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#21
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Earlier, Eric Greenwell wrote:
Are there engineering or manufacturing issues that make spoilers a more desirable choice these days? For example, a fiberglass wing might be more flexible than a metal one, which would make a 90 degree flap harder to implement. The early ASW 20 had problems this way with it's 60 degree flap setting. Boy, you picked up on that one quick! I'm not qualified to address the actual engineering aspects of this issue. But speaking from the perspective of a sailplane development pundit: I think that, absolutely, implementing 90-degree flaps on a composite wing has complications that you wouldn't find on a more rigid metal wing. However, the lessons of the PIK-20B and the Zuni suggest that it is doable. As you point out, the big problem is bending of the wing with fully deployed flaps, which tries to bend the flaps in the plane in which they are most rigid. I suspect that overcoming this issue requires the right layup type and fiber orientation. I'd have to do test sections to be sure, but I think that either aramids or possibly newer polyethelyne fibers on some sort of bias orientation would be required. That might give reasonable torsional stiffness without undue bending stiffness. It seems to work for the LS-6, which uses Kevlar (tm) laminates in the flaperons. Of course, a stiffer wing than the old ASW-20 would help, too. That, and more hinge points and more drive points. Before I tried it for sure, what I'd want to do would be to test a candidate flap section, and see how close I can get it to the predicted wing curvature at the ultimate loading limit. It might turn out to be necessary to either make the wing stiffer, or to limit loading to a lower G value under landing flap deployment. Or perhaps something else entirely. That's what testing is for. Thanks, and best regards to all Bob K. |
#22
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Wallace Berry wrote in message ...
lots of good stuff snipped... Geeze, Wally. Thanks! Just a couple of responses through the entire thread. Floating down the runway? More flaps. With 90 degrees and the nose level...she stops pretty close to right now. Might want to make sure you aren't more than that foot or so above the ground, or you test Schreder's wonderful shock absorbtion. Clouds? Full flaps at whatever speed you are going aren't going to put you up much...and you will come down quite quickly...and out of the cloud. If you go 90 degrees in my 16, you can pretty much let go of the stick (at altitude) and it descends quite docilly...well...it bobs and weaves but it don't scare me much. There is a bunch of drag there. I should note that I am at the forward limit of the CG. My biggest concern about the -16 is that it is gonna ruin me for other gliders. No way will I ever find similar glidepath control. I can modulate out of pretty much any amount of trouble. At any rate, Wally, thanks again. I love to share! And I had to fly tow anyway!! Jim |
#23
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"Eric Greenwell" wrote in message ... Wayne, what's it like to land an HP in a strong, gusty wind? Do you use a higher approach speed and only partial flap? Eric, I am a low time glider pilot and I think more experienced pilots could provide more insight then I; however, from my limited experience you are right on target. Several years ago I purchase a HP-16T (now owned by Brian Case). I search the web for information and found almost nothing, so I started a web site to act as a repository of information relating to Dick's designs. The site was well receive by HP/RS/RHJ owner and article, pictures, etc started arriving. The result is http://www.soaridaho.com/Schreder The information on the site reflects the cooperation of HP enthusiasts, not my expertise. Bob Kuykendall started a complementary service by forming the hp-gliders news group. (http://groups.yahoo.com/group/hp-gliders). The combination of the two resources have served Schreder sailplane design owners over the past five+ years. After I sold my HP-16T to Brian I purchase a HP-14 which I have been restoring for the past 3 years. Here are some relevant landing related articles that I have collected: Dick Schreder -- http://www.soaridaho.com/Schreder/St...r_on_Flaps.htm Steve du Pont -- http://www.soaridaho.com/Schreder/Large-span_flaps.html Bob Kuykendall - http://www.soaridaho.com/Schreder/St..._HP_flight.htm Wayne http://www.soaridaho.com |
#24
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Bob K wrote..
As you point out, the big problem is bending of the wing with fully deployed flaps, which tries to bend the flaps in the plane in which they are most rigid. If one were to bounce, or land in a rough field, in one's ASW-20, with 45 degrees of flap on, the downward motion of the wings would force the deployed flaps to move up, thus bending the internal flap push-rods. I would think some sort of sliding push-rod arrangement might prevent this situation. The Ventus has a gas strut that will allow the deployed flaps to come back up. Do I have the Ventus gas strut figured out correctly, you Ventus drivers? JJ Sinclair |
#25
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On Tue, 18 Nov 2003 07:47:58 -0800, Eric Greenwell
wrote: .... text deleted ... Wayne, what's it like to land an HP in a strong, gusty wind? Do you use a higher approach speed and only partial flap? -- Eric, I resisted jumping into this thread, but for what it's worth, while I no longer fly a PIK, I did own a PIK20B for 18 years and have something over 2000 hours in this 90deg flap only ship. Most of the important points on 90deg flaps have already been said. - they are different, so there is an initial learning curve that is made more difficult by the lack of 90deg flaped trainers. I often recommended new PIK pilots to get an hour in a Cessna 150 to get a feel for high flap deflection behavior. - once mastered, they can be modulated during any portion of the pattern with no problem. As has been said before, if you are floating and can not get the ship down, put on more flap. Once the main wheel is on the ground, dump the flap (full negative (up)) to plant the ship on the ground. - Like any flapped ship, so not get below the flaps up stall speed during the pattern, until your final flare. This allows you to modulate the flaps with no concern about pulling out flap and stalling. - On the PIK, I recommended new pilots move the PIK flap handle (5 turns total) in full 360deg increments, always stopping at the top of the circle. This made modulation like normal spoilers, pulling the handle back from the top position lowered flap, increased drag, just like pulling back a spoiler handle. And the opposite for pushing forward from a top position, less drag. - Relating to your question, the only drawback I found in the 90deg flaps was landing in very gusty conditions. Here I would limit the down flap to something like 45deg. Since this only occured with strong headwind components, I did not need large flap deflections. - The strong advantage to the 90deg flaps was in short field landing, where you could point the ship at a spot on the ground and modulate the flaps to control airspeed. BTW, the only time in all my flying that I used 90deg flaps was in off-field landings over a tree line, and for routine practice. Typical landing flap varied between 30deg and 60deg. Bob |
#26
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Bob Whelan wrote:
... IMHO, about the only situation I can envision where a flaps-only ship IS worse than a spoilers-only one is that of getting low and slow on the approach. Is there a spoilers-only driver alive who doesn't take some comfort in the thought s/he can slam the spoilers shut in that situation and not distinctly improve things in the near-term future? Get yourself in that situation in a flaps-only ship and you're essentially out of options. The GOOD news is that you're much more likely to get low and slow in a ship having weak landing aids...generally not a problem in gliders having _only_ large deflection flaps as landing aids. ... Except for the presence of the runway instead of unlandable terrain below the glider, this is exactly the situation of my question, and so the answer, as I suspected, is that you are out of options. |
#27
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When Slingbys tried to produce the HP14 for the British market they ran into
trouble with the use of flaps only for cloud flying. At that time to get an airworthiness certification the glider had to have speed limiting devices for cloud flying. It had been proved in test flying that the flaps certainly limited the airspeed to "rough air max." but the test pilot ( John Williamson) reported if the airspeed was already high and rising, the effort required to lower the flaps down to 90 degrees was just too much. If the sailplane was genuinely going out of control in cloud the flaps would be useless. Various methods were tried to overcome this including a high pressure air bottle to actuate pneumatic jacks- unfortunately at high speeds forcing the flaps down in this manner caused problems with the supporting secondary spar structure requiring yet further modifications. DB |
#28
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The Ventus Strut is pushing up.
Part of the preflight on my Ventus B is to push down on the inboard flap both sides to feel the gas strut pressure. Al "JJ Sinclair" wrote in message ... Bob K wrote.. As you point out, the big problem is bending of the wing with fully deployed flaps, which tries to bend the flaps in the plane in which they are most rigid. If one were to bounce, or land in a rough field, in one's ASW-20, with 45 degrees of flap on, the downward motion of the wings would force the deployed flaps to move up, thus bending the internal flap push-rods. I would think some sort of sliding push-rod arrangement might prevent this situation. The Ventus has a gas strut that will allow the deployed flaps to come back up. Do I have the Ventus gas strut figured out correctly, you Ventus drivers? JJ Sinclair |
#29
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"Bob Whelan" wrote in message ...
[snip] Speed control is important in gracefully landing flaps-only gliders (spoilers-only too, of course). What I've found - and often seen - is that gliders' large-deflection flaps essentially 'quit working' as drag producing devices if landed 'too fast.' True even for HP-16's. Come in too fast and you _will_ float a long ways in flapped gliders...unless you slowly ease off on the flaps, in which case the ship will gently settle... [good stuff snipped] IMHO, about the only situation I can envision where a flaps-only ship IS worse than a spoilers-only one is that of getting low and slow on the approach. [snip] Regards, Bob W. Hi, Bob and all. With all humility and with the following caveats, I would like to mildly disagree and vehemently agree with a couple of your points. First the caveats: I am not all that experienced, and have only flown my HP-16 for one summer, I think I am qualified to comment, but by no means am an expert. The following comments ONLY apply to my HP-16, N8DC, with 90 degree flaps, standard sized flaps (no flap was sacrificed to improve the ailerons), and flown fairly CG forward. Mild disagreement on the too fast comment. I think that the only way to make my -16 float would be to be going too fast and then roll off the flaps. 90 degree flaps require an impressive deck angle just to keep the speed in the 60mph range on approach. If, when I get close to the ground, I flare, any excess speed, and I mean ANY excess speed is gone very quickly, and I land. Period. An approach with, say, 60 degrees of flap would indeed float if I had too much speed on, and as such, one possible corrective action would be to roll off the flaps, if I had slowed considerably...otherwise, more flaps is usually the right answer. This airplane will not float with maximum flaps. There have got to be 6 square feet of aluminum hanging perpendicular to the airflow...we stop pretty quickly. A minor expansion on that. It is very difficult to get the airplane to accelerate with 90 degree flaps...If I should let the airspeed decay on approach with full flaps, I need to push the nose down to frightening angles...as in hanging from the straps...to accelerate...or just roll off some flaps, which is what I do. This presupposes that we are talking 45-60+ speed range. I would very much not like to get much below 45 with full flaps. The aircraft's stall characteristics are quite benign, but recovery requires a fair amount of altitude with flaps at that level. Conversely, speed control on appoach is quite trivial. Should I, for whatever reason, let the speed creep up...more flaps...less speed. It is amazingly linear...and better than any speed/lift control device I have used, including throttle. To agree emphatically on another point: Low and slow with flaps on is a VERY BAD THING (tm). Too fast is no problem...roll the flaps in to slow, roll them out to stretch. Too slow, and your options are...well...gone. So that is an area of the performance curve that I avoid. I too went into the -16 wondering about all of the forked-tailed flaps of doom talk. Turns out that my airplane is an absolute pussycat. If yer ever planning on being around LaGrange, GA some weekend, drop me a note. We might can work something out! Jim |
#30
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Robert Ehrlich wrote
Except for the presence of the runway instead of unlandable terrain below the glider, this is exactly the situation of my question, and so the answer, as I suspected, is that you are out of options. I think that's rather overstated. Unless you have botched the pattern so throroughly that you are at 30 degrees of flap and coming up short, you do exactly what you do in a spoiler-only ship - you retract the flaps. The difference is this - you can't just retract completely, as you would spoilers, because retracting that last 30 degrees is going to cause a transient drop you won't like. However, going from 90 degrees to 45 causes no loss of lift at all, and a huge loss of drag - thus causing airspeed to increase, which allows lifting the nose and dramatically flattening the approach. This was certainly the case in my HP-11, and I can't imagine it would be much different on other flaps-only gliders. Michael |
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