US shelves new advanced rotors for the CH-47F
Thread Starter
Join Date: Feb 2006
Location: Hanging off the end of a thread
Posts: 32,856
Received 2,811 Likes
on
1,198 Posts
US shelves new advanced rotors for the CH-47F
It would appear they have been unable to solved the vibration problems with the new rotors.
https://www.defensenews.com/digital-...es-in-testing/
https://www.defensenews.com/digital-...es-in-testing/
NASHVILLE, Tenn. — The U.S. Army has decided to shelve its Advanced Chinook Rotor Blades it was developing as part of the Boeing-manufactured CH-47F cargo helicopter’s latest upgrades due to issues that cropped up during testing, according to Brig. Gen. Robert Barrie, the program executive officer for Army aviation.
In 2020, the service was dealing with excessive rotor blade vibrations from the ACRBs as it headed into a limited-user test scheduled for early 2021, so the service decided to cancel that test until it had worked through the issues.
A report from the Pentagon’s chief weapons tester noted vibrations present in ground, hover and forward flight that could pose “safety of flight risk.” Boeing pushed back against the claim it posed a safety risk, but the company did acknowledge vibration issues.
“We’re working closely with the Army on a mitigation system or an adjustment to existing mitigation systems to account for that different vibration frequency,” Andy Builta, Boeing vice president and H-47 program manager, told Defense News a year ago. “It is in no way a safety of flight risk, but it is an issue that needs to be addressed going forward.”
The company may adjust or add dampeners to address the problem, he said. “This is a low-risk, well-known activity that we’ve done across multiple platforms.”The Block II variant returned to some testing in the spring of 2021 and began to log flight hours. The company said the new rotor blades proved the aircraft can handle an additional 2,500 pounds of lift.
But last fall, the Army decided not to move forward with ACRBs. However, the service is proceeding with the rest of the planned upgrades for the helicopter, Barrie said at the Army Aviation Association of America’s annual conference on April 4.
“As we began developmental flight tests on the blade,” Barrie said, “there were two issues that we had. There was a vibration issue and then there was an aft rotor stall. So as the retreating blade on the aft rotor system swept back, there were stall issues that were created, which increased the stress on the rotor system.”
The two issues combined “and the inability to have an affordable way through — that led the Army to make a decision to stop … and shelve that portion of the development,” he said.
In 2020, the service was dealing with excessive rotor blade vibrations from the ACRBs as it headed into a limited-user test scheduled for early 2021, so the service decided to cancel that test until it had worked through the issues.
A report from the Pentagon’s chief weapons tester noted vibrations present in ground, hover and forward flight that could pose “safety of flight risk.” Boeing pushed back against the claim it posed a safety risk, but the company did acknowledge vibration issues.
“We’re working closely with the Army on a mitigation system or an adjustment to existing mitigation systems to account for that different vibration frequency,” Andy Builta, Boeing vice president and H-47 program manager, told Defense News a year ago. “It is in no way a safety of flight risk, but it is an issue that needs to be addressed going forward.”
The company may adjust or add dampeners to address the problem, he said. “This is a low-risk, well-known activity that we’ve done across multiple platforms.”The Block II variant returned to some testing in the spring of 2021 and began to log flight hours. The company said the new rotor blades proved the aircraft can handle an additional 2,500 pounds of lift.
But last fall, the Army decided not to move forward with ACRBs. However, the service is proceeding with the rest of the planned upgrades for the helicopter, Barrie said at the Army Aviation Association of America’s annual conference on April 4.
“As we began developmental flight tests on the blade,” Barrie said, “there were two issues that we had. There was a vibration issue and then there was an aft rotor stall. So as the retreating blade on the aft rotor system swept back, there were stall issues that were created, which increased the stress on the rotor system.”
The two issues combined “and the inability to have an affordable way through — that led the Army to make a decision to stop … and shelve that portion of the development,” he said.
Last edited by NutLoose; 23rd Apr 2022 at 18:09.
It would appear they have been unable to solved the vibration problems with the new rotors.
https://www.defensenews.com/digital-...es-in-testing/
https://www.defensenews.com/digital-...es-in-testing/
P B Martin did his doctoral thesis on trying to cure the problem of the vibration of the MRB, pitch link cyclic loads and transmission vibration.... and then he did it again for Boeing. The cured the VR-7 dynamic stall hysteresis that affects the Cl, CM and CP, and makes a joke of being careful of the section design anyway, the dynamics coefficients have nearly no relevance to a static AOA idealized value. They resolved the hysteresis, but the drag went up by 50%. Was great if you added another engine. With the work I was doing separately, I discovered a device that also removed the hysteresis, and oddly reduced the drag as well. I tested that, and got it certified for the RHC, and then... we actually flew it on Franks test bed on the CMRB, on the SK-61 and also on the HH-3. Flew it on the UH-1H and various OH58s. Craig Whorley was the TP for Frank at that time, and we were given a blade to look at, and tried a simple proof of concept on the blade just to see how that would start looking. The blades had a substantial erosion issue immediately behind the nickel LE, from the transverse vortex structure... The limited testing showed an improvement at some points of the power required curve, in the first effort, at low and intermediate speed, but we didn't do much to help with the first guess at VNE, except for ONE THING. Craig commented that it was quite spooky to fly the SK61 without any vibration. We got busy with the B737 project at that time, and nothing much happened to the rotor, we never tried another configuration, I had tried around 50 configurations on the RHC, 1 on the H500, 1 on the 206, 1 on the UH1, etc.... and 1 on Franks CMRB.
We did get a curious outcome on the Enstrom with Enstrom,, before it was sold off to the Chinese. We got a slight power improvement in the hover, less than normal, for a fairly predictable rotor section (duh) but then we got a huge improvement in the cruise. That system is available if any of the OEMs want to proceed with it, we did develop a better erosion protection material, one that still degrades very slowly in particulate conditions, but survives without damage in rain. Nothing survives in rain impact, it is the most stunningly violent event on a section, but we did get the material.
I have no interest in doing STCs anymore, but OEMs are welcome to use my designs and materials if they so wish, I am just over dealing with idiot investors.
FDR
Oh, P.S.: the RHC power reduction was around 8% on the R22, and the R44 was around 5%, we tried only one config. The UH1 was 8%, as was the B206. The EN280 was 0.5" MAP recovery at the hover, and 2" in the cruise.
The stall RPM went down from 82% ref Nr stall to 77%, and there was a slight recovery of yaw authority at the stall Nr. The reason I went into the LE mod was that I was doing the TE mod when the rotors started to have disbond issues, and that seemed like an easy fix. The TE stuff followed what I had been doing on propellers for 15 years beforehand, which was TE mods. The 82% stall case for the reference with a LE and a basic TE mod went down to 68%, which was spooky. Not as spooky as the fact that at 68% I could do quite easy left pedal turns. When I set up the control position digital recording system (surprised Shawn but he got back by helping me with the OGE hover test point using the same.... That was pretty neat to set the controls and have the aircraft settle to the OGE hover without any other reference),. found the yaw pedal went from standard 100% pedal at stall of the Nr to 50%. The final fun factoid with the TE case was that with the TE modded, I could go to idle Nr, raise the collective fully, and then increase the Nr with the throttle, and fly off the pad. Couldn't do that with any other mod. It was stunning. Wanted to do that for the V-22, seemed like a fun thing, then ran into Ft Eustice's civilian speed bump, even with the assistance of Greg L from L-M APD...
So, to hear that Boeing is messing up the rotor for the CH-47F is just one of those annoyances. 160th SOAR, Boeing Vertol, BELL, if you want to fix your vibes and improve the performance of the helo, you can always contact me, I am done with fighting city hall.
The propeller mod we have done on literally hundreds of props, wanted to do that on the C-130, NIMBY rules, so the opportunity to improve performance went away, until there is a change of heart.
John Raisbeck was pretty interested in what we were doing, as was BLR's former boss before he sold out of the company. BLR would have been a good option, LORD was not.
The "devices" you allude to, presumably are also associated with the LE and TE mods you mentioned?
Other than local VGs, gurney tabs, TE/chord extension or profiling, or LE droop scabs - I am having a hard time imagining just what you were up to! But rather intrigued.
Other than local VGs, gurney tabs, TE/chord extension or profiling, or LE droop scabs - I am having a hard time imagining just what you were up to! But rather intrigued.
The "devices" you allude to, presumably are also associated with the LE and TE mods you mentioned?
Other than local VGs, gurney tabs, TE/chord extension or profiling, or LE droop scabs - I am having a hard time imagining just what you were up to! But rather intrigued.
Other than local VGs, gurney tabs, TE/chord extension or profiling, or LE droop scabs - I am having a hard time imagining just what you were up to! But rather intrigued.
Ref: Martin, P., Wilson, J., Berry, J., & Wong, T. (2008). Passive Control of Compressible Dynamic Stall. 26th AIAA Applied Aerodynamics Conference, 1–33. http://scholar.google.com/scholar?hl...ynamic+Stall#0
Ouch... that's 50% increase in drag, we tested 5-8% reduction (from a NACA clean baseline) using the LE Device, and normalizing hysteresis.
The reason for the drag reduction is discernable when you look at flow structures around a rotating blade... there is this thingy called radial acceleration happening, and so when you shed a vortex structure it is quite different on a rotor to doing the same on your LERX or PA28 micro VGs... unless you are spinning at 200RPM for a rotor, or 2700 RPM for a propeller. A blade or ramp VG on a rotor or propeller is known as a speed brake.
The TE mods are straightforward, aerodynamically, but not structurally. placing something reliably on the back edge of a rotor or propeller or fan blade on a jet engine takes... enthusiasm, and a little thinking through of the issues. NASA has been looking at how to do that since Liebeck wrote up the observations from Dan Gurney's surprise findings. They went high-tech. I went low-tech.
The effect on harmonic loads in the pitch links was spectacular, -30 to -40% in amplitudes.
A few of the most obvious happy reading documents. Dan Troolin did good work, John Lin is gifted and modest, still with NASA I believe. Cavanaugh and Myose both did nice visualizations. I didn't have software that would do a good job at that time, so had the indignity to have to take over the kitchen sink, and play under water, and then go fly the propellers and the rotors.
Prop mods are actually remarkably safe, rotor mods need some care, and the TR is definitely needing of care before flight, but is also disproportionally effective. A TE mod is easy when the TR system is a fenestron, (much relieved) or robust, UH60 style, doing it on an R-22 was not fun, but was spectacular. The R44 was a bit safer for testing.
The poster child for improvement is the V-22 prop rotor. The potential increase in capability is immense, but the increase in operational safety is like helicopters, much more important. The Ch-47 is vanilla, it is a straightforward enhancement to be done, but the will to do it wasn't with the now-departed John Shipman of AATD/Ft Eustice. So if 160th, US Army, or drivers of CH47s want more capability, gizza call.
I'm on +1 850 200 0994
Not holding my breath; the pilots know what they need, the system manages to look after the prime contractors, and the losses accrue as a direct result. This is an open forum, I don't have any interest in helping the regime of Putin or Xi, I have interest in submarine propellers, ship propellers, aircraft propellers and rotors, as well as fan blade enhancements.
Look at the CL, CD changes of an LET, and then consider that a fan blade is a glorified fixed pitch propeller, constrained at both static and high-speed requirements. If that is not clear, consider that at sea level a fan engine has a SFC of 0.35, and at FL350, M0.80 it is 0.70.... A turbojet has 1.00 and 1.00 for the same conditions, now tell me about the efficiency of a fan blade at high speed.... and then look at the CL/CD of a LET again. We got +30% thrust in March 2013, on a JT15D-1A on static testing.... That was using a scrap engine provided by Bob Hale out of ATL, with an independent observation by the manager of the SLAC. I believe that the FL350/M0.8 solution is much more profound.
Anyway.
Lin John C. (1999). Control of Turbulent Boundary-Layer Separation using Micro-Vortx Generators. 30th AIAA Fluid Dynamics Conference.
Lee, T., & Lee, L. (2007). Effect of Gurney Flap on Unsteady Wake Vortex. Journal of Aircraft, 44(4), 1398–1402. https://doi.org/10.2514/1.29555
Greenwell, D. I. (2010). Gurney Flaps on Slender and Nonslender Delta Wings. Journal of Aircraft, 47(2), 675–681. https://doi.org/10.2514/1.46610
Bae, E. S., & York, N. (n.d.). Rotor Stall Alleviation with Active Gurney Flap.
Nikolic, V. R. (2006). Additional Aerodynamic Features of Wing-Gurney Flap Flows. Journal of Aircraft, 43(5), 1325–1333. https://doi.org/10.2514/1.19596
Thesis, (2011). AN INVESTIGATIVE STUDY OF GURNEY FLAPS ON A NACA 0036 AIRFOIL. March.
Yee, K., Joo, W., & Lee, D.-H. (2007). Aerodynamic Performance Analysis of a Gurney Flap for Rotorcraft Application. Journal of Aircraft, 44(3), 1003–1014. https://doi.org/10.2514/1.26868
Papadakis, M., Myose, R. Y., & Matalw, S. (1997). Experimental investigation of Gurney flaps on a two element general aviation airfoil Experimental Investigation of Gurney Flaps on a Two Element General Aviation Airfoil. January.
DUMITRESCU, H., & MĂLĂEL, I. (2010). Analysis of low Reynolds number flow past Gurney flap. INCAS Bulletin, 2(4), 97–105. http://bulletin.incas.ro/files/horia...v2no4_full.pdf
Storms, Bruce L (Sterling Software, Moffett Field, C. 94035), & Jang, Cory S (California Polytechnic State University, San Luis Obispo, C. 93407 E. (1993). Lift enhancement of an airfoil using a Gurney flap and vortex generators. Journal of Aircraft, 31(3), 542–547. http://pdf.aiaa.org/jaPreview/JA/1994/PVJAPRE46528.pdf
Matalanis, C. G., & Eaton, J. K. (2007). Wake vortex control using static segmented Gurney flaps. AIAA Journal, 2(2), 321–328. http://pdf.aiaa.org/jaPreview/AIAAJ/2007/PVJA25956.pdf
Rhee, M. (2004). A Computational Study of an Oscillating VR-12 Airfoil with a Gurney Flap. 22nd AIAA Applied Aerodynamics Conference and Exhibit, August.
Jeffrey, D., Zhang, X., & Hurst, D. (2000). Aerodynamics of Gurney Flaps on a Single-Element High-Lift Wing. Journal of Aircraft, 37(2). http://arc.aiaa.org/doi/pdf/10.2514/2.2593
Traub, L. W., & Freienmuth, E. O. (2011). Effect of Streamwise Attachment Gap on Aerodynamic Characteristics of Gurney Flaps. Journal of Aircraft, 48(1), 348–352. https://doi.org/10.2514/1.C031226
Li, Y., Wang, J., & Zhang, P. (2003). Influences of Mounting Angles and Locations on the Effects of Gurney Flaps Introduction. 40(3).
Traub, L. W., & Galls, S. F. (1999). Effects of Leading- and Trailing-Edge Gurney Flaps on a Delta Wing Introduction. 36(4).
Troolin, D. (2009). A quantitative study of the lift-enhancing flow field generated by an airfoil with a Gurney flap. December.
Cavanaugh, M. A., Tech, V., & Mason, W. H. (n.d.). Wind Tunnel Test of Gurney Flaps and T-Strips on an NACA 23012 Wing. Test, 1–18.
Myose, R., Lietsche, J., Scholz, D., Zingel, H., Hayashibara, S., & Heron, I. (2006). Flow Visualization Study on the Effect of a Gurney Flap in a Low Reynolds Number Compressor Cascade. 6th AIAA Aviation Technology, Integration and Operations (ATIO) 25-27 September 2006, September, 25–27. http://arc.aiaa.org/doi/pdf/10.2514/6.2006-7809
Last edited by fdr; 26th Apr 2022 at 07:24.
My suspicions seem confirmed as based upon your response and the linked whitepapers (many of which I already have copies!) it appears you are teasing the creative implementation of gurney flaps with segmented span and/or minor angle and profile variation.
I presume this technology and its specifics have not been patented, hence the coyness
I presume this technology and its specifics have not been patented, hence the coyness
My suspicions seem confirmed as based upon your response and the linked whitepapers (many of which I already have copies!) it appears you are teasing the creative implementation of gurney flaps with segmented span and/or minor angle and profile variation.
I presume this technology and its specifics have not been patented, hence the coyness
I presume this technology and its specifics have not been patented, hence the coyness
The trick on a rotor or a propeller is pretty much how to add a device and not frag the prop or rotor straight away, you are effectively adding rigidity to the area that has high torsion and bending loads that are cyclical, and so the blade, bond or device are in a compromised state to begin with. Years ago, NASA proposed some segmented devices to get around that problem, my testing showed segmentation was a disaster to the performance outcome. So, yeah, the aero is not what it seems when you do CFD for a non-rotating element, and the mechanics of doing it need some lateral thinking.
The propeller was interesting to do, but it was also educational. The rotor added some risk issues to be considered, changing a part span section CL by 0.4 makes autorotational effects a topic of interest. There was a single engineering note that suggested auto wouldn't end badly, but it was still not a fun first trial. The engineering note was based on a CFD code that I had reservations on, and could have gone either way. The first-ever entry was done from a good speed above ETL so if the driving zone of the rotor was adversely affected, at least a cyclic loading could restore some Nr while trying to add power. In the end, there was a rise in Nr which was gratefully received. I went as far as doing failure tests on the rotor in the hover, having done fully asymmetric setups and having a slight vibration increase and change in tracking. the failure in hover took 6 flights to make it fail, each flight introducing more damage until it came off a blade in the hover. Had rugged up with extra Nomex for that one. in the end it was a non-event, and was observed coming off the rotor and passing off to the side clear of the other blade path, and well clear of the TR.
The aero was fun, the structural issues were interesting, the hardest thing was dealing with water droplet impact. Nothing much is more damaging to a surface that a high velocity, >100m/sec impact. That, and the manufacturing processes is the bit of sensitivity, Some of this I have patented, but the high-value issues are the certification and materials. Particularly trying to add something to a fan blade. The g load giving a shear on the attachment on a rotor is around 3-500g. for a propeller, its around 3,000g. for a fan, a GE90, is around 7500g, 15000g for a CFM56, and 35,000g for a TFR731, 60,000g for a JT15D-1. Even then, that is relatively bland compared to the problem of liquid droplet impact. There was a good lab in Amsterdam, best around, one in Russia, and the least effective was in the USA.
