Flying over square
 

Just sitting around chugging down a cab sav and reading some forums, the one that took my interest was on CSUs and it got me thinking about the practice of flying over square.
I've heard this term mentioned before but don't know much about it.
Just wondering how many pprune folk use it and why do you use it?
What are the benefits if any.

Knox.

What do the instructions say?

Bbbbbzbzbzbzbzbzbzbzbzb

Read the manual for the engine you are operating as fitted to the airframe you are flying, it is all in the book, simple really

Flying square is muppetry in motion :eek:..its for people too lazy to read the book, and certainly won't keep your owner happy.
The only time flying square is acceptable, is an emergency when you don't have time to read the book, OR the book says so.

Classic example is people on Beech 95's... hey lets do our climb at 25/25...quick check reveals you are outside the MCP envelope. Then we'll cruise at 23/23 and wonder why it will only do 150 knots :mad::mad::mad::mad::mad:

Look up John Deakin (Pelicans Perch), download all ten articles and crack a bottle of Cab Sav. Some of the best, most insightful, soundly researched and demonstrably RIGHT info you will ever read. If you cant find 'em, drop me a PM; pretty sure I've still got them on a HDD somewhere.

God I cringe now at the guff the 'highly experienced instructors' sprouted about taking off in the mighty Arrow, then pulling the prop back to 2500 RPM and reducing power to 25" ...... the INCREASING power again to keep it at 25/25 as you climb.:rolleyes:

Pelican's Perch - More Stories

I think the article is called Manifold Pressure Sucks.

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

direct link above.

Great article...ain't seen that in a while :D

Funnily enough, what's best for the engine is to run the highest MP/lowest RPM combination that the power tables will allow for the pressure height you're at.

You'll find that the lycoming that goes in Arrows will give you something like 75% cruise 25.4"MP/2100rpm for a certain height (can't remember the actual figures but it's something with pretty large disparity).

It takes very little effort to look at the book and get it right:ok:

Simple fact is , MAP in inches has zero relation ship to RPM in...well...RPM.

Where would we all be if the MAP were in Mb or the RPM in percentage?

It just so happened that the commonly used figures "sorta" lined up and so people who couldn't be arsed to read the manual came up with a rule of thumb.

100% absolute, utter, breathtakingly ignorant rubbish.:ugh:

WOTLOPSOP as Deakin, Atkinson and Braly preach at their APS workshops.

Wide Open Throttle. Lean Of Peak. Standard Operation Procedures.

Thanks for all the great replies.

I was always taught that if all the gauges (MP & RPM) were in the green you couldn't really go wrong.
I remember once doing bumps and goes with a very experienced testing officer and having the RPM set at 2200 rpm (in a C206) and just using the throttle in the normal way but never exceeding the green arch of the MP. The aircraft preformed well and with no noticeable issues.

I have been told that if you run, for example 25/2300 you can get a few kts extra out of the cruise speed.

And one last thought, a lot of flight schools seem to promote going through to full fine on final approach often with no regard to the prop/engine and in the process creating a gut wrenching scream (for lack of a more descriptive word) from the prop/engine. Is this just poor engine management, as I can always seem to get the aircraft on the ground without doing this.

Knox.

I've always found aircraft to fly a little faster running a higher RPM than MP (say 23/25).

As for valves, they will go sometimes regardless of how you operate the engine, it all depends on who and how they were seated during engine build/overhaul.

Correct me if I'm wrong, but Deakin and crew suggest that with a higher RPM, the engine will run cooler as there is more air being drawn through and the heat is taken away from the cylinder heads quicker... that will make the engine last longer.

Refer here:
http://www.lycoming.textron.com/supp...Operations.pdf
Pages 43-44 and 65
Don't forget to refer to the POH for any power setting restrictions.

A brief bit on CHT page 51-52.

Off the thread a little - One other useful section is 54-56 regarding sticking valves. One such event was a slightly sticking valve at start up that was actually caused by one of the 2 springs broken. At some stage would have ended in tears if left unattended.

A link to the some other Lycoming stuff:
Key Reprints - Lycoming

Continental IO-520 with GAMIjectors. WOTLOPSOP for me. 1100+ hours, and going strong. Never had the TCM factory cylinders off since new.

Millenium pots, however, a different story :rolleyes:

Knox,

Just some hints on what to do with all those complicated knobs. Generally speaking from TOD to parking it outside the hangar, use only the throttle to reduce power either on descent (keep speed under control) and in the circuit. No need to touch the mixture or RPM. Some days you may need a small and I mean small amount of richer fuel air ratio if it gets a bit rough on descent. But only just a small tweak ya hear! ;)

So on finals, boost pump should be on (unless otherwise noted), gear down as required and whatever else you have already checked on downwind.

In the unlikely but possible event of going round, remember you are already flying so there is no need for anything rash here, it is simply red knob, blue knob, and black knob.

As for other items, over square, what do you think happens on takeoff? That is over square. And some engines like those big round supercharged things have limits, but basically the bulk of Lyc's and TCM's are simple operations.

In simple form a flight should go something like this;

1. Start up, and lean until the RPM peaks and just starts to drop.
2. Taxi out and do your runups at say 1700RPM and only richen up enough to get 1700 smooth, do not over do it, watch RPM and EGT's (of course you have an all cylinder monitor) and on each mag, all EGT's should rise together. If any fall there is a plug mag or wire problem.
3. Line up, switch boost pump on, mixture rich....GO!!!!
4. passing through 500-700 feet take note of the EGT on any one cylinder (or the EGT on single probe) and remember it, this is now your TARGET EGT.
5. Depart the circuit and climb, do nothing unless for noise abatement.
6. Passing say 3000' lean back to get your target EGT on whatever cylinder you picked, probably cyl 1, and near enough is good enough. This will keep your fuel air ratio about the same as it was when you were full rich at sea level. Keep climbing.
7. Passing 5000' or there abouts chase that target EGT again, and again at 7000'.
8. Level off at your desired altitude, set the RPM where its smooth and comfy, (better with a dynamically balanced prop) say 2200-2500, and then lean to a setting appropriate to power setting, but lets say around 70-65% that is just LOP to 25LOP .......if you need injectors tuned, do it, in most carby engines you can get this if you try hard enough. If its carby and fixed pitch.....better come see me as its too hard to describe here! :bored:
9. enjoy the cruise and low fuel burn, cleaner pistons, plugs valves etc and MUCH LOWER CHTS!
10. TOD, nose over and reduce throttle setting to keep speed under control, if I am doing a 700'/min ROD I usually pull back to the MP I had in the cruise, and the speeds stay just in the green.
11. Join circuit and land with just throttle movement, shut down as per normal. Going full rich just carbons everything up, so don't do it.

I am sure most here know what this is all about but if there are a number of folk who would like to see this done, and like to learn about the science of it, and can get to SEQ, call me. It can be fun and educational.:ok:

J:ok:

PS Chimbu Chuckles will no doubt correct any errors or omissions above :)

I was always taught to land full rich, full fine pitch, never really liked the sound of fine pitch stops on final.

I've just dug a 182 POH out of the bookcase to compare and it does have pitch full fine for takeoff, landing only says fine and balked landing specifies 2400rpm. From that I guess an interpretation could be made that Mr Cessna is telling us to do it your way with a overall fine setting and not shove the prop control as far forward as you can.

I think I'm inclined to change methods :)

If you have a big enough hand..just push up all 3 at once on go around! At a sensible rate mind..don't want to shock an old donk

If I'm in the 210, I don't touch anything from TOD (regardless of how high that might be) until I shut it down, other than the MP to keep the IAS in the green on descent.
The 172 however, might need a tweak of the mixture on the way down to stop any rough running and keep things smooth, if it's been operated at full throttle up high.
As far as running things oversquare are concerned, that won't be responsible for the junking of cylinders/engines. For a given power setting, you'll generally find the cylinder head and oil temperatures to be slightly less than what they would be running the engine at a higher RPM.
Anytime you fly a T210, Chieftan etc., it's almost always being operated oversquare as a matter of course and it doesn't hurt those engines.
Oversquare in a NA engine? Once you climb above around 4000/5000', it won't be the case anyway.