Question about variable-pitch propeller aircraft & slow flight

[The Green Goblin]

hmmmmm

Very interesting stuff.

Thanks for that link!

[ForkTailedDrKiller]

My two cents worth!

For what its worth, I generally look to the POH for advice on power settings. If I want to just stooge around slowly, I also tend to wind the RPM back (cause I like to have a quiet life) toward the bottom end of the RPM green arc and then set the MP I need to maintain the target speed (eg 2100/18" with 10-20o flap).

Dr

[bushy]

And there are some dead people who did 45 degree turns at 100 feet while checking the water level in a dam etc.
Pax don't like 45 degree turns.
Beechcraft have printed some safety information, and the one I like says many accidents are caused by pilots stalling their aeroplanes, so they suggest we take great care to NEVER allow our aircraft to stall. (when it is more than two feet off the ground)
Think about it.

[ZEEBEE]

Stabilized operation is prohibited above 25" manifold pressure between 2300-2350 RPM and below 15" manifold pressure above 2600 RPM

How do you EVER get stabilised operation above 2600 rpm with less than 15" MP with any of those engine/prop combinations listed ???

[The Green Goblin]

Not that it matters guys but you won't be taking a small donk like this up to 12000 feet unless you are a VFR pilot stuck in cloud trying to get on top in an abnormal situation or a meat bomber with oxygen supplies. (who would usually be using something with a snail on it anyway)

I don't want to clean up a VFR 172 on the way down who is playing test pilot for the day in class E/G airspace.

Stick to your 2000-8000 feet charts and you won't get into trouble

[Jabawocky]

Here Endith the Lesson!!

.enough from me......read here >>>>>

Pelican's Perch #15:<br>Manifold Pressure Sucks!

then

Pelican's Perch #16:<br>Those Marvelous Props

then

Pelican's Perch #18:<br>Mixture Magic

then

Pelican's Perch #19:<br>Putting It All Together

and just something extra for you!

Pelican's Perch #1:<br>Throw Away That Stupid Checklist!

J

[bushy]

Mr Goblin

You are quite likely to find small aircraft well above 8000 feet, usually because they are trying to get out of the thermal turbulence that occurs over much of our country. And they have a perfect right to be there.

[ForkTailedDrKiller]

Stick to your 2000-8000 feet charts and you won't get into trouble

??

Pardon my ignorance, but what charts are those?

Dr

[squawk6969]

Joker 10

In one word YES reckless

Very good sir

And very well spotted, you were probably aware of the fatigue issues of large spans of aluminium as in wing skins.

At low levels and very high air desities those pesky air molecules create far greater force at high angles of incidence and in an older airframe this over time creates severe fatigue cracking around the ribs and rivet heads.

Of course renters would never care and its only the owners that suffer in the long term.

SQ

[The Green Goblin]

Come on fellas a lighty shouldn't be over 10,000 feet without oxygen for the Pilot and once over FL140 oxygen for the punters too.

I was merely pointing out that providing a power chart for what looks like an IO-360 at FL120 and saying that you could not run it 'oversquare' at this altitude is a little pointless.

And yes I'm hearing you about them dreaded thermals especially over red country having spent many hours there myself. If you have a bottle with you and your machine is capable at those altitudes then it's a big sky and we are all welcome!

[Jabawocky]

Forkie, bring the O2, see how far up the Retard Vehicle will go!

Better still, I should get my own, and you bring the Bo and no Turbo's allowed to be fitted!

[baron_beeza]

That "braking" effect you use is provided by the friction in the engine. The friction is between the piston rings and the cylinder walls and is most pronounced at the higher RPMS

.

FGD135

Have you got any references for your comments. I have been in this game for a long time and I am sure I have never heard any of this before.

This engine braking effect you speak of .............
many here have ridden motorcycles, - I am sure they will agree that a Yamaha 500 4 stroke twin will have far more engine braking than a Kawasaki 500 triple. And the Two stroke triple would normally be pulling far more revs.

I admit this was certainly true in the 1970's ........

I chose this mainly because every rider of the period knew only too well the differences in the 2 strokes power, - but also incidentally it was the same period as the engines in our aircraft were produced.

Please don't try and tell me that the 2 stroke has ports in the bore so the rings are not strictly against the cylinder walls the entire time.....




Engine braking - Wikipedia, the free encyclopedia

Please don't tell me that your are involved in aircraft engineering in any capacity also.

[The Green Goblin]

Of course, that friction-induced braking effect is there all the time. You only notice it when you are using it to slow the car down but it is always there. It is there when you are accelerating and there when you are cruising.

The lower the RPM, the significantly more reduced is this friction effect.

This is called "friction"

If your pumping in the gas to keep it turning you'll loose some of the ponies to mechanical friction and receive the rest as torque through the shaft which produces thrust from the propeller. If you lay off the gas the airflow will drive the propeller and the mechanical friction will absorb the energy in the airflow. If the engine has failed you feather the propeller to preserve this energy, if you have a live engine you use it to your advantage to slow down!

Your argument is flawed. Higher rpm equals the propeller taking smaller bites of air with a finer blade angle at a higher rate. Lower RPM equals the propeller taking larger bites of air at a slower rate with a coarser blade angle. The engine does not know any difference! It's still producing 65% power in the cruise via torque from the shaft which is feeding the propeller governor. The prop governor is doing all the work converting the torque from the engine shaft into a set RPM as per what is set on via the CSU which in turn produces thrust from the engine via the propeller.

EDIT

Hmmmm

Having a look at the power graphs from the previous page I pulled two examples.

2500 rpm 22" 66% 124 KTAS 8.8 GPH

2200 rpm 24" 66% 124 KTAS 8.9 GPH

The engine is producing more MP at a lower RPM for the same percentage of power output. I would assume the engine is working a little harder to turn the prop via the governor at a higher RPM loosing about 2" in the process.

[Flopt]

O2 bottles

I got a spare one Jab....I'll loan ya one......The Mo is quite happy at FL130 coming home from YWTN...usually gets 190 g/s...

Flopt

[Flopt]

It's pretty quiet up there too.....

You can check the BOM for CBs [with 3G and a laptop] ,and plan to avoid them, chat with FTDK on skype [ get his opinion about avoiding CBs if you need to!], email the missus with eta, check your bank account , transfer some money, read PPRUNE and post photos , get latest notams &tafs ,lodge fplans/amendments on NAIPS, maintain coms without HF, and VOIP your Airbus Captain mate in Qatar........all the while maintaining a good watch for traffic of course.....and monitoring your panel.

And it's usually as smooth as a baby's bum!!!!!!! 3.5hrs later you're home. And if there is a bit of weather you are usually on top of the benign stuff and you can see the really crappy stuff and compare it with the WX10+/BOM/WZ [wish you had one eh Doc!].

Flopt

[snoop doggy dog]

Toss Pots

A fella ask for some advise on doing a scenic flight.

It some how turns into a Wank fest

Get over yourselves

[das Uber Soldat]

Thanks for your entirely useful input.

The thread posters question was answered some time ago. The thread has now turned into an interesting discussion / debate about what I regard is a fairly poorly understood concept.

I think its good.

[ZEEBEE]

That "braking" effect you use is provided by the friction in the engine. The friction is between the piston rings and the cylinder walls and is most pronounced at the higher RPMS

I was hoping that Harley would weigh in on this one, but since he's allowed it to go through to the keeper, here goes;

While it is true that the higher the engine speed, the greater the friction, it is only a small part of the "braking effect" that one uses with motor vehicles.

In motor vehicles the braking effect is the combination of the gearing of the engine to road speed and the resulting retardation provided by compression pumping within the engine without fuel addition.
If one wants to control the braking effect, then a small amount of accelerator will allow some fuel to arrive at the combustion chamber and use the compression products to deliver power according to the fuel supplied.
With no fuel, the compression developed is still there but it is ALL wasted in the form of retardation provided to the wheels that are driving the engine.

As for you Snoopy if you don't like the discussions then go and play somewhere else.

[Jabawocky]

FLOPPY

I got a spare one Jab....I'll loan ya one......The Mo is quite happy at FL130 coming home from YWTN...usually gets 190 g/s...

Flopt

You sure???? I think you should get your eyes checked!

[bushy]

You have to be nice to them. But they will go there, and higher.