SlamClick
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AH-64 Questions.

Wed Oct 12, 2005 4:14 am

This picture . . .

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. . . posted in another thread got me looking at other pictures of this really lethal-looking aircraft. What caught my eye was that there appear to be two tail rotors. I checked to be sure there were not two aircraft then went searching.

My question is this: At a glance it appears to be coaxial, counter-rotating tail rotors but then all the pictures show the two sets of blades at the same angle. And not at 90o to each other, I might add.


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See what I mean?

So, any Apache troops out there who can explain this? Are the two sets of blades set at that angle on the hub?

Also, back to the head-on shot: What are those weathervane looking objects mounted off each engine?
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WrenchBender
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RE: AH-64 Questions.

Wed Oct 12, 2005 5:40 am

SlamClick
I'll try and answer, (long time rotorhead)/

If you can imagine 2 pieces of 2x4 overlaid on each other at approx 40 deg, no lap joints. Creating 2, 2 bladed tail rotors that operate off the same shaft, turning in the same direction.

Hope that helps

WrenchBender
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aeroweanie
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RE: AH-64 Questions.

Wed Oct 12, 2005 6:02 am

WrenchBender has it right - the tail rotor is a stack of two two-bladed teetering rotors

The weathervane objects are low-speed airspeed sensors. These tilt into the relative wind to provide data for launching missiles.
 
MissedApproach
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RE: AH-64 Questions.

Wed Oct 12, 2005 6:31 am

Quoting WrenchBender (Reply 1):
overlaid on each other at approx 40 deg, no lap joints

Yup. I've seen this referred to as a "squashed x configuration" somewhere. I have no idea why Hughes did this when they built the Apache. Presumably if it was more efficient it would've caught on, yet it seems to be peculiar to the AH-64.
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SlamClick
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RE: AH-64 Questions.

Wed Oct 12, 2005 6:37 am

Quoting WrenchBender (Reply 1):
If you can imagine 2 pieces of 2x4 overlaid on each other at approx 40 deg, no lap joints. Creating 2, 2 bladed tail rotors that operate off the same shaft, turning in the same direction.

I can imagine that. Good explanation and thanks.

It occurred to me that quite a few US made cars had cooling fans that were made up that way. Cheapo stampings, either riveted or spotwelded together at about that angle.

Quoting AeroWeanie (Reply 2):
The weathervane objects are low-speed airspeed sensors. These tilt into the relative wind to provide data for launching missiles.

Must be interesting how they separate relative wind from rotorwash. Weapons systems never even occurred to me. (slick pilot)

That is one good-looking aircraft. Oh, to be a young warrior again. (for a little while anyway)
Happiness is not seeing another trite Ste. Maarten photo all week long.
 
AGM114L
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RE: AH-64 Questions.

Wed Oct 12, 2005 6:43 am

As said before, just one tail rotor with 55 degree narrow angle. The weather vanes are call AADS(air and data sensor).

[Edited 2005-10-12 00:01:43]
My Boeing can blow up your Boeing
 
AGM114L
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RE: AH-64 Questions.

Wed Oct 12, 2005 7:07 am

Quoting SlamClick (Reply 4):
Must be interesting how they separate relative wind from rotorwash.

Computers

Quoting MissedApproach (Reply 3):
Yup. I've seen this referred to as a "squashed x configuration" somewhere. I have no idea why Hughes did this when they built the Apache. Presumably if it was more efficient it would've caught on, yet it seems to be peculiar to the AH-64.

Less noisy, or less distinctively sounds like a helicopter.
My Boeing can blow up your Boeing
 
aeroweanie
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RE: AH-64 Questions.

Wed Oct 12, 2005 7:49 am

Quoting SlamClick (Reply 4):
It occurred to me that quite a few US made cars had cooling fans that were made up that way. Cheapo stampings, either riveted or spotwelded together at about that angle.

The fans in cars use unequal spacing to reduce the noise produced and to spread it out over more frequencies. Evenly spaced blades produce a lot of noise at the blade passage frequency and harmonics of such. Unevenly spaced blades instead produce lower peaks at a variety of frequencies. The AH-64 tail rotor was not set up with unequal spacing for this reason. Instead, it involves the dynamics of teetering rotors (I had a Bell guy explain this to me recently, but CRS has wiped out the reason). On the other hand, Eurocopter uses unequal blade spacing on their newer fenestrons for noise reasons.


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bhmbaglock
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RE: AH-64 Questions.

Wed Oct 12, 2005 12:57 pm

Quoting AeroWeanie (Reply 7):
The fans in cars use unequal spacing to reduce the noise produced and to spread it out over more frequencies. Evenly spaced blades produce a lot of noise at the blade passage frequency and harmonics of such. Unevenly spaced blades instead produce lower peaks at a variety of frequencies. The AH-64 tail rotor was not set up with unequal spacing for this reason. Instead, it involves the dynamics of teetering rotors (I had a Bell guy explain this to me recently, but CRS has wiped out the reason). On the other hand, Eurocopter uses unequal blade spacing on their newer fenestrons for noise reasons.

Was it due to the natural frequencies of the fuselage or tail? A 4P natural frequency would definitely be a problem that could be solved by an arrangement like this. Could also be to control flutter.
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vzlet
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RE: AH-64 Questions.

Wed Oct 12, 2005 9:21 pm

Quoting SlamClick (Reply 4):
Must be interesting how they separate relative wind from rotorwash.

As I understand it, the air sensors are primarily to help aim unguided rockets when firing from a hover or at an airspeed low enough that downwash will influence the rockets' early trajectory because of weathervaning. (Obviously, even a tiny deviation in flightpath right at launch can have a large influence on accuracy.) There'd be no need to separate the two because rotorwash would be a major component of the relative wind. The difference between the two vanes in the picture at the top of the thread gives some idea how complex (disorderly?) the airflow around a hovering helicopter can be.

A similar tail rotor configuration is one of the many characteristics the Mi-28 shares with the AH-64:

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SlamClick
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RE: AH-64 Questions.

Wed Oct 12, 2005 11:52 pm

Quoting Vzlet (Reply 9):
There'd be no need to separate the two because rotorwash would be a major component of the relative wind.

Good point, thanks. I assume that those are "guided" somehow?

I used to fire the 2.75" rockets and everything depended on your being in unaccelerated flight when firing them. They could be quite accurate once you got it down. God I loved that sound!
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vzlet
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RE: AH-64 Questions.

Thu Oct 13, 2005 1:35 am

Quoting SlamClick (Reply 10):
I assume that those are "guided" somehow?

Not sure what you're referring to here. Do you mean the vanes?

As for 2.75" rockets, I once met an O-2 (as in Cessna, not 1Lt.) pilot who said that it was possible to achieve multi-mile ranges by lofting them in a climbing launch, and with decent accuracy. (Of course, for target-marking purposes, "decent accuracy" could be pretty flexible: "Target is 1800 yards south of the smoke.")
"That's so stupid! If they're so secret, why are they out where everyone can see them?" - my kid
 
SlamClick
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RE: AH-64 Questions.

Thu Oct 13, 2005 4:54 am

Quoting Vzlet (Reply 11):
Not sure what you're referring to here. Do you mean the vanes?

No, actually I was referrring to the missiles. Somehow, I missed the "unguided" part of the paragraph. Sorry.

I'd like to try that lofting system for the rockets. I fired them from an O-1 (as in Cessna, not 2LT) and don't know if I'd have had the energy to get much lofting. Smile

I agreee "decent accuracy" is quite a bracket. Might even depend on which branch of the service you got in to work your target. I'll stop there and let any offense taken be theoretical.
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AGM114L
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RE: AH-64 Questions.

Thu Oct 13, 2005 7:11 am

What do you mean by lofting? Any positive rate of climb of the aircraft is going to be nil compared to the rocket thrust. Optimal lauch angle is going to give you the most range, if that's what you're concerned with.

[Edited 2005-10-13 00:26:57]
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SlamClick
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RE: AH-64 Questions.

Thu Oct 13, 2005 11:04 pm

Quoting AGM114L (Reply 13):
Any positive rate of climb of the aircraft is going to be nil compared to the rocket thrust. Optimal lauch angle is going to give you the most range, if that's what you're concerned with.

When fired from fixed-wing, those rockets need to leave the tube in unaccelerated flight, meaning no positive or negative G-load. A "zoom climb" by an Oscar Duck (O-2) should produce this, once stablized in the climb. This would fire the tube up rather than on the usual 40 degree (or so) downline.

Yes the velocity vector of the launch tube adds directly to the rocket velocity. It is just that 140 knots is not a big piece of 1400 knots, but it is not nothing either. You are correct, though about the angle contributing more than the velocity.
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LongbowPilot
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RE: AH-64 Questions.

Fri Oct 14, 2005 7:41 pm

Quoting MissedApproach (Reply 3):
Yup. I've seen this referred to as a "squashed x configuration" somewhere. I have no idea why Hughes did this when they built the Apache. Presumably if it was more efficient it would've caught on, yet it seems to be peculiar to the AH-64.

wrong

Quoting AeroWeanie (Reply 2):
The weathervane objects are low-speed airspeed sensors. These tilt into the relative wind to provide data for launching missiles

inaccurate

Quoting AGM114L (Reply 5):
As said before, just one tail rotor with 55 degree narrow angle. The weather vanes are call AADS(air and data sensor).

close

Quoting AGM114L (Reply 6):
Quoting MissedApproach (Reply 3):
Yup. I've seen this referred to as a "squashed x configuration" somewhere. I have no idea why Hughes did this when they built the Apache. Presumably if it was more efficient it would've caught on, yet it seems to be peculiar to the AH-64.

Less noisy, or less distinctively sounds like a helicopter.

backwards

Quoting AeroWeanie (Reply 7):
The AH-64 tail rotor was not set up with unequal spacing for this reason. Instead, it involves the dynamics of teetering rotors (I had a Bell guy explain this to me recently, but CRS has wiped out the reason).

wrong

Quoting BHMBAGLOCK (Reply 8):
Was it due to the natural frequencies of the fuselage or tail? A 4P natural frequency would definitely be a problem that could be solved by an arrangement like this. Could also be to control flutter.

wtf?

Quoting Vzlet (Reply 9):
As I understand it, the air sensors are primarily to help aim unguided rockets when firing from a hover or at an airspeed low enough that downwash will influence the rockets' early trajectory because of weathervaning. (Obviously, even a tiny deviation in flightpath right at launch can have a large influence on accuracy.) There'd be no need to separate the two because rotorwash would be a major component of the relative wind. The difference between the two vanes in the picture at the top of the thread gives some idea how complex (disorderly?) the airflow around a hovering helicopter can be.

 Yeah sure

To answer the initial question, the reason for the tail rotor design was to be more efficient for maintenance purposes (as stated by an IP/MTP I flew with). The tail rotor is still an ear piercing experiance so i don't think there is much reduction, but trust me it makes the sound of the Apache more distinctive and makes the bad guys run for cover if they hear us coming.

the AADS probes are used by the longbow System Processors to provide accurate wind information. So pilots can see where the winds are coming from, speed, and also provides informations to better enhance ballistic solution for the various weapon systems.

The 2.75" rockets are an unguided folding fin aerial rocket. These rockets are only as accurate as the one squeezing the trigger. The are horribly inaccurate firing from a hover, and are deadly when fired from a running or diving fire. The mantra for firing rockets is, "Target, Torque, Trim, Target" That means you line up on your target and put it in constrants, stabilize your torque so you are not slinging or dropping your rockets, make sure you are in trim so the rockets will track the relative wind to the pods, and ensure you are on target, "squeeze"

The whole nothion of flinging your rockets is possible. You simple rear the aircraft onto it's tail and fire your rocket. It is called super elevating. The apache removes a lot of this requirement because the pylons articulate relative to the range you are requiring them to fire. To increase the range of your rockets (which isn't done except for Illumination rounds) you simple apply max range into the range and the pods will be at the max elevation, than rear the aircraft back and squeeze the trigger... Voila!
 
AGM114L
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RE: AH-64 Questions.

Fri Oct 14, 2005 11:41 pm

Quoting LongbowPilot (Reply 15):
close

uh. i never really braught out a protractor, but I dusted off my student handout and it said 55 degrees.

Quoting LongbowPilot (Reply 15):
That means you line up on your target and put it in constrants

Since when did we put our rockets into constraints or are you thinking of a different weapon system there chief?

Like you, I could write all day about slinging rockets.....but this is a public forum and with the crackdown on OPSEC violations, however ridiculus they are, I would refrain from getting too in depth about our systems, especially your operational knowledge. Granted our -10, 1-140s, and other pubs are easily avialilbe to people who want them and we're talking about a 50 yearold weapons system here and I doubt Hajji in Afcrackistan could use any of this information, its just bad policy to go into too much detail about the weapons, ASE, FCR, tactics, ect. Anyway I wish I was with you and the rest of the 11th instead of stuck here. Good luck man.
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LongbowPilot
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RE: AH-64 Questions.

Sat Oct 15, 2005 1:54 pm

Quoting AGM114L (Reply 16):
constraints

you know there are parameters that have to be met before you can fire the weapons systems. that is one.

I didn't talk about the ASE, or the FCR, I am aware of what is classified and not classified. I am speaking from "Unclassified" documents that are easily accessible through online purchase if you simply investigate a little on the internet. I have seen static displays at air shows where pilots have gone way more indepth than that. You are correct there are OPSEC considerations, but I really believe what I went into was not going into any of our "Classified" items.

As for the "close" you are correct that was not called for, i highlighted the wrong one, and you are right. I apologize for it.
 
aeroweanie
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RE: AH-64 Questions.

Sat Oct 15, 2005 5:29 pm

Quoting LongbowPilot (Reply 15):
To answer the initial question, the reason for the tail rotor design was to be more efficient for maintenance purposes (as stated by an IP/MTP I flew with). The tail rotor is still an ear piercing experiance so i don't think there is much reduction, but trust me it makes the sound of the Apache more distinctive and makes the bad guys run for cover if they hear us coming.

Wrong - go read some Ray Prouty articles in Rotor & Wing and the AHS paper he published on the subject - he helped design the tail rotor. It has nothing to do with maintanence. Its that way due to the dynamics of controlling two stacked teetering rotors.
 
LongbowPilot
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RE: AH-64 Questions.

Sat Oct 15, 2005 5:54 pm

Quoting AeroWeanie (Reply 18):
Wrong - go read some Ray Prouty articles in Rotor & Wing and the AHS paper he published on the subject - he helped design the tail rotor.

Well, I will look into it and if it is right, than I stand corrected. The reason why I state that you were WRONG, is because a Maintenance Test Pilot with 20 years of active duty flying, might know a little more than I or anyone else on the subject. If you are right, thanks for the reference, so that Amry Aviators can put this discussion to rest as well. If it so comes out, than I will tell the 20 year veteran that here is the correct reason and you will have my apology as well, till then I'll stand behind his theory
 
aeroweanie
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RE: AH-64 Questions.

Sun Oct 16, 2005 4:46 am

I looked through my collection of Ray Prouty's publications, but the best I could find was the following quote from "Technology Advances in the AH-64 Apache Advanced Attack Helicopter," by Kenneth B. Amer and Raymond W. Prouty of Hughes Helicopters, presented at the 1983 American Helicopter Society Forum:

"The unequal spacing between pairs of blades, which was initially selected to improve mechanical clearances, also resulted in a reduction in the 4/rev component of tail rotor noise."

In a recent seminar, by a retired Bell dynamicist, I heard more fundamental explanation for the scissored arrangement, which involved the pitch-flap coupling of having two stacked teetering rotors. As to why it was decided to use two stacked teetering rotors, this was probably a simplicity argument, which might have included maintanence concerns.

Your MTP might have 20 years of flying experience, but I have 25 years of experience as an aero engineer. My first job out of college was at Sikorsky. If you fly in a UH-60M or a S-92, you are flying under a rotor airfoil that I co-designed.
 
AGM114L
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RE: AH-64 Questions.

Sun Oct 16, 2005 5:42 am

So AreoWeanie, what do you think about us attack pilots and our winning personalities?

Quoting AeroWeanie (Reply 20):
Your MTP might have 20 years of flying experience, but I have 25 years of experience as an aero engineer. My first job out of college was at Sikorsky. If you fly in a UH-60M or a S-92, you are flying under a rotor airfoil that I co-designed.

I always hear the Hawkdrivers claim that their tailrotor provides 2.5% of its total lift. Is this true?
As you may notice the 64 hovers nose high, I always thought having a tilted tail rotor like the hawk may improve our forward visability, especially for the CPG(copilotgunner), by providing a bit of lift in our ass end. Would this work? What are the drawbacks of a tilted tail rotor?

[Edited 2005-10-15 22:51:20]
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aeroweanie
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RE: AH-64 Questions.

Sun Oct 16, 2005 6:19 am

Quoting AGM114L (Reply 21):
So AreoWeanie, what do you think about us attack pilots and our winning personalities?

I think you are very brave souls.

Quoting AGM114L (Reply 21):
I always hear the Hawkdrivers claim that their tailrotor provides 2.5% of its total lift. Is this true?

I can't remember the number off-hand, but I seem to remember that its higher than 2.5%.

Main rotor forward shaft tilt is used to keep the fuselage level in high speed forward flight, to reduce drag. Of course, this results in a nose up attitude in hover. The S-76 gained chin windows early in the flight test program due to this (it has 5 deg of forward shaft tilt, if I remember right). The UH-60 only has 3 deg of forward shaft tilt, so it hovers less nose up. I don't know if the tail rotor lift is used to level it out in hover. I would doubt it, as this would cause the main rotor to be tipped forward, creating a forward thrust force that would have to be removed using cyclic.
 
2H4
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RE: AH-64 Questions.

Sun Oct 16, 2005 12:45 pm




Quoting AeroWeanie (Reply 7):
On the other hand, Eurocopter uses unequal blade spacing on their newer fenestrons for noise reasons.



Perhaps this is a stupid question, but if unequal blade spacing reduces the noise levels of tail rotors, why isn't it used for aircraft propellers?




2H4


Intentionally Left Blank
 
SlamClick
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RE: AH-64 Questions.

Sun Oct 16, 2005 11:53 pm

Quoting 2H4 (Reply 23):
Perhaps this is a stupid question, but if unequal blade spacing reduces the noise levels of tail rotors, why isn't it used for aircraft propellers?

Just a guess here but I think it is something like this: You can make the spacing unequal but you must do it in opposing pairs to keep the CG of the rotating mass concentric with the center of rotation else - catastrophic imbalance. This means that you could do it with a four-bladed prop at a minimum. Very few four-bladed props being made anymore.

Also other developments in prop blade design are changing prop noise. Don't know if noise is driving the changes but the shapes sure are different.
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2H4
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RE: AH-64 Questions.

Mon Oct 17, 2005 3:53 am




Quoting SlamClick (Reply 24):
This means that you could do it with a four-bladed prop at a minimum. Very few four-bladed props being made anymore.



You certainly don't see very many here in the States, but it seems as if aftermarket four-bladed props are somewhat common in Europe:


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...And not just on Cubs, either...that's just all I could quickly find. I have to assume the props are sold for their reduced noise, but I'm not 100% sure. Perhaps a European Tech/Ops friend can shed a little light on this for us.




2H4


Intentionally Left Blank
 
SlamClick
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RE: AH-64 Questions.

Mon Oct 17, 2005 4:45 am

Quoting 2H4 (Reply 25):
it seems as if aftermarket four-bladed props are somewhat common in Europe:

Then there is the less common single bladed tail rotor:

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The Hiller Hornet. Nothing missing from that tailrotor, one blade and a counterbalance. Note also the slinger ring on the mast, just above the swashplate. A small electric pump pushed fuel up to there, then centrifugal force carried it out to the pulsejets at the end of the main rotor blades which were the powerplant for this aircraft.

I've been told that all the fuel it could lift off the ground would power it only for a few minutes.
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bhmbaglock
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RE: AH-64 Questions.

Mon Oct 17, 2005 5:23 am

Quoting LongbowPilot (Reply 15):
Quoting BHMBAGLOCK (Reply 8):
Was it due to the natural frequencies of the fuselage or tail? A 4P natural frequency would definitely be a problem that could be solved by an arrangement like this. Could also be to control flutter.

wtf?

Sorry, engineer short hand there. With any prop(including rotors) the rotational speed is referred to as "1P". For obvious reasons, it is not desirable to have a natural frequency for the airframe that closely matches this frequency. Another frequency of concern is the multiple of this frequency and the number of blades(assuming equal blade spacing), i.e 3P for 3 blades or 4P for four blades.

My point was that if(I stress that I do not have the answer to this question), the Apache airframe or tailboom has a natural frequency that coincides with the 4P multiple of the tail rotor frequency then this would be an elegant solution assuming that there is no corresponding 2P natural frequency.
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aeroweanie
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RE: AH-64 Questions.

Mon Oct 17, 2005 8:11 am

Quoting 2H4 (Reply 23):
Perhaps this is a stupid question, but if unequal blade spacing reduces the noise levels of tail rotors, why isn't it used for aircraft propellers?

I'm not really certain, but after thinking about it for a while, I have a hypothesis. While there are balanced solutions for unequal blade spacing, they are statically balanced, not dynamically balanced. If the drive shaft to the prop, rotor or fan is short (such as an auto cooling fan or a fenestron), the forces produced by the dynamic imbalance are not so bad. On the other hand, if the shaft is long, such as the crankshaft of a piston engine, this can cause real problems.
 
LongbowPilot
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RE: AH-64 Questions.

Mon Oct 17, 2005 4:53 pm

Quoting AGM114L (Reply 21):
I always hear the Hawkdrivers claim that their tailrotor provides 2.5% of its total lift. Is this true?

I work with an XP and Hawkdriver. He said the tail rotor provides a lift vector to help with the CG while in hovering flight. The transmision is tilted 3 degress forward to help with the aircrafts longitudinal angle during forward flight. The cost to that is at a hover the "Whale" tail dangles really low. So the tail rotor has some lift vector to hold the tail up.

That is what he said
 
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vzlet
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RE: AH-64 Questions.

Tue Oct 25, 2005 8:41 am

For comparison, below are details of AH-64 and Mi-28 tail rotors, both facing forward (and taken from bad_motivs of mine).
Apache:

Havoc:
http://img.photobucket.com/albums/v257/vzlet/mi28.jpg

Quoting LongbowPilot (Reply 15):
the AADS probes are used by the longbow System Processors to provide accurate wind information. So pilots can see where the winds are coming from, speed, and also provides informations to better enhance ballistic solution for the various weapon systems.

LongbowPilot:
Does the AADS provide any output directly readable by the crew, or is the data only incorporated into a fire-control solution?
Can you elaborate on what weapons (other than FFARs) use AADS info? Does the gun benefit?

Thanks,
Mark
"That's so stupid! If they're so secret, why are they out where everyone can see them?" - my kid
 
AGM114L
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RE: AH-64 Questions.

Thu Oct 27, 2005 6:32 am

Quoting Vzlet (Reply 30):
Does the AADS provide any output directly readable by the crew, or is the data only incorporated into a fire-control solution?

Yes, depending what symbology mode is selected (cruise, transition, hover, bob-up) we are given a velocity vector, acceleration cue, and/or flight path vector in the pilots' HMD (helmet mounted display). The HMD is very nifty, its like having a fighter jets HUD except its right in front of the eyeball, the HMD also displays a FLIR image which the pilots use to fly at night.

Unfortunatly the Apache's helmet makes it look like its pilots have down syndrome.


Quoting Vzlet (Reply 30):
Can you elaborate on what weapons (other than FFARs) use AADS info? Does the gun benefit?

The Apache's weapon processors compute ballistic solutions for the gun and provides data to the hellfires as well. I'll let LongbowPilot describe the intricacies of the MUX system.
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bhill
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RE: AH-64 Questions.

Thu Oct 27, 2005 11:18 am

...Well Slamclick sir...you asked!!..Thanks guys..fascinating discussion made me dust of my physics texts from college...

Cheers
Carpe Pices
 
LongbowPilot
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RE: AH-64 Questions.

Thu Oct 27, 2005 5:17 pm

EWWW MUX, thanks... I think  banghead  Where is my -10.
 
LongbowPilot
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RE: AH-64 Questions.

Fri Oct 28, 2005 2:43 pm

Quoting AGM114L (Reply 31):
Unfortunatly the Apache's helmet makes it look like its pilots have down syndrome.

I really think our Brain Pans look awesome with the NVG mount. I fly with that only now, especially here, never know when you are going to get stuck having to mount one, we won't talk about those times here  Wink
 
SlamClick
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RE: AH-64 Questions.

Mon Oct 31, 2005 4:19 am

Quoting Bhill (Reply 32):
...Well Slamclick sir...you asked!!..

I did, and it was answered, fully. Thank you to each of you. Been an interesting and informative thread for me.

LongbowPilot and AGM114Lthank you for the answers and for so much more.
Happiness is not seeing another trite Ste. Maarten photo all week long.
 
jarheadk5
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RE: AH-64 Questions.

Thu Nov 03, 2005 3:31 pm

Quoting AGM114L (Reply 21):
I always hear the Hawkdrivers claim that their tailrotor provides 2.5% of its total lift. Is this true?

The CH-53E gets 2% additional lift, and an expanded longitudinal CG range, with the tail canted 20*.

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Quoting AGM114L (Reply 21):
What are the drawbacks of a tilted tail rotor?

Increased pilot workload to maintain a stable hover, IF there are no control couplings in the flight controls.
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AGM114L
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RE: AH-64 Questions.

Fri Nov 04, 2005 3:47 am

Quoting JarheadK5 (Reply 36):
Quoting AGM114L (Reply 21):
What are the drawbacks of a tilted tail rotor?

Increased pilot workload to maintain a stable hover, IF there are no control couplings in the flight controls.

Yeah I can totally see that, I should have applied some thought before I asked. The vertical lift provided by the tail rotor would change as the anti-torque pedals are moved, but as you said the chopper adjusts for it, do you know if this is adjusted by SCAS or whatever you call it? Did you fly or crew on the 53?...just curious.
My Boeing can blow up your Boeing
 
jarheadk5
Posts: 216
Joined: Thu Nov 03, 2005 2:45 pm

RE: AH-64 Questions.

Sat Nov 05, 2005 3:51 pm

Quoting AGM114L (Reply 37):
The vertical lift provided by the tail rotor would change as the anti-torque pedals are moved, but as you said the chopper adjusts for it, do you know if this is adjusted by SCAS or whatever you call it? Did you fly or crew on the 53?...just curious.

I maintained and crewed the Echo for nearly 11 years.

As far as the flight controls go - the flight control mixing units take care of the control couplings. There's 2 mixing units in the Echo; they are mechanical, and they're the most confusing-looking sets of pushrods, dogbones, bellcranks, walking beams, and one-way bearings I've ever seen. Urban legend has it that the engineer who's job it was to design the 53E mixing unit, had a nervous breakdown when the design was finalized...
There are five control couplings in the 53E flight control system:

collective to pitch
collective to roll
collective to yaw
yaw to pitch
yaw to roll

There's also collective bias, which adds Ng to maintain the set Nr as collective is pulled.

The 53 has AFCS. Probably does the same things as the average SCAS system, but AFCS is what Sikorsky prefers to call it.
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