Nice tip jets helicopter

[Victor Duarte]

Hello,
here is a nice site with videos of a neat tip jet helicopter, certainly the abandonned project "Intora firebird".
we can see a 2 seat enclosed version that is very pretty, looks smooth as silk.

http://www.advancedtechnologiesinc.com/uav_rotorcraft_atlas.asp

[KenSandyEggo]

Interesting. How does one control yaw in a tip-jet helicopter....is it by rudders like a gyro, or is there something else, which I don't see? If it's by rudder, it seems that it wouldn't have the maneuverability of a standard heli with a tail-rotor, especially during ground taxiing.

[Victor Duarte]

Hello Ken,
generally, for low speed manoeuvring, tip jets helicopters are controlled in yaw by 2 additionnal nozzles on the tail , or by deflecting the turbine flow on the rudders (like the DJINN), at higher speeds, the ruddders act just like rudders.
In this helicopter, i don't know how it is achieved but i guess it must be additionnal nozzles.
I also think the yaw manoeuvrability as good as with a tail rotor.

cheers

[karlbamforth]

The Interfora firebird has an auxiliary tailrotor, just for yaw control.
My design has the rudder hinge line at a rearwards sloping 45deg angle to take advantage of rotor downwash. Seems to work OK on the model.

[Victor Duarte]

Hello Karl,
when will you post some pics of your project ? sounds exiting.
cheers

[Ga6riel]

You could use a verticle, rotatable fin that is beneath the wake of the rotor,
ala' Hughes/Shweiser 300

[Sekse]

Ok, I have a question. I am really looking into designing and building a tip jet helicopter, has MANY advantages over all other rotorcraft, and no real disadvantages other than fuel economy that I can see. They are very cheap and easy to build, very low maintenance, and as easy to fly as an autogyro (since they are after all just an autogyro with jets on the rotors instead of a prop behind the seat) My question, though, is what kind of rotors do they use? In pictures, they have very wide rotors. They look much wider than those on helis and gyros. Anybody know where to score a set of these? What pitch are they set at? What kind of cross section do they have? Are the blades in fact the same as an autogyro? (This would require very high rotor RPM to provide lift without forward thrust (for taking off, landing, and hovering)

[Ron Marlett]

since they are after all just an autogyro with jets on the rotors instead of a prop behind the seat Are the blades in fact the same as an autogyro?

Well no, not really. A tipjet helo or any other type for that matter is considerably different than an autogyro. If tip jet helos were so simple to build, more people would probably be doing so. It is a fairly complex engineering problem to get fuel to, and control a jet/rocket operating at the tip of a spinning rotor. Not to mention the rotor being designed to handle the added stersses of that additional motor weight at the tip. The only real gain from the use of tip jets is the lack of rotor torque. The fuel usage, noise and engine control issues needed to gain this one thing are probably why we don't see more of them today. Besides, there are other ways to counter torque as seen with the coaxials, tandem rotors and NOTAR

Rotor blades used for powered rotors are usually different than those used for autorotation. Most helo rotor airfoils are fully symetrical and optimized for powered flight(pitched greater at the root than at the tip). Most gyro rotors are semi semetrical(flat bottomed) and optimized for autorotative flight(pitched greater at the tip than at the root). Helicopters can and do autorotate, but they are very aerodynamically inefficent when doing so.

[Sekse]

I am aware of all that, but the thing about a tip jet heli is it is based on autorotation. In a tip jet heli, there is no collective. To descend you simply reduce throttle on the jets. A tip jet heli's rotors are not typical heli blades, they are closer to an autgyro's, designed to autorotate, but to provide higher lift at lower RPM due to the drag of the tip jets (the reason for making them so wide). The thing is, you can build a typical gyrocopter with no engine / prop, change the rotors and add the jets and plumbing and you have a typical tip jet heli. The control system, rotorhead system, it is all basically identical. I MUST agree with you, though, piping pressurized liquid propane through the rotors is going to be a challenge.

I have been thinking about adding full cyclic and collective control, which would also adjust the pitch the jets giving additional lift. interestring thought.

[Sekse]

also, a tip jet has a rotor disc of 25 feet plus, like a gyro. as i said, it is designed to autorotate

[Ron Marlett]

I think you are not understanding the principle of autorotation. Autorotation is rotor powered by aerodynamics/gravity. Powered rotor is by applying torque to a shaft. In the case of a tipjet, the force is applied from the rotors but the net effect is the same. To be as efficient in that mode as possible, the blades need to be twisted accordingly. I can't think of any tipjet that didn't Have collective pitch. A machine without would have some terrible control lags as you have to wait for the disk to accelerate or decelerate to change the ammount of lift generated. The drag from the tip jets would make them terribly inneficient in autorotation and to fly at a speed slower to reduce drag would require more blade pitch which would probably preclude autorotation all together. You can make a fixed pitch tipjet helo, but I sure wouldn't fly in it.

[Rotor Rooter]

Perhaps mounting the tip jets slightly below the pitch axis of the blades will provide collective. In other words, an increase in the thrust of the tip jet will result in an increase in the positive twist (tip pitch) of the blade.
Yaw, in one direction only, could be achieved by locating a controllable friction device between the rotating rotor hub and the stationary mast.

____________________

3. If it is possible to vary the thrust at a rate of 1/rev. then there is the possibility of controlling cyclic in the same manner that the collective is being controlled.

4. In addition, if a third blade were to be added there is the possibility of better controllability, since the hub can now be equipped with a hub spring (http://www.unicopter.com/B329.html#Hub_Spring).

[brett s]

#1 sounds like an extremely bad idea - disregarding all the ways it could really screw up your day if something goes wrong (like how would you land succesfully in the event of power failure with no pilot control of collective pitch), it would probably make precise altitude control in a hover rather difficult.

[Sekse]

yikes, rooter's ideas scare me, lol. As for Ron, an autogyro's blades can autorotate even when in a verticle drop, just like those seed pods that fall off trees. Traditional tip jet helis are designed the same way. That is why most of the tip jet helis are autorotative. in descent, there is more force on the blades from air moving past them rather than from the jets, allowing it to coast downward by autorotation of the blades. Look at the pictures of the original tipjet helis, the ones designed by the guy who invented the g8 jets. If you look at enough images you will notice it has no collective control, and has monocyclic control over the rotor disc (meaning it can only tilt front and back.) Now I agree with everyone that this design is scary, even though it did work. No roll or collective in my opinion is just too risky, which is why I am trying to find a way to correct those design flaws. I also STRONGLY agree that the control lag would be dangerous. Naturally I am not building the standard tip jet design because it just doesn't have enough control. It would be like having a car where you can only turn the wheel in one direction with a good 20 seconds delay in throttle response and you can only shift upward while driving. Yeah, it would drive, it would make it to point b, but who the hell would want it?

As for rooter, putting a "brake" on the rotor to give one way yaw is suicide. It would steal power from the rotor, causing a massive jolt in torque spinning you out of control, especially since you can't go the other way, and it would also stall the rotor blades. You simply add a rudder mounted at 45 degrees so that it can use both the forward moving air in forward flight and the downwash from the rotors during hovering in order to give yaw control.
And mounting the jets under the rotors to give collective by twisting the rotor blades, that would result in sudden death. If you twist something over and over, one day it brakes. If you ever manage to fly with one or no rotor blades, send me a video, lol.

Not really looking to debate with anyone over the physics of a tip jet heli, I just want to know more about the rotors they use. They are absolutely huge, and there seems to be no info about them on the net.

[Victor Duarte]

Rick,
some infos :
it has been established that a tip jet rotor is better wit a low solidity ratio (smaller chord) and long blades.
If the rotors you have seen look huge it is for another reason : you must bring LOTS or air on the tip jets and the consequence is that you must have a blade section that allows it.
Theorically, you can use any helicopter or gyro airfoil... the trick is to build the airduct.
If you think about cold air, then, pay attention to the "DJINN" helicopter, the only that has been released for production.
If you are thinking about ramjets, there are some experiments that have been made.
I also like tip jets and would be glad to know more about your progresses.
cheers.

[Vance]

Rick, if you are speaking of Eugene Gluhareff, his tip jet helicopter had “full pitch control” and “synchronized fuel delivery”. His prototype has been donated to the Pima Air Museum. I don’t believe it ever flew out of ground effect. It used pressure jets running on propane and had a small round angled tail for yaw control.

Many people experimented with tip jets and I believe that most of them had collective pitch. Stanley Hiller even sold some to the military. The Djinn that Victor mentions achieved significant production numbers and some still fly today. They have a Djinn jet tip helicopter at the American Helicopter Museum in West Chester, PA.

I believe that the people on the forum are trying to help you to not repeat mistakes that others have made.

I have found that studying history has great value when I am trying to design something.

Thank you, Vance

[brett s]

Any truly successfull helicopter has had collective pitch - there are too many bad things with fixed pitch machines. Difficult to control altitude precisely in a hover, engine failure = crash...

One other huge problem with helicopters having hot cycle tipjets (in addition to fuel delivery problems & horrendous fuel burn which means about zero range) is how badly they affect the autorotational performance because of the added drag - the descent rates are far higher than a traditional design, like about 3x. That's partially offset by the added inertia making them more forgiving at the bottom, but you're still paying that drag penalty all the time. There is a reason you don't see those things around - there's no conspiracy, they just have too many issues to ever be practical.

[Sekse]

As I said, I agree with you all, it is too dangerous. I will post some links to pictures here, though. Looking at them I see no possible way for there to be a collective control, and I would like to point out the rotors on them (except for the sketch one) As you look, and look carefully, you will see they seem to mostly be a fixed pitch rotor system, and with the handle bar style cyclic, it would be very difficult to move side to side. I have also read that they were monocyclic controlled, so I am really getting curious.

http://www.alternative-technologies.org/copter.gif
(Monocyclic with no collective)

http://www.vortechonline.com/jets/gallery/grfx/Kestrel(orig).jpg
(has an actual cyclic stick, possible full cyclic control on this one)

http://tipjet.com/images/web_images/flyers/EMG-300_sml.jpg
(The actual emg 300 by Gluhareff. notice monocyclic handelbar controls and wide rotors and no real room for collective)

http://tipjet.com/images/web_images/flyers/gene-meg-2x.jpg
http://tipjet.com/images/web_images/flyers/MEG-1.jpg
(This would be fun to fly. NO COLLECTIVE and wide rotor blades)

These images show why I say what i say.

[Vance]

I was quoting from Irina Gluhareff’s web site on the EMG-300 tip jet helicopter.

Thank you, Vance

[brett s]

Nobody has said you can't build one like those designs you pointed out - only that they either won't work well or are outright dangerous :)

I wish there was a nice simple, cheap, practical helicopter - I'd own it! But there's no such thing, by their very nature they are mechanically complex. That means lots of careful engineering, or you've got a deathtrap with a million different ways to try & kill you (like the Mini 500).

[Sekse]

I swear u guys. I just ask about the rotors and get drawn into a debate on the physics of a tip jet heli, lol. As I said, not saying anyone is right or wrong. I just know in the pictures the only pitch control I see is a monocyclic. I plan to see how well I can build a tip jet heli with full collective and cyclic that works and is truly stable, and as cheap as possible. Never know, may build the world's first heli under 5 grand. I was just wanting info on the rotorblades so I don't screw up the most important part of the whole gizmo.

[Ga6riel]

Any truly successfull helicopter has had collective pitch - there are too many bad things with fixed pitch machines. Difficult to control altitude precisely in a hover, engine failure = crash...

One other huge problem with helicopters having hot cycle tipjets (in addition to fuel delivery problems & horrendous fuel burn which means about zero range) is how badly they affect the autorotational performance because of the added drag - the descent rates are far higher than a traditional design, like about 3x. That's partially offset by the added inertia making them more forgiving at the bottom, but you're still paying that drag penalty all the time. There is a reason you don't see those things around - there's no conspiracy, they just have too many issues to ever be practical.

what Brett states is entirely true, a study into the autorotative performance of EMG equiped tip jet helos proved conclusively that the autorotative performance suffered greatly, however, given a tip jet of considerably lower profile I see no reason why that couldnt significantly change for the better.

Just my wishlist view but....whats required is a tip jet of low profile that runs on easily available fuels ie gasoline.

[karlbamforth]

Sekse try looking at the tipjets on this link. http://www.ckaviation.co.uk/Tipjet.htm
Not all have large chord blades.
Most have flown, and most if not all have collective.

The first message at the bottom of this thread has a link to the Interfora Firebird. It apparently flies well, has small chord blades of 6" and collective.

I would be very careful with the plans that are on the market and research some of the more successful models such as the Djinn. The Interfora Firebird and Fairy Ultralight both flew extremely well.

I may be able to find info on blade chord for the djinn somewhere.

karl

[quadrirotor]

One of the best promising concept!

Think about it, how it could be easy and light!!!:

A Sub engine and a Low Pressure Composite Blower ! hummmm!

[Rotor Rooter]

Andre,

You're advancing the concept and the thread in the right direction. http://www.unicopter.com/ThumbsUp.gif

Root Turbofan Rotor (http://www.unicopter.com/0002.html)

[Victor Duarte]

Andre,
whatever high or low pressure, what you need is AIRFLOW and it must be about 1 KG/sec in a small helico.
Pressure/speed depend on the nozzle section, if you wan high eject speeds, you reduce the nozzle... big nozzles will give higher pressure, lower eject speed.

In your configuration i think you'd need high pressures, lower ejection speeds, more torque than with nozzles at the tip.

[Biggles]

I have a great deal of information to add to this discussion on jet tipped rotor blades. I do not know how to reply to threads in this forum so I will keep it short in case I am wasting my time typing stuff.

The most informative submission to this thread is from karlbamforth - thanking him for his information. Although some ultra simple helicopters have been built without collective this is not relevant to the discussion on the merrits or otherwise of the rotor drive system.

There several quite different types of jet tip drives, it would take me a huge number of pages to discuss each type so I will just touch on the two types which have been certified:

(a) The Djinn so called cold jet type ( not really cold jet since the process of compressing air to the necessary 30 to 40 PSI raises the temperature to around 140 degrees C.)

I have done the mathematics on the this system and the maximum efficiency is produced if the pressure is around 40 PSI giving a nozzle velocity just subsonic, the compressor output temp. is therefore at least 150 degrees C, this heat must be conserved so metal blades are not efficient.

The noise level is low because I think the wake speed is reduced by the rotor tip speed even though the nozzle velocity is just subsonic. As you would know there is no torque reaction and the resulting helicopter is extremely easy to fly. The best results are with large diameter rotors at low tip speeds about 450 Ft/Sec


(b) The Rotordyne system some call the hot jet type ( I call the reheat system where fuel is added to compressed air at the tips for extra thrust)
I do not have to space to go into this technology ( have designed and built reheat jet engines for this purpose)

The Rotordyne was the best heavy lift compound helicopter ever built but due to foolish decisions made by the British Government forcing the merging of at least three helicopter companies and subsequent indecisions by the resulting corporation all the Rotordyne orders were lost and the Rotordyne was totally reduced to scrap and the plans were ordered to be destroyed.

Frank Anders Dr. of La Fayette USA went to England in the late 1980's, spoke with the four key engineers who designed the Rotordyne and wrote the most authentic story about the Rotordyne. He was able to find a few surviving drawings including those of the jet tip engines.

I spoke to him in 1992 and asked him about the drawings but he had given them to Grouen Brothers. Grouen Brothers have just been awarded a $60M defence contract to build a compound helicopter using this Rotordyne technology they were given. (I HAVE NOW GIVEN YOU A WORLD FIRST OF THIS INFORMATION)

Sign - Robert Kelsall



Sekse try looking at the tipjets on this link. http://www.ckaviation.co.uk/Tipjet.htm
Not all have large chord blades.
Most have flown, and most if not all have collective.

The first message at the bottom of this thread has a link to the Interfora Firebird. It apparently flies well, has small chord blades of 6" and collective.

I would be very careful with the plans that are on the market and research some of the more successful models such as the Djinn. The Interfora Firebird and Fairy Ultralight both flew extremely well.

I may be able to find info on blade chord for the djinn somewhere.

karl

[Biggles]

I have a great deal of information to add to this discussion on jet tipped rotor blades. I do not know how to reply to threads in this forum so I will keep it short in case I am wasting my time typing stuff.

The most informative submission to this thread is from karlbamforth - thanking him for his information. Although some ultra simple helicopters have been built without collective this is not relevant to the discussion on the merits or otherwise of the rotor drive system.

There several quite different types of jet tip drives, it would take me a huge number of pages to discuss each type so I will just touch on the two types which have been certified:

(a) The Djinn so called cold jet type ( not really cold jet since the process of compressing air to the necessary 30 to 40 PSI raises the temperature to around 140 degrees C.)

I have done the mathematics on the this system and the maximum efficiency is produced if the pressure is around 40 PSI giving a nozzle velocity just subsonic, the compressor output temp. is therefore at least 150 degrees C, this heat must be conserved so metal blades are not efficient.

The noise level is low because I think the wake speed is reduced by the rotor tip speed even though the nozzle velocity is just subsonic. As you would know there is no torque reaction and the resulting helicopter is extremely easy to fly. The best results are with large diameter rotors at low tip speeds about 450 Ft/Sec

This an ideal type of helicopter for amateur building and would require about 2.2 pounds/sec. of air for a light two place aircraft.

(b) The Rotordyne system some call the hot jet type ( I call the reheat system where fuel is added to compressed air at the tips for extra thrust)
I do not have to space to go into this technology ( have designed and built reheat jet engines for this purpose)

The Rotordyne was the best heavy lift compound helicopter ever built but due to foolish decisions made by the British Government forcing the merging of at least three helicopter companies and subsequent indecisions by the resulting corporation, all the Rotordyne orders were lost and the Rotordyne was totally reduced to scrap and the plans were ordered to be destroyed. It is believed they valued this technology for the future.

Frank Anders Dr. of La Fayette USA went to England in the late 1980's, spoke with the four key engineers who designed the Rotordyne. He subsequently wrote the most authentic story about this great aircraft. He was able to find a few surviving drawings and was able to get copies including those of the jet tip engines.

I spoke to him at his home in 1992 and asked him about the drawings but he had given them to Groen Brothers (he wanted them for an American company). Groen Brothers have just been awarded a $60M defence contract to build a compound helicopter using this Rotordyne technology they were given. (I HAVE NOW GIVEN YOU A WORLD FIRST OF THIS INFORMATION)

Signed - Robert Kelsall (Biggles)

[Victor Duarte]

Robert,
thanks for this sum up, very enlighting indeed.
i have also been around tip jets as amateur and found your numbers too.
2.2 lbs.sec are enough for a 2 seater and, pratically, it can be achieved with a big supercharger, then the power consumption is about 35 KW.
I strongly believe that tip jets can make a valuable safety system for gyros as well as a powerfull prerotator.
I think you need less power for prerotation and partially powered flight.

Now, the hardest is to get in the design of the appropriate rotor...and for this, i think that a rigid 4 bladed rotor (like Chuck Beaty's one) is the best..

I hope someone gets involved in that design.

Thank you.

[Sita]

Sekse,
I have the plans for the Gluhareff back-pack tipjet helicopter and I can assure you that it has collective pitch change.

Cita

[Neil C.]

I think you are not understanding the principle of autorotation. Autorotation is rotor powered by aerodynamics/gravity. Powered rotor is by applying torque to a shaft. In the case of a tipjet, the force is applied from the rotors but the net effect is the same. To be as efficient in that mode as possible, the blades need to be twisted accordingly. I can't think of any tipjet that didn't Have collective pitch. A machine without would have some terrible control lags as you have to wait for the disk to accelerate or decelerate to change the ammount of lift generated. The drag from the tip jets would make them terribly inneficient in autorotation and to fly at a speed slower to reduce drag would require more blade pitch which would probably preclude autorotation all together. You can make a fixed pitch tipjet helo, but I sure wouldn't fly in it.
..This post caught my eye...years late..but ...Concerning autorotation of a tip-driven rotorcraft, one needs to keep in mind that it is probably better suited for this than a conventional rotorhead because the RPM decay would be less since there is no mainshaft, no tailshaft, no tranny gears to turn ..hence..greater autorotation time....agreed?

[brett s]

It's usually worse in steady state autorotation because of the extra drag caused by the tip jets themselves - so much higher rates of descent.

The tip jets can potentially increase the rotor inertia quite a bit because of the weight added at the blade tips, but you can do the same thing to a conventional rotor if desired. Like anything else, that's a tradeoff too...

[Ron Marlett]

No, I don't agree. Brett summed it up nicely. This has been studied long ago, and was probably one of the factors, along with terribly high fuel consumption, that helped doom the tip jet helo. You just can't make it as safe to fly because the autorotation is like a brick. A properly functioning gearbox without a load dosn't have all that much drag. In autorotation, what would the gearbox be powering? The first thing you do after/as you drop the collective to maintain rotor RPM, is to depress a tail rotor pedal fully(which one depends on your main blade rotation direction) to flatten out/depitch the tail rotor blades. No engine torque, no need for tailrotor pitch. So you are left with the aerodynamic drag of the relatively small depitched tailrotor blades cutting thru the air like a knife, and the drag of the bearings and some meshed gears in the system. This is far less than the drag from a un- powered tipjet being drug thru the air at the worst possible spot, out on the tip of a fast moving rotor blade.

Now advances in materials and technology may yet yield a low profile and reasonably fuel efficient jet that would fit into the rotor airfoil and not hamper rotor aerodynamics in flight or autorotation. Unfortunatly, it has been proven again and again that small nozzle/high pressure(jet/rocket engine) is less efficient than wide nozzle/low pressure(prop/rotor). It is like the difference in hover efficiency between a Harrier and a Helicopter. It can be made to work, but it is not typically the best way. The physics and economics are why the helo has evolved into what it is... I am all for a better moustrap, as long as it can catch mice:)

[karlbamforth]

What kind of tipjet you thinking of Ron ?

I agree if you have an engine on the blade tip it will generate a lot of drag but we are looking at ducted hot or cold air similar to the Djinn then I cannot see the drag being any greater than that you describe below for a conventional heli.
.

[Neil C.]

I read a post earlier that stated that there were two types of recognized pressurejets (as opposed to tip-jets). Correctly stated! There are not three ....by which the third would be a warm cycle as opposed to the hot and cold cycle, because it hasn't been successfully done...yet. I believe if you take a look at the Keller pressure-jet rotor head design, which is pressurized by twin turbofans ducted exhaust, this would be an example of the warm cycle.
You should also see that his design has autorotational advantages over other designs. There is, of course no tail rotor in his design. Short-span hollow blades (6-10 his patent covers), attached to a pressurized disk shaped plenum a canard up front and a ducted exhaust aft with directional control nozzle would complete a brief description. Has anyone studied the one being made in Europe with retractable blades that resembles the Keller pressure-jet design at first glance? The Keller system blades do not retract. For good reasons according to Merrill
Peace.