Subject: Prop and psru calculations
From: Paul
Date: 4/14/2001, 11:31 PM

The first table is for a 2.17:1 psru.
The columns are engine RPM HP prop RPM and then prop diameters in inches
The numbers are tip speed in feet per second. The max tip speed of about 900
feet per second is based on a 76 inch diameter prop revving at 2700 RPM.
The rate of HP increase as a function of engine RPM was a guess on my part.

Given that HP in a rotary increases rapidly with engine RPM it is possible that a
a 76 inch dia, or so prop is not optimum. It is possible that by going down
on the diameter of the prop and upping the engine RPM with the
2.17:1 gear ratio could give better performance. It all depends
on how fast the efficiency of the prop drops off with a decrease in
the diameter of the prop. When Vance comes back from S&F we will explore that.

The second table is for the 2.85:1 to one ratio. If you have a tall airplane
you might want to use a larger diameter prop and get the best of both
worlds. More power and more efficiency out of the prop. 

The rotary is not the same as an air-cooled aircraft engine (in case you have
not noticed :-)). A/C engines have a red line for a very good reason. Durability!
Anything over that red line and you will cut the life of the engine. This
red line is around 2700 RPM and that is why most props are designed
for that RPM. The rotary, on the other hand, will happily rev to 8500 RPM
and even higher when the side port comes out with lighter weight rotors.
We need to take this into consideration when choosing a prop and PSRU ratio.
By limiting our take off RPM with a 76 inch prop and a 2.17:1 PSRU
we are giving away a bunch of HP.

Paul Lamar
 
The AirCraft Rotary Engine NewsLetter.              Powered by Linux.

http://home.earthlink.net/~rotaryeng/            http://www.linux.org

TIPSPEED.DAT
RPM  HP  PROP 58  60  62  64  66  68  70  72  74  76  78  80  82  84  86
4000 124 1843 466 483 499 515 531 547 563 579 595 611 627 643 660 676 692
4100 127 1889 478 495 511 528 544 561 577 594 610 627 643 660 676 693 709
4200 130 1935 490 507 524 540 557 574 591 608 625 642 659 676 693 709 726
4300 133 1982 501 519 536 553 571 588 605 623 640 657 674 692 709 726 744
4400 136 2028 513 531 549 566 584 602 619 637 655 672 690 708 725 743 761
4500 140 2074 525 543 561 579 597 615 633 651 670 688 706 724 742 760 778
4600 143 2120 536 555 573 592 610 629 647 666 684 703 721 740 758 777 795
4700 146 2166 548 567 586 605 624 643 662 680 699 718 737 756 775 794 813
4800 149 2212 560 579 598 618 637 656 676 695 714 734 753 772 791 811 830
4900 152 2258 571 591 611 631 650 670 690 709 729 749 769 788 808 828 847
5000 155 2304 583 603 623 643 664 684 704 724 744 764 784 804 824 845 865
5100 158 2350 595 615 636 656 677 697 718 738 759 779 800 820 841 861 882
5200 161 2396 606 627 648 669 690 711 732 753 774 795 816 836 857 878 899
5300 164 2442 618 639 661 682 703 725 746 767 789 810 831 853 874 895
5400 167 2488 630 651 673 695 717 738 760 782 803 825 847 869 890
5500 171 2535 641 664 686 708 730 752 774 796 818 840 863 885
5600 174 2581 653 676 698 721 743 766 788 811 833 856 878
5700 177 2627 665 688 711 734 756 779 802 825 848 871 894
5800 180 2673 676 700 723 746 770 793 816 840 863 886
5900 183 2719 688 712 736 759 783 807 830 854 878
6000 186 2765 700 724 748 772 796 820 845 869 893
6100 189 2811 711 736 760 785 810 834 859 883
6200 192 2857 723 748 773 798 823 848 873 898
6300 195 2903 735 760 785 811 836 861 887
6400 198 2949 746 772 798 824 849 875
6500 202 2995 758 784 810 836 863 889
6600 205 3041 770 796 823 849 876
6700 208 3088 781 808 835 862 889
6800 211 3134 793 820 848 875
6900 214 3180 805 832 860 888
7000 217 3226 816 845 873
7100 220 3272 828 857 885
7200 223 3318 840 869 898
7300 226 3364 851 881
7400 229 3410 863 893
7500 233 3456 875
7600 236 3502 886
7700 239 3548 898

TIPSPEE2.DAT
RPM  HP  PROP 58  60  62  64  66  68  70  72  74  76  78  80  82  84  86
4000 124 1404 355 367 380 392 404 416 429 441 453 465 478 490 502 514 527
4100 127 1439 364 377 389 402 414 427 439 452 465 477 490 502 515 527 540
4200 130 1474 373 386 399 412 424 437 450 463 476 489 502 514 527 540 553
4300 133 1509 382 395 408 421 434 448 461 474 487 500 513 527 540 553 566
4400 136 1544 391 404 418 431 445 458 472 485 498 512 525 539 552 566 579
4500 140 1579 400 413 427 441 455 468 482 496 510 524 537 551 565 579 592
4600 143 1614 408 423 437 451 465 479 493 507 521 535 549 563 577 592 606
4700 146 1649 417 432 446 461 475 489 504 518 532 547 561 576 590 604 619
4800 149 1684 426 441 456 470 485 500 514 529 544 559 573 588 603 617 632
4900 152 1719 435 450 465 480 495 510 525 540 555 570 585 600 615 630 645
5000 155 1754 444 459 475 490 505 521 536 551 566 582 597 612 628 643 658
5100 158 1789 453 468 484 500 515 531 547 562 578 593 609 625 640 656 671
5200 161 1825 462 478 494 510 525 541 557 573 589 605 621 637 653 669 685
5300 164 1860 471 487 503 519 536 552 568 584 600 617 633 649 665 682 698
5400 167 1895 480 496 513 529 546 562 579 595 612 628 645 661 678 694 711
5500 171 1930 488 505 522 539 556 573 589 606 623 640 657 674 690 707 724
5600 174 1965 497 514 532 549 566 583 600 617 634 652 669 686 703 720 737
5700 177 2000 506 524 541 559 576 593 611 628 646 663 681 698 716 733 750
5800 180 2035 515 533 551 568 586 604 622 639 657 675 693 710 728 746 764
5900 183 2070 524 542 560 578 596 614 632 650 668 686 705 723 741 759 777
6000 186 2105 533 551 570 588 606 625 643 661 680 698 717 735 753 772 790
6100 189 2140 542 560 579 598 616 635 654 672 691 710 728 747 766 784 803
6200 192 2175 551 570 589 607 626 645 664 683 702 721 740 759 778 797 816
6300 195 2211 559 579 598 617 637 656 675 694 714 733 752 772 791 810 829
6400 198 2246 568 588 607 627 647 666 686 705 725 745 764 784 803 823 843
6500 202 2281 577 597 617 637 657 677 697 717 736 756 776 796 816 836 856
6600 205 2316 586 606 626 647 667 687 707 728 748 768 788 808 829 849 869
6700 208 2351 595 615 636 656 677 698 718 739 759 780 800 821 841 862 882
6800 211 2386 604 625 645 666 687 708 729 750 770 791 812 833 854 875 895
6900 214 2421 613 634 655 676 697 718 739 761 782 803 824 845 866 887
7000 217 2456 622 643 664 686 707 729 750 772 793 814 836 857 879
7100 220 2491 630 652 674 696 717 739 761 783 804 826 848 870 891
7200 223 2526 639 661 683 705 728 750 772 794 816 838 860 882
7300 226 2561 648 671 693 715 738 760 782 805 827 849 872 894
7400 229 2596 657 680 702 725 748 770 793 816 838 861 884
7500 233 2632 666 689 712 735 758 781 804 827 850 873 896
7600 236 2667 675 698 721 745 768 791 814 838 861 884
7700 239 2702 684 707 731 754 778 802 825 849 872 896
7800 242 2737 693 717 740 764 788 812 836 860 884
7900 245 2772 702 726 750 774 798 822 847 871 895
8000 248 2807 710 735 759 784 808 833 857 882
8100 251 2842 719 744 769 794 818 843 868 893
8200 254 2877 728 753 778 803 829 854 879
8300 257 2912 737 762 788 813 839 864 890
8400 260 2947 746 772 797 823 849 875
8500 264 2982 755 781 807 833 859 885
8600 267 3018 764 790 816 843 869 895
8700 270 3053 773 799 826 852 879
8800 273 3088 781 808 835 862 889
8900 276 3123 790 818 845 872 899
9000 279 3158 799 827 854 882