Indoor News and Views (INAV)
January 1962
Page 3
BUD TENNY "Voice of N.I.M.A.S." JANUARY 1962
| Bill was one of three persons asked the following
questions for comment here:
4. "Dave Call always stresses efficiency and Bill Bigge sent me a formula showing a gain (in efficiency) will result in twice the time gain as if weight were saved." (Quoting from the original source of question) 5. At this point your editor injected a question - How about a discussion of efficiency of indoor models? 6. What is the best prop shape? Records and phenom- enal times have been done as of late with both teardrop and straight shape props. 7. Why do we fly with torque? Why not fly against torque? 8. What is the best way to control torque? Wash-in? Offset? Extra area? Prop offset? Bill responded, answering the one on efficiency first: Let v = the sinking speed of model gliding, with motor and prop replaced with ballast, in feet/second, and: V = energy potential of rubber, foot pounds/pound T = duration in seconds Wr = weight of rubber Ws = weight of structure d = air density A = area of lifting surface Cd = coefficient of drag Cl = coefficient of lift 0= gliding angle E = efficiency, so called Then T = V/v x Wr/(Wr + Ws) x E and v =sq rt(2(Ws * Wr)/dA) x Cd/(C1)3/2 x (cos 0)3/2 Putting in some approximate values, let T = 2000 seconds, V = 2400 ft. lbs./lb., Wr/(Ws * Wr) = 0.5, and v = 0.3 feet/second. Then E = 0.5. That is, the product of what may be called energy storage efficiency, propeller efficiency, and flight pattern efficiency is 1/2. Maybe the value chosen for V is too large - the other figures are reasonable, and E looks almost too good. On question #4 Bill comments, with relation to the formulas already given: A 1% increase in efficiency will increase duration by 1%. A decrease in Ws of 1% with no change in Wr, will decrease (Wr + Ws) by Ws/(Wr + Ws)%. Because of the square root, this decrease in weight will decrease v by 1/2Ws/(Wr + Ws)%, that is, by 3/4% or less if Ws is equal to or less than Wr, as it should be. The model should fly 1/2% higher and farther and 1/4% slower. If Ws and Wr are each reduced 1%, usually a more realistic condition, (and convenient - Ed) the altitude reached is unchanged and the duration is increased 1/2%. Thus the remark that efficiency is twice as important as weight. The ratio of induced drag to total drag, ignored here, could also be called efficiency and is equally important. On Questions #6, #7, and #8, Bill comments: The best prop shape is the one that the individual can use for his purpose with best results. A well balanced, properly flaring prop of any reasonable form is better than a poorly engineered prop of the best form. In other words, I plead ignorance. The initial choice is between one spar and two spars. I have a suspicion that both the best props and the worst props are monospars. A greater variety of blade shapes is feasible with monospars. On theor- etical grounds I lean toward having area concentrated near tho mean radius but would not be surprized if the taper toward the tip should be concave instead of con- vex, at least part of the way. A possible advantage is that spar stiffness toward the tip could be reduced. In practice, structural considerations may be control- ing. I fly with torque because when my 1956 "C" flew against torque the circle opened on high power. If the rudder is adequate a model will turn more readily with torque. To fly against torque requires more extreme adjustments, which tend to reduce efficiency. |
Torque is controlled by extra area and wash-in.
I don't know what offset is unless it is extra area or
swinging the left wingtip forward. Slewing the entire
wing, as mentioned, building the wing with dihedral
ribs rotated clockwise as viewed from above, and left
thrust (offset?) are all essentially methods of getting
extra wash-in on the left tip relative to the right.
Extra area may be the most efficient control means in
steady flight. Wash-in gives the model a better chance
to recover from improper flight attitudes at high
power. It also tends to make the model dive straight
ahead when falling off a girder, and giVes it a better
chance to clear the next time around.
NEWS FROM AROUND THE COUNTRY CALIFORNIA-WILMINGTON Dave Copple reports that the December session at Wilhall had a large turn-out for the contest-record trials. The Easy B class seems to be turning out lots of new people for their sessions. On the following weekend, these boys flew at the Los Angeles Armory, Easy B's again. Over twenty entries in Expert category. Tom Finch topped the crowd in the 44' ceiling, turning 10:30. CALIFORNIA-BAKERSFIELD From Herman Stubblefield in Bakersfield we hear that several fellows in the Bakersfield club are flying miniature gliders in their meeting hall, and plan to give rubber ships a try if they can find a site. INDIANA-KOKOMO During the last month we heard from Chuck Borneman of the Kokomo Knights of The Round Table, who sent a letter and copies of the club newsletter. Anyone in that area interested in indoor flying should contact Chuck at 1401 West Taylor, Kokomo. This club, once exclusively a control line club, has now branched out into free flight events and also indoor events. Their flying site at Bunker Hill AFB is at the low end of Category II with about 45' ceiling. The HLG boys are working toward the 0:40 mark, %he club record is 0:34.6 and there was an unofficial mark of 0:39.0. One of the club Juniors Jumped up with a mike ship which has turned a high of 7:54. Two of the more active indoor flyers at each event are members of the BHAFB Model Club, and are responsible for the site availability. They are Captain J W. Hardin and CWO Herb Summers. ILLINOIS-CHICAGO Times in the weekly Madison Street Armory sessions (75' ceiling) have been climbing, as a result of lots practice flying, Pete Sotich reports. Tom Neumann, 18, has worked a modified Sweepette up to 1:O8.6, while his brother Dan. 14, followed close with 1:02.6. FAI times have been climbing past the times from the elims last year. Bob DeBatty recently topped out at 26:23.0, Charlie Sotich turned 22:00+, and Don Kintzele 20:00. MISSOURI-KANSAS CITY Tem Johnson comments on his record holding Joint effort with Dick Stamm, "The why of the relatively heavy paper covered ship is that paper covering can take hang-ups without losing its skin. Around here there's not much percentage in trying to build except- ionally light planes for the same reason as paper cover- ing and also because the air is usually quite turbulent. Heavy ships ride right through bumps that stall light ones. Of course, as we gain skill and fly closer to a plane's performance limit, lightness will count." MISSOURI-ST. LOUIS Ed Veselsky reports that indoor flying in st. Louis is starting up again after being dormant for 8 or 10 years. Members of the Kirkwood Thermaleers have been putting on flying demonstrations for Boy Scout troops and similar groups, and they feel there is a possibility of getting back into the site of Carl Goldberg's famous 23 minute flight of Years ago. WASHINGTON-SEATTLE Phil Hairier suggests method for test flying Cat. I ships for maximum potential - fly them G-line on .O01 wire. He sez both he and Hu Entrop have broken 13:00 with Class A ROG's in their living room! |
