Maximum performance takeoff?

[Heliport]

.
Maximum power available?
Or minimum power necessary to climb and clear the obstacle(s)?

Most pilots seem to say max power is safer because it reduces time spent in the shaded area of the H/V curve.
Others say minimum power necessary is safer because, in the event of an engine failure, the less power you’re using the more rotor rpm will be recoverable to help in the autorotation.

When you have a choice -

Which technique do you prefer, and why?

.

[S76Heavy]

Are you talking singles or twins, aerea's suitable for emergency landings/ autorotations or hostile area, etc?

I was raised on Cat A profiles, which seem to dictate the minimum power necessary to get the job done, so I may be biased.
Besides, with Cat A you are not supposed to enter the H/V curve at all.

One of the risks of max power to me is indeed that if you lose the donk, you lose NR very quickly, it has a large effect in yaw which makes recovery more difficult and you need to react very quickly and correctly to get it right.
I prefer the better control of the machine in case of an engine failure over the fraction of time less spent in the curve over the total of the flight.

Interesting dilemma though; looking forward to more replies.

[Art of flight]

Think we're talking singles here due to the 'autorotation' scenario.

Been flying twins so long I can't remember, think we used to pull max power and go, no profiles either!

[rotorfossil]

On a single, the best takeoff profile stays outside the H/V curve as per the POH, only using climb power once safety speed is obtained (60 kt in Robinsons). Only use the max performance takeoff technique if there isn't a clear exit path.

[EN48]

Which technique do you prefer, and why?



In a lightly loaded B407 at lower altitudes, max power will likely have you exceeding the 2000 fpm ROC red line and things will be happening fast. I find that 80-85% TRQ usually gives a brisk, manageable ROC and is well below max power. Somewhat more power may be necessary with a heavier load, but have never needed anywhere near max.

A related consideration is the takeoff profile on a max perf takeoff. The FAA RFH technique gets the helicopter moving forward right away. My very seasonsed instructor has taught me not to do it this way. He wants to preserve the space ahead of the helo for an emergency return in the event of an engine failure, or unanticipated change in wind, etc, and recommends a towering TO until obstacles are cleared, and then moving forward. Each technique involves tradeoffs. Opinions?

[Shawn Coyle]

First point:
The maximum climb rate limitation on the Bell 407 is there because it was not possible to demonstrate static stability using takeoff power. It's a silly limitation and should be removed.
Second point:
There is no performance charts for this type of maneuver, and there are so many different techniques used that it's silly to say there is such a thing as a 'maximum performance takeoff'. One of my favorite rants!!
The article(s) in Vertical magazine discuss this at length. Anyone who wants copies should PM me.

[EN48]

It's a silly limitation and should be removed.


It may be silly, but it is still a Limitation. The point I was trying to make was striking a balance between minimizing HV time and maintaining control. In a tight confined area, even 2000 fpm may not be a good idea.:ok:

[OBX Lifeguard]

For my money takeoffs using minimum power come from the day when we flew very low powered aircraft and the difference between minimum power required and max available was tiny. That was also when we were taught "rejected takeoff" to back the helicopter back to the takeoff point if we began loosing rpm before we cleared obstacles. OH-13s and later UH-1B/D's that would only hover 6" high, if at all, were common. (Admittedly niceties like weight & balances were something we just didn't have time for :uhoh:.)

At airports using a runway, who cares, but in other environments getting up and away from obstacles is my priority. The typical helipad or scene landing is fraught with hazards seen and unseen, minimum power takeoffs are trolling for trouble ...

[Brilliant Stuff]

Then again there is the school of thought that you are putting extra strain on the engine when pulling max power and if anything is likely to fail it's under max strain so one uses only the power one thinks one needs to pull away.

How many seconds faster will you clear the danger with max power compared to medium power?

Discuss.:)

[Gordy]

Here is a thought.... why not pull sufficient power to give you a positive rate of climb, but not so much that you are lifting off like the space shuttle.....

I spend a good portion of my flight time inside the H/V curve, and am frequently conducting confined area operations. There is no "Book" way to do it, do what feels right for the prevailing conditions. You all know what feels right---you just need to learn to "feel it" and go with it.

If you maintain smooth control inputs, understand the basics and then adjust them accordingly. I could not tell you how much power I am pulling over hover power, other than I am not red-lining, my eyes are looking outside where they should be. I would hazard a guess that it is somewhere around 10% above hover power.

Incidentally, gauges are color coded for a reason.....on some of my aircraft we have extra critical gauges installed in the door frame arm rest, so that under "normal" conditions the needles will all point the same way----this allows for quick glances at the gauges without having to read the numbers.

[OBX Lifeguard]

That line of thinking was once used by some very misguided fixed wing pilots who in the interest of "saving their engine(s)" would take off using "cruise power" (say 23/23) . That kind of thinking has been put paid except for the near criminally foolish among our starched wing brethren and it is max T/O power every time...(That does not mean necessarily Max power...)

In a lightly loaded aircraft with tons of excess power like a UH-60 significantly less than max T/O power is fine, she'll still go vertical @ 2,000 fpm... But in something like a loaded BK coming off a helipad I'll take max T/O pwr 'til VY as per the book, then reduce to max cont til cruise altitude. Using less to "save your engines" is a lot of hoooey...IMHO...

I also don't buy that engines are most likely to fail under T/O power. It's anecdotal of course but that just has not been my experience...recips or turbines...

[Gordy]

OBX Lifeguard

In a lightly loaded aircraft with tons of excess power like a UH-60 significantly less than max T/O power is fine, she'll still go vertical @ 2,000 fpm... But in something like a loaded BK coming off a helipad I'll take max T/O pwr 'til VY as per the book

Thank you for agreeing with me that

there is no "Book" way to do it, do what feels right for the prevailing conditions.

I have always proclaimed, (rightly or wrongly), the the difference between F/W and R/W is that in the F/W world they rely on "numbers" for everything....V1, VR, etc....where as in the helicopter world we apply common sense and airmanship attain a "sight picture" and "feeling". This is what separates us.

Seems that "newer" pilots these days are not being taught common sense. I see new threads popping up day after day on various forums asking for "numbers" and "power settings" when in fact there is no black and white answer. Generally, if it "feels right" you are probably in the right ballpark. Now we just need to figure out how to show that on paper.

I also don't buy that engines are most likely to fail under T/O power. It's anecdotal of course but that just has not been my experience...recips or turbines...

Agreed. More often than not, people mis-manage their power in these circumstances.

Caveat--- I fly in the utility world and NOT the airport or instrument environment, therefore my answers may not apply in all circumstances.

[zorab64]

I'll go for max power every time - mostly because we've only got a few lbs/kgs to MAUW anyway, so we generally need everything we've got to start getting a move on! :ok:

In a previous life, I used to use max power so that we had some vertical momentum in case one of the donk's stopped. If one had (it never did), at least we'd have enough upward ooomph to reduce the chance of getting wet during the recovery phase!!

Like Art, I've been flying twin turbines too long to translate the above into "single" (30 yrs), or "piston" (never) language. However, his "pull it & go" theory, whilst sounding very gung-ho & military, has merit IMHO.

Certainly, if I was flying a single, (knowing that turbines operate at their most efficient at close to 100%) I'd use everything anyway - when did anyone last hear of a turbine just "failing" on take-off? You've either got max power available when you first pull the lever up, or you've got a fuel flow problem so that, as soon as you demand everything, the engine just doesn't accelerate, & you won't get airborne at all - I don't think I've ever heard of a turbine providing "reduced" power (like the coughing & spluttering of a piston) without some sort of awareness that it could be possible (desert sands / FOD prone area / hot&high etc). Similarly, whilst one always checks the needles during initial take-off, I'd suggest all failures (of the engine-kind being discussed) bring themselves to the pilot's attention by ear :eek: . . . which is automatically linked to the left arm moving down somewhat!!

I think I've just concurred with Gordy - much is done by feel; numbers are there to provide limits, but you don't fly by numbers.

[EN48]

Here is a thought.... why not pull sufficient power to give you a positive rate of climb, but not so much that you are lifting off like the space shuttle..... Generally, if it "feels right" you are probably in the right ballpark.



This is what works for me in the 407.

[OBX Lifeguard]

Gordy...I wasn't disagreeing with what you said because when I wrote what I wrote...I hadn't seen what you said...:O.

Up until a few months ago I had two very experienced pilots working for me (+ 10,000 hours and ATPs) and the differences of opinion sometimes where pretty dramatic. Now one is still here but in the others place is a wet behind the ears kid w/ only 4,500 hrs....and the differences are different (he talks about when he used to fly R44s instead of H-21s :bored:)...but still there. And the damn kid is sometimes the one that's right .

I flew for the Army long enough (30 years) to see "helicopter aerodynamics" change three times...so what I know as the "gospel according to Rucker" may be different tomorrow. (Actually I had a helicopter aeronautical engineer tell me what us pilots learned is still wrong....but close enough for what we need :\ )

[Gordy]

Gordy...I wasn't disagreeing with what you said because when I wrote what I wrote...I hadn't seen what you said....

I know. You actually made a good point in that every aircraft is different, hence sometimes generalized numbers do not work.

What does work for "newer" pilots, is to read these boards and take away information of differing opinions and hopefully form their own. It is tough for them learning the basics, especially due to the way the system works---new CFI's teaching new pilots.

I always liken it to baking a cake.....learn how to make your basic pound cake first. Once you get good at that---by using different ovens, different brands of flour, etc, then and only then can you start to add things like chocolate flavor and frosting.

Flight school is akin to a basic baking school----you should be taught the basics so that you can go into the world and develop your own personal style of flying.

[EN48]

new CFI's teaching new pilots.

My veteran instructor calls this "students teaching students." ;)

[Art of flight]

Great thread, just what rotorheads is good at.

Perhaps all of these posts prove the old adage that fixed wing pilots have principles of flight and we just have theories (as yet to be proven!).

Amongst such theories is the one that says we don't need any power to get airborne, the craft we fly are so ugly that the earth just repels us skywards for periods of time....

[FH1100 Pilot]

Personally, I've never understood the minimum-power-for-takeoff crowd. Yes, I know the helicopter can conduct every maneuver at hover power, I get that. But takeoff with just hover power? Why would I want to do that?

I fly airplanes. We use full power for takeoff. Why? Well obviously because runway lengths are finite. But along with that, we want to quickly get some airspeed and altitude. It's safer up there (as opposed to down low) in case something goes wrong.

In my helicopter it's the same thing: I want airspeed and altitude fast. At our home base airport, when I'm by myself and the thing is hovering at 72%, then maybe I'll only pull 85-90% on takeoff. That gets me up and going right smartly, it does. Trouble is, I'm so very rarely by myself in the machine. If I'm heavy I go all the way to 100%. This is not abusing the engine/trans and I'll be damned if I'm going to worry about the engine quitting just because I'm using full power. Especially if I have to takeoff thisaway when I need to be going thataway. (No, I do not just takeoff in the direction I need to be going, not even from an airport.)

Confined areas are a different story. With them (and I do a lot of them), it's 100% until I'm well clear of the obstacles and have some positive airspeed registering on the meter. But having said that, a lightly loaded 206B has plenty of vertical performance. So if I'm in one of our patented hover-holes and I'm coming out empty, the pull from 72% (or whatever) wouldn't be a mighty yank (although I happen to be a mighty Yank) but a smooth ease-on-up-to-100 even though the actual time spent at 100% might be brief indeed. Get me outta here!

Lately I've been "auditioning" some replacement pilots as I've reached the end of the road of my flying career (I hope!). Some of them have very different philosophies on flying than I. Most are graduates of the just-use-minimum-power school. They seem reluctant to even pull full power, and some do not even climb at BROC as was beat into my head by PHI's training instructors for lo those many years. (But see, JetRangers do not climb well at BROC at "a little over" hover power.) Maybe these aspirants are just trying to impress me with their cautiousness, I don't know. And while their techniques are not mine, I understand that different pilots fly...well, differently, and that there is no singular correct way of doing much of anything in helicopters as long as you don't crash, which I would say demonstrates ipso facto bad technique.

At the end of the day (and the end of the post) I gotta go with Gordy. So much of what we do in helicopters is done by feel. Most everything we do is an improvisation of some sort; it's hard to apply "hard" numbers when every dang landing site is different and requires a slightly different technique. But in general, if you tell me that I have 100% available, then I use it and do not feel guilty about it. I don't like being low and slow near the ground.

[Gomer Pylot]

For many, if not most, modern singles, 'save the engine' is a crock. At or near sea level, you're not likely to be anywhere near engine limits when you hit 100% torque. The TOT should still be in the green range, as should the N1. The transmission won't suddenly fly apart at 100% torque either. Pull what you need, and if you're heavy and in a confined area, 100% is what you need. Pull it in quickly, to get the aircraft moving upward, and hold it there until above the obstacles. If you're very light, pull enough to get the aircraft moving upward briskly, but it doesn't have to be 100% torque. Judgment is always necessary, so use some when pulling pitch. Always use enough, but never too much or too little. The boss pays me for my judgment, not for anything else.

[EN48]

For many, if not most, modern singles, 'save the engine' is a crock


Yep - for many if not most 100% torque is a transmission limit not an engine limit.


Always use enough, but never too much or too little


:ok:

[hoistop]

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..

[Senior Pilot]

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.

[birrddog]

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

[Senior Pilot]

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 :hmm:

[Shawn Coyle]

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.

[topendtorque]

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.

[Brilliant Stuff]

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.

[Gordy]

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%.

Yep, I think that would be a good consensus.

[Vee-r]

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.