Rotorcraft Cat A: to raise or not to raise?

[212man]

Can anyone explain the following seemingly contradictary statements between 29.59 para 5, and 29.67 para 1(ii) regarding landing gear retraction post TDP and OEI? Have I missed something?

JAR 29.59 Take-off Path: Category A

(a) The take-off path extends from the point of the commencement of the take-off
procedure to a point at which the rotorcraft is 1000 ft above the take-off surface and
compliance with JAR 29.67 (a) (2) is shown. In addition :

1) The take-off path must remain clear of the height-velocity envelope
established in accordance with JAR 29.87; JAR 29.59 (a) (continued)

(2) The rotorcraft must be flown to the engine failure point at which point the critical engine must be made inoperative and remain inoperative for the rest of the take-off.

(3) After the critical engine is made inoperative the rotorcraft must continue to the TDP and then attain VTOSS.

(4) Only primary controls may be used while attaining VTOSS and while establishing a positive rate of climb. Secondary controls which are located on the primary controls may be used after a positive rate of climb and VTOSS are established but in no case less than 3 seconds after the critical engine is made inoperative: and

5) After attaining VTOSS and a positive rate of climb the landing gear may be retracted.



JAR 29.67 Climb: One Engine Inoperative (OEI)

(a) For Category A rotorcraft, in the critical take-off configuration existing along the take-off path, the following apply:

(1) The steady rate of climb without ground effect, 200 ft above the take-off surface, must be at least 100 ft per minute, for each weight, altitude, and temperature for which take-off data are to be scheduled with:

i) The critical engine inoperative and the remaining engines within approved operating limitations;

(ii) The landing gear extended; and

(iii) The take-off safety speed selected by the applicant.

[Shawn Coyle]

No contradiction, but it is a bit subtle. The flight path in the first 200 feet, which is what the 29.67 refers to is done at best angle of climb, which is why the rate of climb is lower for this part (up to 200' above takeoff surface) than the second part at 1,000' above takeoff surface.
The inference is that in the first 200 feet of the climb, you'll be too busy to raise the gear anyway.
Actually retracting the landing at these sort of speeds often makes precious little difference to the rate of climb, as the drag due to gear and doors is quite small at these airspeeds.
Hope that cleared it up.

[212man]

Thanks Shawn, sort of but not quite. I realise they are both refering to the first segment climb, but wonder why the regulations allow the option of raising the gear when in fact they expect it to be down still during this phase. The Eurocopter 155 continued take off elects to leave it down until the second segment has been established which is in line with 29.67, but 29.57 would infer you could raise it at Vtoss during the first segment if you wished.

I agree the drag may be minimal (except perhaps on the S-76) but am not sure I agree about best angle of climb. My understanding of types with variable Vtoss (that I am familiar with: 155 and 76) is that it is a function of speed at TDP and the subsequent field length available. ie short field means low TDP which by inference will require a lower Vtoss. This then tends leads to a reduced weight (unless a climb takes place while AEO that allows a drop down when OEI thus giving a larger spread between V at TDP and the subsequent Voss). As the Vtoss increases towards Vy then the second segment tend to become more limiting.

Either way, bring back Group A requirements; much more in hand for the wife and kids!

[Shawn Coyle]

Not sure of the reasons - you are way beyond my knowledge of the Cat A subtle points. As for Group A, I never knew the beast, but anything that can help to make our operations safer (while maintaining commercial reality in sight) has got to be a good thing.

[4dogs]

212man,

The first reference simply tells you (but actually the TP gathering data!!) the earliest point in the profile from which the gear may be retracted when deriving maximum take-off weights and related take-off performance data. The manufacturer's interest is in squeezing the last ounce of performance out of the product as a sales advantage, hence the benchmark says "not before here" to level the playing field.

The 29.67 references (which you selectively quote, thus losing the whole context and import of the provision) is actually a set of performance benchmarks for installed power: there must be sufficient power available at the two distinctly different altitude/configuration/power limits to meet the minimum rate of climb specified. Depending upon the helicopter, either the 200 ft or 1000 ft data point will be the most limiting.

In real life, having met the minimum specified performance benchmarks, the machine may well exceed either or both benchmarks by a significant margin, particularly if the machine has very high installed power for high top speed or high temp/DA operations.

As for how you operate the machine, the gear retraction point will be as per the manufacturer's recommendation and may well be unrelated to these particular installed power benchmarks.

[Xnr]

Hi Shawn

In your previous post you made mention of the "best angle of climb".

We fly S76A models and our company SOP's makes reference to a best angle of climb speed of 45 kts.

I have never seen a best angle of climb speed published for helicopters.

Nobody in the company can tell me where this number came from. Any thoughts.

Cheers

[Shawn Coyle]

xnr:
The reason 'best angle of climb speed' is never published is that there is no regulatory requirement for the speed.
If you can hover OGE with some power margin, your best angle of climb speed is obviously zero, and the angle is infinite. But, if you are unable to hover OGE, then you have a problem. Losing an engine just after lift off, but before Vy (minimum power speed) is also a situation where you would want to know best angle of climb speed. You want to get away from the ground as quickly as possible.
The speed itself is found on the power (vertical axis) vs. airspeed (horizontal axis) diagram by drawing a line down to the right from where the power available touches the zero airspeed point to where it touches the curve of power required.
The problem is that this speed will change with the amount of power available, and you have no idea of what that will be on a day-to-day or flight to flight basis. I would imagine that the amount of change in this speed is not large, probably no more than 5 knots plus or minus the absolute best value.
The number given for Vtoss in the Category A supplement is probably pretty close to this, as the same logic of getting away from the ground applies.
So, thats where it comes from and why its never published.
Hope this helps.