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Model Forum / Radio Controlled / Helicopters / November 2005Disymmetry of lift.....
ok, since we kinda strayed off track with the cyclic trim to compensate for translating tendency thread, I thought I'd start a new one since I'm now curious as to how model helos compensate for disymmetry of lift.. In full scale, you've got three basic types of rotor systems and their methods for dealing with DoL Rigid - blade bending Semi-Rigid - teetering hinge Fully Atriculated - Flapping hinges (I won't get into the composite types...) Obviously wooden blades will bend so the rigid system we've got on our models works well. Carbon blades will bend, but as Beav said, they're much stiffer. (I've never flown carbon blades, but have a set on the "new" Raptor) Flap dampers imply there may be a combination of blade bending and flapping going on. I can see the need for a rigid system in a 3D capable model. A flapping or teetering hinge could invite a boom strike as the blades transition from positive to negative pitch.. What about the tail rotor? I've never seen a model helo with a delta hinge (angled teetering hinge) on the tail rotor like is seen on the Robinson R22/44 and the Hughes/Schweizer 269/300 etc. DoL occurs on the tailrotor as well so it needs to be able to teeter/flap or bend, right? Gyroplane models have a delta hinge setup on their main rotors too. OK, there ya have it. The seeds of a potentially interesting discussion... > ok, since we kinda strayed off track with the cyclic trim to > compensate for translating tendency thread, I thought I'd start a new [quoted text clipped - 30 lines] > OK, there ya have it. The seeds of a potentially interesting > discussion... There are some interesting articles by Colin Mills of CSM all over the net which cover Model Helicopter dynamics, including the above topic. They were originally printed in MHW. They even have diagrams:-)  SignatureAdrian Smith www.YourStadium.com Superb aerial pictures of UK football stadiums. >There are some interesting articles by Colin Mills of CSM all over the net >which cover Model Helicopter dynamics, including the above topic. They were >originally printed in MHW. >They even have diagrams:-) I've had my fill of aviation related diagrams as I've been working on my helo ratings.. Info overload is a way of life for me right now. hehehe (Won't stop me from hunting them down tho!) Probably 99% of the models I've flown are of the semi-rigid rotor type. That includes, The Champion, Scout, X-Cells, Intrepids, Shuttle ZX's, and most currently, my Freya. My first model was a Horizon and it was a flybarless, rigid system with wood blades. The composite rotor blades we have now, didn't exist back then. I've also flown Shuttles and mainly the old Kyosho Concepts with the DDF heads that would be considered fully articulated. Flapping, as I understand it, is the primary means whereby the rotor system compensates for dissymmetry of lift problems. I've noted that the models do show a "slight" shift in roll cyclic trim, rolling away from the advancing side of the rotor disk after entering translational lift. Generally, the amount of cyclic input it takes to correct this is very minor. With the advent of computer radios and allow separated trims for each flight mode, that slight shift in roll cyclic trim is easily nullified and no longer an issue, not that it really was one in the first place. Now that I'm "finally" starting to work on 3D stuff, primarily backwards upright and forward and backwards inverted flight, it's becoming more of an issue. If I trim the model for high speed forward flight, upright or inverted makes little difference, when I roll it inverted, those trims start working against me. As a result, I'm learning to compromise the trim between forward and backward flight so that I don't feel like I'm having to hold a "hard" cyclic correction just to maintain status quo. Since I'm not real comfortable with backwards flight either way, it's turning out to be an interesting exercise. I'm getting there! :-) As for model helicopters with a delta hinge on the tail rotor, you must not have ever gotten hold of one of the original design X-Cells. They had a delta hinge tail hub that floated on a short piece of fuel tubing like material. The hub was secured to the shaft with a pin, angled about 45 degrees to the line of the hub itself. The system worked very well. The main maintenance issue was that you had to do routine replacements of the fuel tubing as it wore out fairly quickly. Here's a link to an exploded view that should make this more clear. http://warhammer.mcc.virginia.edu/ty/heli/xcell/images/xl60-15.gif Fly Safe, Steve R. > ok, since we kinda strayed off track with the cyclic trim to > compensate for translating tendency thread, I thought I'd start a new [quoted text clipped - 30 lines] > OK, there ya have it. The seeds of a potentially interesting > discussion... >Probably 99% of the models I've flown are of the semi-rigid rotor type. >That includes, The Champion, Scout, X-Cells, Intrepids, Shuttle ZX's, and [quoted text clipped - 3 lines] >old Kyosho Concepts with the DDF heads that would be considered fully >articulated. Doesn't semi-rigid imply some sort of teetering or flapping hinge? I ran home at lunch to check out the Raptor rotorhead.. There's a LITTLE bit of up/down movement in "slop" of the blade grip's bearings, but not much... Never seen a DDF head. Was it truly fully articulated with flapping and lead/lag hinges? >Flapping, as I understand it, is the primary means whereby the rotor system >compensates for dissymmetry of lift problems. Correct. Advancing blade has faster relative wind than the retreating blade (Assuming some sort of horizontal airflow across the rotor disc - we'll deal with forward flight only here for simplicity) and therefor creates more lift. This causes the advancing blade to want to fly "higher" than the retreating blade. This upward motion increases inflow and reduces the angle of attack, reducing lift. Conversely, the retreating blade's downward motion decreases inflow and the AoA is increased, increasing lift. >I've noted that the models do >show a "slight" shift in roll cyclic trim, rolling away from the advancing >side of the rotor disk after entering translational lift. This is actually transverse flow effect causing the roll. In full scale, you don't really feel the roll too much, but you definitely do on approach as your speed approaches 25-30 knots.. > Generally, the >amount of cyclic input it takes to correct this is very minor. Even in the full scale helos. > With the >advent of computer radios and allow separated trims for each flight mode, >that slight shift in roll cyclic trim is easily nullified and no longer an >issue, not that it really was one in the first place. It shouldn't be. The corrective (for lack of a better term) inputs become second nature, the same as they become when you finally learn to hover halfway decent. (or any other maneuver for that matter) > Now that I'm >"finally" starting to work on 3D stuff, primarily backwards upright and [quoted text clipped - 6 lines] >comfortable with backwards flight either way, it's turning out to be an >interesting exercise. I'm getting there! :-) I wish I could get this nose-in hover down.. I get it there for 10-15 seconds, it goes to sh.t and then I fly away, come back to nose-in and start over... hehehe >As for model helicopters with a delta hinge on the tail rotor, you must not >have ever gotten hold of one of the original design X-Cells. They had a [quoted text clipped - 6 lines] > >http://warhammer.mcc.virginia.edu/ty/heli/xcell/images/xl60-15.gif My bro-in-law has an old X-Cell 60.. I'll take a drive over to his place and check it out. Kinda sounds like the fuel tube stuff was used as a sort of elastomeric damper to tame the flapping a bit.. >>Probably 99% of the models I've flown are of the semi-rigid rotor type. >>That includes, The Champion, Scout, X-Cells, Intrepids, Shuttle ZX's, and [quoted text clipped - 8 lines] > LITTLE bit of up/down movement in "slop" of the blade grip's bearings, > but not much... The head axle, or cross shaft that holds the individual blade grips is supported by a set of o-rings. It floats, to one degree or another and allows a certain amount of flapping. If you grab each blade grip with each hand and rock them back and forth in a "flapping" type motion, you should see some flapping action within that cross shaft. The slop you mention between the blade grips and it's bearings are just a Raptor trait. When the rotor system is spun up, centrifugal force should pretty much take care of that slop. > Never seen a DDF head. Was it truly fully articulated with flapping > and lead/lag hinges? DDF = Duel Damped Flapping If you ever run into an orginal Kyosho Concept, or the orginal Hirobo Shuttles, you'll find that each main blade grip was mounted to it's own flapping hinge and is independant of the other blade. It's the closest thing I've seen in the modeling world to emmunlating a fully articulated full size rotor system. >>Flapping, as I understand it, is the primary means whereby the rotor >>system [quoted text clipped - 16 lines] > scale, you don't really feel the roll too much, but you definitely do > on approach as your speed approaches 25-30 knots.. Oops, yeah, I think you're right. I hadn't run into the term "transverse flow" in a long time. I remember a conversation a "long" time ago where the speculation was that, considering the size of an average models rotor disk, that transverse flow isn't as much of an issue as it would be in full size birds. The colume of air coming over, and being accelerated by, the rotor disk simply isn't there long enough to significantly change the velocity of airflow between the leading edge of the disk and the trailing edge. What do you think? > My bro-in-law has an old X-Cell 60.. I'll take a drive over to his > place and check it out. Kinda sounds like the fuel tube stuff was > used as a sort of elastomeric damper to tame the flapping a bit.. Assuming it hasn't been upgraded. X-Cells don't use this system any more as far as I know. It may still be used on the base level X-Cell 60. I tried looking that up but didn't have much luck. Fly Safe, Steve R. >The head axle, or cross shaft that holds the individual blade grips is >supported by a set of o-rings. It floats, to one degree or another and [quoted text clipped - 4 lines] >rotor system is spun up, centrifugal force should pretty much take care of >that slop. I'll have to look at the Rappy's assembly instructions again... I wonder what the max flapping angle might be... Maybe it's a combination of that flapping and blade bending that provides the compensation for DoL. >DDF = Duel Damped Flapping If you ever run into an orginal Kyosho Concept, >or the orginal Hirobo Shuttles, you'll find that each main blade grip was >mounted to it's own flapping hinge and is independant of the other blade. >It's the closest thing I've seen in the modeling world to emmunlating a >fully articulated full size rotor system. Know where to find a picture? Sounds interesting. >> This is actually transverse flow effect causing the roll. In full >> scale, you don't really feel the roll too much, but you definitely do >> on approach as your speed approaches 25-30 knots.. Should have said "....don't really feel the roll too much on takeoff,..." >Oops, yeah, I think you're right. I hadn't run into the term "transverse >flow" in a long time. I remember a conversation a "long" time ago where the [quoted text clipped - 4 lines] >airflow between the leading edge of the disk and the trailing edge. What do >you think? I don't know. The head speeds on a model are WAY higher (3+ times) than on a full scale ship so there may be a lot of inflow even in the front half of the disc in forward flight.. I wonder if any flow testing has been done on a model to see if they're really acting like a full scale ship... >> My bro-in-law has an old X-Cell 60.. I'll take a drive over to his >> place and check it out. Kinda sounds like the fuel tube stuff was [quoted text clipped - 3 lines] >far as I know. It may still be used on the base level X-Cell 60. I tried >looking that up but didn't have much luck. Pretty sure it hasn't. All his helos are pretty much bone stock and haven't flown in years. He's trying to get his Whisper back into the air after it's been sitting for 15+ years. >>DDF = Duel Damped Flapping If you ever run into an orginal Kyosho >>Concept, [quoted text clipped - 4 lines] > > Know where to find a picture? Sounds interesting. The closest I've found so far is a PDF file of an exploded view. I'm assuming you've got Adobe Reader. If not, go to www.adobe.com and download the reader. The link is: http://www.kyosho.co.jp/web/download/instructionmanual/gp_heli/pdf/21722_concept 46vr_t.pdf Anyway, the left side of page 1 showed the old DDF head. They don't make this anymore and Kyosho doesn't support those older machines but the system worked pretty well. You'll also notice that the flybar is a co-plane installation. That is, the flybar rotates in the same plane as the main rotor blades. Not above or below as most everyone else does. This is the only rotor system I've seen that does this. If I find a link to an actual photo, I'll post it here. Fly Safe, Steve R. >The closest I've found so far is a PDF file of an exploded view. I'm >assuming you've got Adobe Reader. If not, go to www.adobe.com and download [quoted text clipped - 8 lines] >rotor blades. Not above or below as most everyone else does. This is the >only rotor system I've seen that does this. Hmm. Can't see anything on the left side of any page but the TR assembly on page 3. Might be a version problem as I have to stick with Acrobat 6 for my flight planning software. Adobe did something goofy with the v7 stuff so my planning software chokes and dies when trying to print the flight logs. I just had an interesting thought while looking the the Rappy rotor head.. It appears as if the flybar can flap (I'm looking at it from about 10' away as it's sitting on top of my bookcase) and I'm wondering if the linkage for the flybar is set up with advance angle (to deal with precession) and tweaks blade pitch to compensate for DoL.. I'll have a closer look at it (and the old Schluter) tomorrow after work and see if I'm on to something.. >>DDF = Duel Damped Flapping If you ever run into an orginal Kyosho >>Concept, [quoted text clipped - 4 lines] > > Know where to find a picture? Sounds interesting. Ok, here's another PDF file. http://www.rchelibase.com/concept/c30dxse-1.pdf It's the instruction manual for the old Concept DX / EX model. The DX was the trainer verion. It has "metal" flybar paddles. Anyway, you can follow the assembly steps and it'll give you a much better idea of how the rotor system went together and thus, how it worked. There's also a picture of the completed model on the first page. It's not the best picture in the world but it's better than nothing. Note the way the main rotor blades droop! Fly Safe, Steve R. >Ok, here's another PDF file. > [quoted text clipped - 6 lines] >completed model on the first page. It's not the best picture in the world >but it's better than nothing. Note the way the main rotor blades droop! Definitely shows a flapping hinge setup in step 3... Also it appears as if the paddles flapping would affect blade pitch with the appropriate linkage attachments to the mixing levers 90 degrees "early" in the rotation... >>Ok, here's another PDF file. >> [quoted text clipped - 13 lines] > appropriate linkage attachments to the mixing levers 90 degrees > "early" in the rotation... I'm not sure I'm following you here. Unless you're not interpreting the drawing correctly. Your Raptor uses a moving swashplate (raises and lowers) to effect collective movements. There is what I've always called a "washout" unit that floats between the swashplate and the rotor hub that transfers cyclic commands to the flybar itself but allows for the swashplate to move up and down without binding up on the flybar control links. The Concept model employed a fixed or stationary swashplate. The washout unit between it and the rotor hub was moved up and down by a wire that ran through a groove in the rotor mast and the linkages that controlled this were located below the main gear if I remember correctly. Anyway, there is a double linkage system on the washout unit, one pivoting on top of the other. One set allows cyclic commands to move from the swashplate to the flybar control. The other is the bell/hiller mix arms that allow a percentage of cyclic commands to go straight to the main rotor blades. This are takes the place of the bell/hiller mix arm located on the flybar itself as is the case with your Raptor. There is no "early" mixing issues like what you describe. If you ever get the chance to look at one of these models up close and scrutinize it for a while, what I'm describing will make more sense. Hope this makes sense! Fly Safe, Steve R. >> Definitely shows a flapping hinge setup in step 3... Also it appears >> as if the paddles flapping would affect blade pitch with the [quoted text clipped - 7 lines] >transfers cyclic commands to the flybar itself but allows for the swashplate >to move up and down without binding up on the flybar control links. I took the Raptor down off the bookcase for a quick look this morning and it got me thinking even more.. I didn't study it long enough to determine if the flybar flapping would alter the pitch on the advancing and retreating blades to compensate for DoL, but I'll have a look later. >The Concept model employed a fixed or stationary swashplate. The washout >unit between it and the rotor hub was moved up and down by a wire that ran [quoted text clipped - 9 lines] >models up close and scrutinize it for a while, what I'm describing will make >more sense. My confusion here is my lack of understanding how the Hiller system actually works.. I could draw you a pretty good picture of the Robinson and Hughes 300 rotorhead/swashplate and describe how they work, but I've never studied a Hiller system to figure it out. Sounds like a good excuse to break out the Raptor and try and get it in the air this weekend. (man, I hate when life won't give you two hours to do final tweaking on a helicopter that's been ready to go for two months... ehhee) >Hope this makes sense! > >Fly Safe, >Steve R. > I took the Raptor down off the bookcase for a quick look this morning > and it got me thinking even more.. I didn't study it long enough to > determine if the flybar flapping would alter the pitch on the > advancing and retreating blades to compensate for DoL, but I'll have a > look later. If I'm reading you correctly Kevin, the flybar "flapping" (ie: in responce to any cyclic command given) absolutely "does" feather the main blades. That's easy enough to see. Simply move the flybar up and down and watch what happens to the main blades. Likewise, turn the radio system on and move the appropriate cyclic command and watch the main blades move as a response to the movement of the swashplate directly. There is a lever system on the flybar itself that allows the intermixing of both these inputs. It gives the pilot a percentage of "direct" control to the main blades (the bell side) and "indirect" control (the hiller side). > My confusion here is my lack of understanding how the Hiller system > actually works.. I could draw you a pretty good picture of the [quoted text clipped - 4 lines] > do final tweaking on a helicopter that's been ready to go for two > months... ehhee) The first full size helicopter I ever rode in, and got to fly, was an old Hiller OH23D. The pilot "flew" the flybar via the cyclic control. The flybar's response applied the same cyclic commands to the main rotor blades. Compared to that I've heard the Robinson feels like, the controls on the Hiller are pretty unresponsive. You have to wait for the flybar to react to a control input before that input is passed along to the main blades and the main rotor actually reacts to it. It still seemed overly sensitive to me as I recall! :-) The first successful model helicopters were fixed pitch and hiller only. They flew Ok but weren't very precise compared to the modern birds we fly these days. Someone came up with the idea of mixing a direct control link from swashplate to main blades with the hiller type control they already had. The result was a more crisp response to a given cyclic command without too great a loss of the stability augmentation that the flybar allows and that's how it's been ever since. Fly Safe, Steve R. >If I'm reading you correctly Kevin, the flybar "flapping" (ie: in responce >to any cyclic command given) absolutely "does" feather the main blades. [quoted text clipped - 5 lines] >inputs. It gives the pilot a percentage of "direct" control to the main >blades (the bell side) and "indirect" control (the hiller side). Right, but I'm wondering if the paddles "flapping" helps with the DoL issue.. I'm kinda tempted to model it in Solidworks and see if it might.. Kinda hard to see things in action on the real thing. Too many damned moving parts! >The first full size helicopter I ever rode in, and got to fly, was an old >Hiller OH23D. The pilot "flew" the flybar via the cyclic control. The [quoted text clipped - 4 lines] >main rotor actually reacts to it. It still seemed overly sensitive to me as >I recall! :-) The Robby is a twitchy little bugger to say the least, and there *IS* some amount of "anticipation" required to fly it smoothly, but having something on the order of 120 hours in the thing, I don't even think about it. It kinda just happens.. There's an ag flyer in rec.aviation.helicopters than flies a Bell47 quite a lot. That's got paddles right?? I wonder if he knows.. He's got something like 24,000 hours and if memory serves, he got his ticket in 1954. >The first successful model helicopters were fixed pitch and hiller only. >They flew Ok but weren't very precise compared to the modern birds we fly [quoted text clipped - 3 lines] >too great a loss of the stability augmentation that the flybar allows and >that's how it's been ever since. Hey, if it ain't broke, don't fix it! I've been thinking about that damned Raptor head all day. Not a good idea 'cuz today was the final in my CFI ground school.. Hope I passed! lol > On Fri, 28 Oct 2005 20:41:36 GMT, "Steve R" > [quoted text clipped - 5 lines] > paddles right?? I wonder if he knows.. He's got something like > 24,000 hours and if memory serves, he got his ticket in 1954. Nope, actually, the Bell 47 and the Huey style Bell helicopters have a "stabilizer" bar. It's relatively short and has a set of weights on each end, no paddles, so they're aerodynamically blind. The bar has a percentage of cyclic control over the main blades which is why it can work to stabilize the rotor system but there is no cyclic command going to the bar itself like the flybars do on our models. >>The first successful model helicopters were fixed pitch and hiller only. >>They flew Ok but weren't very precise compared to the modern birds we fly [quoted text clipped - 8 lines] > damned Raptor head all day. Not a good idea 'cuz today was the final > in my CFI ground school.. Hope I passed! lol So do I! I'll keep my fingers crossed for ya! Fly Safe, Steve R. >>If I'm reading you correctly Kevin, the flybar "flapping" (ie: in responce >>to any cyclic command given) absolutely "does" feather the main blades. [quoted text clipped - 30 lines] > rec.aviation.helicopters than flies a Bell47 quite a lot. That's got > paddles right?? Nah, the 47 has weights on the end of the stabiliser bar. the only full sized heli with paddles is the Hiller. Hence the Hiller control system, which has NO direct link between the swash and the blades. The only link is from the swash to the flybar. I wonder if he knows.. He's got something like > 24,000 hours and if memory serves, he got his ticket in 1954. He'll know it's not got paddles ;-)) >>The first successful model helicopters were fixed pitch and hiller only. >>They flew Ok but weren't very precise compared to the modern birds we fly [quoted text clipped - 8 lines] > damned Raptor head all day. Not a good idea 'cuz today was the final > in my CFI ground school.. Hope I passed! lol I'm sure you did. SignatureBeav Reply to "beavis dot original at ntlworld dot com" (with the obvious changes) >>DDF = Duel Damped Flapping If you ever run into an orginal Kyosho >>Concept, [quoted text clipped - 4 lines] > > Know where to find a picture? Sounds interesting. Please pardon the multiple replies here but I keep running into stuff. Here's a picture of a really nice Concept SRX with the DDF head installed. http://www.runryder.com/helicopter/gallery/33269/SRX1.jpg This is the model that the Kyosho Nexus replaced. Talk about a giant step backwards. :-( The SRX was the final evolution of the orginal Concepts which were pretty much a POS when they were first produced but turned into really nice helicopters over time in the form of the SRX. Fly Safe, Steve R. phwaah, you know a lot about helicopters. I'm really impressed. > ok, since we kinda strayed off track with the cyclic trim to > compensate for translating tendency thread, I thought I'd start a new [quoted text clipped - 30 lines] > OK, there ya have it. The seeds of a potentially interesting > discussion... is this disimty thing why my helicopter leans to one side. ? > ok, since we kinda strayed off track with the cyclic trim to > compensate for translating tendency thread, I thought I'd start a new [quoted text clipped - 30 lines] > OK, there ya have it. The seeds of a potentially interesting > discussion... >is this disimty thing why my helicopter leans to one side. ? In a hover? That's caused by translating tendency, the thrust from the tailrotor pushes the helicopter laterally. You need to put in a little cyclic opposite this thrust to keep the helicopter from moving. Makes one skid hang low. Full scale does the same thing.. > ok, since we kinda strayed off track with the cyclic trim to > compensate for translating tendency thread, I thought I'd start a new [quoted text clipped - 14 lines] > much stiffer. (I've never flown carbon blades, but have a set on the > "new" Raptor) Choose carefully Kev (when you get some that is). some carbons are VERY flexible, while others will defy all attempts to bend. > Flap dampers imply there may be a combination of blade bending and > flapping going on. I can see the need for a rigid system in a 3D > capable model. Even the most extreme 3D machines have (and need) a degree of flapping. A flapping or teetering hinge could invite a boom > strike as the blades transition from positive to negative pitch.. Well that's the trouble with flyers who come from the full size world, because full sized heli's will chop their tails off with very little negative G, while models (everyone I've ever flown) will take negativce G (and oodles of neg pitch too) in their stride. The rigidity of the blades stops them bending to the point where they contact the boom, even with huge backwards and forwards stick slamming with 10 or 11 degrees of negative pitch AND with the heli upside down. > What about the tail rotor? I've never seen a model helo with a delta > hinge (angled teetering hinge) on the tail rotor like is seen on the > Robinson R22/44 and the Hughes/Schweizer 269/300 etc. You've never seen an X-Cell 60? The origianl X-cells back in 1989 had delta hinge tails. DoL occurs on > the tailrotor as well so it needs to be able to teeter/flap or bend, > right? Well there is DoL on the tail, but the rpm (around 8 -10,000) makes the differences shrink when compared to the size and rpm of the mains, so teetering isn't necessary. As evidenced by the fact that not many heli's have flapping tail or delta hinges. > Gyroplane models have a delta hinge setup on their main rotors too. As do most models these days. Again, the X-cell 60 of 1989 had negative delta hinges on the mains as well as on the tail and most rotor heads these days have adjustable delta off-set, even to the point it can be VERY negative, making the heli a piece of piss to fly in turbulent conditions, or very positive making it a right bastard. Flyers choice. > OK, there ya have it. The seeds of a potentially interesting > discussion... Or a great flame-fest. I vote for..... :p-) >Choose carefully Kev (when you get some that is). some carbons are VERY >flexible, while others will defy all attempts to bend. The guy I bought it from already had the carbons installed.. Much stiffer than the factory woodies but still bend a little bit. >> Flap dampers imply there may be a combination of blade bending and >> flapping going on. I can see the need for a rigid system in a 3D [quoted text clipped - 12 lines] >backwards and forwards stick slamming with 10 or 11 degrees of negative >pitch AND with the heli upside down. Centrifugal force and lift are your friends. I doubt the helicopter cares either way as long as the disc doesn't become unloaded for very long. Laws of inertia dictate this "unloaded" period would be very short in a +/- 10lb model versus a 1300+ lb full scale ship. >> What about the tail rotor? I've never seen a model helo with a delta >> hinge (angled teetering hinge) on the tail rotor like is seen on the >> Robinson R22/44 and the Hughes/Schweizer 269/300 etc. > >You've never seen an X-Cell 60? The origianl X-cells back in 1989 had delta >hinge tails. Like i said, Bro-in-law has one, but I've never really looked too closely at it. When he got it, I was still working on keeping the JR-50 "flying". >Well there is DoL on the tail, but the rpm (around 8 -10,000) makes the >differences shrink when compared to the size and rpm of the mains, so >teetering isn't necessary. As evidenced by the fact that not many heli's >have flapping tail or delta hinges. DoL doesn't matter much on the tailrotor as there's just not enough moment for it to want to roll the helicopter.. >> Gyroplane models have a delta hinge setup on their main rotors too. > [quoted text clipped - 3 lines] >negative, making the heli a piece of piss to fly in turbulent conditions, or >very positive making it a right bastard. Flyers choice. Not seeing this on the Raptor's head... >> OK, there ya have it. The seeds of a potentially interesting >> discussion... > >Or a great flame-fest. I vote for..... :p-) If it gets to that point, I'll start another thread on transverse flow or loss or settling with power... :) > Centrifugal force and lift are your friends. I doubt the helicopter > cares either way as long as the disc doesn't become unloaded for very > long. Laws of inertia dictate this "unloaded" period would be very > short in a +/- 10lb model versus a 1300+ lb full scale ship. We unload the rotor systems on our models as a matter of course. Try a vertical descent (I'm talking with the nose or tail pointed straight down!) with the collective at 0 degrees and just let it fall. The rotor won't care on a model. Try it with your 1300lb version! ;-) Fly Safe, Steve R. >> Centrifugal force and lift are your friends. I doubt the helicopter >> cares either way as long as the disc doesn't become unloaded for very [quoted text clipped - 5 lines] >with the collective at 0 degrees and just let it fall. The rotor won't care >on a model. Try it with your 1300lb version! ;-) Um, no. :) As soon as the TR got above the CG with an unloaded disk, it'd snap roll the helicopter in the direction of tailrotor thrust. Recoverable? Sure, but the inclination of most people would be to stop the roll with the cyclic. No disc loading = no rotor damping = high degree of flapping = hit the bump stops = potential for lawn-dartus-impactus. Correct recovery would be aft cyclic to reload the rotor disc, THEN correct the roll and yaw. Also, ya gotta rememeber, for all intents and purposes, the model is a rigid system and won't have bump stops or flapping. >>> Centrifugal force and lift are your friends. I doubt the helicopter >>> cares either way as long as the disc doesn't become unloaded for very [quoted text clipped - 9 lines] > > Um, no. :) <snipped> :-D > Also, ya gotta rememeber, for all intents and purposes, the model is a > rigid system and won't have bump stops or flapping. Understood! Actually, there is a certain amount of flapping allowed but you're right, compared to the full size birds, we have very rigid rotor systems in our models. However, even the DDF head we were talking about on the original Concept helicopter, which have a LOT of flapping compared to something like your Raptor, would survive the zero G environment I described with no problems at all. Fly Safe, Steve R. Hi. Just dropped in and was talking on another forum about this very thing. the Hiller system is sluggish, because you are actually flying the paddles up there and then the forces are transferred to the main blades, a total of 180 degrees of lag between pilot input at the control arms of the swashplate and the blades. In the Bell system, the input is only 90 degrees, so response is twice as fast. I learned to fly the OH-23D in the Army and you could sit at a stable 3-foot hover and rapidly stir the cyclic. The result was a nice stable hover. Try that in a Bell OH-13/G-47 and you better lock your shoulder harness; you are in for a wild ride. I would imagine the popularity of the Hiller system in RC helicopters is that they are simple, provide a forgiving nature and easy to manufacture. That's why you don't see too many pure Bell systems or fully articulated systems in models. In fact, I have yet to see a fully articulated rotor system on any model. I flew Chinooks for 24 years and can attest to the complexities of fully articulated systems. Just a few observations from the full size community.. Mike in Seattle http://homepage.mac.com/hookpilot/PersonalPage.html _________________________________________________________^M Posted via MilitaryForums.com http://www.militaryforums.com^M Visit www.militaryforums.com military specific discussions! > Hi. Just dropped in and was talking on another forum about this very > thing. the Hiller system is sluggish, because you are actually flying [quoted text clipped - 15 lines] > Just a few observations from the full size community.. > Mike in Seattle Hi Mike, In the beginning, the fixed pitch (no collective) / Hiller only rotor systems were used for exactly the reasons you mention. The K.I.S.S principle was in full effect. Modern model helicopters use a hybrid system that you won't find on their full size cousins. Most still use a Hiller style control system, that is, the flybar or stabilizer bar with aerodynamic paddles. The flybar's cyclic commands to the main rotor blades also run through a mixing lever. The other side of this lever is attached directly to the swashplate so a percentage of the cyclic commands that reach the main rotor blades comes directly off the swashplate, as in the Bell systems you mention, and the other half comes off the flybar, which is the Hiller side. We call it Bell / Hiller mixing. The model can be set up with differing percentages of Bell to Hiller inputs and thus we can fine turn the flight characteristics / control sensitivity of the model from almost dead to "oh sh*t" fast. As for the full articulated systems, there have been a number of RC models through the years that did employ something very similar. A Japanese company, Kyosho, introduces a small trainer helicopter around 10 years ago that had what we call a DDF rotor head. DDF = Dual Damped Flapping. Basically, each main rotor blade grip operated on it's own independent flapping hinge. The blades had a marked droop when stationary, something most models don't do, and in-flight boom strikes were not unheard of it you let the rpm's drop too low. Beyond that, they were very nice in a hover but not as precise in hard aerobatics so, considering the popularity of what we now call 3D flying, we don't see too many DDF rotor heads any more. And on the subject of a pure Bell control system, aka, flybarless in model speak, they're around. A friend of mine recently took the flybar control systems off of an X-Cell 60 model helicopter to see how it would do. It was quite normal in hover but exhibited some unusual traits in fast forward flight. Loops were pretty straight forward. Rolls were an exercise in "What the.......!!!" ;-) Mainly he was just curious as to how it would compare to the flybar equipped version. For the 3D type of flying, keep the flybar. It does a lot to stabilize the main rotor system. If you're interested in scale ships and scale type flying, the flybarless head will work just fine. Besides, you don't see many Jet Rangers around with flybars! :-D By the way, I do have a few hours of duel instruction in helicopters and my first hour was in an OH-23D. I do understand what you're talking about on slow cyclic responses. Even at that, I still managed to walk that bird all over God's back 40 before finally settling down on it. I thought my RC experience would help me with that. Not! The only thing it helped me with was that I "knew" what I was doing wrong, it just didn't help me do anything about that. At least not at first! Thanks for chiming in! Fly Safe, Steve R. >>> Centrifugal force and lift are your friends. I doubt the helicopter >>> cares either way as long as the disc doesn't become unloaded for very [quoted text clipped - 18 lines] > Also, ya gotta rememeber, for all intents and purposes, the model is a > rigid system and won't have bump stops or flapping. We've got bump stops Kev. Well we have ONE bump stop. It's called a tail boom|:-)) SignatureBeav Reply to "beavis dot original at ntlworld dot com" (with the obvious changes) >>Choose carefully Kev (when you get some that is). some carbons are VERY >>flexible, while others will defy all attempts to bend. > > The guy I bought it from already had the carbons installed.. Much > stiffer than the factory woodies but still bend a little bit. Yeah, some manufacturers make them flexible (for carbons that is) while some still make uber rigid blades. I prefer the feel of the flexible ones, but I also like the rigid ones for their ablity to keep away from the boom. >>> Flap dampers imply there may be a combination of blade bending and >>> flapping going on. I can see the need for a rigid system in a 3D [quoted text clipped - 18 lines] > long. Laws of inertia dictate this "unloaded" period would be very > short in a +/- 10lb model versus a 1300+ lb full scale ship. Short in regards to time, but don't forget that I that short time, the blades have passed the boom 3 or 4 times more often than the full size with their baggy flobby blades just DYING to find someone to chop off:) >>> What about the tail rotor? I've never seen a model helo with a delta >>> hinge (angled teetering hinge) on the tail rotor like is seen on the [quoted text clipped - 6 lines] > Like i said, Bro-in-law has one, but I've never really looked too > closely at it. I caught that reply (to Steve I believe) but that was after I'd responded. Anyway, now you know that delta hinges on tails aren't confned to the big buggers. When he got it, I was still working on keeping the > JR-50 "flying". They were a great flying heli IF you had at least 2000 rpm on the head AND if you removed the flap dampers. (Yes really, they flew much better with an unrestrained teeter) >>Well there is DoL on the tail, but the rpm (around 8 -10,000) makes the >>differences shrink when compared to the size and rpm of the mains, so [quoted text clipped - 3 lines] > DoL doesn't matter much on the tailrotor as there's just not enough > moment for it to want to roll the helicopter.. But it can twist the boom on the frames if it's not locked tightly. >>> Gyroplane models have a delta hinge setup on their main rotors too. >> [quoted text clipped - 7 lines] > > Not seeing this on the Raptor's head... Tell me where the cyclic ball on the end of the pitch horn is in relation to the centre of the hub. >>> OK, there ya have it. The seeds of a potentially interesting >>> discussion... [quoted text clipped - 3 lines] > If it gets to that point, I'll start another thread on transverse flow > or loss or settling with power... :) I'd prefer a thread on gyroscopic precession as it relates to control inputs:) SignatureBeav Reply to "beavis dot original at ntlworld dot com" (with the obvious changes) >Yeah, some manufacturers make them flexible (for carbons that is) while some >still make uber rigid blades. I prefer the feel of the flexible ones, but I >also like the rigid ones for their ablity to keep away from the boom. Keep the thing upright and avoid extreme maneuvers and the blades should stay away from the boom.. (But what's the fun in that?) >Short in regards to time, but don't forget that I that short time, the >blades have passed the boom 3 or 4 times more often than the full size with >their baggy flobby blades just DYING to find someone to chop off:) True.. >They were a great flying heli IF you had at least 2000 rpm on the head AND >if you removed the flap dampers. (Yes really, they flew much better with an >unrestrained teeter) I have no idea what the head speed was. Like I said, I bought it, I fueled it up and I flew it.. >> DoL doesn't matter much on the tailrotor as there's just not enough >> moment for it to want to roll the helicopter.. > >But it can twist the boom on the frames if it's not locked tightly. If your boom is that loose, you should have caught it during the preflight... >> Not seeing this on the Raptor's head... > >Tell me where the cyclic ball on the end of the pitch horn is in relation to >the centre of the hub. I'll have to get back to you on that.. (I knew I should checked for new posts before I left the house this morning) >I'd prefer a thread on gyroscopic precession as it relates to control >inputs:) Two words for you then. Advance Angle. :) >>Yeah, some manufacturers make them flexible (for carbons that is) while >>some [quoted text clipped - 4 lines] > Keep the thing upright and avoid extreme maneuvers and the blades > should stay away from the boom.. (But what's the fun in that?) There isn't any, that's why my heli's spend their time with their legs up. >>Short in regards to time, but don't forget that I that short time, the >>blades have passed the boom 3 or 4 times more often than the full size >>with >>their baggy flobby blades just DYING to find someone to chop off:) > > True.. Did you ever see the video of the Russian heli that looked a lot like a Bell 47J? The pilot pulled a perfect 90 degree nose up climb and stop, then performed a full 540 stall turn. This, with a pylon mounted tail rotor and it ALMOST made it. >>They were a great flying heli IF you had at least 2000 rpm on the head AND >>if you removed the flap dampers. (Yes really, they flew much better with [quoted text clipped - 3 lines] > I have no idea what the head speed was. Like I said, I bought it, I > fueled it up and I flew it.. It's design speed was a minimum of 2000rpm, but with a bit of jiggery pokery, 2300 was possible and it flew better. >>> DoL doesn't matter much on the tailrotor as there's just not enough >>> moment for it to want to roll the helicopter.. [quoted text clipped - 3 lines] > If your boom is that loose, you should have caught it during the > preflight... You can with most heli's but not all. A typical example can be with the plastic frame/ali boom machines have a lot of "stiction", so a twist of the boom shows nothing amiss, but then they fly and the tail's banging about and next thing you see is a VS300:-) >>> Not seeing this on the Raptor's head... >> [quoted text clipped - 4 lines] > I'll have to get back to you on that.. (I knew I should checked for > new posts before I left the house this morning) Ok. >>I'd prefer a thread on gyroscopic precession as it relates to control >>inputs:) > > Two words for you then. Advance Angle. :) Two for you. angle GRINDER :-) I can throw in "Phase angle" too, if you want:) SignatureBeav Reply to "beavis dot original at ntlworld dot com" (with the obvious changes) > Did you ever see the video of the Russian heli that looked a lot like a > Bell 47J? The pilot pulled a perfect 90 degree nose up climb and stop, > then performed a full 540 stall turn. This, with a pylon mounted tail > rotor and it ALMOST made it. Oooo, wouldn't happen to have a link to that somewhere, would you? >>>I'd prefer a thread on gyroscopic precession as it relates to control >>>inputs:) [quoted text clipped - 3 lines] > Two for you. angle GRINDER :-) I can throw in "Phase angle" too, if you > want:) I've heard of "phase angle," but "angle grinder??" Fly Safe, Steve R. >> Did you ever see the video of the Russian heli that looked a lot like a >> Bell 47J? The pilot pulled a perfect 90 degree nose up climb and stop, >> then performed a full 540 stall turn. This, with a pylon mounted tail >> rotor and it ALMOST made it. > >Oooo, wouldn't happen to have a link to that somewhere, would you? Yeah, no kidding... >>>>I'd prefer a thread on gyroscopic precession as it relates to control >>>>inputs:) [quoted text clipped - 5 lines] > >I've heard of "phase angle," but "angle grinder??" Yeah.. I've got a couple of 'em. A 7 incher and a 4 incher. Both Makitas.. >> Did you ever see the video of the Russian heli that looked a lot like a >> Bell 47J? The pilot pulled a perfect 90 degree nose up climb and stop, >> then performed a full 540 stall turn. This, with a pylon mounted tail >> rotor and it ALMOST made it. > > Oooo, wouldn't happen to have a link to that somewhere, would you? I had it for ages Steve, but (as per) my computer did it's bi-yearly death dance and it took the clip with it:-( >>>>I'd prefer a thread on gyroscopic precession as it relates to control >>>>inputs:) [quoted text clipped - 5 lines] > > I've heard of "phase angle," but "angle grinder??" Angle grinder? The best tool in the world. Hand held with a cutting or grinding disc for ripping through just about anything it touches. Fingers included. SignatureBeav Reply to "beavis dot original at ntlworld dot com" (with the obvious changes) >> If your boom is that loose, you should have caught it during the >> preflight... [quoted text clipped - 3 lines] > the boom shows nothing amiss, but then they fly and the tail's banging > about and next thing you see is a VS300:-) Or, as was the case with my old Concept, the tail boom twisted around a few times until it was stopped by the drag link, which was now wrapped around the boom and applying full "down" rudder to the tail rotor (which was now facing the ground). Picture a sort of hybrid Chinook with one big rotor and one small rotor. It actually hovered for a few seconds like that before the shortcomings of its conventional, single-rotor control system became overwhelmingly apparent! Gp >>> If your boom is that loose, you should have caught it during the >>> preflight... [quoted text clipped - 13 lines] > its conventional, single-rotor control system became overwhelmingly > apparent! Did you never have this happen with the X-cell range Greg? It was a BIG problem with the Schluter Champ too and most people drilled the frame and boom and inserted a self tapping screw into the boom to stop it. SignatureBeav Reply to "beavis dot original at ntlworld dot com" (with the obvious changes) > Did you never have this happen with the X-cell range Greg? It was a BIG > problem with the Schluter Champ too and most people drilled the frame and > boom and inserted a self tapping screw into the boom to stop it. Oh man, I forgot about that ol trick. You know, we've had a few conversations about those old Champions this year. It's brought back many fond memories of that bird. It really was light years ahead of it's time in terms of how well it flew, but these conversations have also served to remind me of all the stuff I "don't" miss about them. :-) Fly Safe, Steve R. >> Did you never have this happen with the X-cell range Greg? It was a BIG >> problem with the Schluter Champ too and most people drilled the frame and [quoted text clipped - 7 lines] > conversations have also served to remind me of all the stuff I "don't" > miss about them. :-) I got a few flashbacks too:-)) In its day, the Champ was a superb piece of helicoptery, but I STILL get guys bringing them to me in the hope that they'll be as good as "this" generation of machines but bought for pennies off "a guy down the road". It's hard to tell them the Champ's day has long gone unless you can manufacture parts or make parts from other heli's fit and work, but it generally falls on deaf ears. They never manage to reach the stage where the Champ shows it's foibles (snapping tail rotor push-rods was a classic and it carried over to the X-cell too). Tail rotor too slow and ineffective unless you made a 3 bladed hub and pitch slider, frames that cracked, engine mounts that fell apart. 'Kin hell, the list goes on:-)) SignatureBeav Reply to "beavis dot original at ntlworld dot com" (with the obvious changes) > Fly Safe, > Steve R. |
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