Max performance take-off

October 8, 2010 by Tim McAdams

A maximum performance takeoff is used to climb at a steep angle to clear barriers in the departure flight path. To perform this maneuver successfully a pilot must consider the wind velocity, temperature, altitude, gross weight, center-of-gravity location, and other factors affecting performance of the helicopter.

The textbook procedure is this: After performing a hover power check to determine if there is sufficient power available, position the helicopter into the wind and begin by getting the helicopter light on the skids. Pause to neutralize all aircraft movement. Slowly increase the collective and position the cyclic to break ground in a 40-knot attitude. This is normally about the same attitude as when the helicopter is light on the skids. Continue to slowly increase the collective until the maximum power available is reached. Keep in mind this large collective movement requires a substantial increase in pedal movement to maintain heading. Use the cyclic, as necessary, to control movement toward the desired flight path and, therefore, climb angle during the maneuver. Maintain rotor rpm at its maximum, and do not allow it to decrease since you would probably have to lower the collective to regain it. Maintain these inputs until the helicopter clears the obstacle then establish a normal climb attitude and reduce power. As in any maximum performance maneuver, the techniques you use affect the actual results. Smooth, coordinated inputs coupled with precise control allow the helicopter to attain its maximum performance. Also, the helicopter will most likely be inside the shaded area of the height-velocity diagram where there is very little energy available to perform an autorotation in the event of an engine failure. Using maximum power would decrease the time the helicopter is exposed to a low energy situation.

However, other pilots I have talked to prefer a slightly different technique. Instead of using maximum power available, use the minimum power necessary to safely climb and clear the obstacle. The theory being that in the event of an engine failure the less power the pilot is using the more rotor rpm will be recoverable to help in the autorotation. Also, demanding high power might increase the probability of a part failure at a critical time. I would be interested in hearing comments on the two theories.

Tags:

11 Responses to “Max performance take-off”

  1. Ehud Gavron Says:

    I’m going to go for the “minimum to safely climb and clear the obstacle.” Your reasoning is good!

    E

  2. Garren Says:

    I am in the second group myself. With respect to the proper attitude, I think it is situation dependent and not always a “40 knot attitude.” In cases where the helicopter is very close to needing maximum available power and there is very little space between the helicopter and the obstacle in the departure path, I prefer to lift vertically until I am absolutely certain I have enough performance to clear the obstacle. In other words, I don’t commit to forward movement until I know the obstacle will be cleared. If the helicopter can’t muster the necessary power, I would just come back down vertically rather than being forced to descend and dodge the obstacle. The H/V curve won’t mean much if you are going to plow into a tree.

  3. Avi Weiss Says:

    Tim;

    A big part of deciding which method is preferable, or more to the point, is lower risk, really depends on probabilistic failure modes of the aircraft.

    If the aircraft is well maintained and properly operated, the engine possesses a strong reputation for reliability, and the engine power-production “derated”, the probability of engine failure at “high power demand” is likely no higher than during any other portion of flight, and therefore, all things being equal, the low-risk play would be to minimize the time spent in the “gray area” of the curve in order to go to provide sufficient chance of surviving should a problem occur.

    On the other hand, if the aircraft maintenance history is in question, or performance is already compromised due to some issue, or the engine model has had known issues, particularly at high-power settings, and/or the power-production is not “derated”, then an argument could be made that higher power settings have a higher probability of causing an power interruption than a lower power setting. Therefore, using a lower power setting, and thus spending more time “in the gray”, while decreasing the survivability should something occur, actually lowers the odds of a problem from occurring in the first place,

    As in most aviation operating situations, while there are some “best practices”, each situation requires situation analysis and judgment to be applied on a case-by-case basis.

  4. Brian Lynch Says:

    If the goal of the takeoff is, as the name implies, ‘max performance’, then anything less than max torque available will provide less than maximum performance. Granted pulling all the power may result in such a degree of collective application that a subsequent engine failure may require a change in underwear (and very quick colective reduction). The other aspect of a max performance takeoff that wasn’t addressed is reaching and maintaining your max rate of climb airspeed. That ‘bucket speed’ allows the maximum amount of excess torque to be applied to the climb portion of the maneuver rather than maintainng airspeed. The other techniques mentioned, I think, deal more with why your using the max performance technique e.g., confined area that requires a vertical departure vs one that allows acceleration to max rate of climb airspeed rather than the max performance takeoff itself.

  5. Don Says:

    Tim,
    As a helo pilot in the US Army then medevac for 20 years, I can relate to many max performance take offs, many times at max gross weight. The problem with just using minimum power is you may find yourself halfway up in your departure, and realize you really do need max power. So there you are climbing out…needing more power and not needing to look inside. If the wind shifts, and you lose some lift from the wind-shift, the adding of power could put you in a settling with power (you know, aft cyclic, nose comes up, pull more power, airspeed bleeds off…) So pull max available power, start your ascent, and you’ll know before it is too late if you can get out or not. Remember, you are smack in the lower curve of the H/V diagram, so you are trying to get out of it as quickly as possible. If there is absolutely no forward movement available (right up against the obstacle), then I question why you landed in such a tight spot to begin with.
    With respect to Mr. Weiss’ comments, if you are that worried the engine and or maintenance affects your ability to fly out of a confined area…the helicopter’s primary profile, then you might consider a different company to fly for.

  6. Jim Borger Says:

    What does the RFM say? Is there a procedure described there? Are there limitations? I have flown aircraft that limited the normal takeoff torque to hover power plus 10% because in the event of a power loss the collective could not be lowered fast enough to preserve Nr. Do you really want to pull above that if you don’t need it? Different aircraft require different techniques. In a lower powered aircraft you might need to pull a higher margin than in a higher powered one. In the 76C++ I pull until the Nr droops but in the 92 hover plus 15% works just fine. There is no tecnique that fits all aircraft in all situations.

    If you aren’t thinking that your engine can quit at any moment then you won’t be prepared when it happens. Engines, governors, fuel controls, FADECs, etc can malfunction at any time without any prior warning.

  7. Pete Gillies Says:

    Hi Tim – I enjoy your Hover Power blog very much! You’ve shared lots of good information with your readers, and I hope you’ll keep on doing it.

    I would like to submit comments, if I can, but I’d like to know how to submit them so they get published along with your articles. How can I get to read your blogs the day you publish them?

    Pete

  8. Nick Says:

    I agree…depends.
    If I am in a CAL surrounded by miles of dense woods, I prefer to get up and out quick, and get to bucket ASAP. Personally I do this by positioning to the far downwind side, aiming for the shortest obstacle within about 30 degrees either side of the wind-line, Pull max power (Even a 10 sec limiting time if I REALLY need it…I can count pretty well), then accelerate forward. I do this to get me away from the 0-0 side of H-V and horizontally toward the bottom avoid area, then a cyclic climb with same power level only as extreme as needed to barely keep the skids out of the trees. I have tried many different methods and this one seems to get me up and out quickest and I am 5 knots below bucket at the 100 ft tree top. Experience has shown that if you are going to have a failure, it will be at the most in opportune time. Really no difference to me if I am at 100 ft/0kt hover climbing out of a CAL or 100ft/45kt over trees on the far side of it…either way the landing after an eng fail will not be a nice one!

    It really comes down to knowing your aircraft, and ALL aspects of the aerodynamics. What is the most efficient Nr. In an H-60 (or the above post about S-76) I personally don’t mind the droop since Nr actually gets MORE efficient as it droops from 100 into the 90′s

  9. Carl S Says:

    When using the move toward the obstacle and put up approach, what is your oops back off manuver like? Nose up/back up or right turn down collective ? Or what?
    Im a low time R44 pilot and appreciate your experiance./comments

  10. Eric Says:

    There has been a bit a good feedback on this topic. As it was said many times above you job is to minimize your risk. Here is what i suggest. If you look at NTSB reports find out if more accidents occur by engine failures during a max performance takeoff or because someone was flying forward and hit an obstacle (CFIT). When you have determined where the greatest risk is i would take the route of reduced risk. I want to be home with my wife and kid when I am done flying.

    To tie in with this may i say current industry standard for EMS (this is only one field in the helicopter industry and is what they found is best for them) is to take off straight vertical with no forward airspeed. Why? Because of the number of accidents that occur from hitting wires or CFIT due to last of obstacle clearance. Also this answers carl S’s question of wha is your “oopse back off maneuver like”…you should never need to use one if you fly properly…there should be no pucker factor of “am I going to clear that obstacle…maybe i should close my eyes and hope for the best”.

    With that said I would takeoff completely different in an area i knew was clear of obstacles (i.e. land in often) versus unfamiliar terrain…or night versus day. Once again as mentioned above you need to be the PIC, take the information you have, make a risk assesment and do what you feel is the safest departure you can make.

    Great blog all!

  11. Home Page Says:

    I love what you guys are up too. Such clever work and reporting!

    Keep up the amazing works guys I’ve added you guys to blogroll.

Leave a Reply

*