1055

Item 1055

OTHER: Rotor Concept - Reverse Velocity Utilization - Existing Work

All work that I can find that has been done in regard to Reverse Velocity Blades and Rotors.

Information:

Harold Lemont was 'the' ~or~ 'a' designer of the Reverse Velocity Rotor Blade.

Reverse Velocity is discussed in the article 'Long Range Heavy Lift Aircraft'. http://www.nps.navy.mil/sea/exwar/report/ch14.pdf

Excerpt from this report:

"3. Reverse Velocity Rotor Systems

Reverse velocity rotor systems are a very recent development, designed to address the aerodynamic issues contributing to the retreating blade stall and advancing blade compressibility phenomena that currently limit maximum helicopter forward flight speeds. Reverse velocity rotor systems represent a revolutionary high speed VTOL configuration. By taking a new approach to address high-speed aerodynamic issues, these systems are capable of attaining speeds significantly greater than conventional or even compound helicopters. Initial analysis shows cruise speeds in excess of 300 kts are possible with these systems. Reverse velocity rotor systems are built around double-ended airfoils. This airfoil design minimizes the impact of retreating blade apparent velocity reduction caused by summing the blades rotational velocity and the aircraft's forward flight velocity as illustrated in Figure XIV-9 below. At high forward airspeeds, the retreating blade can, theoretically, be in a reverse flow condition, which, with conventional rotor blades, would completely eliminate the potential to generate lift. Use of a symmetrical, double ended airfoil allows the generation of lift with both forward and reverse flows across the blades, which would allow the generation of lift on the retreating side at a dramatically wider range of airspeeds than conventional blades."

Posting ~ 06/23/2003:
"The Reverse Velocity Rotor (RVR) The RVR tested at the NASA Ames Wind Tunnel flew 380 kts with L/D of 27 @ a disk loading of 8 lbs sq ft. If you want a high speed helicopter.

Sikorsky is reviving the RVR ( I know the test engineer who ran the tests at Ames, He said the rotor was substantially quieter than the fans which ran the tunnel)"

Posting ~by Dave Lednicer in sci.aeronautics 1994-06-11
"Another concept that was tried was the reverse velocity rotor, where double-ended airfoils were used on the inboard part of the blade. In this way, the blade could have a large useable Cl band in both directions. I have the results of a wind tunnel test of the airfoils and I think that a rotor was tested in the 40x80, but the concept died in the mid 70s."

Web Links:

Title : Model Wind Tunnel Tests of a Reverse Velocity Rotor System. Accession Number : AD0911537

http://stinet.dtic.mil/oai/oai?&verb=getRecord&metadataPrefix=html&identifier=AD0911537

Title : An Investigation of the Reverse Velocity Rotor Concept and Its Application to High Speed Rotorcraft

http://www.aiaa.org/content.cfm?pageid=406&gTable=Paper&gID=6962 This could be this 1281

Title : Some problems of design and operation of a 250- knot compound helicopter rotor

http://www.aiaa.org/content.cfm?pageid=406&gTable=japaperimportPre97&gID=43591

Reverse Flow:

In 'Helicopter Theory' by Wayne Johnson. A number of sections and algorithims

In Overview of Autogyros and the McDonnell XV-1 Convertiplane' by Franklin Harris. A couple of graphs,

See 'Helicopter Performance, Stability and Control; page 201 and figure 3.53.

Outside Web Sites:

PIV Investigation of Planar Supersonic Wake Flow

Investigation of Increased Forward Flight Velocities of Helicopters Using Second Harmonic Control and Reverse Velocity Rotor Concept. http://www.stormingmedia.us/94/9460/A946024.html I have a bound hardcopy of this thesis.

It can be obtained off the net by:

Going to http://stinet.dtic.mil/
Enter "reverse velocity" in the 'Search for' box.
Select the 'View Full Text pdf - 2 MB" of the first item.
The file will download but it will be totally blank.
Save the file to disk as an .htm file.
Change the suffix from ".htm" to ".pdf".
Open this saved file. "

Vibratory hub load data reduction and analysis from the reverse velocity rotor wind tunnel test, phase 2B
Taylor, R. B.
NASA Center for AeroSpace Information (CASI)
NASA-CR-137780; D210-11004-1 , 19760101; Jan 1, 1976
The vibratory hub loads data analysis from the reverse velocity rotor wind tunnel test is reported. Vibratory loads were obtained from the rotating hub balance and also by synthesis of generalized coordinates from the blade flap bending moments. Load trends were defined as a function of speed, rotor thrust and 2 per rev cyclic from each of the data methods. These trends were compared to determine the degree of agreement between each method and provide substantiation for the generalized coordinate approach.
Accession ID: 76N16038
Document ID: 19760008950

Hard copy is available for free from NASA; http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19760008950_1976008950.pdf. This test appears to be the foundation of the RVR airfoil shape that was displayed in the 'Investigation of inc...." above and Sikorsky's RVR concept.

Recent Development of Rotorcraft Configuration, page59-60; http://www.bentham.org/eng/samples/eng1-1/Cao.pdf Have hard copy.

Pages at This Site on Outside Concepts:

Last Revised: Sunday, August 17, 2008