Wolfy, chances are almost zero that you’d find a set of Hughes rotor blades lying about with time remaining.
I started with runouts but later found that I could buy surplus blades from the US Army helicopter school at Ft. Rucker, Alabama for scrap prices. Many of those blades weren’t runouts but were blades that had been pulled for other reasons; excess vibration, tracking problems etc, mainly because the Army technicians weren’t paying for the blades themselves. I purchased a truckload for scrap metal (empty beer can) prices.
At the height of the Viet Nam war, Ft Rucker was grinding out helicopter pilots like sausages.
But runouts aren’t all that bad; the helicopter manufacturers are conservative; they don’t want their machines flying with ready to explode rotor blades and the stresses imposed by gyros are much lower than on standard helicopters.
The helicopter tech manuals give inspection procedures for rotor blades, concentrating on root attachments; one step is to examine attachment bolt holes for hairline cracks with a magnifying glass.
I had thought that would be the case now days Chuck probably just a lucky find, right time at the right place is the only option.
I remember reading your story about all those run out blades, good times.
Guessing any of the composite gyro rotor manufactures should be able to knock an equivalent set up, would even get em spinning the right way then.
Are you saying they would be still way more efficient than any of the current offerings, or were they just so much better than anything at the time?
No, a Hughes helicopter blade with NACA 0015 airfoil is not more efficient than modern rotorcraft airfoils but was better than metal rotorblades designed for gyros at that time; Rotordyne, Stanzee and similar.
Almost any modern helicopter airfoil would out perform Bensen’s obsolete 8H12 but does it really make a significant difference? A gyroplane is the most inefficient means of aerial transport possible and a few pounds of drag one way or another is nearly irrelevant when the rotor drag of a gyro rotor is in the range of 1/6 of its gross weight.
A helicopter rotor is propelled by a gear train with an efficiency in the range of 90%+ but a gyro rotor gets its power via a forward thrusting propeller with an efficiency of perhaps 70% and extracts it power from the slipstream with a windmill efficiency in the same range; overall efficiency being the product of the two: 49%.
But as a hobbycopter, appearance is more important than efficiency; or in my usage in chasing feral hogs around Florida bayheads*, safety at treetop heights is the most important attribute.
The 8H12 airfoil was designed by the old NACA shortly after wind tunnels with sufficiently low turbulence to permit laminar flow were developed but it was soon discovered laminar flow can’t exist on a rotor; centrifugal force flings off the laminar boundary layer. During the first full scale test on a whirl tower, the 8H12 had no lower drag than the standard helicopter airfoil of that time, the NACA 0012 and lower maximum lift.
Bensen probably wasn’t aware of the problems of the 8H12 when he picked it up; there was no Internet when he started and to find the whole story, a trip to a well equipped library was essential.
*A Florida bayhead has nothing to do with saltwater; it is a swampy depression in an otherwise flat terrain, overgrown with bay trees and a tangle of vines and undergrowth. Hog heaven.
I do wonder if a REAL 8H12 would not be measurably more efficient than a Bensen rotorblade. Bensen blades are dead flat on bottom, and the top skins tend to flatness, too. On top of that, we have skin gaps, lap joints, rivets and no tip fairing.
Chuck, in the 70's you published some drag data for different rotorblades in the SRC newsletter. You showed Bensens coming in dead last in the efficiency department, compared to other metal blades of the time, a set of wood blades, and your own homemade "skinny" blades.
I flew Bensen 22-foot metal blades, pitched up to about 2.25 deg. from the stock 1.5, until acquiring McCutchen blades. My poor old 1835 VW really struggled to climb out at all in hot weather, with 160-lb. me and those Bensen Erector-set blades.
When I bought an Air Command with (of course) 23-foot McCutchens and a mere 40 hp 447 Rotax, the performance difference was impressive. McC's, IIR, have a much more accurate 8-H-12, faired tips and no parasitic stuff all over the skins.
I imagine that the significant trailing-edge reflex that seems necessary on 8-H-12's is a power-suck, too. It creates a download, leading to trim drag.
Doug, the primary power suck with Bensen metal blades was air pumping via the gaps between upper skin segments. If there was some way of sealing those gaps, Bensen blades wouldn’t be all that far behind Skywheels despite the rivets and flat bottoms.