Robinson R44
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To Dave
To save on (potential) victims the following thoughts:
- as the blades cone progressively the pen will show the increase from rest to max coning
- if they would flap then they have to go negative, which in view of the hard stops (remeber the not pull down instruction) will create victims even without putting BIC pens to the bolts
The reason/conditions why they are coning is
- The blades are sufficiently equal in weight
- The excentricity is small but not too small so the the centrifugal forces have some leverage
- No unreasonable frictions (bolts stuck or so)
Then
- the centrifugal force will create an equilibrium that makes the hub take the average position between the two blades (try this out on a static model, the centrifugal forces will flatten it so to speak)
Remember centrifugal force are at the root the dominant forces. These forces are equal because any inbalance in centrifugal forces great enough to make the hub unequilibred will be able to shake the heli apart.
Delta3
To save on (potential) victims the following thoughts:
- as the blades cone progressively the pen will show the increase from rest to max coning
- if they would flap then they have to go negative, which in view of the hard stops (remeber the not pull down instruction) will create victims even without putting BIC pens to the bolts
The reason/conditions why they are coning is
- The blades are sufficiently equal in weight
- The excentricity is small but not too small so the the centrifugal forces have some leverage
- No unreasonable frictions (bolts stuck or so)
Then
- the centrifugal force will create an equilibrium that makes the hub take the average position between the two blades (try this out on a static model, the centrifugal forces will flatten it so to speak)
Remember centrifugal force are at the root the dominant forces. These forces are equal because any inbalance in centrifugal forces great enough to make the hub unequilibred will be able to shake the heli apart.
Delta3
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delta3,
I agree. The side hinges are intended as coning hinges. These hinges were probably included to minimize out-of-plane bending moments in the roots of the blades and grips. This probably allowed for a lighter rotor.
Some thoughts.
" - as the blades cone progressively the pen will show the increase from rest to max coning"
My previous posting was not clear enough. Both bolts rotate with their blades, therefore the cardboard and the pen will rotate. It would therefore be possible to see if the rotations were synchronized or out of sinc.
" - if they would flap then they have to go negative,"
Not necessarily. This is a low inertia rotor, therefore under heaving loading the rotor will have a reasonable cone.
" - No unreasonable frictions (bolts stuck or so)"
All three R-22 hinges have a resistance to sliding friction of up to 22 ft-lb., under no load, when initially installed. The bearings appear to be of the sliding bushing type, therefor the breakaway friction will be somewhat higher. [Lu ~ for an unrelated reason, would you confirm that these bearings are actually bushings and not needle bearings. Thanks] . Granted that the static friction under load is very small when compared to the centrifugal force, but under small angle consideration, they will be quite close.
IMHO the concern, if there is one, would be that during an abnormal aerodynamic moment and/or control input the flexible blades may cause the rotor assemble to actually 'flap'. This combined with the delta3 MIGHT prove interesting.
Dave
I agree. The side hinges are intended as coning hinges. These hinges were probably included to minimize out-of-plane bending moments in the roots of the blades and grips. This probably allowed for a lighter rotor.
Some thoughts.
" - as the blades cone progressively the pen will show the increase from rest to max coning"
My previous posting was not clear enough. Both bolts rotate with their blades, therefore the cardboard and the pen will rotate. It would therefore be possible to see if the rotations were synchronized or out of sinc.
" - if they would flap then they have to go negative,"
Not necessarily. This is a low inertia rotor, therefore under heaving loading the rotor will have a reasonable cone.
" - No unreasonable frictions (bolts stuck or so)"
All three R-22 hinges have a resistance to sliding friction of up to 22 ft-lb., under no load, when initially installed. The bearings appear to be of the sliding bushing type, therefor the breakaway friction will be somewhat higher. [Lu ~ for an unrelated reason, would you confirm that these bearings are actually bushings and not needle bearings. Thanks] . Granted that the static friction under load is very small when compared to the centrifugal force, but under small angle consideration, they will be quite close.
IMHO the concern, if there is one, would be that during an abnormal aerodynamic moment and/or control input the flexible blades may cause the rotor assemble to actually 'flap'. This combined with the delta3 MIGHT prove interesting.
Dave
Delta 3 - fabulous diagrams which show a basic problem with flying a helicopter - as you increase forward speed the lift on the advancing and retreating sides of the rotor disc are different and therefore the aircraft will try to roll towards the advancing side. We (brits) call it Inflow Roll, others (Americans) call it Transverse Flow. All that stops it happening is the interference of the pilot who moves the stick towards the retreating side to keep the'wings' level. IIRC the R22 has a little spring/weight combination that reduces the lateral stick force required in cruise flight to ease pilot workload.
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Crab
To Crab,
To funny thing which took me 3 sleepness nights is that this picture may seem unbalanced, but in fact its fully balanced.
- the proof is of course in the result: the rotor is nicely level as follows from previous published time plots of flapping angle versus time or rotation (I also have a plot of the rotor disk to have a proof of that as part of my reports)
But wat happens, how the understand:
- the total lift diagrams certainly shows a lot of (total) lift on the forward blade
- looking at the distribution one observes that the retreating blade gets all lift from the top while the forward blade gets it from the middle
- why : because of the twist in the blades, when the forward blade flaps such as to reduce lift it gets from the high speeds , the tip gets near zero lift because of twisting. The retreating blade has to coop with a large ineffective area, so it gets all the lift from near the top.
- the middle of the blad has however a far smaller leverage arm than the top, so this is why the rotor, even with those very assymetric pictures is quite in balance.
One thing that triggers my curiousity : the rotor must feel important higher order harmonics:
- tip with large lift alternating with tip with zero or even negative lift
stated otherwise
- center of lift forces shifting all the time from middle to top.
Delta3
To funny thing which took me 3 sleepness nights is that this picture may seem unbalanced, but in fact its fully balanced.
- the proof is of course in the result: the rotor is nicely level as follows from previous published time plots of flapping angle versus time or rotation (I also have a plot of the rotor disk to have a proof of that as part of my reports)
But wat happens, how the understand:
- the total lift diagrams certainly shows a lot of (total) lift on the forward blade
- looking at the distribution one observes that the retreating blade gets all lift from the top while the forward blade gets it from the middle
- why : because of the twist in the blades, when the forward blade flaps such as to reduce lift it gets from the high speeds , the tip gets near zero lift because of twisting. The retreating blade has to coop with a large ineffective area, so it gets all the lift from near the top.
- the middle of the blad has however a far smaller leverage arm than the top, so this is why the rotor, even with those very assymetric pictures is quite in balance.
One thing that triggers my curiousity : the rotor must feel important higher order harmonics:
- tip with large lift alternating with tip with zero or even negative lift
stated otherwise
- center of lift forces shifting all the time from middle to top.
Delta3
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R-44 Rotorhead. Sorry guys I just couldn't help myself.
Surely they must be only coning hinges as the bearing surfaces are a hardened steel bush running against some form of fibre outer bush. If these areas were subject to continous movement ie once per rev then I think the wear rate would be too great for this type of bearing plus the pivot bolts are tightened to some hundred foot pounds of torque which would suggest they are not designed for a thousand or so direction changes per minute. I think they cone up to accomodate the weight of the machine and any flapping takes place in the form of bending of the blade. I dont suppose anyone has film footage of a Robinson rotor system in action do they?
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flapping
Delta3,
Nice graphs. Especially the delta3 graphs which show that Robinson had good reason to build in the delta3 angle.
I am not sure from reading your posts if you included the effects of flapping in your modelling of lift distrubution.
It seems to me that the disymmetry of lift shown in the graphs is exactly what flapping is supposed to take care of. Flapping will create a cyclical change in angle of attack that should balance the lift across the disc. The graphs don't seem to reflect this.
The massive imbalance shown in the graphs cannot be explained by invoking twist, I don't think. There are numerous helicopters and gyros with untwisted blades that achieve perfect symmetry of lift through teetering rotors.
Nice graphs. Especially the delta3 graphs which show that Robinson had good reason to build in the delta3 angle.
I am not sure from reading your posts if you included the effects of flapping in your modelling of lift distrubution.
It seems to me that the disymmetry of lift shown in the graphs is exactly what flapping is supposed to take care of. Flapping will create a cyclical change in angle of attack that should balance the lift across the disc. The graphs don't seem to reflect this.
The massive imbalance shown in the graphs cannot be explained by invoking twist, I don't think. There are numerous helicopters and gyros with untwisted blades that achieve perfect symmetry of lift through teetering rotors.
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From the R22 Maintenance Manual 5/7/82
bugdevheli,
The bolts, nuts, journals, and bearings have the same part number for all three hinges. The only difference is a slight length change in the journal and the associated shims.
The teetering hinge bolt is installed with a torque to give the bolt 0.016" - 0.017" of stretch. Unfortunately, I do not have the cone hinge bolt torque value.
Dave
The bolts, nuts, journals, and bearings have the same part number for all three hinges. The only difference is a slight length change in the journal and the associated shims.
The teetering hinge bolt is installed with a torque to give the bolt 0.016" - 0.017" of stretch. Unfortunately, I do not have the cone hinge bolt torque value.
Dave
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R44 AD 95-26-05 Rescinded by FAA
For some reason, I couldn't find the Robinson Tech thead (merged), so I'll start a new one.
Yesterday, I received an update for my R44 POH. RHC sent a notice that says:
The page at the end of Section 2 is the R44 Limitations Section and specifies what most of us consider the "SFAR." You know, < 200 hours and/or < 50 R44 hours prohibits flight if winds are > 25 knots or if wind gust spreads > 15 knots. If further goes on to recommend 60 KIAS in moderate to extreme turbulence, provides a few definitions, etc.
The page at the end of Section 3 is is the R44 Emergency Procedures Section and discusses right roll in Low-G conditions, flight turburlence, etc. The short end is to apply gently aft cyclic to reload the rotor and in other conditions do what is necessary to maintain positive G.
The page at the end of Section 4 is the R44 Normal Procedures Section. This provides detailed recommendations concerning factors that contribute to Main Rotor Stall and Mast Bumping. Mostly it recommends keeping your head out of your a$$ when flying and to avoid sideslip and large, rapid forward cyclic inputs, etc... keeping a cruise speed > 60 KIAS.
Now, none of the Safety Notices have been removed and these aren't FAA mandated either. Obviously, these notices were required to be in the POH as part of the AD 95-26-05. My question is, does this mean Frank finally agreed to take the R44 off SFAR requirements (especially wind restrictions relating to hours in type)?
During the last discussion of the SFAR, Frank actually pushed the FAA to continue applying it to the R44 when he really didn't have to. Is this a change in RHC philosophy that is more driven by marketing? Of course, the insurance companies will probably continue to have requirements of their own... especially Pathfinder. Interesting change of events, isn't it? Does anybody have the inside scoop on this?
Yesterday, I received an update for my R44 POH. RHC sent a notice that says:
NOTE: AD 95-26-05 has been rescinded by the FAA. The pages inserted at the ned of Sections 2, 3, and 4 to comply with the AD are no longer required and may be removed.
The page at the end of Section 3 is is the R44 Emergency Procedures Section and discusses right roll in Low-G conditions, flight turburlence, etc. The short end is to apply gently aft cyclic to reload the rotor and in other conditions do what is necessary to maintain positive G.
The page at the end of Section 4 is the R44 Normal Procedures Section. This provides detailed recommendations concerning factors that contribute to Main Rotor Stall and Mast Bumping. Mostly it recommends keeping your head out of your a$$ when flying and to avoid sideslip and large, rapid forward cyclic inputs, etc... keeping a cruise speed > 60 KIAS.
Now, none of the Safety Notices have been removed and these aren't FAA mandated either. Obviously, these notices were required to be in the POH as part of the AD 95-26-05. My question is, does this mean Frank finally agreed to take the R44 off SFAR requirements (especially wind restrictions relating to hours in type)?
During the last discussion of the SFAR, Frank actually pushed the FAA to continue applying it to the R44 when he really didn't have to. Is this a change in RHC philosophy that is more driven by marketing? Of course, the insurance companies will probably continue to have requirements of their own... especially Pathfinder. Interesting change of events, isn't it? Does anybody have the inside scoop on this?
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To Chiplight
You are right, my explanation is probably misleading.
When validating the results, if removed twist to get a different insight. Also untwisted blades display a comparitive behaviour, since the angles of attack are also influenced by the change in speed (for instance forward blad tip also will have smaller angle then middle of blade in case of untwisted blade, because of speed difference). I just used the twist argument to clarify this behaviour, because it makes it more outspoken.
I may try to build up sequences of graphs in an number of cases, but I had/have to be shure the equations were ok, which by now I believe. This will produce lots of graphs (I have more parameters such as mach nr, angle of attack etc).
The goal would be to have some kind of animation with cyclic and collective as input. I do this now point wise : right now load, and speed are the input and the program calculates the rest (pitching or hub-plane angle, cyclic, collective induced velocities etc as input for the detailed dynamic blade model)
The animation will involve extra programming work, that will take time.
Delta3
You are right, my explanation is probably misleading.
When validating the results, if removed twist to get a different insight. Also untwisted blades display a comparitive behaviour, since the angles of attack are also influenced by the change in speed (for instance forward blad tip also will have smaller angle then middle of blade in case of untwisted blade, because of speed difference). I just used the twist argument to clarify this behaviour, because it makes it more outspoken.
I may try to build up sequences of graphs in an number of cases, but I had/have to be shure the equations were ok, which by now I believe. This will produce lots of graphs (I have more parameters such as mach nr, angle of attack etc).
The goal would be to have some kind of animation with cyclic and collective as input. I do this now point wise : right now load, and speed are the input and the program calculates the rest (pitching or hub-plane angle, cyclic, collective induced velocities etc as input for the detailed dynamic blade model)
The animation will involve extra programming work, that will take time.
Delta3
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R44 Door Hinge Cracks
Just wondering if anyone else has encountered this before.
On our R44 I found that both upper rear door hinges had cracks radiating from the same area which is about 10 mm behind the pin where the bend starts. Hinges should be checked every 100 hrs but due to one of them cracking underneath the paint it could be very easily missed. If you do check it yourself make sure that you dont use a sharp scraper that will burr over the crack but better still get your maintainer to do it with paint stripper and dye penetrant.
If it does crack all the way through and the door comes off in flight it could really spoil your day. So for this reason I have put in a defect report and notified the manufacturer but the due to the way the red tape wheel turns I thought I would post it on PPrune as a heads up to others. Please PM if anybody has seen it as well.
Thanks.
On our R44 I found that both upper rear door hinges had cracks radiating from the same area which is about 10 mm behind the pin where the bend starts. Hinges should be checked every 100 hrs but due to one of them cracking underneath the paint it could be very easily missed. If you do check it yourself make sure that you dont use a sharp scraper that will burr over the crack but better still get your maintainer to do it with paint stripper and dye penetrant.
If it does crack all the way through and the door comes off in flight it could really spoil your day. So for this reason I have put in a defect report and notified the manufacturer but the due to the way the red tape wheel turns I thought I would post it on PPrune as a heads up to others. Please PM if anybody has seen it as well.
Thanks.
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R44 Preflight checklist
Can anybody explain why on the preflight checklist for the R44 that it is not required to check the altenator belt condition / tension.
If I remember correctly this item is listed in the R22 checklist so why not the R44??
Regards
Raven2
If I remember correctly this item is listed in the R22 checklist so why not the R44??
Regards
Raven2
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I would imagine because it's not easily accessible.
Exposed on the R22, but under the rear engine cover on the 44.
You'll soon know if there's a problem when you fire up because of the Alt warning light.
Exposed on the R22, but under the rear engine cover on the 44.
You'll soon know if there's a problem when you fire up because of the Alt warning light.
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The altenator is easily accessable if you get down and lie down underneath the machine. From there you can easily check the altenator tension and condition.
If you want to properly inspect the “Exhaust system” for “No cracks” you will have to lie down underneath the machine anyway. Or are you expected to view it from the lower cowl door on the right side? If this is the case then you would need a fibre optic camera in your toolbox!
Raven
If you want to properly inspect the “Exhaust system” for “No cracks” you will have to lie down underneath the machine anyway. Or are you expected to view it from the lower cowl door on the right side? If this is the case then you would need a fibre optic camera in your toolbox!
Raven
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HF in R44
Hi to our Oz operators
Does anyone know of an approved HF system for R44's? The Sat system is too expensive , about US30,000, so trying to find alternative as we work from sea level with good VHF coverage to zero within 50 nm due to mountain environment. It is not safe specially during our wet season operation
Thanks
WLM
Does anyone know of an approved HF system for R44's? The Sat system is too expensive , about US30,000, so trying to find alternative as we work from sea level with good VHF coverage to zero within 50 nm due to mountain environment. It is not safe specially during our wet season operation
Thanks
WLM
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Why can’t you use a new generation Satphone and have it installed just like any other phone? They do come with an external mount aerial. Something like:
http://www.telstat.com.au/comm12.htm
I don’t think they cost much, the calls are expensive, but if you’re just using them for SAR.....
http://www.telstat.com.au/comm12.htm
I don’t think they cost much, the calls are expensive, but if you’re just using them for SAR.....
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There is an aeronautical kit for the Motorola 9500 series phones. Includes a cradle and interface to your ICS and an external antenna etc. Same as an in car kit really. They used to be around USD 3500 then the phone on top which can vary depending where you go. Iridium charge is USD 1.50 a minute from anywhere to anywhere else on the planet regardless of distance. The unit was made by Icarus Instruments in the US who may have moved on to be called Sky Connect. These newer units cost a little more but do offer more with automated flight following, data (low speed text etc) the text is very cheap and could be very useful .
Google - Icarus Sat Talk II or Sky Connect.
Google - Icarus Sat Talk II or Sky Connect.
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WLM,
There is a new Qualcom CDMA/SAT that has just come on to the market, works quite well on the globalstar system (vodafone)
Worked most of the way from Alice to the east coast on CDMA a little while back.
There is a new Qualcom CDMA/SAT that has just come on to the market, works quite well on the globalstar system (vodafone)
Worked most of the way from Alice to the east coast on CDMA a little while back.
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R44 simulator
Some new examples of the R44 simulator I am building.
Presently I am working on the output..
The program now superimposes the technical results on a 3-dimensional graphical representation of the heli in its position in space.
Still not finished, but some feedback is welcome (especially from pilots/teachers).
If some of you want to use the pictures in classes, feel free, but please reference the author (pm me for that).
Delta 3
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--
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Presently I am working on the output..
The program now superimposes the technical results on a 3-dimensional graphical representation of the heli in its position in space.
Still not finished, but some feedback is welcome (especially from pilots/teachers).
If some of you want to use the pictures in classes, feel free, but please reference the author (pm me for that).
Delta 3
--
--
--
Last edited by delta3; 15th Nov 2004 at 00:20.