Silencing Rotor Blades

[Lawman]

The wide chord blades have the following characteristics:

• Increased maneuverability in hot/high conditions
• Increased lift (535 lbs at sea level)
• Increased level flight performance >19k lbs, DA > 8000'
• Anhedral droop of 20 degrees
• Inboard & outboard trim tabs
• 24.25" chord vs 21.75"
• 16.3 degrees twist
• 30 degree sweep of tip
• Carbon/fiberglass main spar with no BIM indicators

Other than that, any effect on blade stall would be as a result of the above. Ie. a smaller angle of attack to produce the same lift.

Do they have any effect on Nr speed during Autos and such?

We're supposed to be going to an all composite rotor blade on the block III Longbow. Wonder if it will include any of this kind of technology at all.

 

[Gatordev]

Do they have any effect on Nr speed during Autos and such?

Does it matter? When you FCF, you do an auto RPM check. The book tells you what it should be, which is much higher than what you would normally fly for a real auto. They may have to rewrite the book (and vibe manual) but I'm guessing it's not something you would actually see shooting normal autos.

 

[exhelodrvr]

Does it matter? When you FCF, you do an auto RPM check. The book tells you what it should be, which is much higher than what you would normally fly for a real auto. They may have to rewrite the book (and vibe manual) but I'm guessing it's not something you would actually see shooting normal autos.

More Nr would give you a greater glide ratio, wouldn't it, which would affect the control inputs.

 

[Gatordev]

More Nr would give you a greater glide ratio, wouldn't it, which would affect the control inputs.

I'm talking more from an operator point of view. The little cubes will go up, regardless of what blades are on there, it's just a matter of if they go up enough or too much. I understand what you're getting at now, though.

Helo aero question though...wouldn't higher Nr mean you're falling faster which would give you a lower glide ratio, no? Unless the blade allows for higher Nr w/ the same given descent rate, which may be what you're getting at.

Sorry for lobbing the science nerd grenade into this discussion.

 

[slug]

More Nr would give you a greater glide ratio, wouldn't it, which would affect the control inputs.

Does it matter? When you FCF, you do an auto RPM check. The book tells you what it should be, which is much higher than what you would normally fly for a real auto. They may have to rewrite the book (and vibe manual) but I'm guessing it's not something you would actually see shooting normal autos.

Rotor inertia and being able to maintain Nr in an autorotation as long as possible is critical for any helicopter without power. Ask any Kiowa pilot who went from the high inertia rotor system of the 2-bladed OH-58 A/C to the low inertia 4-bladed OH-58 D which aircraft autos better. More inertia gives you more reaction time at the moment of engine failure, and you don't have as many tricky Nr over/underspeeds when you are in the autorotational profile (makes the manuever just that much more complex if you have to constantly change collective position). It will also give you more cushion and ability to decel at the bottom of the auto, that critical time right before you smack the ground.

Yes, an autorotation is not very likely in a twin engine UH-60, but is possible in situations such as fuel contamination or pilot error if he pulls the wrong PCL offline (and has happened in the past). I think anything that improves the lift and inertia of a rotor system gives you a better chance of surviving an auto.

 

[Lawman]

Slug got what I was getting at. Im just too aero retard to understand how to say it.

We've got a low inertia rotor on the 64 so Im kinda curious as to whether or not the composite blades will provide any advantages outside the maintinance side of things. Stuff like will it change my best glide/best rate of decent margin significantly. Will it grant me a better (lower) minimum single engine speed for the aircraft.

And Im all about lowering my noise signature.

 

[exhelodrvr]

I'm talking more from an operator point of view. The little cubes will go up, regardless of what blades are on there, it's just a matter of if they go up enough or too much. I understand what you're getting at now, though.

Helo aero question though...wouldn't higher Nr mean you're falling faster which would give you a lower glide ratio, no? Unless the blade allows for higher Nr w/ the same given descent rate, which may be what you're getting at.

Sorry for lobbing the science nerd grenade into this discussion.

This is based on (now) 13 year old memories of flying the H-3, which wasn't exactly "state-of-the-art" at that time, and we didn't fo "full" autos in it, other than in the simulator. But from what I remember, when the conditions led to higher Nr, that could be traded for distance in the "glide" and "flare". That could be desirable or not, depending on how big a landing area you had, and where it was in relation to you. There were various methods to use to increase the descent rate if needed, which had varying affects on the Nr.

 

[RobLyman]

OK, so looking through the 60A/L and the 60M MTF manuals, I get the following predicted auto RPM at 80 kts/GW 17,000 lbs:


UH-60A/L

• 1000' DA 111.2%
• 8000' DA 119%

UH/HH-60M (wide chord blades)

• 1000' DA 108.5%
• 8000' DA 117%

What does this mean? Since I have no rate of decent data, it is hard to draw conclusions from this.

I looked at Q required to hover IGE at 1000' PA/17,000 lbs:
UH-60A = 74%
UH-60M = 77%

Adding to exhelodrvr comments:
I know from my 100s (if not 1000s) of autos teaching at HSL-40, higher rpm in the flare dissipates less rate of descent.

 

[PhrogLoop]

I know from my 100s (if not 1000s) of autos teaching at HSL-40, higher rpm in the flare dissipates less rate of descent.

Good point: Rate of Decent in an auto usually says more than glide performance when the objective is to walk away from an unplanned/unexpected/unwanted landing!

 

[Gatordev]

Rotor inertia and being able to maintain Nr in an autorotation as long as possible is critical for any helicopter without power. Ask any Kiowa pilot who went from the high inertia rotor system of the 2-bladed OH-58 A/C to the low inertia 4-bladed OH-58 D which aircraft autos better. More inertia gives you more reaction time at the moment of engine failure, and you don't have as many tricky Nr over/underspeeds when you are in the autorotational profile (makes the manuever just that much more complex if you have to constantly change collective position). It will also give you more cushion and ability to decel at the bottom of the auto, that critical time right before you smack the ground.

Yes, an autorotation is not very likely in a twin engine UH-60, but is possible in situations such as fuel contamination or pilot error if he pulls the wrong PCL offline (and has happened in the past). I think anything that improves the lift and inertia of a rotor system gives you a better chance of surviving an auto.

Um, thanks.

Slug got what I was getting at. Im just too aero retard to understand how to say it.

We've got a low inertia rotor on the 64 so Im kinda curious as to whether or not the composite blades will provide any advantages outside the maintinance side of things. Stuff like will it change my best glide/best rate of decent margin significantly. Will it grant me a better (lower) minimum single engine speed for the aircraft.

And Im all about lowering my noise signature.

It was my understanding that it's not a rotor head change, it's slapping some different blades up there. The head itself is still the same (with some adjustments, of course), so it's still a low-inertia head.

OK, so looking through the 60A/L and the 60M MTF manuals, I get the following predicted auto RPM at 80 kts/GW 17,000 lbs:


UH-60A/L

• 1000' DA 111.2%
• 8000' DA 119%

UH/HH-60M (wide chord blades)

• 1000' DA 108.5%
• 8000' DA 117%

Interesting. I guess it makes sense that they would already have the numbers run at this point. I'm assuming 117% in a Lima equals 117% in a Mike?

Adding to exhelodrvr comments:
I know from my 100s (if not 1000s) of autos teaching at HSL-40, higher rpm in the flare dissipates less rate of descent.

Exactly, which is why (if I'm understanding your wording) I was postulating that it would be a lower glide ratio since you're coming down faster for a given distance over time (80 nautical miles/hour). But obviously weird things happen with whirly-birds.

 

[RobLyman]

Interesting. I guess it makes sense that they would already have the numbers run at this point. I'm assuming 117% in a Lima equals 117% in a Mike?

Yes, 100% Nr in UH-60A/L = 100% Nr in UH/HH-60M.

 

[phrogpilot73]

Helo aero question though...wouldn't higher Nr mean you're falling faster which would give you a lower glide ratio, no? Unless the blade allows for higher Nr w/ the same given descent rate, which may be what you're getting at.

Remember, glide ratio for the aerodynamic brick that is a helo during an auto refers to how far you travel over the ground in the flare... So, yes - higher Nr means you fall faster - but when you're in the flare, you go further. So you'd want to maintain high Nr if you are doubting that you can make that farmer's field and need the glide ratio, low Nr if you're closer to the field and don't want to overshoot it.

 

[slug]

Remember, glide ratio for the aerodynamic brick that is a helo during an auto refers to how far you travel over the ground in the flare... So, yes - higher Nr means you fall faster - but when you're in the flare, you go further. So you'd want to maintain high Nr if you are doubting that you can make that farmer's field and need the glide ratio, low Nr if you're closer to the field and don't want to overshoot it.

This arguement may be getting too much into the weeds, but my limited aero knowledge compels me to counter a few points. I haven't done autos out of the sim in about 2 years, but I did many of them for 8 years before that. That said--

I think you guys are confusing Nr Hi/Lo with Max Range/Min Rate of Descent airspeed. In the 58/57/206 it was something like 70 knts max range and 43 knots Min Rate of Descent. To use Phrog's situation, max range will get you to that distant field, but if you are close to the field, Min Rate of Descent will get you down (in altitude) the slowest. I don't think Nr makes you fall faster or slower if you are straight and level (maybe in a 180 turn). Obviously high Nr is good (within limits--don't spin the top off) since that inertia stored in the rotor will be available for cushion at the bottom.

An old IP, one of the smartest I knew, taught me way back in primary that pulling the collective in a little until Nr droops to about 92%, just above the Low Rotor Horn and flying Max Range Airspeed will get you the absolute farthest with no engine. We tried it a few times, and it worked. Just drop collective again and get Nr back to 100% before you decel (increase that inertia to be available for the cushion).

Gatordev, I have to argue that rotor blade weight DOES matter to the inertial characteristics of the rotor system (head). In my KISS mind I think of a kid spinning on the edge of a merry-go-round or a big fat dude--if they are both spinning at the same speed, the fat dude has much more inertia and will spin longer every time.

 

[Gatordev]

Remember, glide ratio for the aerodynamic brick that is a helo during an auto refers to how far you travel over the ground in the flare... So, yes - higher Nr means you fall faster - but when you're in the flare, you go further. So you'd want to maintain high Nr if you are doubting that you can make that farmer's field and need the glide ratio, low Nr if you're closer to the field and don't want to overshoot it.

I'm with slug on his first part. It's not the Nr that gets you the max glide, it's the airspeed. High Nr is still going to make you fall faster per unit/time. The glide ratio (at least as I'm referring to it) is how far you go while gliding, not flaring. Once in the flare, though, I'm with you.

Gatordev, I have to argue that rotor blade weight DOES matter to the inertial characteristics of the rotor system (head). In my KISS mind I think of a kid spinning on the edge of a merry-go-round or a big fat dude--if they are both spinning at the same speed, the fat dude has much more inertia and will spin longer every time.

I'm with you, but I haven't heard anyone say that the Mike blades have significantly more inertia or change the dynamics of the head (low-inertia to high-inertia).

 

[exhelodrvr]

Are the stats available for how many actual autos that have been done over the past ten years (i.e. Afghanistan and Iraq), and what the damage and injuries were?