Lumps

You getting all this down Ilikeflying?

yr right

jaba leadsled just of a matter of interest how many CofA have you done and placed on the aust register


cheers

yr right

Jaba just as a matter of interest is the course you are running casa approved and are you an approved casa trainer under part 66 (sorry think part 66 late and can't be bothered looking it up.

Cheers

cockney steve

IO'll try and make this easy a
At hand-rotation, (s l o w l y ) the Static timing is set, say 20* BTDC

@60 RPM, that's 1 rev /sec =360* = 36* in 1/10 of a sec...agreed?
Ignore the speed of the points opening, for the purpose of this illustration, and call it instantaneous. You agree that there is a finite TIME taken for the Primary flux to collapse and induce a voltage into the secondary. ?
Now , the same engine is turning at 2400 RPM...So, in that same 1/10 of a second, the crankshaft has turned 144* (cos it's now doing 4 times the speed in the same amount of time.

THE SPARK- PROPOGATION IS TIME-CONSTANT, THE DEGREES OF CRANK- ROTATION ARE VARIABLE.

Therefore, timing between static and dynamic will vary and this is directly proportional to crank speed.

Similarly, the time taken for the mixture to burn and start expanding, is a constant for a given mixture-ratio,compression-ratio air temp. etc......but the faster the crank is revolving, the more degrees it will have turned in the TIME it takes for the fire to get burning.

The fixed- timing works because Aero-engines are virtually constant speed....Road- vehicles aren't . that's why they benifit from both mechanical and vacuum A/r or the current, sophisticated electronic brain controlled ones also use Lambda and knock-sensing.

Incidentally, 1-litre petrol cars are now commonly doing 60 mpg....20 years ago, you'd expect something approaching 40....this extrapower has come from a weaker mixture!...the same size gallon is now spread over50 percent more miles....agreed?
So, how come, the bane of motoring, BURNT EXHAUST VALVES has also virtually vanished in the same time frame.

A Squared

Thanks for the explanation. For the record I wasn't disputing that difference between static and effective running timing exists, I was just wondering what was behind it.. One tends to think of electronic events as happening instantaneously, even though, having spent considerable time staring at the patterns on an R-2800 ignition analyzer, I know better.

jdeakin

A comment on POHs in the GA world, if I may.

At the end of the weekend, George sits down with excerpts from roughly a dozen POHs, and points out "problems" in them for our class. Direct contradictions, in the same manual! Contradictions between manufacturers of different airplanes with the same engine! Contradictions between airplanes of the same model, identical engines, but with differing model years! After an hour of this, no one in the class views the POH as "divinely inspired" again!

In a recent class, George had just dissected a particularly egregious section of the manual, and the class was sitting there in shock that it would say such a ridiculous thing.

A voice came out the semi-darkness, saying "George, may I interrupt?"

"Sure, go ahead."

"When I was a freshly minted private pilot, and also a freshly graduated lawyer, I went to work as an intern at Cessna, in Wichita. To me fell the task of writing the POH for that year's Cessna 210. I will confess that it was I who wrote that specific language. It is only now, as a result of this weekend that I realize how very bad that POH was. I am deeply embarrassed by it."

And he sat down in dead silence.

Everyone here might do well to take a moment of equally dead silence to consider his words. He is highly visible person, well respected in aviation today. I certainly respect him for his candor.

POHs for GA aircraft contain a section on LIMITATIONs. If something is written in LIMITATIONS, you'd best pay attention to it. APS has never suggested anything against those LIMITATIONS, and I doubt we ever will. In general, they have been reviewed very carefully by experts both at the factory, and by the FAA. They are short, clear, and to the point.

The section on PERFORMANCE is much the same, for it contains the results of actual testing, and as such is HARD DATA.

The rest of the material, I'm sad to say, runs the gamut of quality, from "pretty good" (Cirrus) to "abominable." In many POHs it is material written by inexperienced people (some not even pilots) to satisfy the FAA and the inexperienced CFI with 400 hours. The FAA has even stated time and again that "Limitations are required, everything else is optional."

If CASA has gone beyond this, it is a tribute to the remarkable institutional stupidity of that organization, amply and vividly demonstrated by the Wyalla Report. It needs to be changed. How to change is above my pay grade.

So please, do what you must to satisfy the morons who work there, but DON'T make the mistake of thinking they are right, when they are most definitely not in suggesting the "How to fly" text in the POH came down from Mt Sinai, along with the Ten Commandments.

No Hoper

No one would dispute that there may be a difference between static timing and dynamic. The initiall proposition was that the difference was in the order of 13 degrees or more. A degree or so is the allowable tolerance when setting the timing and between the magnetos.
Cockney steve, there are material Reasons why valves don't burn in modern auto engines

Aussie Bob

No Hoper (and others) please correct me if I am wrong, but say you set the static timing carefully to 20 degrees before TDC.

When the engine is running at around 2500 RPM, the actual timing will be around 12 degrees BTC?

No Hoper

Aussie Bob, from engine runs with a strobe light the most variation I have seen is about 1 to 2 degrees. Anymore was reason to suspect the initial setup or integrity of the system. If the timing is drifting back to TDC there is noticeable loss of power on the dyno run.

Jabawocky

no hoper
If you are reffering to me....that is simply wrong.

If I have somehow written that...I am perplexed. Having said that, set at 20 with one magneto setup, at idle you can get the occassional events like that. Typically is is more like a less than 5 degree lag. And a up to one degree variation on that or any point around there.



yr right

When will you answer all my questions so far? Or are you afraid to? They were not set up as traps. I would hat to be the Judge in a court case with you on the stand. Contempt of court perhaps?

How many CofA's I have done or been very involved in between 2-5. Not many. Some of you might ask what this has to do with the price of fish in Bondi ?

CASA approved training? You have got to be kidding. The answer is no and no thanks. But I would ask you to make contact with me so I can put you in touch with an extremely senior CASA employee, direct report to the DAS, and he can explain why the Authority has paid (I assume) for him to attend about 8 years ago and again last year.

Certain folk here were witness to this if you can't take my word for it. In fact I can think of 6, yes SIX people on pprune who can back that up. Do I need to name them all too?

And who needs it to be CASA approved? If you go to a Lycoming engine assembly school in PA do they need to be also?

Please do not book in for our class. The data would drive you over the edge.


UL........that is so true.

Creampuff

Yes – ‘ish’, on bog standard piston aero engines. The static timing depends on the specific engine model – some 22, some 24 for example. The amount of delay between the points physically opening at e.g. 22 and 24 BTDC and the spark happening is in the order of half a dozen to a dozen degrees, depending mainly on engine RPM.

The kind of timing referred to by No Hoper – using a strobe light – has its own built in delays. To put this another way around, the strobe does not flash the instant the points physically open. Often the strobe flash is triggered by the spark itself by a sensor on the spark lead, and the timing mark has been marked based on that assumption.

But I’ve had an awful revelation. I’ve just looked at the POH for one of the aircraft I usually fly, and have realised there is no procedure for descent! That is, it doesn’t say lower the nose or pull the power or anything else about how to get from cruise altitude to terra firma. What will I do?

Aussie Bob

Thanks no hoper

QFF

John, I always thought POHs were were written by the marketing department. Now you are suggesting lawyers were involved.

What is the world coming to? Soon they'll be asking pilots and engineers to write them next....

Jabawocky

POTY by Creampuff;
The less it says the more it tells you. Like Leadie's Boeing examples. Unfortunately most people be they pilots or LAME's are not critical thinkers.

yr right

Jaba
I asked about CofA for one particular reason. The CofA among many things is also a document chasseing exercise . Now one of the documents that has to be done is the POH, it has to show all areas of the aircraft performance in regards to any additional modifications that may incur engine airframe avionics fuel systems etc.
It is a legally binding document.


Now there is a big difference between static timing and the losses that you have said, a small loose is is explainable but the looses you have quoted arnt.also are your dyno models simulated ie computer based or actual runs with a hard full noise engine,


now a question was ask about automotive engines and why the don't burn out valves well there are few reason's one the size of a cly volume for a start now electronics that monitor the engine at incredible speeds, but the main reason correct me if im wrong and im sure you will is that air is quite an inefficient way of cooling as compared to a water based cooling system where you have the heat removed from the valve areas with 100 precent contact of the fluid surface to the substrate which it flows over, now also the main reason that you have forgotten is we gone away from 2,3, to 4,5,6,7,8, and now to 9 speed transmissions to allow the engine to run at its most efficient rpm range


Now Jaba
Your not Casa approved you not running a Casa approved course. Im sorry but that tells myself and I bet others quite a lot as well. (no personal attack here at all)
You see as a LAME I cant do a PT6or any other course for that matter or do a course any were I wish, if its not on the approved list it is not recognised at all despite having spent thousands of dollars on it.
This not only give credibility to that approved course but also shows they have met a standard.


I will also tell you I am also hold trend qualification and I am approved to read the data and act on it.


Cheers

yr right

mmm electricity stuff travels and the speed of light and the speed of light must travel at the speed of light or close to it so there for the rotating mass of an engine travailing at 2500 rpm must be moving at faster than the speed of light or fuc& we on to something here.


cheers

wishiwasupthere

I take it there is no requirement for LAMEs to be able to write legible English?

No Hoper

Creampuff, not on my engines. The same timing marks are used for static and dynamic.

Jabawocky

yr right
Absolutely, , and I am involved in a round about way in delivering a CASA approved training module that teaches EXACTLY that.

So in that case the POH Creamie describes above is creating thousands of illegal descents and landings????

How many have you written? Have you had a few moments to reflest on Mr Deakins comments through this thread. He at least has written a few.

I think you would ask a different question had you spent even just a few minutes watching this for real. I am quoting you from HARD DATA, REAL ENGINE RUNS with real engines and no computer modelling involved. You would enjoy it, it would be very confronting, uncomfortable and challenging. The opportunity I extended to you to see it still exists, although I would need a strong curtailing of your present attitude though, unlearning and relearning takes a preparedness of the mind to accept that what we knew to be true is not. Just like the folk who thought the earth was flat. Very difficult to accept at first when all you knew was proven to be different.

Air cooled Vs water cooled is another kettle of fish....we should save that for face to face discussion. Or at least when I have a few hours.

It tells me a lot too. It tells me that all the LAME's many of whom you know and respect apparently are wrong and foolish. So did you ever call Mr Bowden, Paynter or Denyer? How about you PM me your email address and phone number and I will put you in touch with the CASA folk (current and past) who have attended and ask them. You might find that educational as well.

I do not know how much more I can do.

I think it is fair to say you are a diligent hard working and passionate man with many many years of experience. But there is scope out there for more learning. I have found the more I know.....the more I want & need to know, and there is so much more to know. I know realise how little I do know.

Yes it does, once the electron flow starts this is true, it is the triggering of this that has the delay. If you take a wing on a B747 and examine the spars and maybe pick up a section of spar, it will be very strong and sturdy. So much so despite all your strength, you can't make it twist or deflect, but somehow when you taxi out of Paine Field in Everett WA the wings are bouncing up and down like a piece of rubber. And worse as the aircraft lifts off I think you get my point. Have you ever seen the loads on a crankshaft? Again, eye opening stuff.

Creampuff

Let’s say a propeller is being directly driven by a crankshaft is rotating at 2,700 revolutions per minute.

That is 45 revolutions per second.

That is 16,200 degrees per second.

That is 16.2 degrees per millisecond.

That is 8.1 degrees per 0.5 milliseconds.

(For yr right, that’s one half of one thousandth of a second for the crankshaft to rotate 8.1 degrees.)

When the mechanical points open in that steam driven magneto, the spark does not happen instantaneously. It takes time for the secondary to build up to a sufficient voltage to cause a spark. How long it takes from the points opening to the spark actually varies from cycle to cycle. The crank’s twisting and the fuel air charge is slightly different each time, but all it takes is a delay of one half of one thousandth of a second and the crank’s already rotated 8.1 degrees. Sometimes it will be quicker and sometimes it will be slower, but the laws of physics dictate that it’s never instantaneous with the opening of the points (except when the static timing is being set up and the crank isn’t rotating).

NH: Please state, precisely, the kind of ignition system and procedure for setting static and dynamic timing: That is, what test or other equipment you connect, where, and what you are measuring.