Robinson R55? (Merged)
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Underground R55
Having heard the rumours I thought it would be prudent to throw this one at the forum readers for some illumination.
I heard last year while on the factory course of a room deep within the Torrance Factory which resembled Fort Knox in security and inside of which a new bird from Frank’s stable was being put together…..called the R55.
Dismissed the story as a flight of fancy then, but have recently heard that such a machine has been test flown. Does anyone out there in cyberspace have any information.
Cheers
Bluegold
I heard last year while on the factory course of a room deep within the Torrance Factory which resembled Fort Knox in security and inside of which a new bird from Frank’s stable was being put together…..called the R55.
Dismissed the story as a flight of fancy then, but have recently heard that such a machine has been test flown. Does anyone out there in cyberspace have any information.
Cheers
Bluegold
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R55...
Went to safety course last year, as well (December). Tim Tucker hinted that it may be a turbine ship because they've reached the performance limit with pistons. Nothing confirmed.
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R66
I attended the course end of last April where some guy at the front (attendee not instructor) was going about a diesel ship, and the name R66 was being thrown about ... but everyone seemed more preoccupied with the free beef jerky that appeared out the back (priorities I guess)
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I do hope they incorporate a decent luggage compartment in their design and also get rid of the 3 foot long rotor mast with something more pleasing to the eye!!
Not being an engineer or a mechanic so I don't know if it's possible or not, but with regards to a diesel engine, would that be modified to run JetA else we'd be very limited to which airfield we could land to get fueled up. Just think of the savings on the fuel bill
Not being an engineer or a mechanic so I don't know if it's possible or not, but with regards to a diesel engine, would that be modified to run JetA else we'd be very limited to which airfield we could land to get fueled up. Just think of the savings on the fuel bill
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Them motors is DESIGNED to run on Jet A-1, that's the whole idea!
IMHO It's the way forward. NO magnetos, NO mixture control and NO carb icing.
Or fly turbines anyway,
IMHO It's the way forward. NO magnetos, NO mixture control and NO carb icing.
Or fly turbines anyway,
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No magnetos and no carb heat on a diesel makes sense to me, but the "no mixture control" has me boggled. I've been thinking about that and it's still rattling around in my skull. How is that possible?
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Rudolph Diesel didn't think of it.
Diesel engines have injectors. There are two basic types. Injector units and unit injectors.
If I remember correctly, the positioning of a helix, which is controlled, by the commanded throttle position controls injector unit fuel flow into the cylinder. The helix is a part of a piston whose movement up and down in the pump cylinder is controlled by a cam much like the cam in the engine. The stroke of the cam is constant but throttle position causes the helix to rotate in relation to the cylinder in which the piston (helix) rides. The amount of fuel delivered to the engine is dependent upon the positioning of the helix in the cylinder. The fuel pump will consist of a cam driven by the engine and as many helix cylinder combinations as there are cylinders in the engine.
Unit injectors operate in the same way but there is one per cylinder and the controls are ganged together to get uniform fuel distribution to each cylinder. These injectors have a similar helix piston arrangement and are actuated by a cam similar to that operating the valve train on the engine.
Aspiration of the engine can incorporate a blower or, the engine can be normally aspirated. When the fuel is delivered to the engine it will speed up causing an increase in the air volume until there is a balance between fuel delivered and the air delivered to the combustion chamber.
To my knowledge there has never been a system whereby the fuel air ratio can be modified like it is with a carbureted engine.
I guess my mind is not as fuzzy as I thought. I went to engine school in 1947. If I am wrong then I will plead Oldtimers disease.
If I remember correctly, the positioning of a helix, which is controlled, by the commanded throttle position controls injector unit fuel flow into the cylinder. The helix is a part of a piston whose movement up and down in the pump cylinder is controlled by a cam much like the cam in the engine. The stroke of the cam is constant but throttle position causes the helix to rotate in relation to the cylinder in which the piston (helix) rides. The amount of fuel delivered to the engine is dependent upon the positioning of the helix in the cylinder. The fuel pump will consist of a cam driven by the engine and as many helix cylinder combinations as there are cylinders in the engine.
Unit injectors operate in the same way but there is one per cylinder and the controls are ganged together to get uniform fuel distribution to each cylinder. These injectors have a similar helix piston arrangement and are actuated by a cam similar to that operating the valve train on the engine.
Aspiration of the engine can incorporate a blower or, the engine can be normally aspirated. When the fuel is delivered to the engine it will speed up causing an increase in the air volume until there is a balance between fuel delivered and the air delivered to the combustion chamber.
To my knowledge there has never been a system whereby the fuel air ratio can be modified like it is with a carbureted engine.
I guess my mind is not as fuzzy as I thought. I went to engine school in 1947. If I am wrong then I will plead Oldtimers disease.
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The "throttle" is effectively the mixture control on a diesel engine.
A diesel has no true throttle like a spark ignition engine (i.e. no restrictor plate in the intake). The intake pipe is fully open all the time and the power is controlled by varying the amount of fuel entering the cylinders. The cylinders take a "full gulp" of air irrespective of power demand.
At low power, therefore, the mixture is very weak. More power is achieved by increasing the amount of fuel injected (richening the mixture). Older systems did this mechanically by increasing the stroke of the fuel pump but modern systems may do it by varying the opening time of the injectors, controlled electronically. The black smoke emitted by some road vehicles on acceleration is a sign of a poorly adjusted fuel system, causing over-fuelling
Diesels work at much higher compression ratios than gas engines (typically 19:1 or higher to ensure ignition takes place) and because the volumetric efficiency is also higher (no throttle acting as a restrictor) the fuel economy is much better. This is also why the low speed torque is very good.
A disadvantage of compression ignition is that it is difficult to advance the ignition timing (because of slower combustion) which means that the engine will not rev as highly as a spark ignition engine, limiting the max power that can be produced. However, the power output can be increased significantly at lower rpm by fitting a turbo-charger which simply shoves more air through the engine at lower rpms, allowing more fuel to be burned. On an aero engine this isn't a great disadvantage at all because the engine is normally required to work in a fairly constant rpm band.
N.b. It is very important to keep a diesel's air filter clean, as the throughput of air is much higher than on the equivalent spark ignition engine. There is no danger of carb ice because there is no carb, all that is required for cold weather is to ensure the intake doesn't get blocked by snow!
Nerd mode off as my brain now hurts....
A diesel has no true throttle like a spark ignition engine (i.e. no restrictor plate in the intake). The intake pipe is fully open all the time and the power is controlled by varying the amount of fuel entering the cylinders. The cylinders take a "full gulp" of air irrespective of power demand.
At low power, therefore, the mixture is very weak. More power is achieved by increasing the amount of fuel injected (richening the mixture). Older systems did this mechanically by increasing the stroke of the fuel pump but modern systems may do it by varying the opening time of the injectors, controlled electronically. The black smoke emitted by some road vehicles on acceleration is a sign of a poorly adjusted fuel system, causing over-fuelling
Diesels work at much higher compression ratios than gas engines (typically 19:1 or higher to ensure ignition takes place) and because the volumetric efficiency is also higher (no throttle acting as a restrictor) the fuel economy is much better. This is also why the low speed torque is very good.
A disadvantage of compression ignition is that it is difficult to advance the ignition timing (because of slower combustion) which means that the engine will not rev as highly as a spark ignition engine, limiting the max power that can be produced. However, the power output can be increased significantly at lower rpm by fitting a turbo-charger which simply shoves more air through the engine at lower rpms, allowing more fuel to be burned. On an aero engine this isn't a great disadvantage at all because the engine is normally required to work in a fairly constant rpm band.
N.b. It is very important to keep a diesel's air filter clean, as the throughput of air is much higher than on the equivalent spark ignition engine. There is no danger of carb ice because there is no carb, all that is required for cold weather is to ensure the intake doesn't get blocked by snow!
Nerd mode off as my brain now hurts....
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"all that is required for cold weather is to ensure the intake doesn't get blocked by snow!"
And some form of pre-heat for the fuel - diesel fuel gets very sludgy as the mercury heads for 0.
Wiksch in Northampton are going through the process of certification for their diesel - an engine designed from the bottom up for aviation. They have it flying (with a datalogging system) in several non-CofA kits.
And the Mercedes A class diesel has been converted and is running in several production planes in Europe. Both these engines make use of alloys to reduce the inherent weight that has previously made diesels useless for light aviation.
Mark Wilksch (ex-Cosworth, decent Aussie) was at Aerofair this year - and is desperately keen for Frank to let him put one in a Robinson.
What will make it happen quicker:
(a) the predicted end of 100LL: refineries are struggling to justify it. Demand has slackened off in the USA - but more dramatically in the UK.
(b) USA "gas" prices to reach $2.50 - $3 a gallon.
And some form of pre-heat for the fuel - diesel fuel gets very sludgy as the mercury heads for 0.
Wiksch in Northampton are going through the process of certification for their diesel - an engine designed from the bottom up for aviation. They have it flying (with a datalogging system) in several non-CofA kits.
And the Mercedes A class diesel has been converted and is running in several production planes in Europe. Both these engines make use of alloys to reduce the inherent weight that has previously made diesels useless for light aviation.
Mark Wilksch (ex-Cosworth, decent Aussie) was at Aerofair this year - and is desperately keen for Frank to let him put one in a Robinson.
What will make it happen quicker:
(a) the predicted end of 100LL: refineries are struggling to justify it. Demand has slackened off in the USA - but more dramatically in the UK.
(b) USA "gas" prices to reach $2.50 - $3 a gallon.
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OK. Now you've got me started.
Fuel injection technology for small diesel engines has now moved into the realms of electronically controlled 'common rail' systems. The rail in question is little more than a highly pressurised tube that acts as a reservoir, feeding all cylinders. Pressure is provided by a separate pump, usually mechanical but can be electrical. Apart from the rail's ability to provide very high pressure fuel right where it's needed, ie: atop the injector (thereby doing away with pressure pulse and other problems inherent in old style pump-line-nozzle designs) clever lock-out valve technology allows that pressure to be retained when the engine is shut down. This means full injection pressure is available during slow-speed cranking on that inevitable cold-n-frosty morning. This solves much of the age-old problems of cold-starting light 'high-speed' diesel engines, especially those designed around indirect injection (idi) combustion chambers.
The injectors have become electronically controlled, and far more efficient (and hardy) than ever they were. Electronic control means the start and end of injection can be advanced or retarded as necessary for optimal performance, whether cold starting or in the cruise. The volume of fuel injected can also be varied, both by the length of the injection period - controlled by the former two parameters - and by something called flow volume control, in other words, opening the tap a bit more.
Cold weather effects diesel fuel proper, but Jet A1 lacks the full wax content and is treated with inhibitors to keep the wax at bay. Don't go putting conventional diesel fuel in your aeroplane. Apart from it being a lot more expensive, the whole engine has been set up to work best on Jet A1. Always remember that the fuel in any compression-ignition engine is doing three jobs: 1) it's a fuel, 2) it's a coolant for the components pumping it and the electronics controlling its flow (yes really), and 3) it's a lubricant for those same mechnical components - eg: the injectors.
I'd love to see a diesel R44. Just think...a modern helicopter with a modern piston engine, FADEC, three times the endurance, etc, etc.
The injectors have become electronically controlled, and far more efficient (and hardy) than ever they were. Electronic control means the start and end of injection can be advanced or retarded as necessary for optimal performance, whether cold starting or in the cruise. The volume of fuel injected can also be varied, both by the length of the injection period - controlled by the former two parameters - and by something called flow volume control, in other words, opening the tap a bit more.
Cold weather effects diesel fuel proper, but Jet A1 lacks the full wax content and is treated with inhibitors to keep the wax at bay. Don't go putting conventional diesel fuel in your aeroplane. Apart from it being a lot more expensive, the whole engine has been set up to work best on Jet A1. Always remember that the fuel in any compression-ignition engine is doing three jobs: 1) it's a fuel, 2) it's a coolant for the components pumping it and the electronics controlling its flow (yes really), and 3) it's a lubricant for those same mechnical components - eg: the injectors.
I'd love to see a diesel R44. Just think...a modern helicopter with a modern piston engine, FADEC, three times the endurance, etc, etc.
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Headsethair,
Diesel fuel isn't used in the new aviation diesels, they were designed for Jet A-1 as mentioned earlier. This allows the aircraft to be refuelled at most airports, using fuel that meets aviation quality standards (water checks etc).
However, if the Jet fuel does need pre-heating, that feature can be designed in. Some helicopters, for example the S-76, have engine oil heated fuel components (such as filters) where the waxing problem might occur. Most modern diesel cars also have electric fuel pre-heaters.
Or you could try the old lorry driver's trick of lighting a fire under the engine on cold mornings.........
Hehe
Diesel fuel isn't used in the new aviation diesels, they were designed for Jet A-1 as mentioned earlier. This allows the aircraft to be refuelled at most airports, using fuel that meets aviation quality standards (water checks etc).
However, if the Jet fuel does need pre-heating, that feature can be designed in. Some helicopters, for example the S-76, have engine oil heated fuel components (such as filters) where the waxing problem might occur. Most modern diesel cars also have electric fuel pre-heaters.
Or you could try the old lorry driver's trick of lighting a fire under the engine on cold mornings.........
Hehe
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...or the other old trick of rolling up a couple of magazines, dipping one end in the fuel tank and setting light. Hold your now blazing torch by the air intake vent and start to crank.
Works much better than EasyStart. (showing me age , now)
Works much better than EasyStart. (showing me age , now)
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The idea of a Jet-A1 turbo-diesel is fine. But the real justification (around here anyway) is the difference in fuel price. Jet A1 is from 20-40 p per litre - Avgas is 100 p per litre more or less! It would make a massive difference to operating costs. Power/weight ratio is still an issue though, especially for a helicopter. The economics all change, of course, if the politicos start to change the tax regime.
If Frank lived/worked in the UK/Europe, and the main Robbo market was here it would have happened already......... (but if that was the case, the Robbos would never have had carburetors and carb heat either)
If Frank lived/worked in the UK/Europe, and the main Robbo market was here it would have happened already......... (but if that was the case, the Robbos would never have had carburetors and carb heat either)
R44/55/66T
This stuff is all of great interest to me. I have a couple of comments that might be of interest to others.
For Robinson to put a diesel into the R44 he only has one engine option - a derivative of the SMA SR305-230. www.smaengines.com
[Yes i'm aware of Zoche, but that program is a long way off]
The problem is that allthough the new engines have a higher TBO 3000hrs, include fuel injection and burn jet fuel which is an enormous advantage in Europe, the engines are extremely heavy. All of the helicopter manufacturers that have used piston engines over the years have had terrible trouble with the fact that even the trusty Lycomings are too heavy really for use in helicopters due to the unique sensitively of helicopters to airframe weight (Thrust Balances weight etc etc). This is hampered further still by the need for 'power in reserve' for helicopters - i.e in the R22's case that bit between 25-27 MAP that your NOT SUPPOSED TO USE but could if it was essential.
Couple this with the fact that helicopters have an extremely demanding duty cycle for engines and we are then faced with the grim reality that if we want our engines to reach overhaul, then they need to be sustantially derated ~ i.e Robinsons approach, 131hp from a 160/180hp engine for R22. [There are also altitude effects to be considered in non turbo'd engines.]
So.....what does all this mean for the R44........
Well if Mr R want's to use the SMA unit he would have to use the future derivative of the SMA 305-230 (which is only a 230hp unit), the 300hp unit with an increased compression ratio (from 17:1 for the 230hp unit, to 19:1 for the 300hp unit)
This engine is likely to weigh approx 250kg and be derated to 250hp for heli apprlications the non-fuel injected Lycoming used in the Raven 1 weighes 170kg - that 80 kg of extra dead weight using the diesel (A whole passenger)! There will of course be a saving in fuel weight of approximately - 10kg per hour flight-time of fuel carried - for a typical 2hr mission fuel load the deisel configuration is still heavier by 60kg. To add insult to injury, the SMA crank speed is slower so the transmission would need to be changed and the slower spinning elements would have to be beefed up to cope with the additional torque - more weight!
In summary while it is theoretically possible to produce a SMA powered R44 that would not result in too significant a loss of performance, it would be difficult, expensive, and is most unlikely to provide an extra seat (unless it was for show!), further, to get more weight out of the airframe 'other' things would have to be compramised.
I refer you to:....
Low Interia Rotor System
Lack of Crash Protection
Low Airframe TBO
Now a turbine, thats a different kettle of fish, but while that would be a dream from a weight and performance point of view (and could mean 5-seat with high performance, or six seats with contemporary performance) the cost would be substantial. The only sutable engine is the Roll Royce C250, nominally 370hp MAX Cont and 420 for 5 mins - That enough for 2 R44's WOW!
If Mr R decided to go for 6 seats, then i'm sure we would have the most cost effect and commerically viable 6-seater ever designed...I guess we'll have to wait and see!
PS: I heard a rumour that Mr 'R' has had a Jet A1 Tank and pump fitted at the factory!
CRAN
For Robinson to put a diesel into the R44 he only has one engine option - a derivative of the SMA SR305-230. www.smaengines.com
[Yes i'm aware of Zoche, but that program is a long way off]
The problem is that allthough the new engines have a higher TBO 3000hrs, include fuel injection and burn jet fuel which is an enormous advantage in Europe, the engines are extremely heavy. All of the helicopter manufacturers that have used piston engines over the years have had terrible trouble with the fact that even the trusty Lycomings are too heavy really for use in helicopters due to the unique sensitively of helicopters to airframe weight (Thrust Balances weight etc etc). This is hampered further still by the need for 'power in reserve' for helicopters - i.e in the R22's case that bit between 25-27 MAP that your NOT SUPPOSED TO USE but could if it was essential.
Couple this with the fact that helicopters have an extremely demanding duty cycle for engines and we are then faced with the grim reality that if we want our engines to reach overhaul, then they need to be sustantially derated ~ i.e Robinsons approach, 131hp from a 160/180hp engine for R22. [There are also altitude effects to be considered in non turbo'd engines.]
So.....what does all this mean for the R44........
Well if Mr R want's to use the SMA unit he would have to use the future derivative of the SMA 305-230 (which is only a 230hp unit), the 300hp unit with an increased compression ratio (from 17:1 for the 230hp unit, to 19:1 for the 300hp unit)
This engine is likely to weigh approx 250kg and be derated to 250hp for heli apprlications the non-fuel injected Lycoming used in the Raven 1 weighes 170kg - that 80 kg of extra dead weight using the diesel (A whole passenger)! There will of course be a saving in fuel weight of approximately - 10kg per hour flight-time of fuel carried - for a typical 2hr mission fuel load the deisel configuration is still heavier by 60kg. To add insult to injury, the SMA crank speed is slower so the transmission would need to be changed and the slower spinning elements would have to be beefed up to cope with the additional torque - more weight!
In summary while it is theoretically possible to produce a SMA powered R44 that would not result in too significant a loss of performance, it would be difficult, expensive, and is most unlikely to provide an extra seat (unless it was for show!), further, to get more weight out of the airframe 'other' things would have to be compramised.
I refer you to:....
Low Interia Rotor System
Lack of Crash Protection
Low Airframe TBO
Now a turbine, thats a different kettle of fish, but while that would be a dream from a weight and performance point of view (and could mean 5-seat with high performance, or six seats with contemporary performance) the cost would be substantial. The only sutable engine is the Roll Royce C250, nominally 370hp MAX Cont and 420 for 5 mins - That enough for 2 R44's WOW!
If Mr R decided to go for 6 seats, then i'm sure we would have the most cost effect and commerically viable 6-seater ever designed...I guess we'll have to wait and see!
PS: I heard a rumour that Mr 'R' has had a Jet A1 Tank and pump fitted at the factory!
CRAN
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Just an idea
The use of twin reciprocating engines is another alternative. This will significantly increase the reliability of the power source; even if each of the smaller engines has reliability that is lower then the single engine, which they replace.
Integrating the two engines into a single 'package', in respect to timing, power division, etc., has been done in other applications.
Integrating the two engines into a single 'package', in respect to timing, power division, etc., has been done in other applications.
That make matter even worse!
Dave,
The reliability point is valid (ish), but the weight consideration once again rules it out.
Say we need 224hp, we could use
(a) 2 x Lycoming O-235L producing 112hp @2600rpm and weight 99kg each (198kg and 224hp total).
Or...
(b) 1 x Lycoming O-540J producing 235hp @2400rpm and weighing 165kg. (This is a derated engine aswell while the O-235's are screaming!)
This is why it hasn't been done!
It's expensive, heavy and more complicated....
CRAN
The reliability point is valid (ish), but the weight consideration once again rules it out.
Say we need 224hp, we could use
(a) 2 x Lycoming O-235L producing 112hp @2600rpm and weight 99kg each (198kg and 224hp total).
Or...
(b) 1 x Lycoming O-540J producing 235hp @2400rpm and weighing 165kg. (This is a derated engine aswell while the O-235's are screaming!)
This is why it hasn't been done!
It's expensive, heavy and more complicated....
CRAN
Iconoclast
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Reliability?
To: Dave Jackson
Having two engines driving in parallel with each of the two engines having a lower reliability than the single engine being replaced is great on paper. However the failure rate of each of the two parallel engines would be at a higher rate so in your proposal each of the two parallel engines must be able to carry the weight of the helicopter in the event of a single power plant failure. The transmission would have to be redesigned to accept two engines and the engineers will have to do some serious analyses and testing to eliminate any vibratory problems from the two engines firing at differing intervals.
On the S-55, 56 and 58 Sikorsky had the engines driving at a 34˝-degree offset to minimize vibratory effects between the engines and the transmission. Even then, there were some serious problems with the engine cooling fans at certain rotating speeds.
Having two engines driving in parallel with each of the two engines having a lower reliability than the single engine being replaced is great on paper. However the failure rate of each of the two parallel engines would be at a higher rate so in your proposal each of the two parallel engines must be able to carry the weight of the helicopter in the event of a single power plant failure. The transmission would have to be redesigned to accept two engines and the engineers will have to do some serious analyses and testing to eliminate any vibratory problems from the two engines firing at differing intervals.
On the S-55, 56 and 58 Sikorsky had the engines driving at a 34˝-degree offset to minimize vibratory effects between the engines and the transmission. Even then, there were some serious problems with the engine cooling fans at certain rotating speeds.
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Just an idea
CRAN
There is no disagreement with what you are saying. The Lycoming is already considered a reliable engine, so to have two of them would be over
-reliability.
I am suggesting going in the other direction. For example, use two lightweight 2-stroke engines. They will have less reliability than a Lycoming, but the probability of the simultaneous failures of both engines should be much less frequent than the failure rate of the single Lycoming. Hopefully, this would offer a greater time between complete failures, plus a reduced total weight.
Lu,
Yes, the total failure rate will be higher, but the second engine need only support the craft at the minimum power setting, and possibly only until a safe landing site was found.
The following example is not going to deliver the horsepower that CRAN is talking of but it does convey the basic concept.. Hirth has developed a 2-cylinder inline engine for the single seat Ultrasport helicopter, and 4-cylinder opposed engine for the two seat Ultrasport helicopter. Most of the components are common to both engines.
The idea would be to position the 2-cylinder engines in an opposed arraignment. This would cause these engines to be very similar to a single opposed 4-cylinder engine, except that there are two crankshafts. Just as Hirth has modified two engines specifically for helicopters, they might be willing to develop a lower crankcase housing for two crankshafts. Of course, they would have to synchronize the engines etc., but this should not be a significant problem.
There is no disagreement with what you are saying. The Lycoming is already considered a reliable engine, so to have two of them would be over
-reliability. I am suggesting going in the other direction. For example, use two lightweight 2-stroke engines. They will have less reliability than a Lycoming, but the probability of the simultaneous failures of both engines should be much less frequent than the failure rate of the single Lycoming. Hopefully, this would offer a greater time between complete failures, plus a reduced total weight.
Lu,
Yes, the total failure rate will be higher, but the second engine need only support the craft at the minimum power setting, and possibly only until a safe landing site was found.
The following example is not going to deliver the horsepower that CRAN is talking of but it does convey the basic concept.. Hirth has developed a 2-cylinder inline engine for the single seat Ultrasport helicopter, and 4-cylinder opposed engine for the two seat Ultrasport helicopter. Most of the components are common to both engines.
The idea would be to position the 2-cylinder engines in an opposed arraignment. This would cause these engines to be very similar to a single opposed 4-cylinder engine, except that there are two crankshafts. Just as Hirth has modified two engines specifically for helicopters, they might be willing to develop a lower crankcase housing for two crankshafts. Of course, they would have to synchronize the engines etc., but this should not be a significant problem.