ACRE wrote:
Incidently, the stated twist distribution for the LAEV blades is very
strange, and I have not heard any response on the reason and logic
of that decision - Vance J
As a guess Vance what speed would you say it is twisted for.
I think Bill made some assumptions as to the actual direction of the in
flow
around the hub. I think he assumed a certain amount of external
diffusion
directly in front of the cowl as I recall. Is it the hub angles
of attack you are concerned with?
Paul Lamar
That's what I thought too Vance when I tried to figure out what the
"pitch" of the blade was at various tip angles. All I could figure was
Bill de-pitched it near the hub because he knew it was for a tractor.
But I haven't asked him (yet).
--
Perry Mick
Vance W Jaqua wrote:
Here are a couple of plots of pitch distribution versus radial portions
of the blade versus a bunch of tip angle settings. The first is a simp;e
table, which I am sure a lot of the guys and gals have already
computed. The second is a graphic plotted against radius squared
which better shows the amount of disk area impacted by each radial
zone. The twist does not appear to be optimized for major areas of
true helical pitch. at any speed. In virtualy all settings, over 30 percent
of disk area
near the tip appears to be at least 20 percent under pitched ??
It will probably work reasonably well, since propellers are really
rather forgiving devices - but???
Vance J
Bill had some pretty good reasons for doing this at the time Vance.
As I recall we discussed this at length. If I get time I will look
up the pertinent messages.
>From memory I think the outer de pitching was to reduce the
transonic drag rise.
Paul Lamar
Here are a few of the charts Bill used as I recall.
Paul Lamar
The AirCraft Rotary Engine NewsLetter. Powered by Linux.
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Copyright 1998-2002 All world wide rights reserved.
dia = 68
RPM Tip FPS Vel FPS Vel MPH Mach
2200 653 716 488 0.70
2250 668 729 497 0.71
2300 682 743 506 0.72
2350 697 756 516 0.74
2400 712 770 525 0.75
2450 727 784 534 0.76
2500 742 798 544 0.78
2550 757 811 553 0.79
2600 771 825 563 0.80
2650 786 839 572 0.82
2700 801 853 582 0.83
2750 816 867 591 0.84
2800 831 881 601 0.86
dia = 69
RPM Tip FPS Vel FPS Vel MPH Mach
2200 662 724 494 0.71
2250 677 738 503 0.72
2300 692 752 513 0.73
2350 708 766 522 0.75
2400 723 780 532 0.76
2450 738 794 541 0.77
2500 753 808 551 0.79
2550 768 822 560 0.80
2600 783 836 570 0.81
2650 798 850 580 0.83
2700 813 864 589 0.84
2750 828 878 599 0.86
2800 843 893 609 0.87
dia = 70
RPM Tip FPS Vel FPS Vel MPH Mach
2200 672 733 500 0.71
2250 687 747 509 0.73
2300 702 761 519 0.74
2350 718 775 529 0.76
2400 733 790 538 0.77
2450 748 804 548 0.78
2500 764 818 558 0.80
2550 779 832 567 0.81
2600 794 847 577 0.82
2650 809 861 587 0.84
2700 825 875 597 0.85
2750 840 890 607 0.87
2800 855 904 616 0.88
dia = 71
RPM Tip FPS Vel FPS Vel MPH Mach
2200 682 742 506 0.72
2250 697 756 516 0.74
2300 713 771 525 0.75
2350 728 785 535 0.76
2400 744 799 545 0.78
2450 759 814 555 0.79
2500 774 828 565 0.81
2550 790 843 575 0.82
2600 805 857 584 0.83
2650 821 872 594 0.85
2700 836 886 604 0.86
2750 852 901 614 0.88
2800 867 916 624 0.89
dia = 72
RPM Tip FPS Vel FPS Vel MPH Mach
2200 691 751 512 0.73
2250 707 765 522 0.75
2300 723 780 532 0.76
2350 738 794 542 0.77
2400 754 809 552 0.79
2450 770 824 562 0.80
2500 785 838 572 0.82
2550 801 853 582 0.83
2600 817 868 592 0.85
2650 833 883 602 0.86
2700 848 898 612 0.87
2750 864 912 622 0.89
2800 880 927 632 0.90
