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View Full Version : Flight tests of a Mono Tiltrotor (MTR)


gdbaldw
23rd Nov 2010, 02:38
I've lurked. And now I'm putting this video out for come what may. Constructive comments welcomed. We're testing at a scale that our current funding supports.

vBfW4mbrodA

gdbaldw
23rd Nov 2010, 10:48
@cattletruck: The aircraft has pitchlinks/swashplates to beat air into submission. Look closely and you will see the coaxial swashplates. Thank you for viewing and commenting.

John R81
23rd Nov 2010, 11:46
Very interesting.

Do you have anything written (or a patent application) that would detail how the rotor works? The blades seem in the video to have elements of propeller and rotor design. Is the head constant speed or variable?

gdbaldw
23rd Nov 2010, 12:22
@John R81: Yes, conference papers summarizing restricted access technical reports are available. Design has constant RPM in heli mode, and reduction to 84% of hover RPM for airplane mode cruise. Proprotor twist is similar to V-22/XV-15, with slight vairiation at lower rotor to account for upper rotor's wake. See bottom of http://www.baldwintechnology.com/deepdive.html for the documentation.

Agaricus bisporus
23rd Nov 2010, 12:26
John, look at the end of the video, a whole list of patent applications...

gdbaldw
23rd Nov 2010, 12:51
@John R81: The design has a constant RPM in heli mode, and 84% of hover RPM in airplane mode. Blade twist is similar to V-22/XV-15, with a slightly modified lower rotor blade to account for the upper rotor's wake. Documents are available on our website. You'll see the link in a subsequent post, when the forum moderator approves. Thank you for your comments.

John R81
23rd Nov 2010, 13:44
Thx

Will do that. When I watched the video it hit "an error ocurred" before the end. Still can't get the end to play. Back in UK (hopefully) tonight and off the mobile connection!

Rigga
23rd Nov 2010, 20:25
Hi gdbaldw,

I'd guess your model to be about 4ft wing span.

Do the wings rise/lower under "lift" or are they powered up/down? (I believe that would cause a major power drain when you most need it)

How do you (can you) balance the wings when transiting?

What do you recon the wing lift/weight ratio to be? I think that would be the main ratio to make this cost effective.

I assume you controls are based on Kamov designs?

Just a nosey
Rigga

gdbaldw
23rd Nov 2010, 23:23
@Rigga: Nosey is fine by me. Let's see if I can answer.

>I'd guess your model to be about 4ft wing span.
Pretty good guess. Wing span is 5ft and rotor blades are 550mm diameter.

>Do the wings rise/lower under "lift" or are they powered up/down? (I >believe that would cause a major power drain when you most need it)
You are correct, they lift themselves so no power drain.

>How do you (can you) balance the wings when transiting?
CG is correctly positioned at the mast in hover and at the wing quarter chord in airplane mode. You'll notice that the gearbox/motor move aft and under the wing during conversion. When fully deployed, the wing actually behaves like a large horizontal stabilizer in helo mode.

>What do you recon the wing lift/weight ratio to be? I think that would be
>the main ratio to make this cost effective.
In helo mode, has basically the same weight fraction as a helicopter, less the added weight of the wings which is slightly under 10% of gross weight. In airplane mode, a cleaned-up fuselage and appropriate wing together have an aerodynamic L/D of about 10, and with the proprotor propulsive efficiency in the neighborhood of 75-85% yields an Lift/Drag effective of better than 7. Studies show breakthrough range and speed while still having helo agility, for design scales up to heavy lift.

>I assume you controls are based on Kamov designs?
The small functional demonstrator has upper and lower swashplates linked, and a differential collective rod up the hollow shaft for the upper head only. Our target performance demonstrator design has independent upper and lower shashplates, with control rods for the upper swashplate inside a standpipe and controlling from above the upper head. Kamov is different from both these designs, with upper and lower swash plates linked together like our small model, but a more complex arrangement for differential collective that affects both upper and lower rotors equally.

Doug

IFMU
24th Nov 2010, 12:35
Nice work!

IFMU

John R81
25th Nov 2010, 11:10
So, given we have helicopters and the Osprey, what is your USP?

The mono design is fantastic engineering, but can your design offer something not covered by either helicopters or conventional tilt rotors?

I can see potential disadvantages compared to the osprey - central location of the tilt mechanism makes locating the pilot interesting, the twin rotor is more complex engineering than the osprey - but not clear to me the advantages. Do you think it will be cheaper, or have more lift capacity, or less maintenance?

gdbaldw
25th Nov 2010, 13:34
Hi John,

> So, given we have helicopters and the Osprey, what is your USP?

Unique selling point (USP) is a the combination of range AND speed AND vertical agility, ALL on the same mission. Design studies have concluded this aircraft is 1/2 the size, 1/3 the weight, 1/3 the fuel of conventional helicopters for long range missions. The structure is basically a helicopter with the added weight of a wing. This added weight more than pays for itself in increased range. The basic total gross weight metrics are 1/2 structure, 1/6 fuel, and 1/3 payload for a long range (750nm to 1000nm, 200 knots to 260 knots cruise at 20,000 ft) mission.

> The mono design is fantastic engineering, but can your design offer something not covered by either helicopters or conventional tilt rotors?

This project started in 2004 with a conceptual study that concluded the design would have fantastic performance if technically feasible, see http://www.baldwintechnology.com/FY04_MTR_Conceptual_Design_Report.pdf
This was followed by a conceptual/preliminary point design reaching the same conclusions, see http://www.baldwintechnology.com/MTR_AHS_Jan07.pdf and http://www.baldwintechnology.com/MTR_AHS_08.pdf .

> I can see potential disadvantages compared to the osprey - central location of the tilt mechanism makes locating the pilot interesting, the twin rotor is more complex engineering than the osprey - but not clear to me the advantages. Do you think it will be cheaper, or have more lift capacity, or less maintenance?

Pilot location becomes easier at larger scales. My preference is out front in helo mode for excellent field of view, which places the pilot below the gearbox in airplane mode and requires sensors for topside situational awareness. This also requires a swivel seat which is doable, but I'm very concerned about proximity to turbine burst. That's why larger scale makes this more practical.

Let's try to avoid a riot, as comparisons of helicopters can become an emotional topic. I think a fair assessment would conclude that the Osprey's a pair of cross coupled, wingtip mounted tiltrotors are significantly more complex than a coaxial helicopter. When you add-in the wing structure and actuators to support the wingtip gyroscopic forces and the cross coupled gearboxes for one engine inoperative, you have a rather complex and weighty subsystem. By comparison, coaxial helicopters cancel the gyroscopic forces within the rotor shaft and have just one gearbox with no added weight for one engine inoperative.

In answer to your question, cheaper and more lift capacity for long range missions is a direct result of the conceptual and preliminary design study conclusions referenced above. Of course, if the mission is predominantly vertical lift with limited range and speed, then nothing will ever beat a pure helicopter. Note that this mono tiltrotor design could self deploy and then the wings could be removed for overweight maximum vertical lift capability.

Regarding maintenance costs, industry leaders have speculated that maintenance costs are correlated with vibration which of course is reduced in airplane mode. I've seen no evidence to support this, and the Osprey does not bear this out likely due to the rotor drive complexity discussed above and the harsh desert environment.

Maintenance cost is also correlated with component access. This design exposes most all subsystems to a single level deep maintenance repair action.

Hope I've addressed your questions in the way you had intended.

Doug

John R81
25th Nov 2010, 16:27
I'm sold - aside from the pilot seat. Would love to see the full scale.

John

glum
25th Nov 2010, 22:34
I'm part of this year's intake at Cranfield in the UK studying aircraft design, and we're looking an 8 seat tiltrotor aimed at the corporate, SAR and offshore rig market.

It's at the early stages of design, but the number one risk of the project is mass, and keeping it low enough to achieve a sensible payload. With an AUW of 7500kg, we have a payload of 2500kg. Not great when compared to some of the pure helicopters in that range!

Range of 750nm, ceiling of 25,000 feet and cruise of mach 0.55.

Big problem is as you say the extra stuff required for two engines hung on the wingtips, with the OEI shaft and linkages. It's very unlikely we'll meet the EASA requirements for climb under OEI conditions - as I understand it, the Bell609 isn't capable yet either.

Your project looks very interesting in comparison!

Are you looking to certify in CS 25 and CS 29? One of our problems is that a tiltrotor doesn't fit anywhere, so we spend hours trawling the documents for gotcha's!

How big will the final aircraft be (I see a figure of 9,400lbs - is this the final plan or will you go bigger once the concept is proven)?

Does there need to be a pilot at all, and if so, does he really need to be sitting where he can see the load, but have to suffer a swiveling cockpit and the fear of rotorbust, when perhaps he could sit further back out the way and let CCTV be his eyes?

Can you land in conventional aircraft mode, or does it have to be helicopter?

I'm sure there will be many more questions after I've read the info fully!

Best of luck.

Glum.

212man
26th Nov 2010, 10:56
With an AUW of 7500kg, we have a payload of 2500kg. Not great when compared to some of the pure helicopters in that range!

Do you mean 'payload' (i.e. fuel is already accounted for) or 'disposable load' (payload plus fuel)? Ballpark figures for 2 or 3 types in the 5-9T range I know of give disposable loads of around 33% of MTOM - which is the figure you come up with for payload. So, if true payload then your figure would seem good but if not it would still seem reasonable given the performance benefits over a true helicopter.

Are you looking to certify in CS 25 and CS 29? One of our problems is that a tiltrotor doesn't fit anywhere, so we spend hours trawling the documents for gotcha's!

What's the plan for the AW609 certification basis - seems daft to reinvent the wheel? I don't think anything exists at present, but I believe the plan is for a kind of blended Part 23,25,27,29 solution giving a new category of "Powered Lift."

gdbaldw
26th Nov 2010, 13:31
@glum

Regarding your design...

With an AUW of 7500kg, we have a payload of 2500kg. Not great when compared to some of the pure helicopters in that range!

I agree with 212man that these seem optimistic. In general, I find historic structural weight of aircraft to be roughly 1/3 for fixed wing and 1/2 for rotary wing, +/-. The remaining 2/3 and 1/2 is fuel plus payload. Any performance projections significantly better are usually based on stripped down aircraft, or expections of some future breakthrough in materials or engines. All our work is done at current, off-the-shelf, component and subsystem technology levels to enable an apples-to-apples comparison.

Range of 750nm, ceiling of 25,000 feet and cruise of mach 0.55.

Range and ceiling are what one would expect for a tiltrotor, but cruise mach seems optimistic. Physics caps efficient fixed diameter proprotor aircraft speed in the neighborhood of 200kts to 260kts. Squared/cubed law pushes cruise speed higher for heavier aircraft, but for 7500kg would be closer to 200kts.

A methodology for sizing rotorcraft was developed and reported in the following U.S. Government report, http://www.baldwintechnology.com/FY04_MTR_Conceptual_Design_Report.pdf , and was implemented in a MATLAB program.

Are you looking to certify in CS 25 and CS 29?

Actually, I'm looking to develop a community of overwhelming support that motivates action towards a sustained U.S. Government development program. I've been successful so far with cadres of support in the US Army, Marines, DoD, and Congress which pays the bills on a year-to-year basis. Seems to me a military demonstrator preceeds civil certification.

How big will the final aircraft be?

Our initial concept studies in 2004 spanned from 2ton to 20ton payload. We then created a conceptual/preliminary point design at 3000 lbs payload (9400 lbs gross weight), and have developed a lot of engineering and CONOPS data on this design. We're currently flight testing at 10-15 pounds.

Does there need to be a pilot at all, and if so, does he really need to be sitting where he can see the load?

Depending on the aircraft's application and the maturation of autonomy, a piloted configuration could likely be needed. For weight and balance a cockpit is best located forward of the mast in hover, particularly for smaller configurations where the pilot's weight impacts balance. On the other hand, the U.S. Marines are testing unmanned cargo helicopters, and the U.S. Navy is testing the VTUAV. Pilot location is less critical if tasks are more managerial than hands on sticks. To cover all our bases, we've began working with acedemia on some tremendous breakthroughs in helicopter autonomy.

Can you land in conventional aircraft mode, or does it have to be helicopter?

The design has tail dragger landing gear configuration on the airframe. We will likely test forward flight horizontal landing with the mast vertical using our small RC functional flight demonstrator.

I'm sure there will be many more questions after I've read the info fully! Best of luck.

Thanks. Anytime.

Doug

Graviman
3rd Dec 2010, 11:53
I became aware of the MTR on reading a paper by Leishman. It is an interesting concept because it overcomes the disk loading limitations of a conventional tilt-rotor for a given landing area. The swing wing could add a lot of complication (read weight) when it is notable that "fixed" wing have moved away from swing wings. There are still the concerns over autorotation during transition, when the rotor is inclined forwards but the wings are not flying. At least there is only one rotor system which could be subject to VRS.

What type of role is envisaged for the machine other than cargo?
I ask because cargo seems to be less restrictive on aircraft planform size.

Mart

gdbaldw
3rd Dec 2010, 18:29
@Graviman


I became aware of the MTR on reading a paper by Leishman.


Yes, Dr. Leishman lead the initial study in 2004 that concluded the MTR, if ultimately found to be technically feasible, would be half the size, 1/3 the weight, and 1/3 the fuel burn compared to convention helicopters for long range (750nm to 1000nm) missions. In 2005-2006, he performed the fundamental aerodynamic analysis and efficient performance design of the coaxial proprotor blade planform.


It is an interesting concept because it overcomes the disk loading limitations of a conventional tilt-rotor for a given landing area.


Yes, the single MTR rotor design has twice the disk area compared to a conventional wingtip mounted dual tiltrotor for the same tip-to-tip clearance when viewed from above in hover. Dr. Leichman concluded the effective disk area benefit is even greater, because the coaxial is best analyzed as two interfering rotors which results in an effective disk area closer to the sum of the two independent rotors.


The swing wing could add a lot of complication (read weight) when it is notable that "fixed" wing have moved away from swing wings.


No, its not a swing wing. A swing wing rotates about its yaw axis, pivots on a short titanium pin, and has a powerful actuator to overcome aerodynamic and mechanical forces.

The MTR's hinged wing has relatively insignificant additional weight when compared to a conventional wing. The hinge extends from leading edge to trailing edge; the wing's inboard spar extends outboard of the hinge to serve as a "doorstop" and to connect with the outboard spar after the wing fully deploys. Wing deployment is effected by aerodynamic forces and so adds no weight. Engineering analysis of our full scale design reveals additional weight only for the hinge along one wing rib and for a zero insertion force latching mechanism to connect the inner and outer spars. For our flight demonstrator, we built both conventional and hinged wings, and the weight difference is insignificant.


There are still the concerns over autorotation during transition, when the rotor is inclined forwards but the wings are not flying.


This aircraft design is most stable at a 45 degree conversion angle. This statement does not directly answer your concern, but it does indicate an interesting feature of the flight envelope that can be explored for powered off behavior. The MTR design places the CG forward of the wing leading edge in helicopter mode, and underneath the wing quarter-chord in airplane mode. At 45 degrees, half the GW is carried by the rotor and half by the wing which acts as a large horizontal stabilizer just aft of the aircraft CG. The rotor at this 45 degree tilt condition is essentially neutrally stable in pitch and so in combination the stabilizing wing results in a stable aircraft configuration. Yes, we have some work to do to develop a complete answer regarding autorotation, which is planned for both our functional demonstrator and in computer simulation.

At least there is only one rotor system which could be subject to VRS.


True, the value of which should not be underestimated.

What type of role is envisaged for the machine other than cargo?
I ask because cargo seems to be less restrictive on aircraft planform size.


I think it reasonable to envision all roles performed by vertical lift aircraft at all scales, manned or unmanned. I personally have focused on pure technical efficacy, and have so far been influenced by my customers to primarily tailor the design for cargo. The video at Post#1 indicates a JMR attack role.

Doug

Graviman
15th Dec 2010, 11:46
Apologies for slow response, Doug - put this down to my being off with flu...

Thanks for providing answers that demonstrate that a lot of thought has gone into this concept. Agreed about the lack of need of heavy hydraulics for the hinged wing - clever in concept by way of minimising complexity for a given advantage. Don't underestimate the potential requirement for complex hydraulic accumulators to power rotor mast tilt actuators though: I am of course thinking about the need to recover from engine failure during transition, which would require a quick and absolutely failsafe reaction.

Out of interest, what sort of assumptions are you making about structural loads: g loads, gust loads, pitch and roll rates etc? This interests me because you will need to consider both helicopter mode and fixed wing load - apart from the difference in forward speed i assume the loading performance envelope will look similar (at least during transition). Are there any particular control aspects that will need significant deviation from the stick and lever control? Does the lever simply become a prop pitch control in forward flight? Also are you seeking to minimise any flapback forces on the rotor during operation above transition?

As you gather from the X2 thread, i am fascinated with pioneering aviation projects. It goes without saying that i wish you well with your endeavours.

Mart

Shawn Coyle
15th Dec 2010, 15:34
Aside from being impressed with the concept, the level of technical discussion on this thread is impressive and indicative of what pprune can be all about.

gdbaldw
16th Dec 2010, 23:49
@Graviman

Apologies for slow response Doug - put this down to my being off with flu...

Hope you are feeling better.

Don't underestimate the potential requirement for complex hydraulic accumulators to power rotor mast tilt actuators though. I am of course thinking about the need to recover from engine failure during transition which would require a quick and absolutely failsafe reaction.

While longitudinal stability is greatest at a 45-degree mast tilt angle as discussed earlier, this trimmed flight condition also has zero load on the conversion actuator. To understand this behavior, first think of hover in which the tilt actuator must push the tailboom up to horizontal. Then think of cruise in which the tilt actuator must pull the gearbox and engines underneath the wing. At some point during conversion the actuator will have zero load as it crosses over from pushing to pulling, and a static stability analysis reveals that this point is in the neighborhood of a 45-degree conversion angle. So, if the conversion actuator were to completely fail in forward flight, static trim analysis indicates that the aircraft would tend towards a stable flight condition at a 45-degree tilt angle. Again, this doesn't fully address your concern, nor does it address dynamic stability, but it does provide a good starting point for failure mode/autorotation analysis and flight testing.

what sort of assumptions are you making about structural loads?

We developed a set of V-n diagrams based on representative military certification limits for helicopters and fixed-wing aircraft in the cargo/utility class. These diagrams were then augmented in order to meet the agility requirements for cargo/utility class aircraft and gust load requirements. I have more detail in a restricted access report produced under subcontract by Army Research Labs. While it is my intent to openly publish all data from our work, this particular data never quite made it into a publicly released conference paper.

Are there any particular control aspects that will need significant deviation from the stick and lever control? Does the lever simply become a prop pitch control in forward flight?

The 1:10 scale functional flight demonstrator controls work as follows. The rotor has 3-axis angular rate stabilization so that stick inputs generate pitch/roll/yaw moments in the reference frame of the rotor (in the RC world this is known as CCPM flybarless electronic stabilization). During a 90-degree conversion we swap rotor roll and yaw controls in proportion to the conversion angle (both conversion and swap are controlled by the same knob on our transmitter). Other than that, all controls are as you would expect of a fixed wing airplane. We increase collective in airplane mode for increased cruise speed, but so far have not found any need to lock out rotor cyclic or pedal while in airplane mode. Of course, XV-15 (and I suppose V-22) phase out cyclic during conversion and we could do the same if appropriate.

Also are you seeking to minimise any flapback forces on the rotor during operation above transition?

I had been warned that flapback could be an issue during conversion of our 1:10 scale model, but no. The pilot reported that in forward flight the aircraft handled like a conventional airplane at all mast angles. As you may have noticed in the flight video, we performed conversion while in a banked turn. Our mid-sized MTR Scaled Demonstrator (9400 lbs GW) has a rigid unarticulated hub design, but larger designs will likely require an articulated rotor and thus need a control schedule to fly the rotor into axial inflow airplane mode.

@Shawn Coyle
Thank you sir for your kind observation.

gdbaldw
17th May 2011, 13:54
Vertiflite Magazine (of the American Helicopter Society) - Summer 2011 - has an illustrated feature article on the Mono Tiltrotor (MTR), available here (http://www.baldwintechnology.com/VertifliteSummer2011.pdf) .

Lonewolf_50
17th May 2011, 14:18
Doug, much obliged for the update. You folks are doing some wonderful stuff, hope the funding/investment stream can be found.

Advantage over the unmanned KMAX (for a maritime VERTREP mission) appears to be speed. How does payload comparison stack up, (if you can say) at this point? :confused:

pba_target
17th May 2011, 19:44
looks like a good concept to my mind. Interesting article and great to see the scale demonstrator actually flying.

The things that spring to my mind are failure modes. Whilst someone has already brought up a total loss of power in the transition to forward flight, which would be an area of concern, what about the tilt actuators failing in the forward flight configuration? I would imagine that would make the landing somewhat tasty? (As an aside, how does the osprey deal with a landing in "plane" mode?)

Also, whilst you say the aircraft has a fairly good lift/drag ratio, how well do you think it will glide in the forward flight configuration with the proprotor dangling out the front?

Anyhow, best of luck with the project, early day, but I hope someone provides the cash to look at it further, as it looks interesting!

gdbaldw
19th May 2011, 16:15
@Lonewolf_50

...hope the funding/investment stream can be found.

While staying under the radar screen over the past few years, all studies and functional flight demonstrations were paid through small Government R&D contracts. However, as is highlighted in the Vertiflite article, DoD policy effectively restricts available prototype funds to Government contractor controlled IR&D, otherwise known as Government dollars paid as an overhead line item on production contracts. As you might expect, producer's interests are not necessarily aligned with this project.

Advantage over the unmanned KMAX (for a maritime VERTREP mission) appears to be speed. How does payload comparison stack up, (if you can say) at this point?

An initial study performed in 2004 shows the advantage increases with mission radius. For up and down missions, nothing beats helicopter, be it intermeshing, coaxial, dual, or with tail rotor. When range is needed, helicopters burn more fuel and transport less payload than this design. Specific performance numbers are in the Gov't reports on our website.

@pba_target

...what about the tilt actuators failing in the forward flight configuration?

My 3 DEC post touches on this; the actuator caries no load at approximately 45 degrees tilt in trimmed forward flight. We've actually experienced this in-flight failure mode. Early in our functional tests of a small RC demonstrator we had a structural failure resulting in complete loss of the conversion servo, and loss of one swashplate servo. Remarkably, the RC pilot was able to fly in to a flaired landing. Fixed wing controls in forward flight compensated for partial loss of rotor controls, and the powered rotor was able to soften the landing.

(As an aside, how does the osprey deal with a landing in "plane" mode?)

As I understand, the Osprey operational procedure for total power loss is a conventional airplane mode glide landing, with rotors destroyed on impact and theoretically the blade fragments being tossed away from the aircraft. Obviously, this has yet to be tested or demonstrated.

I hope someone provides the cash to look at it further...

A very senior Government official initiated an effort to do just that. Unfortunately, the rotorcraft pre-acquisition train is carried by production inertia. has no central leadership, and its prototypes are funded through producer IR&D (undirected Government overhead dollars).

Doug