Question about variable-pitch propeller aircraft & slow flight
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So, away from the aerobatics, aces, and back to the question 
I've never flown sight-seeing trips per se but I do have a fair few hours with twisty props. At the risk of delving into egg-sucking lessons, one of the important things to remember with VP props is not go get 'over-square' or, put another way, have too much MAP for the RPM. To keep it simple in my beer-oddled brain, I always likened it to trying to drive your car up a hill in too high a gear. You can put your foot down all you like but it's still going to judder away and not accelerate.
So, in your scenario, firstly I would reduce the MAP and then increase the RPM (23-2400 sounds about right, having never flown a 172 with VP prop) and then you will have the ability to increase power during your turns, without having to worry about the nasty chugging sound if the RPM was too low.
My time in the military showed me that they always enjoyed their rules-of-thumb and many of these seemed to work very well. It's probably old-hat to many of you but we were always taught to take the first 2 numbers of the RPM, add 2.5 to that and that was the max MAP you should apply. So, RPM of 2400 = max MAP of 26.5in.
Of course, this doesn't apply to all aircraft, e.g. those big-engined things with boost gauges, but it does apply to the vast majority of engines that are found in light aircraft IO-360s etc.
That rule + "Rev up, Throttle back" and that's the end of the VP endo
PS: When it does stall in the turn, depending on which way the prop spins, remember the quickest recovery to the horizon might be rolling under....might upset the fare payers though
I've never flown sight-seeing trips per se but I do have a fair few hours with twisty props. At the risk of delving into egg-sucking lessons, one of the important things to remember with VP props is not go get 'over-square' or, put another way, have too much MAP for the RPM. To keep it simple in my beer-oddled brain, I always likened it to trying to drive your car up a hill in too high a gear. You can put your foot down all you like but it's still going to judder away and not accelerate.
So, in your scenario, firstly I would reduce the MAP and then increase the RPM (23-2400 sounds about right, having never flown a 172 with VP prop) and then you will have the ability to increase power during your turns, without having to worry about the nasty chugging sound if the RPM was too low.
My time in the military showed me that they always enjoyed their rules-of-thumb and many of these seemed to work very well. It's probably old-hat to many of you but we were always taught to take the first 2 numbers of the RPM, add 2.5 to that and that was the max MAP you should apply. So, RPM of 2400 = max MAP of 26.5in.
Of course, this doesn't apply to all aircraft, e.g. those big-engined things with boost gauges, but it does apply to the vast majority of engines that are found in light aircraft IO-360s etc.
That rule + "Rev up, Throttle back" and that's the end of the VP endo
PS: When it does stall in the turn, depending on which way the prop spins, remember the quickest recovery to the horizon might be rolling under....might upset the fare payers though
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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)
Not to mention the fact that you wouldn't want to be in finals configuration while trying to maintain altitude
one of the important things to remember with VP props is not go get 'over-square' or, put another way, have too much MAP for the RPM.
Over to chuck
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
Don't these city instructors teach Airmanship anymore?
Slow down and a 15 AOB is sufficient for seeing anything that is worth seeing on a scenic! (your passengers may even give you a tip)
stalls are not the silent assassin, you get many clues one is about to happen & therefore the opportunity to avert one developing.
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Remember VH-XXX stalls are not the silent assassin, you get many clues one is about to happen & therefore the opportunity to avert one developing.
What do you mean VH-XXX?
Last edited by VH-XXX; 7th Sep 2009 at 08:06.
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Lets take away what I've said because some people are missing the point of my original question.
I'm cruising (24"/2450RPM, which is the control configuration for my aircraft) in the middle of nowhere at 3000 feet flying solo in the same aircraft as described in my first post.
I randomly decide I want to slow the aircraft down in straight & level flight to say 70 knots, from your experience what would you do to achieve this? I would just reduce the manifold pressure with the throttle until I reached 70 knots.
Now I want to do a turn where by I need maximum power (say a max rate turn); should I bring the pitch control to full fine first before I increase the MP to full (full throttle). I think I would need to but what would you guys do from your experience?
Sorry to those who have answered me on my original question, I'm just trying to find a consensus.
I'm cruising (24"/2450RPM, which is the control configuration for my aircraft) in the middle of nowhere at 3000 feet flying solo in the same aircraft as described in my first post.
I randomly decide I want to slow the aircraft down in straight & level flight to say 70 knots, from your experience what would you do to achieve this? I would just reduce the manifold pressure with the throttle until I reached 70 knots.
Now I want to do a turn where by I need maximum power (say a max rate turn); should I bring the pitch control to full fine first before I increase the MP to full (full throttle). I think I would need to but what would you guys do from your experience?
Sorry to those who have answered me on my original question, I'm just trying to find a consensus.
I'm cruising (24"/2450RPM, which is the control configuration for my aircraft) in the middle of nowhere at 3000 feet flying solo in the same aircraft as described in my first post.
I randomly decide I want to slow the aircraft down in straight & level flight to say 70 knots, from your experience what would you do to achieve this? I would just reduce the manifold pressure with the throttle until I reached 70 knots.
Now I want to do a turn where by I need maximum power (say a max rate turn); should I bring the pitch control to full fine first before I increase the MP to full (full throttle). I think I would need to but what would you guys do from your experience?
I randomly decide I want to slow the aircraft down in straight & level flight to say 70 knots, from your experience what would you do to achieve this? I would just reduce the manifold pressure with the throttle until I reached 70 knots.
Now I want to do a turn where by I need maximum power (say a max rate turn); should I bring the pitch control to full fine first before I increase the MP to full (full throttle). I think I would need to but what would you guys do from your experience?
If in the turn I need to get out of there quickly (say a potential collision) I'd fire wall it maneuver as required (paying attention to collision avoidance and who has right of way etc) and worry about the pitch later.
Also note that in "most" CSU equipped machines 24" 2400rpm cruise power is more than enough performance for a 45 AOB turn.
I would also talk to your instructor and take what is written on the internet with a pinch of salt (a slice of lemon and a shot of tequila also helps)
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Thanks The Green Goblin that's one of the best replies I've got so far.
Obviously the flight manual will help answer my questions on engine management but as I said it's worthwhile getting information on how others go about it (with a grain of salt) in the mean time.
Obviously the flight manual will help answer my questions on engine management but as I said it's worthwhile getting information on how others go about it (with a grain of salt) in the mean time.
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This situation happens every flight in PJE ops, reduce the MAP to around 16-17 inches and bring back the RPM to about 2200RPM, that usually gives you 70-80kts. Increasing the MAP up to 22in will give you more than enough power for a turn, you wont even get that above 7,000ft in a normaly aspirated engine, and its quite common to do a 'wing over' (not really ) as the last person jumps out to watch them fall away, thats easily a 60 degree turn at low speed and you would be lucky to loose more than 500ft through the whole thing!
In a Cutlass, I imagine that the configuration given for slow flight (its in the POH somewhere) would give you what you need, im pretty sure that calls for gear down though. Just try it and see what works, but you will be looking at close to the settings listed above.
) as the last person jumps out to watch them fall away, thats easily a 60 degree turn at low speed and you would be lucky to loose more than 500ft through the whole thing! In a Cutlass, I imagine that the configuration given for slow flight (its in the POH somewhere) would give you what you need, im pretty sure that calls for gear down though. Just try it and see what works, but you will be looking at close to the settings listed above.
Have a nice flight.
From memory, we use to keep the RPM where it was for cruise, about 2400 rpm, throttled back to about 15-18 inches with the first stage of flap out and this usually gave us about 70 kts (I think .?) and a bit more margin over the stall. This way you could push and pull on the throttle as you needed for power.
That was for mustering and other low level stuff. Just try it out and see if it works mate. It was a while ago and I'm sure Cessna fly the same as they did 10-15 years ago. We flew C182 and C172 with variable props.
I'm no expert and I'm no egg sucking teacher. Just know the aircrafts', your limitations and all will be safe as you already know. Most of all, enjoy your flight
.?) and a bit more margin over the stall. This way you could push and pull on the throttle as you needed for power.That was for mustering and other low level stuff. Just try it out and see if it works mate
. It was a while ago and I'm sure Cessna fly the same as they did 10-15 years ago. We flew C182 and C172 with variable props.I'm no expert and I'm no egg sucking teacher. Just know the aircrafts', your limitations and all will be safe as you already know. Most of all, enjoy your flight
Last edited by snoop doggy dog; 7th Sep 2009 at 09:25.
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one of the important things to remember with VP props is not go get 'over-square'
Better not let all the WWII pilots hear you say that!
For example the P-51 Mustang has a maximum MP of around 61 inches! I bet the prop is not turning at 6200 RPM...
In the days when I flew scenics, I quite often had the RPM 2-300 less than the cruise setting in the 210, made for a very quiet cabin. Can't say I would be recommending it in 172RG though!
Remember VH-XXX stalls are not the silent assassin, you get many clues one is about to happen & therefore the opportunity to avert one developing.
I suggest the following: Get a C-172, as per this discussion, a sightseeing flight, make certain you are loaded close the the aft C.of G., and with some flap extended, and in the aforementioned 45 degree angle of bank, slowly reduce the speed until "something" happens.
It might not "legally" be an aerobatic maneuver, but please don't try the first one at 1500'. Then you will find your statement above is NOT based on training or experience, preferably in that order. Just a hint, I usually went to 5-6000 ft for that exercise.
Suddenly the staid and steady, soggy as a blancmange good old C-172 behaves like a Yak 52 in the same circumstances. Oh! Boy! can it flick over the top fast and into an (incipient) spin, it always comes as a great surprise to the student.
I have had some wonderful reactions from instructors, when I ask them to demonstrate this on a check ride, it gives me a good idea what kind of a pilot (let alone instructor) they really are.
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Is that right?
Better not let all the WWII pilots hear you say that!
For example the P-51 Mustang has a maximum MP of around 61 inches! I bet the prop is not turning at 6200 RPM...
Better not let all the WWII pilots hear you say that!
For example the P-51 Mustang has a maximum MP of around 61 inches! I bet the prop is not turning at 6200 RPM...
Please, if you're going to cast aspersions then at least do me the favour of reading my whole post, instead of selectively quoting. I thought I made it clear about such things when I wrote
Of course, this doesn't apply to all aircraft, e.g. those big-engined things with boost gauges, but it does apply to the vast majority of engines that are found in light aircraft IO-360s etc.
And it is very true to say that you CAN have RPM low and, in a normally aspirated engine this is arguably the most efficient way to fly it but that's in the cruise, whereas I suggest you don't want really want to be flying around slow speed in this configuration 'cos when you need the engine to respond to your firewalling the throttle it ain't gonna happen.
Not this old wives tale rearing its head again.
I randomly decide I want to slow the aircraft down in straight & level flight to say 70 knots, from your experience what would you do to achieve this? I would just reduce the manifold pressure with the throttle until I reached 70 knots.
Now I want to do a turn where by I need maximum power (say a max rate turn); should I bring the pitch control to full fine first before I increase the MP to full (full throttle). I think I would need to but what would you guys do from your experience?
Now I want to do a turn where by I need maximum power (say a max rate turn); should I bring the pitch control to full fine first before I increase the MP to full (full throttle). I think I would need to but what would you guys do from your experience?
I enjoy mucking around on sunny days in light aircraft and boring my kids with how many vertical rolls (up) we can squeeze in before running out of ideas and becoming a brick but, despite my teachers being very capable and knowledgeable chaps, I think it's best to keep it simple and stick to jet engines
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Minor point to start -the prop on the 172 you mention is not 'variable pitch', it's actually 'constant speed' - there is a notable difference between the two, with variable pitch not havig been used (to my knowledge - go on someone, correct me) since during WWII. Anyway, moving right along:
As has been done to death already, what you are proposing is all ok in theory -a bit of flap, slow-ish speed and some bank for visibility. All you wanted to know what how much MAP and RPM would be a good idea.
First, I'd probably not bank excessively - the poor old 172 ain't travelling that fast that high angles of bank are required to required for a good look as you sail past those on the ground who are probably awaiting your arrival.
On that basis, high power settings should not be required. Regardless, you expose yourself to the possibility, at higher angles, of the chance of some stall symptoms: here's where a little bit of covering one's backside might help if you do plan high angles and flap usage- have the prop in 'full increase' so that full power is available so you can do the pukka stall recovery should you need.
The 'need' might be greater than you think: one danger of orbitting around a ground feature at low level (though 1500ft is not THAT low), is that you tend to be looking at it too much (target fixation?), the result being bank angles greater than intended, perhaps an unitentional descent (which would actually help), possibly decaying airspeed and the effect on your ground track in strong wind conditions (perhaps causing you to pull a little tighter to achieve the desired ground track, wih the effects as previously discussed). The attention to the task, rather than the pure flight path control can also add to the distraction, and result in not being so sensitive to to the symptoms of stall onset.
So, protect yourself from yourself and avoid low level aerobatics with pax: set the rpm so power is available, put the boost pump on, do HASSELL checks (they are not just a routine for aerobatics), fly the aeroplane first and demostrate your professionalism not your daring. Try it without flap (keep it simple) -I can't think of a time, in a clear area, where the turn radius was so m uch better with a little flap, compared to clean, or that the slower speed (between what 90 kias with 10° and 110kias clean?) made a jot of practical difference in the time over the target..
TM
If you were thinking of using a lot of bank to show the 172 off I wouldn't bother -if you don't have smoke you need noise; unfortunately the 172, great as it is, has neither!
As has been done to death already, what you are proposing is all ok in theory -a bit of flap, slow-ish speed and some bank for visibility. All you wanted to know what how much MAP and RPM would be a good idea.
First, I'd probably not bank excessively - the poor old 172 ain't travelling that fast that high angles of bank are required to required for a good look as you sail past those on the ground who are probably awaiting your arrival.
On that basis, high power settings should not be required. Regardless, you expose yourself to the possibility, at higher angles, of the chance of some stall symptoms: here's where a little bit of covering one's backside might help if you do plan high angles and flap usage- have the prop in 'full increase' so that full power is available so you can do the pukka stall recovery should you need.
The 'need' might be greater than you think: one danger of orbitting around a ground feature at low level (though 1500ft is not THAT low), is that you tend to be looking at it too much (target fixation?), the result being bank angles greater than intended, perhaps an unitentional descent (which would actually help), possibly decaying airspeed and the effect on your ground track in strong wind conditions (perhaps causing you to pull a little tighter to achieve the desired ground track, wih the effects as previously discussed). The attention to the task, rather than the pure flight path control can also add to the distraction, and result in not being so sensitive to to the symptoms of stall onset.
So, protect yourself from yourself and avoid low level aerobatics with pax: set the rpm so power is available, put the boost pump on, do HASSELL checks (they are not just a routine for aerobatics), fly the aeroplane first and demostrate your professionalism not your daring. Try it without flap (keep it simple) -I can't think of a time, in a clear area, where the turn radius was so m uch better with a little flap, compared to clean, or that the slower speed (between what 90 kias with 10° and 110kias clean?) made a jot of practical difference in the time over the target..
TM
If you were thinking of using a lot of bank to show the 172 off I wouldn't bother -if you don't have smoke you need noise; unfortunately the 172, great as it is, has neither!
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At the moment I'm building my command time for my CPL in a C72RG.
Over the weekend I was doing the Harbour Scenic one with me and two friends (220kg) and about 180 litres of fuel on board. 20"/2300RPM with one stage of flap was sufficient to stay straight and level and slow enough to have a nice look around during the orbits and on the transit to and from the bridge. I didn't pull more than 20 degrees of bank as I wanted to give my friends a chance to enjoy the view and to not have them worrying about what the plane was doing. The controls were sloppy enough at that speed and power setting as it was so I don't think it would have been wise to go and push the envelope.
Over the weekend I was doing the Harbour Scenic one with me and two friends (220kg) and about 180 litres of fuel on board. 20"/2300RPM with one stage of flap was sufficient to stay straight and level and slow enough to have a nice look around during the orbits and on the transit to and from the bridge. I didn't pull more than 20 degrees of bank as I wanted to give my friends a chance to enjoy the view and to not have them worrying about what the plane was doing. The controls were sloppy enough at that speed and power setting as it was so I don't think it would have been wise to go and push the envelope.