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  #1  
Old 08-30-2004, 03:50 AM
Helidev II Helidev II is offline
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Default Tip Jet Helicopters

Let the Games Begin!!!!!

Dividing into 3 catagories;
1, cold cycle pressure driven, where compressed air is expelled from the tips of the blades

2, hot cycle, gas from a turbine exhaust expelled from the tip

3, tip burning, where either compressed air is piped to the tips, and mixed with fuel to provide the propulsion, or rockets like hydrogen peroxide, or self contained motors like ram jets or pusle jets, or even mini turbines.

Im pretty much ruling out No 2. I dont really want to use a turbine, they are expensive, plus the ducting of the hot exhaust gasses seems like a pain in the butt. Even though the X-50 has gone this route, I think that the expense of the heat tollerant materials, the cost of the turbine, will all add up to put it out of reach for most builders.

As far as Hydrogen peroxide goes, Im not a big fan of carrying 2 fuels on board, plus the endurance seems to be very limited.
Ram jets, pluse jets and mini turbines, all suffer from the same disadvantage in the extra drag caused by having the motor out on the tips, instead of in the nice streamlined fuse.

Which really leaves 2 options. either cold cycle or tip burning. Both have had their relative successes, however the cold cycle is the only one to have gone into production, with the Sud Djinn. However the Fairey Rotordyne and the XV-1 both had successful test programs.
One of the disadvantages of tip burning is they suck fuel like pigs. The XV-1 could only hover for about 1 hour, before running dry, not sure on the rotordyne, havent been able to find any figures.
Cold cycle requires more air, at pressure to work, with a sufficient compressor they can work, finding the compressor is the trick.

Tip Jets always seem to have 2 problems to overcome. 1, the relative inefficiency compared with a trans driven helo. 2, Once you get rid of the tail rotor, how do you achieve yaw control.
Dealing with No 1 first. Recently Ive been looking over the old tip jet designs, and comapring them with the only modern tip jet, the X-50. One of the most striking differences between them is the nozzles. Typically the nozzles on the early tip jet designs seem to be quite small, relying on high velocity, lower pressure air. The X-50 has much larger nozzles, and Im guessing a lower velocity. The reason Im guessing about the lower velocity is because funnily enough, Boeing and DARPA dont like to share info on their research projects.
Most of us would be familiar with the principal that its more efficient to move a large mass of air slowly, than move a small amount of air quickly. Following this on, it should also be quiter.
One of the problems with this theory is the tips of a helo blade are moving fairly quickly. This means that the efflux velocity must be atleast equal to this speed to maintain RRPM.
2 possible solutions, 1 reduce the RRPM, this would have benefits in terms of noise and vibration. 2 move the tip jets inboard. This would mean the jets are located in a thicker part of the blade, reducing the profile drag, and by placing the jets inboard of the tip, the required velocity of the jet goes down, however this comes at the cost of a higher required power for the jets due to the reduced leverage.

2, The NOTAR problem. Interestingly one of the percieved failures of the XV-1, was the requirement of two small tailrotors to ba added for yaw control in low speed and hover flight.
This seems to me to be a relatively monor concern. Utilising the method employed by the Fairey Rotordyne, 2 pitch controled props, each side of the fuse. Differential thrust enables good yaw control.

I think thats enough for now, feel free to comment, critisize or suggest, see where we end up.
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  #2  
Old 08-30-2004, 04:20 AM
birdy birdy is offline
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Forgive me if this a stupid idea Heli,but it's been in me head since I started fly'n gyros.[and is a little off topic.]If you shoot it down in flames then I can forget about it and not loose sleep over it anymore.

A jump start[vto]gyro has one major problem if the rotors are mechanicaly driven,torque.
I thought,if you had a prerotor powerful enough to lift off,could the torque be countered with a BIG rudder,with two hinges.One controle would activate a 45 degree hinge to deflect rotor and prop thrust to counter torque and the other for yaw control in autorotation S/L.
Obviosly it wouldn't be a true vto coz the prop thrust would have you moveing forward befor you broke ground,but it would be a STOAL at least.With the stick back on the stoper,the rotor thrust would assist the ground breaks to minamise ground roll.

Is this feasable or am I talk'n out me a.. again.??
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  #3  
Old 08-30-2004, 04:49 AM
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Victor Duarte Victor Duarte is offline
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hi christian, i m glad you created this thread, i said in other i am very interested about tip jets.

for me (for a light or ultralight) the best way is cold air... the more the air is cold the more it is "heavy" .

the venturi effect is less pressure, more speed, less speed, more pressure (like traffic jams in sydney or paris )

if you want a good output speed (more than 600 km/h at least, for slow rotors to 900km/h) you need speed AND pressure to output enough air...

i agree improvements are possible on the nozzles to master a good flow.

the yaw IS another problem, in forward flight, rudders do the job, in hover they dont, i thought in use the engine exhaust gases for yaw control, but really unsufficient, in the djinn as in the lockheed model 120 the turbines exhausts blow on rudders, a few persons i talked with told me it is quite a "must be".

you reached the MAIN problem : air production.
the chalenge of the day is : produce enough air with cheap and light devices...
i was thinking in using a piston engin coupled with 1,2 or 3 turbochargers, this solution is employed in the best compressors in the marker, but... sould be too heavy for air production... perhaps someone should overcome this...

for a ultralight, i evaluated the needs of air : at least 2 bars and about 6 m3/second, huge.. must be confirmed by some one else

if you consider to build a commercia VTOl aircraft as i readed your posts, it seems that turbine is really the only way ...

i send again this link :
http://www.technologie-entwicklung.d...bocharger.html

a car turbo could be used as a small turbine... no eng here to fit that?

see lockheed model 120, nice and powerfull bird..

i still thinking something good sould be found.... i wish it will be..

a suivre....

victor
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  #4  
Old 08-30-2004, 08:41 AM
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quadrirotor quadrirotor is offline
André Martin, Ph.D., Etc.
 
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I expressed many times my position in the previous posts; to sum up:
Tip-jets for an helicopter are noisy and thirsty!... but can be done with success with stock peaces, centrifugal compressor ($5000) belted to a big Subaru etc...(specs can be found for the HELICOP-JET on the site of the CELAG (given previously)...
BUT cold-air-tip-jets could be use for a low powered (15 to 20 hp) offset hinged blades rotor of a jump-take-off gyro with in flight added power (IFAP); using the turbo of the engine...
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Discussing, exchanging, giving ideas...going towards a non expensive, safe and easy homebuilt rotorcraft which is not a gyro nor an helico but a mix of both!!! Keeping the best of each!!!....
THE TOURINGCOPTER:http://www.rotaryforum.com/forum/att...0&d=1167007089
THE GYROCOAX:http://www.rotaryforum.com/forum/att...4&d=1169478953
THE ULTRALITECOAX:http://www.rotaryforum.com/forum/showthread.php?t=18431
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  #5  
Old 08-30-2004, 08:52 AM
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hi andre,
what you say looks VERY interesting !
have you further info about a such mounting? i thouth exactly the same way, but with a 503 or 586 , not sufficient on my opinion, so, if you could saiy "yes it works" i d jump to the roof !

thanks andre

victor
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  #6  
Old 08-30-2004, 09:37 AM
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quadrirotor quadrirotor is offline
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the power needed depends on your requirements and your mission profil! all is trade off!!!
The tip-jet helicopter exits and is flying since 1952! 52 years!!! THE DJINN...
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Discussing, exchanging, giving ideas...going towards a non expensive, safe and easy homebuilt rotorcraft which is not a gyro nor an helico but a mix of both!!! Keeping the best of each!!!....
THE TOURINGCOPTER:http://www.rotaryforum.com/forum/att...0&d=1167007089
THE GYROCOAX:http://www.rotaryforum.com/forum/att...4&d=1169478953
THE ULTRALITECOAX:http://www.rotaryforum.com/forum/showthread.php?t=18431
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  #7  
Old 08-30-2004, 10:19 AM
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right andre,here, we agree with each other...

so some of expected data

empty weight : about 120 kgs
cruise speed : 130 km/h
payload : at least 50 kgs plus pilot

as i said earlier here, i had the chance to live with a pro pilot who began as mech crew on DJINN and learned to fly on it .. i asked him lots of questions, he s still thinking it is a good helo and regrets that lots of them come out of their lifetime.
this person , Aimé Fabrégat, said to me "there is no "better" pilot, only alive ones", i made this thought mine.

if i can have good info on engines, i have not enough about centrifugal compressors.. have you some?

best regards andre and others

victor
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  #8  
Old 08-30-2004, 10:19 AM
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quadrirotor quadrirotor is offline
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for an helico, you can overcome (to some extents) the inefficiencies of the tip-jets by using a light turbo diesel engine (mecedes smart engine) and the synchropter set-up (only synchronization with homocinetics joints...Dave Jackson's site...no gears.).
For the noise, you can use newly technics of electronic noise suppression (concellation with a sound system by opposing a generated sound to the sources of noise...) experimental. army classified!
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Discussing, exchanging, giving ideas...going towards a non expensive, safe and easy homebuilt rotorcraft which is not a gyro nor an helico but a mix of both!!! Keeping the best of each!!!....
THE TOURINGCOPTER:http://www.rotaryforum.com/forum/att...0&d=1167007089
THE GYROCOAX:http://www.rotaryforum.com/forum/att...4&d=1169478953
THE ULTRALITECOAX:http://www.rotaryforum.com/forum/showthread.php?t=18431
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  #9  
Old 08-30-2004, 10:33 AM
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Victor Duarte Victor Duarte is offline
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andre

"mercedes smart engine" > yes a german manufacturer is on it ... in my hometown's aeroclub they build a fixed-wings with a 90 hp OPEL TD... i ll go and have a look.

"no gears" >

"For the noise, you can use newly technics of electronic noise suppression (concellation with a sound system by opposing a generated sound to the sources of noise...) experimental. army classified!"
> you're right, but classified... not at all ... you may talk about the interior noise, dont know if it could suppress outer one, good blade tips design is actually the best way to avoid "flaps".. the sound system works with compressed air (my brother owns a music studio and some speakers use this device)

i think we can obtain acceptable noise by a better nozzle design or by using elastomeric materials , a kind of noise wall in the nozzle, i dont really know.

did you remark how the night birds are silent... maybe a way to investigate..

best regards

victor
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  #10  
Old 08-30-2004, 10:40 AM
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quadrirotor quadrirotor is offline
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Default No Gears!

clic on the pic!
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Discussing, exchanging, giving ideas...going towards a non expensive, safe and easy homebuilt rotorcraft which is not a gyro nor an helico but a mix of both!!! Keeping the best of each!!!....
THE TOURINGCOPTER:http://www.rotaryforum.com/forum/att...0&d=1167007089
THE GYROCOAX:http://www.rotaryforum.com/forum/att...4&d=1169478953
THE ULTRALITECOAX:http://www.rotaryforum.com/forum/showthread.php?t=18431

Last edited by quadrirotor; 11-16-2006 at 06:06 AM.
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Old 08-30-2004, 10:53 AM
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oh ok ok sorry, i m confused, i knew that .. if you have not twin engine, you still need a synchro gearbox , no ? i may misunderstand you.

if a was a malicious guy (for shure i am ) i would say that in this part there are much more sources of failure than in gears, am i wrong ? or can we thrust it just like gears ?.
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Old 08-30-2004, 11:03 AM
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quadrirotor quadrirotor is offline
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Default homocinetic joints!

Yes this kind of joints are fragile, but the one used in your car (with balls) are fail-safe as they make a noise a long long time before braking! anyway they are not loaded, only synchronization!

for compressor, there is a link:
http://www.vortron.com/products/blowers.html
make a searsh with googles too!
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Discussing, exchanging, giving ideas...going towards a non expensive, safe and easy homebuilt rotorcraft which is not a gyro nor an helico but a mix of both!!! Keeping the best of each!!!....
THE TOURINGCOPTER:http://www.rotaryforum.com/forum/att...0&d=1167007089
THE GYROCOAX:http://www.rotaryforum.com/forum/att...4&d=1169478953
THE ULTRALITECOAX:http://www.rotaryforum.com/forum/showthread.php?t=18431

Last edited by quadrirotor; 08-30-2004 at 11:10 AM.
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  #13  
Old 08-30-2004, 11:15 AM
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Victor Duarte Victor Duarte is offline
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yeah ! thanks for link .. filed in my database....

for the car joint, i know well by having experimented it by myself, i could hear the noise much before failure, i agree, but when the balls crushed...no way to go further... i changed both bearings myself.

thanks andre

victor
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Old 08-30-2004, 11:22 AM
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quadrirotor quadrirotor is offline
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As the synchonization is not loaded, you could use a flex cable as the one used for the wunderlich prerotator!!!! I am joking!!!!
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Discussing, exchanging, giving ideas...going towards a non expensive, safe and easy homebuilt rotorcraft which is not a gyro nor an helico but a mix of both!!! Keeping the best of each!!!....
THE TOURINGCOPTER:http://www.rotaryforum.com/forum/att...0&d=1167007089
THE GYROCOAX:http://www.rotaryforum.com/forum/att...4&d=1169478953
THE ULTRALITECOAX:http://www.rotaryforum.com/forum/showthread.php?t=18431
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Old 08-30-2004, 11:34 AM
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i m reading about the compressor, still have problems with units conversion
looks interesting ...
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