Sikorsky XV-2 stop rotor
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Sikorsky XV-2 stop rotor
Found this while trying to understand what state of tip jet development was:
http://www.fantastic-plastic.com/SikorskyXV-2Page.htm
Not sure how practical such a concept would be in the modern world:
Mart
http://www.fantastic-plastic.com/SikorskyXV-2Page.htm
Originally Posted by Site linked
By 1951, Sikorsky, the world's leading helicopter manufacturer, had fashioned a creative way to fuse the two concepts, the result being jet-powered aircraft with a single-bladed helicopter rotor that could be used for VTOL-style take-offs and landings, then collapsed stowed when the aircraft commenced horizontal flight.
Dubbed the XH-36, the plan was given the green light by a joint U.S. Army/Air Force development team charged with building a VTOL aircraft that could be used for difficult rescue operations. Unfortunately, the outbreak of the Korean War turned Sikorsky's attention and resources to more practical matters, and the XH-36 -- now known as the XV-2 -- remained a study project only until the entire project was cancelled in 1960.
Dubbed the XH-36, the plan was given the green light by a joint U.S. Army/Air Force development team charged with building a VTOL aircraft that could be used for difficult rescue operations. Unfortunately, the outbreak of the Korean War turned Sikorsky's attention and resources to more practical matters, and the XH-36 -- now known as the XV-2 -- remained a study project only until the entire project was cancelled in 1960.
Mart
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The 'tip jet' technology was used on the XV-1. The other two aircraft in the XV series, the McDonnell XV-1 compound autogyro and Bell XV-3 tiltrotor, were actually built with two prototypes of each being produced. (The Sikorsky XV-2 was not built as mentioned in the textual description; the 'picture' shown of the XV-2 in a hangar on the linked site is a model that was super-imposed on a photo.) The XVs were all designed for competitive comparison in a program sponsored by the US Army Transportation Command with NASA involvement. The XV-1 and XV-3 prototypes were flown successfully and had flight programs lasting several years. Although a lot of good research material was gathered, neither was a viable option for production due to obvious limitations (too heavy, not enough power, etc., and resultant performance/payload inadequacies).
Last edited by 21st Century; 28th Mar 2007 at 17:48.
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Wasn't sure from text that Sikorsky XV2 was a tip jet, 21st Century, but i can't see a means for torque reaction either...
Actually, what i was interested in is why tip jet suffers from such low fuel efficiency. A ram jet is a non-starter, because it would be operating nowhere near fast enough. However, a turbo charger or radial compressor is limited by tip speed for similar reasons to a rotor blade (compressibility). Such a compressor will generate ~2 bar in unideal conditions and ~4 bar in ideal conditions. This means that if the nozzle was designed to convert all pressure to velocity (convergent-divergent if necessary) then even a tip burning design should be reasonably efficient. Similarly if the design was ducting compressor bleed it should also be efficient (ignoring duct losses). The nozzle area is relatively small, but travelling at high speed so you would still get a good mass flow rate.
The question may be unfair on this forum, but there are some smart engineers out there who might chip in.
Mart
Actually, what i was interested in is why tip jet suffers from such low fuel efficiency. A ram jet is a non-starter, because it would be operating nowhere near fast enough. However, a turbo charger or radial compressor is limited by tip speed for similar reasons to a rotor blade (compressibility). Such a compressor will generate ~2 bar in unideal conditions and ~4 bar in ideal conditions. This means that if the nozzle was designed to convert all pressure to velocity (convergent-divergent if necessary) then even a tip burning design should be reasonably efficient. Similarly if the design was ducting compressor bleed it should also be efficient (ignoring duct losses). The nozzle area is relatively small, but travelling at high speed so you would still get a good mass flow rate.
The question may be unfair on this forum, but there are some smart engineers out there who might chip in.
Mart
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Mart,
Wish I could help you on the technical questions, but I’m only familiar with the historical details of the XV programs. I believe the 'tip jet' technology was only used on the XV-1 and not on the XV-2 proposed design, but cannot confirm. I have a friend at NASA who worked on a later XV project, and if he approves I will send you his e-mail address (check your PMs).
Wish I could help you on the technical questions, but I’m only familiar with the historical details of the XV programs. I believe the 'tip jet' technology was only used on the XV-1 and not on the XV-2 proposed design, but cannot confirm. I have a friend at NASA who worked on a later XV project, and if he approves I will send you his e-mail address (check your PMs).
Last edited by 21st Century; 28th Mar 2007 at 17:53.
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Mart,
Most tip drives would be very loud for this environment.
An interesting experiment with hydrogen peroxide tip drive is now being done by a guy in Sweden.
Link here:http://www.peroxidepropulsion.com/
Most tip drives would be very loud for this environment.
An interesting experiment with hydrogen peroxide tip drive is now being done by a guy in Sweden.
Link here:http://www.peroxidepropulsion.com/
Last edited by slowrotor; 28th Mar 2007 at 17:05. Reason: add link
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Actually the XV-3 did not have tip jets, it was driven by a single radial engine.
http://www.vstol.org/wheel/VSTOLWheel/BellXV-3.htm
http://www.vstol.org/wheel/VSTOLWheel/BellXV-3.htm
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True. As mentioned above, only the XV-1 (a compound autogyro) had 'tip jets.' The XV-3 tiltrotor had a 450shp radial engine mounted in the center fuselage connected to the two fully-articulated three-bladed proprotors (originally). Later the proprotors were changed to two-bladed semi-rigid systems due to a 'flutter' problem found with the three-bladed proprotors. The rotor rigidity also helped to resist gyroscopic effects during transition.
Last edited by 21st Century; 29th Mar 2007 at 06:46.
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Slowrotor, HTP is actually a very good oxidiser - better than LOX in many ways. The only real problem for heli usage would be availability, although it would work well with Jet A1.
I'm really curious about problems which would occur using rotor as a centrifugal compressor stage, either pre or post combustion. Avoiding powertrain complexity for either recip or turbine may have cost and reliability benefits. Clearly nozzle design is critical to keep noise down. The other potential disadvantage is having additional tip mass, both for rotor dynamics and durability (hingeless assumed).
The main reason quoted for dropping tip jets is high fuel consumption, although most tip burners were not designed with noise reduction in mind. Historical development has abandoned the tip-jet, but as an engineer it is my duty to establish whether the problems could be overcome with modern development techniques like CFD.
Mart
I'm really curious about problems which would occur using rotor as a centrifugal compressor stage, either pre or post combustion. Avoiding powertrain complexity for either recip or turbine may have cost and reliability benefits. Clearly nozzle design is critical to keep noise down. The other potential disadvantage is having additional tip mass, both for rotor dynamics and durability (hingeless assumed).
The main reason quoted for dropping tip jets is high fuel consumption, although most tip burners were not designed with noise reduction in mind. Historical development has abandoned the tip-jet, but as an engineer it is my duty to establish whether the problems could be overcome with modern development techniques like CFD.
Mart
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Mart,
I think steam tip drive might be worth a look.
A flash boiler could power the tips for a brief liftoff, then switch the steam pipe to the forward drive prop powered by a steam turbine. The steam could be condensed for the turbine drive and a small amount of water would be lost for each tip drive use.
I think steam tip drive might be worth a look.
A flash boiler could power the tips for a brief liftoff, then switch the steam pipe to the forward drive prop powered by a steam turbine. The steam could be condensed for the turbine drive and a small amount of water would be lost for each tip drive use.
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From the Department of Demented Designs
Here is a steam engine for a coaxial rotor craft; http://www.unicopter.com/1311.html
Like slowrotor, I suspect that the tip jet is inefficient for forward flight. This is due to the fact that the thruster(s) on the retreating blade(s) are opposing the forward movement of the craft. If it was possible to develop a high-voluming - low-velocity thrust this might do; http://www.unicopter.com/0002.html
Dave
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Feet on the ground with head in the clouds...
Slowrotor, steam is a non-starter. You have to carry all the water you are going to boil, in addition to the fuel. Also steam is not efficient because you have to add extra energy to overcome latent heat of vapourisation. Been a while since i looked at that stuff, but Sir George Cayley did some calcs for his rotorwing ideas and realised power-to-weight was way below that required. I've seen a museum for some steam powered fixed wing model's in south UK - but that's about it.
My interest is to take a proven system, Jet A1 powered turbines, and see if there is a better way to design the powertrain. Tip jets have flown, in both compressor bleed form and tip burner form. The system is flight proven, if not comercially competetive. It is really to establish whether, for a tailrotorless design, the best concept is son-of-notar coanda effect tail system or rotor tipjet. Both in principle are similar concepts, but will have to struggle hard to stay competetive with tail rotor efficiency.
Dave, retreating jet may well be limiting factor for fuel burn (speed ratios are badly matched). Tip jets need to be at tips for maximum torque, but autorotation with additional propulsion at speed is a possibility. However, tip jet looses it's appeal once the system gets too complex. Maybe a cyclic valve to the jet gives it one last chance at surviving the engineering evolution process.
Thanks for feedback all.
Mart
My interest is to take a proven system, Jet A1 powered turbines, and see if there is a better way to design the powertrain. Tip jets have flown, in both compressor bleed form and tip burner form. The system is flight proven, if not comercially competetive. It is really to establish whether, for a tailrotorless design, the best concept is son-of-notar coanda effect tail system or rotor tipjet. Both in principle are similar concepts, but will have to struggle hard to stay competetive with tail rotor efficiency.
Dave, retreating jet may well be limiting factor for fuel burn (speed ratios are badly matched). Tip jets need to be at tips for maximum torque, but autorotation with additional propulsion at speed is a possibility. However, tip jet looses it's appeal once the system gets too complex. Maybe a cyclic valve to the jet gives it one last chance at surviving the engineering evolution process.
Thanks for feedback all.
Mart
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Hmmm, wasn't expecting this...
Originally Posted by er, me...
Sir George Cayley did some calcs for his rotorwing ideas and realised power-to-weight was way below that required. I've seen a museum for some steam powered fixed wing model's in south UK - but that's about it.
Maybe i need to give my "hat source" bottle a shake, Slowrotor, since there have been a few more attempts at steam aircraft than i thought:
http://www.flysteam.co.uk/
Still, must admit the idea of offseting payload against boiler water makes little sense to me....
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Mart,
I am suggesting reuse of the water for the main engine. A lightweight condenser would be needed, perhaps the rotors or other structure could serve as a condenser with a minor weight penalty.
A very light FLASH BOILER would be needed. (read about at your link)
I believe the thermal efficiency of a modern steam turbine is much better than a gas turbine. The savings in fuel weight could offset some of the system weight.
Also, I think the change of state from water to superheated steam is an advantage over hot air gas turbines. Check your statements about latent heat.
It's been 30 years since I studied marine steam turbines.
I am suggesting reuse of the water for the main engine. A lightweight condenser would be needed, perhaps the rotors or other structure could serve as a condenser with a minor weight penalty.
A very light FLASH BOILER would be needed. (read about at your link)
I believe the thermal efficiency of a modern steam turbine is much better than a gas turbine. The savings in fuel weight could offset some of the system weight.
Also, I think the change of state from water to superheated steam is an advantage over hot air gas turbines. Check your statements about latent heat.
It's been 30 years since I studied marine steam turbines.
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Slowrotor,
I certainly make no claims against your steam turbine design experience, but it's the "lightweight condenser" bit i'm not convinced about. Heat exchangers always end up large and heavy for a given power transfer. Look at your car radiator if you don't believe me, it will be designed to sink about the same heat power as your engine propshaft power (with 50 to 100 celcius temp difference). I know how much effort the radiator suppliers go to to minimise size/mass, and in this case the working fluid starts as a liquid.
I put that steam aircraft link in for interest, since like link provided by usmc_helo, it contained good general interest content. If the design is a tip jet, then by definition it has to be a total loss system anyway, which means air has to be the working fluid. There may well be better concepts out there, but turbines and recips work - every day, and for many 1000s of hours.
My interest is purely wether the function of turbine compressor and tip jet can be combined into the rotor system. The motive is really to provide an alternate against which to compare the idea of coanda effect tail jet mixer, for future Notar concepts. I just realised that there may be a side benefit of powertrain complexity/cost reduction for tip jet, so wanted to see what problems had already been found. Think of it as scoping out a possible future CFD project - gotta get up to speed sometime.
Mart
I certainly make no claims against your steam turbine design experience, but it's the "lightweight condenser" bit i'm not convinced about. Heat exchangers always end up large and heavy for a given power transfer. Look at your car radiator if you don't believe me, it will be designed to sink about the same heat power as your engine propshaft power (with 50 to 100 celcius temp difference). I know how much effort the radiator suppliers go to to minimise size/mass, and in this case the working fluid starts as a liquid.
I put that steam aircraft link in for interest, since like link provided by usmc_helo, it contained good general interest content. If the design is a tip jet, then by definition it has to be a total loss system anyway, which means air has to be the working fluid. There may well be better concepts out there, but turbines and recips work - every day, and for many 1000s of hours.
My interest is purely wether the function of turbine compressor and tip jet can be combined into the rotor system. The motive is really to provide an alternate against which to compare the idea of coanda effect tail jet mixer, for future Notar concepts. I just realised that there may be a side benefit of powertrain complexity/cost reduction for tip jet, so wanted to see what problems had already been found. Think of it as scoping out a possible future CFD project - gotta get up to speed sometime.
Mart
