Less airspeed effect on single engine performanceof Bell-412 helicopter
 

Hello.
I am investigating a Bell-412 helicopter crash. I need to know that what is the ideal air speed of Bell-412 helicopter which should be maintained once resorting to single engine configuration ?

That will depend on the gross weight of the helicopter at the time, and the density altitude (among other factors). Do you know those values?
Do you have access to a Bell-412 operator's manual/flight manual? The resulting airspeed is typically available in a chart if those values are known.

75kt seems to ring a Bell...

Which phase of flight?

Either Best Angle of Climb airspeed OEI if near the ground immediately after the engine failure or Best Rate of Climb Airspeed after clear of obstacles then as desired.

Lonewolf is correct on the proper source for calculating those speeds prior to flight.

Thank you for you valueable input guys.
I do have Rotorcraft Flight Manual (RFM) of Bell-412. I have also consulted the OEI rate of climb performance graph but could not find the airspeed in straight and level flight.
The helicopter at the time of crash had a gross weight of 10500 pounds, OAT: 34 degree Celsius and altitude : 7000. Though putting these values the on the graph it shows rate of descend of 200 feet per minute. The pilot who survived is giving the statement that he got the sink immediately shutting down one engine. I am unable to comprehend that whether it was the less speed ot it was the rotor RPM which depleted causing the sink and developed high rate of descend ?

I haven't flown the B-412EP since 2002, but I seem to recall Single-Engine Safety Speed (SESS) - indeed governed by AUW, DA, USL(?) (probably not as you can pickle that off).

I have dug out my Griffin notes (I don't seem to have an ODM to hand in the archives!) and they say:

Circuits:
Climb - 70 kts
Level - 1000' 90 kts
Finals - 20-25 % power
Roll out - 50 kts + wind

Autorotations:
HASEL cx
Datum - 70 kts
Range - 90 kts / 91% NR
Low speed - 40 kts (70 kts by 1000')

Now without crunching the AUW/DA figures, would a SESS be in the region of 40 kts, as you would want to be at that speed if you lost your single engine and started autorotation...?

CS, it should be possible to get full performance figures from the Bell helicopter company in support of your investigation.From your figures the aircraft would have been `operating`,engine/rotor performance wise at a DensityAltitude of approx. 10500 ft, but Pressure Alt of 7000 ft..It would be useful to check records of POWER Checks carried out on each engine,and the condition and rigging settings of the rotor blades,as these will also have an effect on `actual` aircraft performance..Like wise ,engine instrumentation calibration ,torque/tit/etc.,and rotor governor settings.
I am not familiar with the -412,but have spent a few years as a maintenance test pilot.Do you do engine compressor washes regularly , and power performance checks...?
Hope you get your answers..

A long time since I flew a 412, nor have any books available, but with the figures you give that would put the density altitude up near 10,800 feet. With an engine failure in those conditions I would expect the pilot may well be correct that he had a drift down rate of descent of 200ft/min. Nothing to do with rotor RPM, but not flying at the optimum speed (best rate of climb is 70 knots clean, 60 knots with main cargo doors open) could have an effect.

I would suggest getting in touch with your Bell Helicopter Tech Rep....or the Corporate Office and ask for assistance with those calculations and airspeeds, etc.

They should be quite helpful I would think knowing their reputation for Customer Support.

This RFM indicates 70 Knots as being the Best Rate of Climb airspeed, allows for a droop of Nr to 97% in transition from AEO to OEI and upon archiving Vbroc of 70 Knots....increasing Nr to 100% but maintaining OEI engine Limitations.

It does mention reducing Airspeed to remain within OEI Engine Limits.

A thought would be to look for Best Angle of Climb airspeed which would be slower than Best Rate of Climb Airspeed as a number to consider.

I suppose one could also consider looking at Take Off Safety Speed too.... just as a Bench Mark for a very bottom number.



http://www.maunaloahelicopters.com/l...copter/412.pdf.

This particular RFM might not apply to the aircraft in question... ensure you use the correct RFM during your investigation.

If you've calculated that the best oei rate of climb was -200'/min in the circumstances of the engine shutdown then it was not possible to level flight at any speed at this altitude. I.e the helicopter had to descend to a lower density altitude to achieve level flight performance.

The question from the OP was "should be maintained", I would not think of flying around at 40 KIAS, so VY, or best rate of climb speed seems to the correct answer.
Obviously that speed changes with weight, altitude, temperature (density altitude).

Should not one take into consideration the stage of flight before calling for a particular airspeed....and I would submit it be a specific indicated airspeed.

Lets attack this from a theory perspective. Flying at an airspeed that results in the minimum power required for level flight, Vy, for the DA and aircraft configuration including Nr will provide either:

a. The largest power margin, if power required is less than power available AEO or OEI. or

b. The minimum rate of descent, if power required exceeds power available AEO or OEI.

Should power available and power required be equal then level flight is possible. If power required is less than power available then the aircraft can climb, fly faster, fly slower or a combination of those. If power required is greater than power available then a descent is inevitable.

The RFM will provdie the accepted manufacturer data to determine these numbers. The cruise chart for the appropriate DA would a good place to start. This chart will show the Vy, and resulting power required, for the DA and aircraft GWT and the maximum power available. Should the maximum power available not be on the chart then this figure will also be published in the RFM.

SAS et all, best sustained as requested by the OP is referred to in the OEI rate of climb chart in the Section 4 Performance that you provided.
70 KIAS at 100% rotor RPM. I believe that is fairly close to Vy. Depending on aircraft weight and Hd, you may need to use MCP, even though the best rate of climb at that speed (or any speed for what matters), is achieved with 30 minutes OEI power.
Thanks for that .pdf BTW, it did bring back quite some memories.

Been quite a while since I flew the 412, but without the charts in front of me and with Max gross around 11 700 those numbers look reasonable to me. An engine failure with that kind of DA could very likely result in an instant descent rate, with the least descent rate likely at around 70 kts and increasing descent rates as you get slower or faster than that.

Assuming the pilot didn't pull collective hard enough to fry the remaining engine and/or droop the rotor to avoid terrain. Sometimes we work in ugly places and there just isn't enough sky under you.

Well said, .... and true.

Back in the mid-late 70's in Iran before the revolution, we were operating Bell 212s in the mountains with an almost always negative SE ROC. We requested from the company the same extra pay (Mountain hazard pay) that the Bell 205 crews were getting but were denied due to the fact that we were flying twins. Fortunately, never had a problem.

Engine Chip Caution Light Emergency Procedure
 

Guys i am grateful for your guidance based on your knowledge and experience.
Can anyone guide me regarding one of the procedural steps for 'ENGINE CHIP' written down in the pilot's checklist of Bell-412 helicopter :-
"Shut down engine as soon as practical"
What does as soon as practical means ?

"Practicable" (this is the word used mostly, not "practical") is when you are confident that with one engine only, you can make it to a safe chosen place to run it on.

A civil RFM ain't got any of that.

Bell uses practical.