Maximum performance takeoff?
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For many, if not most, modern singles, 'save the engine' is a crock
Always use enough, but never too much or too little
To stir a bit more with technical point of view..
Most, probably all commercial airliners use "flex T/O power" scheme, meaning, power required is determined before T/O and put into computers... to use only power necessary to fit within safe acceleration/stop distance, not using power available. Reason is: saving engines - most FADEC turbofans calculate life cycles according to actual loads, so reduced power usage saves some $$ to company.
With helicopters, 100% means XMSN limit most of the time, not engine limits, particularly true with twins..
Most, probably all commercial airliners use "flex T/O power" scheme, meaning, power required is determined before T/O and put into computers... to use only power necessary to fit within safe acceleration/stop distance, not using power available. Reason is: saving engines - most FADEC turbofans calculate life cycles according to actual loads, so reduced power usage saves some $$ to company.
With helicopters, 100% means XMSN limit most of the time, not engine limits, particularly true with twins..
Chief Bottle Washer
Wasn't one of the contributing factors to the Qantas A380 engine failure the extra take off thrust used by Qantas on the trans Pacific departures? I believe that they are still departing at reduced weights to reduce the TO thrust.
As already mentioned many (most?) helicopter power limits are transmission related so actual engine exposure shouldn't be as extreme as the QF A380, but it is worth considering IMO.
As already mentioned many (most?) helicopter power limits are transmission related so actual engine exposure shouldn't be as extreme as the QF A380, but it is worth considering IMO.
SP, the A380 is a different beast and I don't feel a fair comparison
A) newer aircraft with less known, proven capabilities and operational limitations (I.e. The bounds of most single engine helicopters have been pushed and tested way more than the newer A380
B) the A380 is a much bigger beast, and material sciences are pushed to their limits building things that big and that light, way more than in smaller engines and transmissions
Edited to add: IMO a better comparison on point B is the Quantas A380 to the Cougar S92 issue and the materials issues on the oil filter, I.e. Issues of advanced materials on the bigger machines
A) newer aircraft with less known, proven capabilities and operational limitations (I.e. The bounds of most single engine helicopters have been pushed and tested way more than the newer A380
B) the A380 is a much bigger beast, and material sciences are pushed to their limits building things that big and that light, way more than in smaller engines and transmissions
Edited to add: IMO a better comparison on point B is the Quantas A380 to the Cougar S92 issue and the materials issues on the oil filter, I.e. Issues of advanced materials on the bigger machines
Last edited by birrddog; 11th Apr 2011 at 02:21.
Chief Bottle Washer
Playing the Devil's advocate here, we haven't really established this to be a thread solely about single engine operations but more about the use of full power or partial power on departure, and why 
Apart from the size of the A380, the issue of partial vs full power is proven to be an issue in the Qantas incident. I think that to introduce the materials aspect of failures in the Cougar S92 is drifting way off topic, though
Apart from the size of the A380, the issue of partial vs full power is proven to be an issue in the Qantas incident. I think that to introduce the materials aspect of failures in the Cougar S92 is drifting way off topic, though
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FW jets use partial power on takeoff to save money - most of the engines are leased (not owned) and they pay by the amount of power used and cycles.
The material issue was not the real issue on the S-92 crash - maybe that should be a different thread. The real issue was the assumptions made about the number of times the oil filter would be removed, versus the number of times it was actually removed. The folks making the assumption about removal rates didn't realize the actual rates, and the folks making the removals didn't realize that it was never intended to be removed as often.
Back to the 'maximum power takeoff' issue. From a certification point of view, the engines and transmissions are tested quite thoroughly to ensure they will be able to handle takeoff power, and there should be no qualms about using that power repeatedly. Lots of old wives tales still hanging around.
The material issue was not the real issue on the S-92 crash - maybe that should be a different thread. The real issue was the assumptions made about the number of times the oil filter would be removed, versus the number of times it was actually removed. The folks making the assumption about removal rates didn't realize the actual rates, and the folks making the removals didn't realize that it was never intended to be removed as often.
Back to the 'maximum power takeoff' issue. From a certification point of view, the engines and transmissions are tested quite thoroughly to ensure they will be able to handle takeoff power, and there should be no qualms about using that power repeatedly. Lots of old wives tales still hanging around.
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I was taught a technique which was described as "maximum performance take off" It was a description befitting the highest angle of sustained climb with the maximum weight at that angle.
Nowadays I don't teach it as it requires plenty of experience to contemplate and a small error of judgement can leave one in the trees very easily. Apart from the fact that we don't carry freight, we chase cows. (I now teach vertically only for confined areas, with the power you have available or you unload some gear, comprez? When applying power only apply what it is you require, and slowly too please.)
First I had to go fly, record some values and then plot a graph, power required against A/S. That is power increasing vertically on the left and A/S increasing laterally to the right.
Two values could be deternined, firstly a tangent from the zero (AX) position touched the curve on the increasing - power / airspeed side at the best range airspeed. For the 47 this was around 60 knots.
Secondly another tangent back from the minimum power A/S of around 45 knots to the decreasing power side touched the curve at around 25 knots.
Then we went and immediatly as we took off set an attitude of 25 knots, pulling smoothly through to full throttle and hey presto, the aircraft climbed straight as a dye very steeply (for as long as you wished) and would carry much more than an attempt at the vertical. Firstly one must do a hover to gain confidence in the engine's continued operation.
Of course that was also much less than it could carry at an IGE T/O accelerating to the minimum power aispeed in comfort.
This technique was designed to educate pilots not to jerk themelves vertically and then find themselves over pitched over the canopy with no RPM left. A fact of life in the early days in NG, my instructor informed me, especially when pilots were battling with low and very low power machines.
The same nomeclature (max perf T/O) was used to describe the shortest field T/O in a fixed wing, which always amused me as the best performance in both types comes from a long flat surface. There you go.
The idea was that if wanted to lift anything and make money out of it, find if possible a clearing which with a little application of some elbow grease and a sharp axe could be turned into a profitable operating area.
From the ground the disc had to sit about two fingers of the outstretched arm above the canopy.
Rule of thumb to attemp it was 3 to 4 " margin over the power to hover OGE, where-as the vertical was always 5" margin.
Nowadays I don't teach it as it requires plenty of experience to contemplate and a small error of judgement can leave one in the trees very easily. Apart from the fact that we don't carry freight, we chase cows. (I now teach vertically only for confined areas, with the power you have available or you unload some gear, comprez? When applying power only apply what it is you require, and slowly too please.)
First I had to go fly, record some values and then plot a graph, power required against A/S. That is power increasing vertically on the left and A/S increasing laterally to the right.
Two values could be deternined, firstly a tangent from the zero (AX) position touched the curve on the increasing - power / airspeed side at the best range airspeed. For the 47 this was around 60 knots.
Secondly another tangent back from the minimum power A/S of around 45 knots to the decreasing power side touched the curve at around 25 knots.
Then we went and immediatly as we took off set an attitude of 25 knots, pulling smoothly through to full throttle and hey presto, the aircraft climbed straight as a dye very steeply (for as long as you wished) and would carry much more than an attempt at the vertical. Firstly one must do a hover to gain confidence in the engine's continued operation.
Of course that was also much less than it could carry at an IGE T/O accelerating to the minimum power aispeed in comfort.
This technique was designed to educate pilots not to jerk themelves vertically and then find themselves over pitched over the canopy with no RPM left. A fact of life in the early days in NG, my instructor informed me, especially when pilots were battling with low and very low power machines.
The same nomeclature (max perf T/O) was used to describe the shortest field T/O in a fixed wing, which always amused me as the best performance in both types comes from a long flat surface. There you go.
The idea was that if wanted to lift anything and make money out of it, find if possible a clearing which with a little application of some elbow grease and a sharp axe could be turned into a profitable operating area.
From the ground the disc had to sit about two fingers of the outstretched arm above the canopy.
Rule of thumb to attemp it was 3 to 4 " margin over the power to hover OGE, where-as the vertical was always 5" margin.
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So am I right the consensus is:
Using one's common sense accrued over one's career pull power for the situation as you see it for the aircraft you feel. Don't be scared to use 100%.
Too many myths running around the industry on this, that's for sure.
Using one's common sense accrued over one's career pull power for the situation as you see it for the aircraft you feel. Don't be scared to use 100%.
Too many myths running around the industry on this, that's for sure.
So am I right the consensus is:
Using one's common sense accrued over one's career pull power for the situation as you see it for the aircraft you feel. Don't be scared to use 100%.
Using one's common sense accrued over one's career pull power for the situation as you see it for the aircraft you feel. Don't be scared to use 100%.
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Consensus?
This is the internet people! We can't have a consensus!
I can't imagine using a minimum-power take off from a confined area either, I would try to minimize exposure to any obstacles in the area. My (short) experience tells me hitting something happens more often than power failures, in confined areas.
I can't imagine using a minimum-power take off from a confined area either, I would try to minimize exposure to any obstacles in the area. My (short) experience tells me hitting something happens more often than power failures, in confined areas.
