POH questions for R-44 pilots

[napalm]

Here are some questions from the POH that I have been wondering about. Please let me know if you have the answers to them.

 

1. Why is autorotation VNE 100kts?

 

2. Why can't your exceed 100kias when operating at power above MCP?

 

3. On the Center of Gravity limits chart, why is there a dashed line with the statement, "Most FWD CG with Full Fuel"? Why can't I have a CG forward of this line at heavier weights?

 

4. The O-540 F1B5 is rated at 265hp. Why then does Robinson derate it to 205hp for MCP and 225 for MTOP for 5 min.?

 

5. Why is VNE dropped to 120kts above 2200lb TOGW?

 

If you have any additional questions is interesting things in the R-44 POH or have had an examiner ask you something interesting please feel free to ask them here.

[PA Pilot]

Here are some questions from the POH that I have been wondering about. Please let me know if you have the answers to them.

 

1. Why is autorotation VNE 100kts?

 

2. Why can't your exceed 100kias when operating at power above MCP?

 

3. On the Center of Gravity limits chart, why is there a dashed line with the statement, "Most FWD CG with Full Fuel"? Why can't I have a CG forward of this line at heavier weights?

 

4. The O-540 F1B5 is rated at 265hp. Why then does Robinson derate it to 205hp for MCP and 225 for MTOP for 5 min.?

 

5. Why is VNE dropped to 120kts above 2200lb TOGW?

 

If you have any additional questions is interesting things in the R-44 POH or have had an examiner ask you something interesting please feel free to ask them here.

1. Dunno

 

2. I believe because you have at higher AoA that retreating blade stall will occur at a lower airspeed than MCP operation. Same for high DA.

 

3. Because the CG moves forward as you use fuel. You can start inside the envelope and end up outside it, particularly if there's no weight in the back.

 

4. RHC says in their safety class that the derating is for two reasons -- better performance at high DA, more engine reliability. The IO-540 in a Raven II can, I suspect, put out 300 hp if you ask it to.

 

5. Same answer as 2 -- higher AoA.

 

Last question -- expect to be grilled on emergency procedures. What does uncommanded left yaw tell you? Right yaw?

[spw1177]

1. At airspeeds above 100 kts ias it may not be possible to maintain sufficent autorotational RPM even with full down collective. This has to do with the relative airflow through the disk at high airspeeds. As the aircraft accelerates in an autorotation the incoming airflow becomes more hoizontal. This increased horizonal airflow decreases the AoA on the disk and lessens the rotational force produced.

 

2. In a 206, I don't know if this applies to a R44 as well, the high speed restriction at power settings above MCP is prohibited because of the forces that are exerted upon the mast.

[Goldy]

Yes the 540 can put out a lot more HP than the rating. However that does not mean that the transmission, shafts, main rotor masts, and airframe can handle it. It's de-rated to give you more of a safety margin at higher DA's.....and to make the engine last to 2200 hours instead of 1500....or 1200 like some helicopters out there. Also, be aware that the specific engine in the R44 is built by Lycoming JUST for the R44...the walls of the engine are thinner to save weight...and they can allow this because the HP it has to produce is less.

 

If you're going to fly the R44 (or the 22) take the safety course. You can sign up now, the wait list is 6 months, you just have to have completed your private prior to attending.

 

Good luck, Goldy

 

Oh here's a good one. Why is the R22 allowed to fly faster ( according to the POH) with doors off than the R44 ? Don't believe me? Just look it up.

Edited February 14, 2007 by Goldy

[napalm]

Thanks for your input folks. I really appreciate it. I am scheduled to take the safety course in April which I am very much looking forward to.

[Goldy]

Oh here's a good one. Why is the R22 allowed to fly faster ( according to the POH) with doors off than the R44 ? Don't believe me? Just look it up.

 

 

Come on guys..somebody MUST know the answer to this one???? The R44 lists a doors off VNE of 100K, the R22 does not list a doors off VNE ....so the question is why ?

[The_Sandman]

Come on guys..somebody MUST know the answer to this one???? The R44 lists a doors off VNE of 100K, the R22 does not list a doors off VNE ....so the question is why ?

 

 

OK...i'll try one. The rear cabin area of the r44 creates an area of drag which in turns limits max speeds (w/doors off) and I imagine may cause controlability issues at high speeds - they are light, low-inertia vehicles after all right?

 

am I even close?

 

Sandman

Edited February 19, 2007 by The_Sandman

[Goldy]

OK...i'll try one. The rear cabin area of the r44 creates an area of drag which in turns limits max speeds (w/doors off) and I imagine may cause controlability issues at high speeds - they are light, low-inertia vehicles after all right?

 

am I even close?

 

Sandman

 

 

Not close at all....but you score points for trying...especially for a new student! The engineer at the time of filing the form with the FAA felt it would be too dangerous to stick your arm out at speeds over 100 Knots. So to try and limit Robinsons liability, he added that doors off maximum into the POH. It has nothing to do with the aerodynamics of the two ships at all..actually not a bad idea if you can imagine sticking your hand out at 130MPH ( top speed on the 44)...probably rip half of it off !

 

Thanks for playing,

 

Goldy

[delorean]

On the Bells, it's a a/f integrity issue. I think it's 90 or 95 kts on the front doors and 85 or 80 on the rears? We're not allowed to remove them, so I never took the time to look it up.

 

On the R44, it's the threat of breaking your arm. Out at safety school they said it was just a nice round number and it meshed with the 3 other 100kt numbers and the blue line on the a/s indicator:

 

100kts is max auto speed (mast bending)

100kts is max speed above MCP (mast bending, again)

100kts is max range speed, and

100kts is max doors off speed.

[troll.detector]

Any further clarification on these? Especially 1,2 & 5. AoA, mast bending or something else?

[cryesis]

I thought the 100kts above MCP had to do with having to do with getting the collective down if the engine were to quit.

[Carpenter]

#3 If the aircraft CG becomes too far forward, then there is not enough aft cyclic travel to adequately "flare" to arrest airspeed and descent rate in the event of an autorotative landing.

Edited June 19, 2014 by Carpenter

[DieselBoy]

SPW is correct on #1. To simplify it, an autorotation needs an upflow of air, in fast cruise you are nose low with horizontal airflow.

 

2. Power above MCP is for takeoff, not to go fast. Above MCP you have a very high AoA, if you're also flying in excess of 100kts then you are nose low as well, refer to #1. This can quickly lead to blade stall in the event of an engine failure.

 

5. High AoA and nose low again

[Machinegun21]

As I understand it,

 

#2, Operation above MCP above 100 KIAS puts a lot of stress on the main rotor components, Blades, Pitch Links, etc. This is due to the much higher AOA that they blades are now being exposed to, combined with the increased flapping. All of this will wear out components much faster and that is why you are limited to 100 KIAS above MPC

 

#4, Robinson Derates the Lycoming engines for 3 reasons, 1 is to increase performance at altitude. 2 is to limit pilots exposure to full throttle situations which lead to low rotor and rotor stall. 3 is to increase engine life. The big reason is like Goldy said, just because the engine can output that much horsepower does not mean the belts, XMSN, blades, etc can handle that.

 

#5, Simple as they come, Operation above 100 KIAS without a door on is a lot of wind rushing next to you and if you were to stick your arm, leg, foreign object outside the aircraft while boogying along at 120 KIAS it can really do some serious damage. This is another classic example of Robinson performing preventive safety.

 

Like I said, this is how I understand all of these questions/answers

 

Fly Safe!