So you really truly want to build a better helicopter?

[Dave_Jackson]

So you want a rotorcraft configuration that has a future?
So you want a craft that is easy to fly and can popularize vertical flight?
So you want an arraignment where different companies in different countries can supply the different component assemblies?
So you want safety, reliability and low unit costs?
So you realize the advantages of the new Very-Light Rotorcraft category?
So you're a little skeptical about rotor-to-rotor vibration and yaw authority on the intermeshing configuration?
And, you're an intelligent, open-minded person, who is willing to contemplate all options.

http://www.unicopter.com/Temporary/1447-Small.gif

Then this web page is for your consideration. (http://www.unicopter.com/1447.html) :8


Dave

[slowrotor]

I really truly want to build a worse helicopter.

In performance that is. Hopefully better in terms of overall safety.

Speed kills is the old saying. Speed always costs much more as well.

Where are you going in such a hurry anyway?

Fast or slow, more designs are needed, so get busy. I would build a simple model using the small electric helo components that are available at hobby shops.
I can feel the vibrations in my model just holding it my hand and spinning around. You should make one with two rotors and see how bad it vibrates.

P.S. spinning around with a model in your hand makes you sick just like it did when you were a kid.

[Dave_Jackson]

Hi Slowrotor,

This particular interleaving helicopter is not intended for speed. It's indented for ease of piloting. -----> more pilots -----> more rentals ----> more craft -----> more production ----> lower cost & higher safety.

Yes, all 2-blade rotors when combined with any type of flap/teeter restriction (offset hinge, hub spring, etc.) will experience 2/rev vibration during horizontal flight, however, this craft has 3 blades.

A friend in Kelowna just built and hovered a simple model of the 3-blade Interleaving this week. He said that it had good stability, due to the precone in the two disks. Next week he wants to build a slightly more advanced model. :ok:

Dave

[Graviman]

Must admit to howling with frustration on reading this post! This means you are juggling three concepts, with a reduced chance of any seeing the light of day!!! :{


Please see the following in the constructive way in which the criticism is intended:


I'm afraid i really don't agree with a lot of the thoughts on this one. Lateral stability will be improved, but longitudinal stability will still need continous pilot input in hover - unless you build a 4 rotor version. Gyro augmentation (Lockheed) sounds much simpler, and really would work much better. You have introduced a drive shaft, with catastrophic consequences of failure - which could result from either gearbox or couplings. Cost and practicality (like hanger storage) become unreasonable.

Regarding aerodynamics, i really do see disadvantages over the intermesher. For a start the downwash velocity in interleaving region will definately not be additive, since downwash from one rotor reduces AOA on the other. You now have a pylon which causes both hover download and/or foward flight drag, even if you do put a nice NACA floating fairing on it (which limits the structural cross section). Retreating blade tip stall becomes an issue again, unless the "wing" is producing lift, as shown in:

http://www.unicopter.com/1372.html

Compared to the compactness of say an R22 (which would be a doddle to fly with lockheed gyro augmentation), or even Unicopter, this looks like Frankensteins monster! Sorry Dave, i just don't like it. :ugh:

I think you really do need to start to mock-up some of these ideas in 3D cad at least. Then you will start to see the packaging and structural headaches that you may be making for yourself. If i were a heli company, listening to a presentation, i would need to see some aerodynamic and structural simulations to convince me to back this design. Next you'll want to tilt the rotors ...


On further consideration: Dave I think what you need to do is to invest in 3D cad so you can play around with the crossover between intermesher and interleaver. I appreciate that you are trying to address concerns over rotor clash, but feel that you have probably gone too far in this concept. The advantage of a good 3D cad package is you can repostion rotors at will, until you feel the thing looks right. Then go on to the calculation/simulation stage.

Mart

[helmet fire]

Dave,
I think it is exciting that rotorcraft design is still being looked at, and I hope that one day we get the holy grail: cheap safe relieble rotory wing (or at least VTOL) vehicles.

Last time we went through this design, I raised the following point: Your concept seems to rely very heavily on the advantages of an (almost) "Absolutely Ridgid Rotor" in that lead lag, flapping, etc are issues that can be done away with to leave a simple, easily controlled and stable machine - and this is where we differ.

Lead/lag and flapping play important parts in the stability of a rotor system: They actually aide stability, but as you point out, they add complexity and thus cost.

Firstly, The ridgidity of the system you are talking about is very unlikely to be achievable given the complexity of metallurgy/composite technology that needs to be developed in order to provide the kind of ridgidity Vs weight ratios required.

Secondly, the gyroscopic precession involved here in forward flight will be of such significant force as to require a tremendous leap in structural technology. As none of these forces are absorbed aerodynamically, the considerable lift generated on each advancing blade will cause a considerable gyroscopic precession. I note that you believe the contra rotating properties of your design will allow these forces to cancell each other out. that you pass off as cancelling each other out, and this is where I suggest a re-evaluation.

Accepting for a moment that the issues of the retreating blade dont exist,(as you believe they will become irrelevant with a ridgid system) it can be said that the advancing blade will generate nearly all the lift. Due to the ridgidity, flapping to equality will not occur, thus there will be a large upward force on the rotors on the advancing side. As your design depicts the outboard sections as advancing, the two lift forces will be produced on the outboard side of the aircraft in forward flight.

Each rotor willl induce a large gyroscopically precessed force 90 degrees later in the direction of rotation. If we look at your design, we see that each rotor will impart that force on the front of the aircraft, so they are not opposite at all, but in fact "gang up". Each will impart a stong force on the mast in one direction, which will in-turn require a significant structural ridgidity within the drive shafts, gearboxes, shaft mounting systems and cross member structure to avoid it simply ripping the aircraft apart. That is if it gets fast enough to avoid the forces so interrupting the longtitudanal C of G sensitivities in the first place.

But, I think it is only through such dreams that we will ever progress, and if the attributes you desire here can be somehow used by overcoming the negatives, WOW! That will be a beast I want to fly, so get a wriggle on and make it happen Dave!

[Graviman]

"But, I think it is only through such dreams that we will ever progress ... so get a wriggle on and make it happen Dave!"

I agree wholeheartily with the sentiment. My frustration comes from the way in which rather than converging on a single ultimate design, the concept seems to be spouting ever more variations! This is why i strongly suggest 3D cad, to bottom out the design. I am begining to see Nick Lappos' frustration - sorry Dave. :uhoh:


"Lead/lag and flapping play important parts in the stability of a rotor system: They actually aide stability, but as you point out, they add complexity and thus cost."

This is a point i have frequently put across. The tri-teetering hub is extremely clever, and i feel it deserves to see the light of day. But, to obtain the optimum performance the hub eventually has to become rigid, which means lead-lag. Dave has some good ideas for dealing with coriolis force, and i have suggested some lines of thought - attempting to keep blade centroid equidistant to hub axis. You still need lead-lag (ideally compliant hysteretic elastomeric bush, for soft centreing and damping) to keep the blade angular separation constant, otherwise you risk manouvreing vibrations.

Mart

[Flingwing207]

Hi Dave,

I've been following your unicopter concept and all the collected ideas on your website for some time. I share the observations made in the preceding posts. I offer a suggestion: build a scale R/C flying model. R/C helicopters offer pretty much an "absolutely rigid rotor", and could provide an initial proof-of-concept for the viability of your basic ideas. Barring that, you could show folks more than just some cryptic line drawings which basically leave EVERYTHING important up to the viewer's imagination. Heck, I'm not sure which way you plan to spin those rotors, so I imagine you would have the blades over the cabin advancing - that way they would flap up and away from the airframe?

Beyond the rotor design, you have some other issues to solve. How do you deliver the power to the rotors? Will there be 90-deg gearboxes in the nacelles, or will you use some kind of belt or chain drive? How will control inputs be made - cables, pushrods and bellcranks, hydraulic? What will the pylons look like, how will you design them to have the required strength without imposing undue drag? How will you shield the passenger compartment from rotor-blade intrusion in an extreme event? How will you package the engine/fuel/luggage for weight and balance?

Lots of folks have said already that you seem to have a design in search of a mission, and it is a design which is largely theoretical. Perhaps you are going to surprise us all, but I'd be happy to see a model with moving parts rather than a constant barrage of enigmatic and semi-decipherable drawings.

I applaud your enthusiasm and tenacity. Now, how about something tangible?

[Dave_Jackson]

Graviman, "Must admit to howling with frustration on reading this post! This means you are juggling three concepts, with a reduced chance of any seeing the light of day!!! " How cruel. :D

All the primary concepts have a strong commonality of objective. The ultimate objectives being 'easy of piloting' and 'faster forward flight'. Many of the sub concepts have a commonality of application. For instance, the different rotor concepts can be applied to the different rotor configurations. IMHO, the best chance of "seeing the light of day" is by finding the route that shows the best light at the end of the tunnel.

Actually, the first item that must be built is the CNC router / filament-winder (http://www.unicopter.com/B438.html ) , for producing blades. It is intended that this machine have the ability to produce any of the proposed blades for any of the proposed concepts. "Lateral stability will be improved, but longitudinal stability will still need continous pilot input in hover - unless you build a 4 rotor version." Yes the Interleaving configuration should have better lateral stability than the Interleaving. Why is the longitudinal hovering stability singled out for continuous pilot input and how will 4 rotors help? I think you really do need to start to mock-up some of these ideas in 3D cad at least. 3D cad would be nice. The current method is that of producing a full size mockup, refining the detail on items as required and eventually replacing the items with the real thing.


Helmet fire & Flingwing 207

Thanks for the comments. I would like to fully consider the points you are bringing up before rushing to respond.


Dave

[Graviman]

"...The ultimate objectives being 'easy of piloting' and 'faster forward flight'... finding the route that shows the best light at the end of the tunnel."

OK i do see this, but at times i'm convinced the tail is wagging the dog. The only justification for the complexity of intermesher/interleaver, to my mind, is the possibility of an efficient downwash pattern in all regimes of flight - thus better fuel consumption. Having flown an R22, i can safely say that the only real problem from a (heli novice) pilots point of view is hovering - this is easily cured with the Lockheed gyro augmentation system (or more piloting experience :} ). At £250 an hour, i shudder to think how much the above machine would cost for a fun run - especially since it wouldn't be that good on fuel...


"Actually, the first item that must be built is the CNC router / filament-winder , for producing blades..."

OK, but again the complexity of IRAT control does show my point. In engineering you have to justify complexity in performance gains, this is why i suggested the tip flap blade AOA optimisation. This does not limit you to this approach, but it does give you a good economic start.


"Why is the longitudinal hovering stability singled out for continuous pilot input and how will 4 rotors help?"

In hover i don't see that the horizontal tailplane will make much difference. A rear rotor would respond more to any longitudinal air velocity. Again, the point i was really trying to make is that a gyro augmentation system is a much more practical approach - anyhow i thought you were keen on gyro dynamics, having read the intermesher thread...


"3D cad ... current method is that of producing a full size mockup ... eventually replacing the items with the real thing"

To me it sounds like the long way around. The company i (now) work for has just made the step to 3D - i don't think they will ever go back to 2D! The advantage is you can throw away concept you don't like, or just play around with them until you are happy - ideal for positioning rotor and drive assys when package space is tight. It will make your life much easier when you do the stress analysis, since hand calcs really don't catch all the stress raisers. There are even methods of simulating the dynamics - but it is easy to get carried away...

Mart

[Dave_Jackson]

Thank guys for the comments and suggestions

helmet fire

You're correct in that a craft with twin counterrotating main rotors, which are close to absolute rigidity, is a challenging project. There are many places to stumble and you have mentioned a few of them. The good news is that this is not just a crazy idea on my part. The Sikorsky ~ XH-59A ABC (http://www.unicopter.com/0891.html) had very rigid coaxial rotors and it utilized an advancing blade concept.

Many years ago Paul Cantrell made the following statement " "I know the ABC is currently shelved, but I hope that it will started up again. I wonder whether intermeshing wouldn't work better - perhaps Sikorsky didn't want to have to deal with Kaman? I don't really know why they picked coaxial rather than intermeshing..."

This is not the time to get into too much detail but one example might be interesting. You've mentioned a valid concern about strength and the resulting weight. When Sikorsky built the blades for the ABC they used a titanium spar because 30 years ago they were not willing to trust carbon composite construction. Today the lighter and stronger composite spar is becoming the norm.

Most of the ideas in the Unicopter are from the brains of others. I am attempting to unify these ideas in a single craft.

Flingwing207,

The R/C approach is a certainly a valid one. It was considered when the SynchroLite was being developed and then rejected because at a maximum weight of 254 lbs. the full size helicopter wasn't too much heavier than an R/C. :D

The Interleaving helicopter in the first post is to be mechanically similar to the tiltrotor, except that this one does not tilt. The intent of this thread is to present a concept for a very-light and easy-to-fly rotor craft in the hope that it might stimulate ideas and motivation in others.


Dave

[Graviman]

"When Sikorsky built the blades for the ABC they used a titanium spar because 30 years ago they were not willing to trust carbon composite construction."

Dave, you might seriously schedule in a visit to a wind farm. The large, ideally rigid, blades present similar difficulties. Although composite, they seem to abandon NACA profiles near the hub using a near cylindrical cross section. There in one near me, i could take photos...

Mart

[Dave_Jackson]

Mart,

For the spar, a cylindrical cross-section at the root, changing to an oval, and then to a flattened shape at the tip looks like the optimal design.

It allows the carbon tow to be laid spanwise in straight lines, for maximum bending strenth and minimum twist resistance.

In addition, blade twist causes very little differential length change between the individual tows.

This page has pictures, drawings and calculations on the above. (http://www.unicopter.com/0932.html)

Dave

[Graviman]

Had a look at you pages at lunchtime, Dave. Yes i can see what you mean about section - this probably gives about the most rigid structure possible. I am still concerned about active blade twist, since so far all you have are mockups. If i understand your concept, the root will end up with two concentric flanges - inner for tip, outer for root. The two swash plates will then tie up to the seperate flanges.

You will need to come up with a better swash design than the sketch in http://www.unicopter.com/1363.html , since clearly there would be clash here. I suggest a concentric swashplate design. Being honest i really feel you are jumping a step here, and should prove out blade flexure with fixed tip tabs first - especially from a fatigue point of view. With full IRAT control you will be spending a lot of effort developing the control system, before the blades have proven themselves.

Overall, i think i see what you are trying to do. The first effort is to design the rotor blades and hub, to prove this out. Then you will move on to the control system, to prove this out. Once these are shown to be viable then the choice of helicopter design is made. For my money, concentrate on the Unicopter layout (although ideally bigger - say 2 people in tandem: pupil + instructor). This really does offer the most perfomance gains for the additional complexity - especially if rotor gyro augmented. I would seriously just use the Synchrolite concept as a step to Unicopter, and drop the above concept - this really feels to me like the best engineering solution...

Mart

[Dave_Jackson]

Mart,

Your understanding of the root is correct. Root End Layout (http://www.unicopter.com/1353.html)

Here is one idea for a 2/rev blade root control (http://www.unicopter.com/Swishring.html) :8

You are also correct in suggesting that the current emphasis should be on the Independent Root & Tip blade; and in particular the characteristics of its spar and torque-tube.

Two of us are getting together later today to discuss the building of this blade and the CNC machine that will be necessary to produce its components. We think that if the IRAT blade doesn't work, we still have a machine that can make blades for rotorcraft that are; in the Very-Light category, have 2 main rotors, and 3 blades per rotor.

Dave

[Graviman]

"Here is one idea for a 2/rev blade root control"

Way way too complicated! Prove out the basic concept of blade twist first. Twin swash plates will be hard enough to package, especially in 2D. I think servo trimming, with 1P mechanical, makes more sense anyway - what if the aircraft suffers total electrical failure, from say a solonoid jamming? Anyhow would you subcontract the control system to DARPA or NASA, to get the blade cyclic AOA to match CFD streamline predictions? :uhoh:

You were a powertrains man, and must have seen a few modes of failure in your time - something about keeping it simple. Bladetwist could, as an example, introduce unwanted flutter due to the need to keep stiffness down. The reverse flow region could cause divergence. The circular root may prove to be unbeliebably draggy. The dreaded coriolis monster is always lurking. I understand where you are going, but just suggest a very methodological approach.

Still, good luck getting the IRAT blade to work. :ok:

Mart