trying to figure out the "ata" gauge

[bDAWg]

so the ata gauge is actually used for a few reasons.....for keeping the intake manifold pressure to the values specified in the pilot's notes for peak performance during the different work loads ...and also just as importantly it's used to prevent engine failure due to detonation....or what I've always referred to as "knocking"

great info guys...you know I googled about this earlier today and was unable to find anything about this subject...this will probably help out quite a few of us who are new to this somewhat more demanding CEM.

[Babi]

Originally Posted by bDAWg

.this will probably help out quite a few of us who are new to this somewhat more demanding CEM.

Yep, and a sticky thread would be a good idea too.

[Babi]

did a little testing on detonation with the spit mkIIa.

sea level, throttle to max, boost cut out (the instrument was reading +9, but that's the max), pitch to a minimum (1700 rpm). the plane flew on for 20 minutes. no damage. I thought this was the worst possible scenario for detonation (max pressure, min rpm).

did the same thing with max rpm (3100 rpm) this time intermittent black smoke appeared, (that would go away if i put boost level back to +6), but again no damage. after another 15 minutesi grew tired and closed the radiator, which led to "perforated water radiator" in a few seconds.

what am i doing wrong? i thought the engine were much easier to damage.

[MadBlaster]

Likely the spit's constant speed unit won't allow you to do as much damage with the governor in place, verses 109 where you can directly control the load (in manual prop mode) and screw it up really fast. In other words, they probably designed the CSU as much as possible to mitigate the extreme situations on the engine (lug and over-speed).

[Crumpp]

So you can see how lightly boosted the German engines were:

Because the German engines typically had higher compression ratio's....

Increasing the compression ratio of an engine is one of the best ways to increase horse power and torque.

http://www.nightrider.com/biketech/h...ompression.htm

This is another advantage to direct fuel injection and by product of a more accurate fuel metering system.

More efficient, higher compression ratios are usable, due to accurate fuel metering.

http://www.twminduction.com/faq/faq.html

[Crumpp]

most engines tended to both be rated in multiples of 50hp

An Engines rated power is a percentage range over a manufacturer's guaranteed mean. That means it has considerable variation even on the same assembly line.

Aircraft engines are built to very tight safety margins like all aircraft components. It is not like a ground vehicle where you can overbuild using large safety margins.

Stress aircraft components beyond what the engineers allow for in the Operating Instructions and they will break. It is the engineers that set those instructions based on the work an airplane is designed to perform. Fighters are built for top performance in order to destroy enemy fighters for example. There is no wiggle room in that.

If you do your research, you will find that all of the "boost increases" are accompanied by technological advances that maintain the same minimal safety margin.

To hold an aircraft specifically designed for a world record attempt as anything representative of any type of service or engine designed for normal operations is ludicrous. It is apples and oranges from which you cannot draw a single conclusion about what goes in front of the firewall on a practical aircraft. It is like drawing conclusions about capability of the car in your driveway engine by examining a top fuel dragster.

Those airplanes are specifically designed to achieve one goal and nothing else. They don't care if the engine last's 15 minutes if it only takes 5 minutes to set the record.

Many of these record breakers were completely impractical designs for anything other than that attempt. The Me-209 for example was a stability and control nightmare and was impractical for anything more than a few minutes flight of rather risky flight. That is typical of these "record breakers".

[justme262]

I enjoyed your post Viper2000. Fascinating.

Any one know why the German engines were so lightly boosted? Was it a design decision or the quality of the fuel they had?

Such a complicated and interesting subject it is hard for me to understand late at night... For a second I wondered if the Merlin engines superchargers had a ratio of 2.7 because that is the natural log "e"... then in a moment of inspired confusion I imagined that was also why they have optimum RPM at 2700! hehehe
I'm going to bed...