Last minute pattern adjustments- When?

Sac Arrow said:
Group hug?
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slapdown.gif
 
Whatever you do, it should be routine. When I was more orthodox, I would not advance the RPM until relatively short final and would always advance the mixture passing thru 3000 MSL. Now, on my Bonanza, I leave the prop set to my cruise value, usually 2500, which will provide plenty of RPM if I decide to go around. I normally operate the engine LOP and don't enrichen the mixture on descent, often until I am on the ground. For me it is no big deal to advance the throttle and follow up with the mixture and prop if I need to go around.
 
mikea said:
I need try it out but I think the flat prop adds drag that you'd have to adjust for. I end up advancing the power with a flat prop to get on right side of the power curve. When I'm on final and making small power and pitch adjustments to stay on target on the right slope to my touchdown point the last thing I'd want to do is change the engine setup and chase back to where I was.
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You do realize that when a constant speed propeller is at the low pitch stops (as it is on short final in most GA airplanes and as I described above) and you push the blue lever forward, nothing actually changes on the prop, right?

That is why there is no surge in RPM or change in noise.....and no change in drag.
 
If I'm doing a pattern entry, I put one notch of flaps in before entry, then at pattern altitude I slow to at least 10 kts below gear extension speed (safety margin) and put the gear down, mixture full rich. MP at 21", prop still at cruise (2300 or 2400). Abeam the numbers, reduce MP to 16", prop goes all the way in, GUMPS check. Turn base, 20 degrees flaps. Turn final, last GUMPS check. Final notch of flaps when the runway is made.

On approach, reduce MP to 21" and add first notch of flaps approaching the IAF. Gear down, mixture full rich at the FAF, then reduce MP to 17". Prop goes all the way in (but using the vernier to avoid a sudden surge). No more flaps until short final (or turning base when doing a circling approach). Then full flaps when the runway is made.

I'll confess I do start cleanup on the rollout once I'm slow enough to no longer be flying. How slow that is depends on conditions. If the winds are squirrely, I wait until I'm off the runway and stopped.
 
John Collins said:
...I normally operate the engine LOP and don't enrichen the mixture on descent, often until I am on the ground. For me it is no big deal to advance the throttle and follow up with the mixture and prop if I need to go around.
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While I'm sure its routine for you, that sounds like a recipe for disaster for an inexperienced pilot. LOP mixture settings won't work with full power at low altitudes. That's when you need max power for a go around and there may be several distractions going on at that time.

I prefer to run the engine properly leaned at all times "except" take off and landing.
 
bob_albertson said:
I wasn't trying to imply that you were different from anyone. I was completely agreeing with what you said and then directing the rest at that towards Jesse's bashing of your earlier posts. Basically, saying that you're right and he seems unwilling to accept that other methods are in no way any less safe or wrong than what someone else might be doing.

Bob
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Bob -- Jesse wasn't "bashing" -- he was questioning my technique.

That's usually do to one of three reasons:

  1. The technique is flawed and will result in problems (i.e. "wrong")
  2. The technique was poorly explained
  3. The technique does not comport with the listener's technique
Apparently 2 and 3 were the main issues in this thread. I provided more explanation. That seems to have ended the contradiction.

Or maybe not -- we'll see.

:redface:

There's a dangerous reductionism that infuses much of our discourse these days -- contradiction becomes "hate," disagreement becomes "bashing," differences become "lines in the sand."

When that happens we lose the very benefit of debate -- exposure of different points, exploration of the assumptions underlying those points, and either further refinement or correction of the original positions.

I prefer honest, open debate as it helps me think through what I think I know. Many times I'm confirmed that what I thought I knew was, in fact,correct (or close to correct), but most times I find my explanations are lacking.

So I fix that.

And we all benefit from the exchange since we post publicly.

:)



Oh -- and no sleep was lost in the making of this thread. :yesnod:
 
jesse said:
lmfao. Okay mr airline pilot guy. I'll let you battle this out with Ron, I don't have the time right now.

Replace 100 with X, it was just a value. Your lack of experience with complex pistons clearly shows by stating one should be turning 2700rpm for no good reason other then to make noise and **** folks off.
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Your edited part just goes to show that you haven't read what I wrote and have a problem understanding the benefits and reasons for doing something differently than you currently do. With more time in a complex aircraft you'll find that when on final and using full prop setting that you are already at a power setting near the bottom of the governing range. You won't wake up the baby sleeping under the approach end any more than a fixed pitch Cessna over the same spot so long as you are not doing a go-around (where the prop setting will let you climb faster to the tune of minimizing noise produced at low altitude). Everything you say about the technique is wrong compared to what actually happens. I'm not bashing the way you or anyone else do it. I started comparing opinions about the techniques with Ron, but that's not what your trying to carry on. I really don't see the point in continuing with a conversation where the other is so set in a way that it prevents them from seeing the benefits of anything (such as the speed a pattern is flown at).

I have to go too, I don't have time to get the books and copy and paste from them for ya right now, but it is a difference in technique like the Saab vs Q400. Difference between those is they carry enough power on approach that there is a large difference in sound

Bob
 
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I'll add this tidbit -- I usually start power reduction pretty far out and gradually. So when I reduce power to 19" (let's say) and slow up to within the white arc on downwind, pushing the prop full forward results in -- no change.
 
dmccormack said:
I'll add this tidbit -- I usually start power reduction pretty far out and gradually. So when I reduce power to 19" (let's say) and slow up to within the white arc on downwind, pushing the prop full forward results in -- no change.
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Sorry Dan I didn't see your post above my last one. You and I are on the same page. Even though we had talked about the possible rpm difference between cruise and full prop setting. Fact of the matter is at approach power setting the prop won't surge because of being at or near the bottom of the governing range.
 
Greg Bockelman said:
Why??
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Long descents etc in this condition could cause ring flutter. When I flew for a freight carrier, we had quite a document from Lycoming covering this subject in our training materials...Wish I could pub that here great document.

http://www.sacskyranch.com/pubsem.htm

You do not want to do a long let-downs with the prop driving the engine. This causes ring flutter and broken piston rings. High rpm's increase the up and down inertial load on the rings in the piston ring grooves. Cylinder pressure helps to keep the ring seated to the bottom of the ring groove. Reducing rpm to low cruise will be beneficial by reducing ring inertial and increasing cylinder pressures.
 
Here is the link
Engine Operation - Descent

Make the initial temperature change slowly. We want to start the temperatures going down early. Once you establish the downward trend in temperatures, there is far less likelihood of causing engine damage by fast cooling.

There are three ways in which you are going to cool the engine:

Reduction of power.
Increase in airspeed.
Enrichening the mixture.
The worst thing you can do is to do all three of them at once. Start the initial cooling trend by lowering the nose by keeping the power and mixture the same. Try to make small changes in RPM and manifold pressure. Limit yourself to 1 or 2 inches of manifold pressure reduction at a time. To prevent rapid turbocharger cool down during descent, the desired EGT is 1350F.

Every flight, you should anticipate a rapid descent and start a cool-down before the let-down. Reduce power or open the cowl flaps part way to start reducing the temperature of the engine. When you have to do the fast descent, you can close the cowl flaps and be less concerned since you have already reduced engine temperatures.

You do not want to do a long let-down with the prop driving the engine. This causes ring flutter and broken piston rings. High RPM's increase the up-and-down inertia load on the rings in the piston grooves. Cylinder pressures help to keep the rings seated to the bottom of the ring groove. Reducing RPM to low cruise will be beneficial by reducing ring inertia and increasing cylinder pressures. Of course, at some time (as on final) the prop will be driving the engine and this is okay for a short time. But a long descent at high RPM and low manifold pressure is hard on the piston rings.

Prolonged engine idle during glide, particularly in cold weather conditions with a carbureted engine, may result in engine stoppage. The primary cause of this type of engine stoppage is the inability of the engine to receive adequate fuel/air mixture ratios. During idling flight, propeller wind-milling induces an engine RPM that is higher than the ground idle RPM for which the mixture adjustment of the carburetor was set. This produces a lean fuel/air mixture ratio. When the throttle is opened rapidly, the fuel delivery by the carburetor lags behind the throttle motion due to surface tension and inertia in the fuel, and this further leans the available mixture. The cylinders have inadequate fuel and the engine misfires or quits.
 
Greg Bockelman said:
Why??
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It comes down to if you're letting the prop drive the engine versus te engine driving the prop. Forces start to be applied in reverse which can possibly be a less than ideal thing.

You're talking pretty low pressures to accomplish that though, like full rpm and mps less than 15" in most of the stuff we fy.
 
jesse said:
It comes down to if you're letting the prop drive the engine versus te engine driving the prop. Forces start to be applied in reverse which can possibly be a less than ideal thing.

You're talking pretty low pressures to accomplish that though, like full rpm and mps less than 15" in most of the stuff we fy.
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Not quite, see article above your post. It's isn't forces being applied in reverse. It's a lack of pressure to keep the rings properly seated, the forces don't oppose piston travel.
 
taters said:
Long descents etc in this condition could cause ring flutter. When I flew for a freight carrier, we had quite a document from Lycoming covering this subject in our training materials...Wish I could pub that here great document.

http://www.sacskyranch.com/pubsem.htm

You do not want to do a long let-downs with the prop driving the engine. This causes ring flutter and broken piston rings. High rpm's increase the up and down inertial load on the rings in the piston ring grooves. Cylinder pressure helps to keep the ring seated to the bottom of the ring groove. Reducing rpm to low cruise will be beneficial by reducing ring inertial and increasing cylinder pressures.
Click to expand...

Ring flutter. Interesting thought but more than just a little suspect since every other trip up the cylinder there is little pressure on the piston. I'm certainly not believing the story without a lot of supporting documentation.
 
Back on topic...

My technique for a VFR approach to a pilot controlled field doing a standard 45deg entry to downwind in a NA (O-470-L) CS prop single engine aircraft (straight tail 182):

If the air is calm then I don't touch anything during descent except to gradually back off the throttle while coming down to maintain cruise MP. I aim to be at TPA at 2 to 3 miles out. I do a GUMPS on the 45 but don't touch the prop and I gradually slow the bird and aim to be at the top of the white arc (100mph) when I'm abeam the numbers on downwind.

Abeam the numbers on downwind I pull the engine to idle, do another GUMPS check, including prop high rpm this time (engine is already at idle), add the 1st notch of flaps & trim to 80mph.

While trimming, I scroll the engine monitor to carb temp and check it. If it's not below 35dF (or if it is below 15dF) I DON'T add carb heat. If it's between 15 & 35dF then I do.

Turn base, add 2nd notch of flaps (bird settles in at 75mph w/o additional trim)

Turn final, add 3rd notch of flaps (bird settles in at 70mph w/o additional trim)

Short final, runway assured, add 4th notch of flaps (bird settles in at 65mph w/o additional trim).

Land.

Yes, I too clean up the airplane while rolling out (I know, me bad). But I'm not flying a retract and I have johnson bar controlled flaps that are easily raised almost immediately after landing. And they're raised immediately, especially if it's windy/gusty. I also lose the carb heat (if I used it) and re-trim for take-off shortly thereafter.
 
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Clark1961 said:
Ring flutter. Interesting thought but more than just a little suspect since every other trip up the cylinder there is little pressure on the piston. I'm certainly not believing the story without a lot of supporting documentation.
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Interesting point, Clark.
 
FWIW I don't push the blue knob untill the engine has slowed off the govenor, so basicly as soon as a power is reduced to the point the RPM drops the prop comes forward. This is usually around the end of the downwind leg.
 
Skylane81E said:
FWIW I don't push the blue knob untill the engine has slowed off the govenor, so basicly as soon as a power is reduced to the point the RPM drops the prop comes forward. This is usually around the end of the downwind leg.
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I do it after turning final, but it seems like the two main techniques are sometime around final power reduction and only prior to a go-around. So for the original question the answer is choose the procedure that fits with your SOP and don't vary from that due to the possibility of a change causing a possible missed step. For those who don't use checklists religiously that can be a problem, and from what I've seen there aren't too many GA pilots who use a checklist once the run up is completed. That's their prerogative too, I choose to use one but I'm not going to tell someone else they must do it my way unless they are a primary student or ask me how I do it. All other times I preface what I say with.... This is a matter of technique, not procedure, but I like to back up my flows with a checklist. They can then try it if they want or keep doing it their way. As long as it isn't a safety item, that's how I suggest things during a flight review.
 
dmccormack said:
Bob -- Jesse wasn't "bashing" -- he was questioning my technique.

That's usually do to one of three reasons:

  1. The technique is flawed and will result in problems (i.e. "wrong")
  2. The technique was poorly explained
  3. The technique does not comport with the listener's technique
Apparently 2 and 3 were the main issues in this thread. I provided more explanation. That seems to have ended the contradiction.

Or maybe not -- we'll see.

:redface:

There's a dangerous reductionism that infuses much of our discourse these days -- contradiction becomes "hate," disagreement becomes "bashing," differences become "lines in the sand."

When that happens we lose the very benefit of debate -- exposure of different points, exploration of the assumptions underlying those points, and either further refinement or correction of the original positions.

I prefer honest, open debate as it helps me think through what I think I know. Many times I'm confirmed that what I thought I knew was, in fact,correct (or close to correct), but most times I find my explanations are lacking.

So I fix that.

And we all benefit from the exchange since we post publicly.

:)



Oh -- and no sleep was lost in the making of this thread. :yesnod:
Click to expand...

Adolf doesn't like your technique either :D:D:D
 
bob_albertson said:
Not quite, see article above your post. It's isn't forces being applied in reverse. It's a lack of pressure to keep the rings properly seated, the forces don't oppose piston travel.
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Meh. Was just a poorly worded iPhone post while waiting for an airplane to be filled with gas.

At the high rpm and low mp setting - there is a lack of pressure during the intake stroke that could possibly cause the ring to lift. During the compression stroke there is a sudden increase in pressure that will push the ring back down. Rince and repeat.

Personally I don't subscribe to the theory that the prop driving the engine is nearly as bad as some people claim. I mostly just consider it poor pilot technique because when it happens it's mostly people pulling out way too much power to have to suddenly add it back in.

John Deakin wrote a really good article about this. I really wish AvWeb still had the quality content that it did years ago. It really touches on this very discussion quite well:
http://www.avweb.com/news/pelican/186778-1.html
 
jesse said:
Meh. Was just a poorly worded iPhone post while waiting for an airplane to be filled with gas.

At the high rpm and low mp setting - there is a lack of pressure during the intake stroke that could possibly cause the ring to lift. During the compression stroke there is a sudden increase in pressure that will push the ring back down. Rince and repeat.

Personally I don't subscribe to the theory that the prop driving the engine is nearly as bad as some people claim. I mostly just consider it poor pilot technique because when it happens it's mostly people pulling out way too much power to have to suddenly add it back in.

John Deakin wrote a really good article about this. I really wish AvWeb still had the quality content that it did years ago. It really touches on this very discussion quite well:
http://www.avweb.com/news/pelican/186778-1.html
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And this quote:

If the RPM is very high, and the MP is very low, there is a large, negative pressure created in the combustion chamber during the intake stroke, due to the closed throttle plate and the piston trying hard to suck air in. This may lift the ring off its land during that stroke. The next stroke is the compression stroke, and while the pressure will be greatly reduced because not much air got in, it's still enough to push the ring back down again. This repetition may well cause the rings to "flutter," beating up and down within the land, and this may well cause damage.
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...supports the contention that if you slow and then push the prop forward High RPM / LOW MAP will not happen.
 
jesse said:
Meh. Was just a poorly worded iPhone post while waiting for an airplane to be filled with gas.

At the high rpm and low mp setting - there is a lack of pressure during the intake stroke that could possibly cause the ring to lift. During the compression stroke there is a sudden increase in pressure that will push the ring back down. Rince and repeat.

Personally I don't subscribe to the theory that the prop driving the engine is nearly as bad as some people claim. I mostly just consider it poor pilot technique because when it happens it's mostly people pulling out way too much power to have to suddenly add it back in.

John Deakin wrote a really good article about this. I really wish AvWeb still had the quality content that it did years ago. It really touches on this very discussion quite well:
http://www.avweb.com/news/pelican/186778-1.html
Click to expand...

There has been a debate about the effects of running MP higher than prop RPM for cruise for at least 50 years. Still, I seems to recall that no engine failure has been directly linked (of those studied). With this issue you have both the shock cooling and engine wear debates wrapped up in one scenario based off of configuration settings. I'm in the camp that high rpm and low MP may cause accelorated wear but unlikely to cause a failure due to any shearing force or overstressing. I am of the opinion that it causes accelorated wear and possible failure due to that but no acute failures. In the hot rod world the saying is the faster you go the less time you spend going fast. That's related to this by the fact that a prolonged descent with full props is gonna produce enough of a pressure difference to impose similar forces as when the engine is producing full t/o power
 
Clark1961 said:
Ring flutter. Interesting thought but more than just a little suspect since every other trip up the cylinder there is little pressure on the piston. I'm certainly not believing the story without a lot of supporting documentation.
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It's very plausible because with low MP the air availible for the compression stroke is less so the overall pressure on the piston head is less. A matter of a lower volume of air will be drawn, and as a result both the compression and power strokes will have lower pressures. Air cooled engines have wide ring clearances (something like .016" for a O-360). So I could also concievably see the rings contracting a little bit because of the lower temps from that power setting - giving more room between ring face and cylinder walls opening the possibility of flutter :)
 
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bob_albertson said:
It's very plausible because with low MP the air availible for the compression stroke is less so the overall pressure on the piston head is less. A matter of a lower volume of air will be drawn, and as a result both the compression and power strokes will have lower pressures. Air cooled engines have wide ring clearances (something like .016" for a O-360). So I could also concievably see the rings contracting a little bit because of the lower temps from that power setting - giving more room between ring face and cylinder walls opening the possibility of flutter :)
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Bob, while it's very nice to argue theory without practical data, you seem to be ignoring my point that the rings are essentially unloaded during the exhaust and intake phases. From my perspective ring flutter is pretty much a myth or we'd see it in motorcycle, auto, and truck engines. About the only damage I've heard attributed to the load pushing the engine is valve drops on the old in-line Cummins and gear train damage on geared aviation engines.

On the other hand, detonation will destroy rings along with other parts.
 
Clark1961 said:
Bob, while it's very nice to argue theory without practical data, you seem to be ignoring my point that the rings are essentially unloaded during the exhaust and intake phases. From my perspective ring flutter is pretty much a myth or we'd see it in motorcycle, auto, and truck engines. About the only damage I've heard attributed to the load pushing the engine is valve drops on the old in-line Cummins and gear train damage on geared aviation engines.

On the other hand, detonation will destroy rings along with other parts.
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How many people have heard a sportbike decelerating from high RPM? Standard technique is to not disengage the clutch. In this scenario, the rear wheel is driving the clutch, engine and transmission. Motorcycle engines live a hard life, but this is standard technique for all manual transmissioned engines (car/ bike, truck) that I know of (no-freewheeling).
 
Clark1961 said:
Bob, while it's very nice to argue theory without practical data, you seem to be ignoring my point that the rings are essentially unloaded during the exhaust and intake phases. From my perspective ring flutter is pretty much a myth or we'd see it in motorcycle, auto, and truck engines. About the only damage I've heard attributed to the load pushing the engine is valve drops on the old in-line Cummins and gear train damage on geared aviation engines.

On the other hand, detonation will destroy rings along with other parts.
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No, I'm not ignoring it. I just said it was plausible and the reasoning behind it, much like shock cooling is plausible. I didn't, however, say that I agree with either theory but I can understand the basis behind the thinking of those who do. I haven't seen practical data for shock cooling other then some research papers done by individuals that both ended up contradicting themselves, yet because the rational for the theories is neither outlandish or far fetched then it becomes very believable to those who dont have an intrest in looking any further into it other than word of mouth.

Bob
 
bob_albertson said:
You need the extra RPM on hot days with underpowered planes.
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Maybe in some max gross load /high density altitude situations when you're going around from low speed near the flare point, but it's rare, and most planes with constant-speed props aren't particularly underpowered.
 
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bob_albertson said:
You lack of experience with complex aircraft is actually showing here.
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So is yours.

1) The RPM difference between cruise power setting (which is what the last setting will be) and full RPM isn't 100 RPM - unless you have been incorrectly setting cruise power.
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Or you're flying one of the airplanes with fairly low max RPM's, like newer 182's, Aztecs, and a lot of other planes with max RPM's in the 2400-2575 range. In addition, if you're like me, you push the props to the climb power setting (usually about halfway between cruise and max) when you configure for the approach, using the flattened blades to help slow to gear/flap speed.
 
dmccormack said:
Cranky tonight?

:rolleyes:

A36
Vs1 = 59 KIAS
59 x 1.5 = 88.5 KIAS

C205
Vs1 = 50 KIAS
50 x 1.5 = 80 KIAS

T182RG
Vs1 = 50 KIAS
50 x 1.5 = 80 KIAS

So, which HP complex would 80 KIAS be a "really crappy profile?"

What's your point again?
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Point 1: Your arithmetic sucks. Point 2: You said Vs0, not Vs1.
 
TB20Pilot said:
While I'm sure its routine for you, that sounds like a recipe for disaster for an inexperienced pilot. LOP mixture settings won't work with full power at low altitudes. That's when you need max power for a go around and there may be several distractions going on at that time.
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Do you also leave the carb heat off in carbureted airplanes for the same reason? Personally, I teach my trainees to push on all the levers on go-arounds -- carb heat, throttle, prop, mixture, the works -- so there's no issue with forgetting anything which might interfere with max power generation on a balked landing.

I prefer to run the engine properly leaned at all times "except" take off and landing.
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I prefer not to foul plugs and lead up valves, since landing and after landing is when you pick up the worst fouling, but YMMV.
 
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Ron Levy said:
Maybe in some max gross load /high density altitude situations when you're going around from low speed near the flare point, but it's rare, and most planes with constant-speed props aren't particularly underpowered.
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Doesn't have to be low to the ground, at all.
 
Ron Levy said:
So is yours.

Or you're flying one of the airplanes with fairly low max RPM's, like newer 182's, Aztecs, and a lot of other planes with max RPM's in the 2400-2575 range. In addition, if you're like me, you push the props to the climb power setting (usually about halfway between cruise and max) when you configure for the approach, using the flattened blades to help slow to gear/flap speed.
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Actually, it isn't as you've yet to prove otherwise

The newer planes also come with cruise power settings using RPMs in the 2200 range for the engines runing 2500 rpm. That looks a lot farther than 100 rpm to me, but I don't know why you would be runing enough power to be in the governing range on final so that your trainees see that 300 rpm increase :dunno:.
 
Ron Levy said:
Point 1: Your arithmetic sucks. Point 2: You said Vs0, not Vs1.
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What Ron said. The 1.5 Vs0 is what got me (not vs1). That's not really the ideal speed for normal pattern ops in many complex hp.
 
bob_albertson said:
Actually, it isn't as you've yet to prove otherwise

The newer planes also come with cruise power settings using RPMs in the 2200 range for the engines runing 2500 rpm. That looks a lot farther than 100 rpm to me, but I don't know why you would be runing enough power to be in the governing range on final so that your trainees see that 300 rpm increase :dunno:.
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You want to start playing with specifics I have a redline of 2400 and often cruise at 2200-2300 so depending on how fast I was going...

But that is one specific airplane.
 
jesse said:
What Ron said. The 1.5 Vs0 is what got me (not vs1). That's not really the ideal speed for normal pattern ops in many complex hp.
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There's is no discernible difference between Vso and Vs1 as far as pattern ops in an A36, BE35, C182, C205. We're not exactly power OFF.
 
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