Couple of blade construction questions.
Also, more blades on a rotor system must mean that they can "slipstream" behind the other blade to some degree, and therefore have less air resistance per blade as compared to a rotor design where the blades can't "hide in the wake of the blade ahead of it", as in a 2, 3, 4, maybe even 5-blade system?
It's not quite like drafting a truck with your geo metro. First, the induced airflow is from the top, the wake wants to depart downward, so you can't hide one blade behind another. Unless, of course, your solidity is 1.0, but then there is no place for the air to go because you just have a solid disk.
And, when one rotor does hit the wake of another rotor, usually there is vibration associated with it. And if there is vibration associted with it, you can bet it is causing drag and loss of performance.
-- IFMU
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IFMU,
You are on the right track about blade interference - impact by the wake of the preceeding blade costs power, adds vibration and makes noise. Otherwise, it is nice....
You are on the right track about blade interference - impact by the wake of the preceeding blade costs power, adds vibration and makes noise. Otherwise, it is nice....
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Adam, you might like to get hold of a copy of Prouty "Helicopter Performance Stability and Control". It is in imperial units, but is well layed out and covers all the stuff you need. There are newer texts, but it is always Prouty i refer back to.
It took me a while to get the "Coefficient of Thrust", "Solidity Ratio" and "Figure of Merit", but Nick patiently guided me through it.
That is actually a good question - and the only one not answered! A turbine stage is operating with bounded tips, albeit an idealistic simplification. This means that a pressure differential can exist across the stage without causing tip vortices. A helo rotor is in free space, so the tip vortices equalise the total pressure above and below (although blade surface will see pressure differential to produce lift). This means that while a tubine rotor must be designed to avoid leakage, a heli rotor is designed to optimise tip vortex induced flow. Thus the number of blades is greatly less in a heli rotor.
Before the introduction of Computational Fluid Dynamics aerodynamicists often produced suprisingly accurate results by modelling the flow field resulting from the tip vortices. Vortices have the characteristic of rotational velocity being inversely proportional to radius, outside of the vortex tube (so linear velocity is constant in the rotor plane). The field can be estimtated from an idealised tip vortex distribution (from observations usually) - you may be familar with the Biot-Savart equation from magnetic fields around coils from A-level phys. A tip vortex will stay in plane, until the following blade pushes it out of position. In fact the latest generation of rotor blades are optimised to position this vortex as far out from the rotor as possible, with no doubt further improvements to come.
Mart
It took me a while to get the "Coefficient of Thrust", "Solidity Ratio" and "Figure of Merit", but Nick patiently guided me through it.
Originally Posted by AdamFrisch
Basically, what I'm getting at - when you look at fanjet engine on an airliner, they have tremendous amounts of blades. There must be a reason for that - why don't they have just 2 fan blades if that's just as good?
Before the introduction of Computational Fluid Dynamics aerodynamicists often produced suprisingly accurate results by modelling the flow field resulting from the tip vortices. Vortices have the characteristic of rotational velocity being inversely proportional to radius, outside of the vortex tube (so linear velocity is constant in the rotor plane). The field can be estimtated from an idealised tip vortex distribution (from observations usually) - you may be familar with the Biot-Savart equation from magnetic fields around coils from A-level phys. A tip vortex will stay in plane, until the following blade pushes it out of position. In fact the latest generation of rotor blades are optimised to position this vortex as far out from the rotor as possible, with no doubt further improvements to come.
Mart
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Thanks so much everyone.
But, haha, I don't give up easily. I might have found a fatal error in my earlier blade design question - I quote myself:
"Most modern rotors in helicopters seem to have constant chord blades where the tip has been twisted donwards towards the tip so as to produce less lift the further away from the hub you get. But the same thing could be achieved by having the chord change (and the twist remain unchanged) - by narrowing the blade the further you go out from the hub, the less lift it would produce (this was common in earlier helicopters). A twisted blade must be so much more expensive and complicated to make, so why was the changing chord design abandoned?"
Now, in an autorotational state, the outer part of the rotor drives the inner part (roughly 1/3 of the blade is driving, as I've been told) by having less angle of attack (or even negative). This can only be achieved by having a twisted blade. Now, let's say we had a constant chord blade design instead (where the angle of attack stays the same over the entire blade), would it be able to autorotate?
Why I'm asking is because I'm almost 100% sure early heli's had CC blades - and they did autorotate. So how did they achieve this?
But, haha, I don't give up easily. I might have found a fatal error in my earlier blade design question - I quote myself:
"Most modern rotors in helicopters seem to have constant chord blades where the tip has been twisted donwards towards the tip so as to produce less lift the further away from the hub you get. But the same thing could be achieved by having the chord change (and the twist remain unchanged) - by narrowing the blade the further you go out from the hub, the less lift it would produce (this was common in earlier helicopters). A twisted blade must be so much more expensive and complicated to make, so why was the changing chord design abandoned?"
Now, in an autorotational state, the outer part of the rotor drives the inner part (roughly 1/3 of the blade is driving, as I've been told) by having less angle of attack (or even negative). This can only be achieved by having a twisted blade. Now, let's say we had a constant chord blade design instead (where the angle of attack stays the same over the entire blade), would it be able to autorotate?
Why I'm asking is because I'm almost 100% sure early heli's had CC blades - and they did autorotate. So how did they achieve this?
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A twisted blade (that looks like an airplane prop) will lift more in hover but not as good in autototation, but still will auto well enough usually.
A flat blade (no twist) is better for autorotation and almost all gyrocoters have no twist because they are always in autorotation.
A flat blade (no twist) is better for autorotation and almost all gyrocoters have no twist because they are always in autorotation.
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Adam, that is a good point (if i understand correctly): Why not design a tapered blade instead of twisted blade?
To be correct the blade would need have it's chord length inversely proportional to radius from hub centre. This blade would then be equally efficient in hover, climb and autorotation - each element would always present optimum AOA to inflow. In fact many performance props are based on this design, with a cutout or inverse taper to meet the maximum chord radius (generally chosen to match spinner diameter).
The problem comes when you consider cruise, the speed of which has being pushed up in modern turbine helis. Here the taper becomes a disadvantage because the advancing side sees air with a large component of uniform flow. The reatreating side is the real limitation though, since the tip has to pull high AOA to keep the lift in balance. Wide chord tips are the order of the day.
In practice OEMs spend a great deal of resource getting just the right twist and taper to suit the average mission profile, and variations of it. All things considered, the benefits of taper are lessened so the additional cost pushes the designer towards constant chord. In modern machines the benefits of anhedral tips are more easilly exploited with a constant chord design too.
Hope this helps. Like i say Prouty is a very enjoyable read, but even better if you can gain insight from this forum to see how the theory ties up with practice. I have learned a lot on this forum.
Mart
To be correct the blade would need have it's chord length inversely proportional to radius from hub centre. This blade would then be equally efficient in hover, climb and autorotation - each element would always present optimum AOA to inflow. In fact many performance props are based on this design, with a cutout or inverse taper to meet the maximum chord radius (generally chosen to match spinner diameter).
The problem comes when you consider cruise, the speed of which has being pushed up in modern turbine helis. Here the taper becomes a disadvantage because the advancing side sees air with a large component of uniform flow. The reatreating side is the real limitation though, since the tip has to pull high AOA to keep the lift in balance. Wide chord tips are the order of the day.
In practice OEMs spend a great deal of resource getting just the right twist and taper to suit the average mission profile, and variations of it. All things considered, the benefits of taper are lessened so the additional cost pushes the designer towards constant chord. In modern machines the benefits of anhedral tips are more easilly exploited with a constant chord design too.
Hope this helps. Like i say Prouty is a very enjoyable read, but even better if you can gain insight from this forum to see how the theory ties up with practice. I have learned a lot on this forum.
Mart
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Thanks. Yes I do see that the retreating blade will suffer in this regard with a narrow tip airfoil in a tapered blade.
I was also reading up on the Boeing Hummingbird unmanned helicopter that you mentioned. Not much info has leaked, but it seems terribly interesting. For instance, they reduce blade RPM at different altitudes and different weights. And the endurance and performance figures for the 6-cylinder heli are nothing short of astounding! 2500nm range, ceiling of 30.000ft and 24h endurance - all very quiet, too. Amazing.
Has anyone experimented with reducing rotor RPM at altitude? I assume this could safely be done in any helicopter given enough height. It seems quite logical to do so, yet that's not part of the way heli's are operated - they run at constant RPM's all the time throughout.
I think Boeing are def on to something here - helicopters stress out components and are expensive to use simply because they're flown at the limit all the time. If there was a procedure to safely reduce rotor RPM and engine RPM at altitude, many benefits might be had, no? FW aircraft lean out and throttle back for long flights - who says heli's can't do the same?
I was also reading up on the Boeing Hummingbird unmanned helicopter that you mentioned. Not much info has leaked, but it seems terribly interesting. For instance, they reduce blade RPM at different altitudes and different weights. And the endurance and performance figures for the 6-cylinder heli are nothing short of astounding! 2500nm range, ceiling of 30.000ft and 24h endurance - all very quiet, too. Amazing.
Has anyone experimented with reducing rotor RPM at altitude? I assume this could safely be done in any helicopter given enough height. It seems quite logical to do so, yet that's not part of the way heli's are operated - they run at constant RPM's all the time throughout.
I think Boeing are def on to something here - helicopters stress out components and are expensive to use simply because they're flown at the limit all the time. If there was a procedure to safely reduce rotor RPM and engine RPM at altitude, many benefits might be had, no? FW aircraft lean out and throttle back for long flights - who says heli's can't do the same?
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AdamFrisch,
This earlier thread started by slowrotor should be of interest to you.
http://www.pprune.org/forums/showthr...rd#post3037184
This earlier thread started by slowrotor should be of interest to you.
http://www.pprune.org/forums/showthr...rd#post3037184
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Adam, there was a good thread on this which i can't find right now. S76, among others, does vary Nr with speed, load factor, and height. It is becoming the norm now.
The headache is that the rotor blade eigenmode frequencies are a function of Nr. Since many orders of P may be aerodynamically excited, and could work there way back into the structure and systems, the machine must be carefully evaluated at different Nr. Worst case is that blades vibrate in phase to compromise fatigue life. The other problem is that the azimuth lead angle is a function of Nr, so you need additional complexity in the control system.
The golden panacea is the ability to vary rotor Nr from 100% all the way down to near 0%, in an advancing blade concept helicopter. This means that while efficient hover can be achieved, the machine can have a cruise factor unlimited by advancing blade compressibility. The limitation is the need for a heavier rotor system to transfer the root bending moments.
I am a very keen fan of the Sikorsky X2 project, although do not know it's current status (scrounging for resource probably).
Mart
The headache is that the rotor blade eigenmode frequencies are a function of Nr. Since many orders of P may be aerodynamically excited, and could work there way back into the structure and systems, the machine must be carefully evaluated at different Nr. Worst case is that blades vibrate in phase to compromise fatigue life. The other problem is that the azimuth lead angle is a function of Nr, so you need additional complexity in the control system.
The golden panacea is the ability to vary rotor Nr from 100% all the way down to near 0%, in an advancing blade concept helicopter. This means that while efficient hover can be achieved, the machine can have a cruise factor unlimited by advancing blade compressibility. The limitation is the need for a heavier rotor system to transfer the root bending moments.
I am a very keen fan of the Sikorsky X2 project, although do not know it's current status (scrounging for resource probably).
Mart
Everybody needs a hobby!
The headache is that the rotor blade eigenmode frequencies are a function of Nr.
Got to keep things in order. I think you are due to drag out the eigenmode thingy on the "You want me to test fly what...?" thread before this one.
-- IFMU
Mart,
I am about to go swimming out of my depth here so I will try to stick to what I know.
You probably need to check your facts on this statement; apart from experimental craft, it is not clear that variable NR is being used (at the moment) in other than two cases:
There has been an interesting discussion on the Bell 412 thread which appears to warn against reducing the Nr in the cruise unless it has been authorised by the manufacturer. The thread discourages experimental excursions outside the RFM as it could take the helicopter outside of its design envelope. The net result may not affect the offender but could impact on later users.
Jim
I am about to go swimming out of my depth here so I will try to stick to what I know.
Adam, there was a good thread on this which i can't find right now. S76, among others, does vary Nr with speed, load factor, and height. It is becoming the norm now.
- Reducing Nr - to lower the speed of the tail rotor in the cruise to reduce noise.
- Increasing Nr - to improve the (stored) energy in the blades thus providing a short term benefit should an engine fail early in the take-off or late in the landing manoeuvre (mainly used for Category A procedures).
There has been an interesting discussion on the Bell 412 thread which appears to warn against reducing the Nr in the cruise unless it has been authorised by the manufacturer. The thread discourages experimental excursions outside the RFM as it could take the helicopter outside of its design envelope. The net result may not affect the offender but could impact on later users.
Jim
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minibirdpilot,
I haven't read the article to know what it said, but I do know that nothing has changed on the S-76 models to make the noise different. The S76A had variable RPM, and it worked well, but when the MGW rose as power was added to later models, the rpm was kept at the upper boundary to keep the speed up and reduce the blade stall factor.
This thread is interesting, but shows the flaws of the socratic method, where a question and answer session leads to debates that try to find out if witches are made of wood...(apologies to Monty Python!)
Some funny things Adam has said (this is not criticizing you, Adamfrish, just pointing out how much strange belief exists in the land of the regular people):
Has anyone experimented with reducing rotor RPM at altitude? I assume this could safely be done in any helicopter given enough height. It seems quite logical to do so, yet that's not part of the way heli's are operated
Yes, and it really makes the helo stall and go out of control, just like we knew it would. However, this didn't seem to be what the customer wanted, so we didn't deliver it that way.
Lift is a product of disc loading.
This proved to be a mystery, since we thought the blades lifted the helicopter, and when we removed the blades, the disk performed badly.
helicopters stress out components and are expensive to use simply because they're flown at the limit all the time
We had thought they were expensive because of all those pesky machined parts that are flight critical, so we were working on that, but now we find that if we just gave the parts valium everything would be easier.
Adam, it seems that most of the beliefs in your worldview about helicopters comes from a hodge-podge of press releases and TV shows, and a strong belief that a few quick phrases explain how a rotor works. I strongly suggest that you drop out of the Hummingbird press release school of engineering and just buckle down with a good Prouty or Padfield or Stepneiwski for a while, because most of the starting places for your concepts are not only wrong, they are dead wrong.
Here are some rotor basics:
The blades do the lifting, and they want speed. This means that you must mix blade area (number times width times length) and RPM (tip speed) properly so that there is enough lift to make the helo go.
The best blade design is not one design point, because hover and high speed cruise conflict. The hover where the blade should work a bunch, at maybe 3/4 of its maximum lift so that the power it eats is smaller for the lift it produces. High speed where the blade should be working less, where you would like the balde to be at 1/3 of its max lift. This paradox makes a variable rpm attractive, where you slow down the rotor RPM at hover, and speed RPM up at high speed cruise flight.
The rotor disk determines the size of the air package the blades move, and the bigger the disk, the less power the rotor needs in a hover. This means big, slow rotors are better for hover efficiency, which is why Harriers and tiltrotors eat so much power. It is also why older piston helos had big rotors (the 8300 lb piston H-19 had the same rotor diameter as the 21,000 lb turbine Black Hawk!) Turbines throw power away, because the weight of a somewhat bigger turbine engine isn't that much, realtive to the weight of a bigger rotor.
Areodynamics excites us, but weight, structures and dynamics is what designs a flying machine. The "best" rotor and blade is seldom chosen, but the lightest, strongest one almost always wins. It is like going to the movies, we watch Scarlett Johanssen, but we bring the girl next door. Mundane aspects like weight, cost to build, vibration suppression end up dominating the designer's life. Variable rpm sounds cool, until you try to match the vast band of rotor frequencies (which tickle the whole aircraft) to the structure, and find that you can't permit a 40% rotor rpm range without beefing up the tailcone so much the advantage is lost.
Helo designers aren't stupid, their "mistakes" that you notice are testaments to what you don't know about designing helicopters. The matchbook school of engineering says there are two or three simple rules, the real world says there are hundreds of comprimises that make a helicopter.
Here is a crash course on helo design with thanks to Lakshmi Sankar of Georgia Tech:
www.ae.gatech.edu/people/lsankar/AE6070.Spring2004/Part1.ppt www.ae.gatech.edu/people/lsankar/AE6070.Spring2004/Part2.ppt
www.ae.gatech.edu/people/lsankar/AE6070.Spring2004/Part3.ppt
also a touch of the same from a micro-lite site:
http://halfdome.arc.nasa.gov/publica...ung_AIAA02.pdf
I haven't read the article to know what it said, but I do know that nothing has changed on the S-76 models to make the noise different. The S76A had variable RPM, and it worked well, but when the MGW rose as power was added to later models, the rpm was kept at the upper boundary to keep the speed up and reduce the blade stall factor.
This thread is interesting, but shows the flaws of the socratic method, where a question and answer session leads to debates that try to find out if witches are made of wood...(apologies to Monty Python!)
Some funny things Adam has said (this is not criticizing you, Adamfrish, just pointing out how much strange belief exists in the land of the regular people):
Has anyone experimented with reducing rotor RPM at altitude? I assume this could safely be done in any helicopter given enough height. It seems quite logical to do so, yet that's not part of the way heli's are operated
Yes, and it really makes the helo stall and go out of control, just like we knew it would. However, this didn't seem to be what the customer wanted, so we didn't deliver it that way.
Lift is a product of disc loading.
This proved to be a mystery, since we thought the blades lifted the helicopter, and when we removed the blades, the disk performed badly.
helicopters stress out components and are expensive to use simply because they're flown at the limit all the time
We had thought they were expensive because of all those pesky machined parts that are flight critical, so we were working on that, but now we find that if we just gave the parts valium everything would be easier.
Adam, it seems that most of the beliefs in your worldview about helicopters comes from a hodge-podge of press releases and TV shows, and a strong belief that a few quick phrases explain how a rotor works. I strongly suggest that you drop out of the Hummingbird press release school of engineering and just buckle down with a good Prouty or Padfield or Stepneiwski for a while, because most of the starting places for your concepts are not only wrong, they are dead wrong.
Here are some rotor basics:
The blades do the lifting, and they want speed. This means that you must mix blade area (number times width times length) and RPM (tip speed) properly so that there is enough lift to make the helo go.
The best blade design is not one design point, because hover and high speed cruise conflict. The hover where the blade should work a bunch, at maybe 3/4 of its maximum lift so that the power it eats is smaller for the lift it produces. High speed where the blade should be working less, where you would like the balde to be at 1/3 of its max lift. This paradox makes a variable rpm attractive, where you slow down the rotor RPM at hover, and speed RPM up at high speed cruise flight.
The rotor disk determines the size of the air package the blades move, and the bigger the disk, the less power the rotor needs in a hover. This means big, slow rotors are better for hover efficiency, which is why Harriers and tiltrotors eat so much power. It is also why older piston helos had big rotors (the 8300 lb piston H-19 had the same rotor diameter as the 21,000 lb turbine Black Hawk!) Turbines throw power away, because the weight of a somewhat bigger turbine engine isn't that much, realtive to the weight of a bigger rotor.
Areodynamics excites us, but weight, structures and dynamics is what designs a flying machine. The "best" rotor and blade is seldom chosen, but the lightest, strongest one almost always wins. It is like going to the movies, we watch Scarlett Johanssen, but we bring the girl next door. Mundane aspects like weight, cost to build, vibration suppression end up dominating the designer's life. Variable rpm sounds cool, until you try to match the vast band of rotor frequencies (which tickle the whole aircraft) to the structure, and find that you can't permit a 40% rotor rpm range without beefing up the tailcone so much the advantage is lost.
Helo designers aren't stupid, their "mistakes" that you notice are testaments to what you don't know about designing helicopters. The matchbook school of engineering says there are two or three simple rules, the real world says there are hundreds of comprimises that make a helicopter.
Here is a crash course on helo design with thanks to Lakshmi Sankar of Georgia Tech:
www.ae.gatech.edu/people/lsankar/AE6070.Spring2004/Part1.ppt www.ae.gatech.edu/people/lsankar/AE6070.Spring2004/Part2.ppt
www.ae.gatech.edu/people/lsankar/AE6070.Spring2004/Part3.ppt
also a touch of the same from a micro-lite site:
http://halfdome.arc.nasa.gov/publica...ung_AIAA02.pdf
Last edited by NickLappos; 17th May 2007 at 17:14.
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No, I don't know anything about helicopter aerodynamics except from what I learned in my PPL (H) training and have gathered around the net - that's why I'm asking all these (apparently) stupid questions. Never did allude or pretend to be eductaed in the same either - I just like to educate myself and am naturally curious.
Now that we know I'm an uneducated fool and that's out of the way, let's get back to business and leave haughtiness behind.
"Reducing RPM in flight"
If you were to reduce RRPM in a, say, H269 just for the hell of it, it will of course stall at some point. But not immeditaley at lower red line - there must be an area of lesser performance before it stalls, no? Also, if I recall correctly from my aurorotation days, one had to keep a vigilant eye on the RPM so as not to over-rev the rotor on the H269. Therefore, if you were to reduce RPM to just when it stalls, can not the RPM be regained by a combination of/or autorotation and throttling up again?
"We had thought they were expensive because of all those pesky machined parts that are flight critical, so we were working on that, but now we find that if we just gave the parts valium everything would be easier"
Of course, but there is a reason that Robinson de-rated his Lycoming engine so it would last longer. No engine likes to run at top RPM for long periods. That's why Rotaxes don't last. The H269 is apparently quite known for having a highly strung engine that fails quite a lot, which I myself experienced.
I will definitely look into reading Prouty and other aerodynamic books, but forums like these are invaluable for empirical data.
Now that we know I'm an uneducated fool and that's out of the way, let's get back to business and leave haughtiness behind.
"Reducing RPM in flight"
If you were to reduce RRPM in a, say, H269 just for the hell of it, it will of course stall at some point. But not immeditaley at lower red line - there must be an area of lesser performance before it stalls, no? Also, if I recall correctly from my aurorotation days, one had to keep a vigilant eye on the RPM so as not to over-rev the rotor on the H269. Therefore, if you were to reduce RPM to just when it stalls, can not the RPM be regained by a combination of/or autorotation and throttling up again?
"We had thought they were expensive because of all those pesky machined parts that are flight critical, so we were working on that, but now we find that if we just gave the parts valium everything would be easier"
Of course, but there is a reason that Robinson de-rated his Lycoming engine so it would last longer. No engine likes to run at top RPM for long periods. That's why Rotaxes don't last. The H269 is apparently quite known for having a highly strung engine that fails quite a lot, which I myself experienced.
I will definitely look into reading Prouty and other aerodynamic books, but forums like these are invaluable for empirical data.
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Adam,
Reducing the RPM of the rotor will require that the pitch of the blades be increased to maintain the same thrust. This is an advantage in that the efficiency (power/thrust) is increased.
Unfortunately, this also increases the risk that a perturbation, malfunction, etc. will cause the rotor to loose all lift.
The Boeing Hummingbird is an Unmanned Aerial Vehicle therefore its crash would be unfortunate but not tragic. The loss of life in a helicopter crash is much more serious. With all regards for the relatives and associates of the deceased, helicopter fatalities have also resulted in the demise of a number of aspiring helicopter manufacturers.
IMHO, and subject to elaboration or correction by others.
Dave
Reducing the RPM of the rotor will require that the pitch of the blades be increased to maintain the same thrust. This is an advantage in that the efficiency (power/thrust) is increased.
Unfortunately, this also increases the risk that a perturbation, malfunction, etc. will cause the rotor to loose all lift.
The Boeing Hummingbird is an Unmanned Aerial Vehicle therefore its crash would be unfortunate but not tragic. The loss of life in a helicopter crash is much more serious. With all regards for the relatives and associates of the deceased, helicopter fatalities have also resulted in the demise of a number of aspiring helicopter manufacturers.
IMHO, and subject to elaboration or correction by others.
Dave
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The engineering books agree with Nick and state "Optimum hovering performance requires a lower tip speed than is desired for forward flight".
Adam,
I think Nick gets frustrated with some of the wild claims of promoters such as the A-160 Hummingbird and unleashed his anger toward you.
The A-160 claims a fivefold increase in endurance. This is a rather extraordinary claim. "Extraordinary claims require extraordinary proof" (quote from Carl Sagan, I think)
Adam,
I think Nick gets frustrated with some of the wild claims of promoters such as the A-160 Hummingbird and unleashed his anger toward you.
The A-160 claims a fivefold increase in endurance. This is a rather extraordinary claim. "Extraordinary claims require extraordinary proof" (quote from Carl Sagan, I think)
The A-160 claims a fivefold increase in endurance. This is a rather extraordinary claim. "Extraordinary claims require extraordinary proof" (quote from Carl Sagan, I think)
-- IFMU
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Thanks you guys. I enjoy learning more about these things. I didn't think Nick was harsh at all...
"Lighten up Francise or I'll have to kill you" seems like a good, famous quote to apply. Remember it must be said through clenched teeth.
"Lighten up Francise or I'll have to kill you" seems like a good, famous quote to apply. Remember it must be said through clenched teeth.