daniel@petrus.UUCP (Daniel W. Nachbar) (01/23/86)
An engineering question -- Most gliders have spoilers. Most simple singles do not. Is there any good reason for the difference? Dan Nachbar BELLCORE -- Morristown, NJ bellcore!daniel
ark@alice.UucP (Andrew Koenig) (01/24/86)
Dan Nachbar noticed that gliders tend to have spoilers and simple singles don't. I don't know for certain why that is, but I suspect it might be because most singles today have flaps. Also, a windmilling prop is draggy enough that you can descend at a plausible angle without brakes or flaps. You can now buy a Mooney with speed brakes installed at the factory.
ahv@masscomp.UUCP (Tony Verhulst) (01/24/86)
In article <5@petrus.UUCP> daniel@petrus.UUCP (Daniel W. Nachbar) writes: >An engineering question -- >Most gliders have spoilers. Most simple singles do not. >Is there any good reason for the difference? >Dan Nachbar >BELLCORE -- Morristown, NJ >bellcore!daniel The FAA claims thet the primary purpose of flaps is to increase the rate of descent without increasing airspeed. Although this certainly is true, most of use use flaps because using them on landing lowers the nose (providing a better view of the runway) and because they lower the touch touch down speed. Spoilers increase the rate of descent. Period. Sail planes don't need flaps because final approach speed is considerably higher than cruise speed (weird ain't it?) so the nose is already low enough to provide good visibility of the runway. Also, the landing speed of most sailplanes is in the 40mph ball park so the lower touch down speeed that flaps provide is not that crucial. Note that Mooney is offering spoilers as an option on some of their singles. It seems that Mooneys are so clean (parasitic drag wise) that their descent rate wasn't high enough to satisfy air traffic controllers. Those poor Mooney pilots were going too fast to use flaps (enroute descents) and couldn't throttle back any further without cooling their engines too much and were still being requested to increase their rate of descent. Now, with the spoilers, the Mooney pilot can throttle back and fall out of the sky with the rest of us. OK, so much for the background. The reason that sailplanes have spoilers and airplanes don't is because airplanes have throttles and sailplanes don't. In an airplane, you control your descent on final with the throttle. If you are too low on the approach you add power, if you are too high you decrease power. This is tough to do in a sailplane. What you do instead is to initiate the approach a little high and add a some spoiler. If you find yourself under shooting the approach, remove some spoiler. If too high on the approach, just increase the amount of spoiler. So, basically, on final approach the spoiler does for the sailplane that the throttle does for the airplane. Incidentally, besides flying airplanes and sailplanes I also fly hang gliders (11 years). For several years I have been pushing for spoilers on hang gliders. Hang glider performance has increased tremendously over the years. Here in the northeast, a typical hang gliding landing area is the parking lot of a ski resort surrounded by 70 foot oak trees. Naturally a parking lot in the woods on a sunny day is a great thermal generator and the turbulence .... well never mind, it's too painful. It's easy to come over the parking lot at tree top level and get a REAL good look at the trees on the other side before you land. Some fancy low level turning occurs to stay within the boundaries of the parking lot (a good glide angle has SOME disadvantages). Spoiler in this situation could make the difference between an uneventful landing and parking it in the top of a tree. We claim that if a New England hang glider pilot has never landed in a tree, he hasn't been flying long enough. Iv'e been flying long enough to land in three trees. A tree landing is not a bad as it sounds. Basically, once you know that you can't reach an open clearing and commit to the tree landing, you find a bushy tree (Lord spare me from the pointy dead pine trees) and stall the glider (15-16mph) just ever so slightly above the tree. The glider will settle in the tree (getting it out bill be discussed in the next chapter) and you just climb out of the tree. Out of the dozens of tree landings I have heard about and seen, I know of only one injury. Al Mulazi (connecticut) broke his wrist while climbing out of a tree he had landed in. Wow, I started of by answering Dan's spoiler question and kind of went off on a tangent. yours in good flying, Tony Verhulst treasurer; Windward Kite & Gliding Club Private pilot - ASEL student - sailplane (35 flights)
cfiaime@ihnp3.UUCP (J. Williams) (01/26/86)
In article <5@petrus.UUCP> daniel@petrus.UUCP (Daniel W. Nachbar) writes: >An engineering question -- >Most gliders have spoilers. Most simple singles do not. >Is there any good reason for the difference? >Dan Nachbar >BELLCORE -- Morristown, NJ >bellcore!daniel COST!!!
robs@tektools.UUCP (Robert Sleator) (01/26/86)
A sailplane has spoilers to control its glide path. (Some sailplanes have 90 degree flaps or drogue chutes instead of spoilers.) Maximum glide ratios on production sailplanes range from around 23:1 up to one with a measured 60:1 (the Nimbus 3). A sailplane pilot usually flies the pattern with around half spoilers, adjusting them as needed to hit the runway at the desired spot. Without spoilers, you would have to rely on slipping or rearranging your pattern to put the plane down at the intended point. And remember, you don't have the option of going around again. Without glide path control, a slight miscalculation at 60:1 and you could wave to your friends on the field as you made a low pass over the runway and flew into the trees at the far end. A power pilot can achieve the same effect as spoilers by adjusting the throttle. With engine idling, I think most single engine planes have glide ratios of less than 10:1. Robert Sleator tektronix!tektools!robs
phil@isieng.UUCP (Phil Gustafson) (01/28/86)
In article <4872@alice.UUCP> ark@alice.UucP (Andrew Koenig) writes: > >You can now buy a Mooney with speed brakes installed at the factory. The WWII Taylorcraft spotter plane (I forget the military designation) had two neat features: an aft seat that turned backwards, allowing the spotter to spot through a big greenhouse window; and spoilers. Between the spoilers and frowrd slip, the sucker could land anywhere. The aircraft can be certified for civilian use only if both these features are disabled. phil