flight given they're not the most gentle way of banking an aircraft. I more or less mentioned the 45 degree bank for arguments sake with relation to my question about MP & RPM.
I felt like a kamikaze pilot with some of the replies I've gotten here & I pride myself on being the best/safest pilot I can be so was surprised to hear a 45 degree bank through 100 or so degrees at 1500 feet is seen by some as being dangerous.
I can bet some of you guy's imagine me flying over a city with pax & strictly performing 45 degree turns, that's not how it is at all, as mentioned I have made the odd 45 degree bank through 100 degrees or so on the odd occasion, but who hasn't right?
rcoight I agree with you about the margins thing but where do we draw the line? Only having Cessna's taking off on 4km runways because their safer than 500m ones? Obviously that's at the extreme end of the scale but you can see what I mean.
I felt like a kamikaze pilot with some of the replies I've gotten here & I pride myself on being the best/safest pilot I can be so was surprised to hear a 45 degree bank through 100 or so degrees at 1500 feet is seen by some as being dangerous.
I can bet some of you guy's imagine me flying over a city with pax & strictly performing 45 degree turns, that's not how it is at all, as mentioned I have made the odd 45 degree bank through 100 degrees or so on the odd occasion, but who hasn't right?
rcoight I agree with you about the margins thing but where do we draw the line? Only having Cessna's taking off on 4km runways because their safer than 500m ones? Obviously that's at the extreme end of the scale but you can see what I mean.
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Do you guy's think a 45 degree bank at full power & at 1500 feet AMSL with pax briefed about the turn is reckless?
I would be flying 1500 feet above sea level so worst case scenario I would be a safe height to recover from the onset of a stall.
Its not necessarily 'reckless'.
More 'pointless'. Why do you need to turn so steeply? Passengers in general won't enjoy it and you're erroding safety margins for no reason. What kind of ground feature requires such a steep angle of bank?
45 deg = 1.41g = Vs + 20%
If you're sightseeing, you've probably slowed it down to help people see things. You've eroded this safety margin by a further 20%. This might be fine when everything works perfectly. What if something doesn't? You overbank slightly, you get a decent gust. What if you need to turn more steeply due reason x?
In my personal opinion, decision making is about maximizing options, and by doing something like this, you are reducing them for no reason at all.
I reiterate though that I wouldn't call it 'reckless'. Just unnecessary. All the above is my personal opinion only.
More 'pointless'. Why do you need to turn so steeply? Passengers in general won't enjoy it and you're erroding safety margins for no reason. What kind of ground feature requires such a steep angle of bank?
45 deg = 1.41g = Vs + 20%
If you're sightseeing, you've probably slowed it down to help people see things. You've eroded this safety margin by a further 20%. This might be fine when everything works perfectly. What if something doesn't? You overbank slightly, you get a decent gust. What if you need to turn more steeply due reason x?
In my personal opinion, decision making is about maximizing options, and by doing something like this, you are reducing them for no reason at all.
I reiterate though that I wouldn't call it 'reckless'. Just unnecessary. All the above is my personal opinion only.
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I don't know what planes you fly Captain Nomad but I've never stalled or come close to stalling a plane doing a 45 degree bank. Let's say in the unlikely event I'm doing a 45 degree bank the stall warning chirps & the plane feels like it's on the edge of a stall... ease off pressure on the control column now I'm out of the near stall roll wings level. Maybe I lost 100 feet or so, what a rebel & a danger to society I am!
Last edited by steve181; 7th Sep 2009 at 04:23.
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I've never stalled or come close to stalling a plane doing a 45 degree bank
Chill mate, I'm sure you can probably handle a 45 turn at 1,500ft fine. BUT, in a past life I have seen the shock on people's faces as they experienced practicing stalls out of turns and the little warning and vicious onset of the stall itself - it is NOT something you want to do at 1,500ft especially if the outer wing stalls... I have also had a previous life maneouvering at those angles of bank regularly around intimidating terrain and wx and in a loaded aeroplane it can become very uncomfortable VERY quickly...
45deg turn with a high wing doing a scenic? Now all they get is a pic of the wing not the ground. Having flown around a bit at 1000-1500ft on scenics I can recommend S+L for just about everything.
As far as stalling in a turn... having done a bit of instructing I have deliberately stalled many times in turns (power on-off-flap-no flap) I would go with steve181
As far as stalling in a turn... having done a bit of instructing I have deliberately stalled many times in turns (power on-off-flap-no flap) I would go with steve181
ease off pressure on the control column now I'm out of the near stall roll wings level.
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OK theory of flight covered!
How are you paying ? Tacho hour or hour meter?
If it's tacho; it most probably divides the revs by some number like 2400 and registers it as minutes
OK guys ... yes they're in tenths of an hour.
What I'm getting at is; fly for an say, an hour, at 2100 RPM; the tacho says 52minutes while the hour meter comes up with 60 minutes. From start to stop the difference is even greater... low RPM on approach and taxiiing while the clock ticks on relentlessly..
At 200 bucks plus, per hour, you pay over thirty bucks less for the same flight and bung the sixty five or seventy minutes total flight time in the log book.
Cheating ??? NO! The tacho time is what the maintenance is done on and the flying schools get paid by the hirers, for the time the clock runs... probably get paid for 110 hours in the 100 hourly period.
You can open the window in a Cessna and get good clear photos or see clearly in medium turns and aviod the need for forty five degree turns.
How are you paying ? Tacho hour or hour meter?
If it's tacho; it most probably divides the revs by some number like 2400 and registers it as minutes
OK guys ... yes they're in tenths of an hour.
What I'm getting at is; fly for an say, an hour, at 2100 RPM; the tacho says 52minutes while the hour meter comes up with 60 minutes. From start to stop the difference is even greater... low RPM on approach and taxiiing while the clock ticks on relentlessly..
At 200 bucks plus, per hour, you pay over thirty bucks less for the same flight and bung the sixty five or seventy minutes total flight time in the log book.
Cheating ??? NO! The tacho time is what the maintenance is done on and the flying schools get paid by the hirers, for the time the clock runs... probably get paid for 110 hours in the 100 hourly period.
You can open the window in a Cessna and get good clear photos or see clearly in medium turns and aviod the need for forty five degree turns.
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I've never stalled or come close to stalling a plane doing a 45 degree bank
FYI - Stalling is not an aerobatic maneouvre and you DO NOT have to be at 3,000ft to do it.
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Oh I completely agree that 45 degree turns in a high wing aircraft on a sight seeing flight is not necessary (wing might block the sight, less comfortable for pax etc etc). The handful of times I have performed one in this circumstance was more so the passengers could experience a G or 2 as opposed to performing the turn for the purpose of viewing sights on the ground.
In hindsight if I knew my original comment about the 45 degree turn was going to be the focus of replies then I would have said a 30 degree turn just as an example of how an increase in power would be needed to perform the turn if going from slow flight re: juggling the throttle & pitch lever.
In hindsight if I knew my original comment about the 45 degree turn was going to be the focus of replies then I would have said a 30 degree turn just as an example of how an increase in power would be needed to perform the turn if going from slow flight re: juggling the throttle & pitch lever.