Best Angle of Climb

[Xnr]

What is the best angle of climb speed for an S76A?

For those of you who say 45 knots, where did you get this info.

[w_ocker]

Always thought best angle is at 0 KIAS, max pwr, (as long as you have a power surplus). Do you mean max rate perhaps?

[Aesir]

Wow.. I never thought of that, but of course "Best angle of climb" Vx in Helicopter has to be O kts, cause its the most climb for least distance travelled and not best ROC.

No idea though what "Best rate of climb" Vy in the S-76 is?

I fly a helo with 2/2/2 blades/engines/skids and its Vy is 60 kts.

[pitchlink]

Vbroc S76 i believe to be 74kts minus 1kt for every 1000ft pa. May also be minimum drag speed.

[roundwego]

w_ocker's answer to the original question is obviously correct from a technical point of view but it could put you in the avoid curve for take off. The best angle of climb is usually quoted as circa 45kts which should also give you oei climb in the event of a power unit failure in a twin engine helicopter. This could obviously reduce as AUM is reduced depending on power/weight ratio for the helicopter type. See your Flight manual for details.

As far as best rate of climb speed is concerned, for every helicopter I have flown, it has been 70 kts give or take 5kts. Every Flight Manual should declare it.

Easy to find out by experiment. Establish a 500'/min. rate of climb at 60 kts in calm conditions and increase speed very slowly by trimming forward incrementally. Your ROC should increase slightly and then will start to decrease. You will then have have just passed through your best rate of climb speed. It equates to the bottom of the power required vs speed graph. It's also your best speed for maximum endurance (but not range).

[ShyTorque]

W_ocker,

You are correct to say that the best angle of climb speed is zero knots BUT only if the aircraft can hover OGE or better. For a limited power situation (where there is no OGE hover) there has to be another "best angle" climb speed.

This "limited power" best angle of climb speed will occur for the best rate of climb for the smallest increase in airspeed above zero knots.

I have just searched all my old notes; unfortunately I can't find the diagram I thought I had showing this and Prouty's Aerodynamics books don't seem to mention it at all. However, I think it occurs on the "Power required / Airspeed" graph where a line from the origin meets a tangent to the curve at right angles. Obviously this is quite a bit slower than the best rate of climb speed (where a line from the origin touches the curve at a tangent). Probably difficult to visualise, just draw yourself the bucket curve on a piece of paper.

Without thinking too deeply (as I am suffering from a cold:() this is reflected in 'Perf. A' technique where in the event of engine failure after CDP at V1, V2 is held until clear of obstructions (best angle?) and then the aircraft is accelerated to Vy (for best rate) of climb.

V2 is variable but about 50 kts on the S-76. I'm not 100% certain that V2 is actually best angle of dangle per se. Will research a bit more! :)

[Xnr]

Maybe I should ask the question in another way.

Has anyone ever seen in print a best angle of climb speed for the S76A model.

p.s. Not the best rate of climb...... we all know that.

[Joker's Wild]

I have never seen a best angle of climb speed published anywhere for the S76A.

Having spent my fair share of time flying them, I'd like to think if that speed existed, I'd have come across it by now.

My two cents.

Cheers

[ShyTorque]

Xnr,

I have never seen it published.

It would be a variable. :)

[Nick Lappos]

There really is no such thing for helicopters, except in the limited context of a specific procedure, where we use Vtoss. For Cat A procedures, the whole thing is included, from the aceleration distance to the angle of climb.

Angle of climb would be 90 degrees for a vertical climb, and would flatten gradually as the gross weight were increased and all other variables held constant (such as wind, alt, temp, engine power assurance margin).

For airplanes, the induced drag at low speeds near stall domnates, so Vx falls in a relatively small band of speed, and so Vx is a useful tool for pilots. It would freak an airplane driver out to know that at 10,000 pounds his Vx was 25, and at 9300 pounds, it was zero., and in fact, he could take off backwards if he was under a cliff, so his climb angle would be maybe 135 degrees.

For helos, the speed for Vx is probably below 25 knots if you can hover IGE, so it is not even registered on the pitot system.

For a helo that can just hover IGE, at 15 knots (just above ETL) it can climb at perhaps 100 feet per minute while advancing forward at 900 feet per minute. The climb angle would be about 6 degrees in that case. If that helo were accelerated to 20 or 25 knots, it might climb at 500 feet per minute, so it would make perhaps 9 degrees of angle, but it would eat lateral distance getting the extra speed, and that might flatten its total angle of climb from the takeoff point. Same is tre going to 60 knots, where its angle might be 12 degrees (with 1500 FPM).

For Cat A, we assume a 35 foot barrier, and show the distance to clear that barrier or the distance to reject and stop short. The Speeds and powers specified in the flight manual cook in some Vx logic.

[Xnr]

Thanx guys,

The company I work for seems to think that the best angle of climb speed is 45 knots but I could never find the reference.

Probably because it is not there.

Cheers

[Nick Lappos]

Interesting logic! I once heard that the Tennessee legislature passed a bill making Pi = 3.00 to avoid all that confusion with 3.14159......

Does anyone out there know of a helicopter with a published Vx?

[heedm]

For fixed wing aircragt in still wind, max angle of climb occurs at the airspeed for which you have max excess thrust. Classically this occurs at Vl/d max, or the bottom of your drag curve. When thrust is dependant on airspeed, max angle of climb could occur elsewhere.

In helicopters, this doesn't hold. Reasons are obvious, have been pointed out by Nick, ShyTorque, and others. However, it seems to me that above a certain speed (somewhere around ETL I imagine) the fixed wing theory is close. So if we were to restrict ourselves with a minimum speed, then a max angle of climb speed may be identified.

I can imagine using this for obstacle clearance when you want to maintain forward airspeed. If you were in cloud, above HIGE, or were concerned with OEI performance, then you may want to restrict your airspeed.

This has happened to me when stuck in a valley with broken cloud above. Back out of it or climb through a hole. Couple of times I found a hole big enough to go through..I used min drag airspeed just because I new the highest rate of climb would be possible, but really the max angle should have been used.

I think the easiest way to work this out on your helicopter is to flight test it. Record ground speed, true airspeed, and rate of climb at max power for various airspeeds/altitudes. I'm guessing it would be close to Vl/d max.

[rotorque]

Nick,

I have seen a Vx speed published. In a KH4 manual it stated 39 knots max angle. I have always remembered it. To give it some comparison, the max rate for the KH4 is 45 knots, so it fits the profile.

Obstacle clearance in a heli has always been a favourite topic of mine...... I like to be good at it.

For the VFR guys out there, it should be noted that obstacle clearance takes on a whole different meaning in day to day flying compared to IFR. For those who do any bush work in limited powered machines, you will know how much will power it takes to keep the nose down when accelerating towards a fixed object. However, it is only 'speed' (and usually ground effect) that will allow you to clear the barrier at the appropriate time. More often than not it will look to the uninitiated as a gung-ho fast and furious takeoff........ if they only knew what was at stake.

The reason I make this point (for the young fella's out there) is that you may find yourself not, in fact, being able to hover more than a couple of inches off the ground. The only way you will be able to get over those trees is to stick to the ground, and go like hell. The distance between the tree tops and your skids when you pull up to clear them is wasted energy.

Some instructor type pilots may feel that the above 'trade secret' should not be mentioned to low time pilots. Instead they should be told to either not find themselves in the situation i.e: a tight area with no power, or stay in a steady hover until a gust of wind comes along. Fine. But it will be technique alone that gets you out of a situation like this.

Good topic.

[Pub User]

The best angle of climb can't be published, for any helicopter, because it depends on the surplus power available in a given situation. Obviously the best angle is available at 0 kts, but as Power Available reduces towards Power Required, then the speed has to increase, ulimately to Min Power Speed, which is the normal best Rate of Climb. A typical speed would, therfore, be midway between 0 and Vy.

As the best rate of climb is normally in the 65 to 80 kt range, it follows that a typical Vx would be in the 37 to 40 range. Add a bit for the 'autoflare' when anything goes wrong, and you have 45kts. The RAF teach 40kts in a single and Vse + 5 for a multi.

[Red Wine]

Most folk South of Zero Latitude in the "A" model have used.....

52knts for VBROC & 74knts for Vy [Vyse].......

Interesting to note.......what IAS would you go for in the event of OEI in a critical stage of flight??

Work it out now....not when it happens.!!!

If you aim straight for Vy.......NR will suffer and your ROD will increase.....try VBROC then when away from the surface SLOWLY accelerate to VY..........try it in training.

Vy = 74 = Min Power Required = Max Endurance as well.

[Nick Lappos]

Red Wine,

I know you meant Vtoss in there instead of Vbroc.

There is a reason why Vbroc and Vendurance are the same. Min power to stay up (and so min fuel consumption) is the same place as most extra power left over to climb.

BTW, Tyrell's Long Flat Red is awesome, but hardly available around here. Were it more so, I would possibly change my log in to Red Wine2!

Nick

[donut king]

Anything in the U.K (CAA) version, 76A Flight manual, pertaining to best angle of climb?

D.K

[212man]

Not sure why anyone would be asking this question. There is no fixed best angle of climb speed: as has already been stated it is the speed at which a line drawn from where the power required curve meets the vertical axis (TAS = zero) hits the curve tangentially. This does not factor for wind.

The curve, however, is only valid for a given weight and ambient condition. You cannot have a fixed speed, therefore.

The subject of Vtoss is more related to reject distance, as the minimum reject distance is a function of a minimum speed at TDP. However to meet the Cat A continued T/O requirements you need to be able to get to Vtoss from the V at TDP (now often using 30" ratings), so normally a 5-10 kt difference can be accommodated and still meet the obstacle clearance requirements during this acceleration phase. So a manufacturer will nominate different Vtoss' really to offer a reduced ASDR (from a lower V at TDP) and then reduce the weight to allow the CAT A climb requirements for each Vtoss. The lower the Vtoss, the lower the weight has to be as the power required curve is at its steepest, increasing range.

Now that we are no longer using BCARs in the UK, we should find that CAT A profiles in FLMs are no the same for both FAA and CAA versions (of newly certificated types) as they will both conform to FAR/JAR 29/27.

[John Eacott]

Nick,

Long Flat Red? We'll have to get you down here for a proper education.........:rolleyes: :rolleyes:

[Shawn Coyle]

Best angle of climb airspeed is not published in any Flight Manual because there is no regulatory requirement for it.
As others have noted, the airspeed is quite variable (depends on the power available and the power required, and is in an area where the pitot system is not particularly reliable.
There were some tests done on different techniques for 'short field' takeoffs in helicopters (UH-1H) unable to hover OGE back in the 70s, but these results won't read across to other types particularly well.

[Nick Lappos]

John,
I was referring to a wonderful friend I had a few years back. Did you think I meant wine???;)