+++ #2177 From: bearhwk272 Subject: Bearhawk: Attitude and Drag in Flight I am not really weighing in on this, just kind of letting a soft litttle Butterfly drift away. Budd, when you flew the Bearhawk at FnS where you at gross( Weight I mean) ? At what altitude. ( Density ) ? How much fuel?( I will read the pirep at Airbum.com) Without messing with major aerodynamic issues and geometry it seem to me that speed is not what the Bearhawk was about ( we all know that ! ) I do not plan any major aircraft changes, just go back to basics, keep it light clean up the drag with fairings and pants. Watch out for cooling drag and lost HP from bad exhaust systems. Speed is aerodynamic clean, Climb is power. Prop it right. If you are fortunate enough to accidently stuff a monster motor in, well try just a little more down thrust ( 3 deg more ? ) and possibly a reflex position at cruise on the flaps. ( Adaptive geometry?) I will postulate that a good comprimise will result. If the above does not work try huge tundra tires and a canoe to fair the under belly. ;-), +++ #2188 From: Russ Erb Subject: RE: [Bearhawk] SnF/P-II comments > In layman's terms what I believe Budd was describing is the fact that > with the current setup, at 260hp, the wing is producing too much lift > above about 135mph. Close but not quite. In level flight, to the first order of approximation, lift must equal weight. Lift comes from three things: angle of attack, airspeed (really dynamic pressure), and wing area. We can't change wing area, so don't worry about that. As we go faster, we must decrease the angle of attack of the wing so that the resulting lift is still equal to weight. What budd is saying is that for the 260 HP Bearhawk, the resulting angle of attack is so low that the airfoil is not working in its optimum range, and the fuselage is so nose down that it is creating extra drag. Clipping the wings reduces area, so it forces the wing to a higher (more efficient in this case) angle of attack. Decreasing the incidence doesn't change anything about the wing, it just lines the fuselage up with the airflow better while leaving the wing in the same condition. This is not as meaningless of a discussion as some of you might think. This is an optimization issue, and budd brought it up and I talk about it because we think it is important. Unfortunately, like most things, anything done to improve this issue will degrade performance somewhere else. Of course, something budd didn't mention that would improve the fuselage angle somewhat--load the sucker up to gross weight (not sure what weight budd was at). That will increase the weight, demanding more lift, which will give a higher angle of attack. Still, it would reduce performance in other areas. Time to go to bed... +++ #2192 From: budd davisson Subject: Re: wing comments Russ hit most of the naisl on the head but missed one other aspect that differentiates one airfoil from the other and that's camber and this is the culprit in this case. The 44 series airfoils have a fair amount of camber of product lots of lift at low speeds and low angles of attack (AOA). A simple change to a an airfoil with a slightly lower camber line (24 series is what Bob is talking about) would make the difference and the lower coeffecient of lift would probably add a penalty of about 2 mph at the low end. This change, coupled with a lower angle of incidence straightening out the fuselage in cruise would probably add at least 10mph at cruise. However, loading the airplane up (we were two people with full fuel, probably about 1900 pounds) would indeed partially straighten the wing out. Also climbing higher would probably make this one of those rare airplanes that either goes up in indicated airspeed or at least holds it to a higher altitute because the AOA of the wing will increase as the atltitude goes up. So, at altitutde, it will have a fairly good increase in TAS. As I said at the beginning of this discussion, if speed and pure efficiency isn't important, forget about all the foregoing conversations and just build it as it is. It's truing 150-152 at 23 square which isn't ligtening fast, but it isn't bad. +++ #2206 From: budd davisson Subject: Re: Final Comments on Speed Potential Alright, already. Let me put this entire speed/wing thing to bed right now, since I'm the only one with time in the 260 prototype. First of all, negative on the 135 top end. I never went above 23 square at which point it was truing 152-155 mph (145 indicated, 80°F, 3,000 ft, someone check my figures as I only have an E6B prayer wheel). I'd guess 23 square to be something like 65%. Without changing anything other than wheel pants, cuffs around the bottom of the gear "V" where the shock structs attach (super dirty area) and longish cuffs on the top end of the lift struts, that would go up to 160 mph, TAS, WITHOUT EVEN TRYING. There's another 3-5 mph in the cooling area and probably 3 in flap and aileron gap seals. Cuffs on the tail struts and streamlined tail wires would be maybe another 3 mph. Build this thing the way it is, light, straight and clean it up and 165-170 true is probably an honest 65% cruising speed with a 540. The 180 hp version would be within 7-10 mph of that but wouldn't have the high altitude cruise or the blinding takeoff. Even so, the 180 will surprise you with its takeoff performance. I mean REALLY surprise you. I'm sorry I started this whole wing controversy. Shame on me. The airplane is terrific, as is. It could be "terrificer" with a different airfoil, that's all. My thoughts have just been the old hotrodder in me talking and the engineer in me complaining. Just ignore everything I've said and build the airplane. +++ #2216 rom: Russ Erb Subject: [Bearhawk] Re: wing comments > Russ hit most of the naisl on the head but missed one other aspect > that differentiates one airfoil from the other and that's camber and > this is the culprit in this case. The 44 series airfoils have a fair > amount of camber of product lots of lift at low speeds and low angles > of attack (AOA). A simple change to a an airfoil with a slightly lower > camber line (24 series is what Bob is talking about) would make the > difference and the lower coeffecient of lift would probably add a > penalty of about 2 mph at the low end. This change, coupled with a > lower angle of incidence straightening out the fuselage in cruise > would probably add at least 10mph at cruise. Well said, budd. I had thought about that but forgot it in the rush to get the e-mail out. Though not necessarily intended by NACA (pronounced as four letters, not a two syllable word like NASA by the old heads) it works out that the first number of a NACA four digit airfoil divided by ten is the approximate design lift coefficient of the section. Hence, a 4412 has a design lift coefficient of about 0.4. A 2412 has a design lift coefficient of about 0.2. In case you're wondering, the NACA 4 digit series really means: First digit: Maximum camber in hundreths of chord Second digit : Location of maximum camber in tenths of chord Third and Fourth digit: Maximum thickness in percent chord Hence, our vaulted 4412 has a maximum camber of 4%, located at 40% chord, and a maximum thickness of 12% chord. +++ #2217 Donald Schindler Subject: Re: RE: [Bearhawk] SnF/P-II comments Bruce, I called Bob quite some time ago and questioned him about going negative with the flaps. Is this what you mean by reflexing? We discussed that Maule's have a 6 degree negative setting for cruise that dumps lift(and drag). Bob was very favorable that this would be easy to incorporate in the Bearhawk system. This is in my plans but I am not to that stage yet. We also discussed clipping the wings but he felt there were to many negative tradeoffs(slower climb, decreased ceiling, higher stall) and you would probably gain only 5mph. Don 068 +++ #2220 From: Tim Anderson Subject: Re: RE: [Bearhawk] SnF/P-II comments I have my kitfox sit up this way. I don't have a true airspeed trim control, so I use the negative settings for cruise attitude fine tuning. It should be a matter of adjusting the control rod length on the flap drive to allow a negative deflection in the full up position, but have the "Zero" flap notch on the cabin flap lever at the appropriate place. When in cruise, one can fine tune at attitude. +++ #2237 From: Collin Campbell Subject: negative flags on Maule I have been listening to the comments on the negative flaps on the Maule. I think this might be helpful on the Bearhawk as well. On the Maule that I am presently flying, this works quite well. I haven't done any precise tests but can say that a definite speed increase is noted. As a side note, the negative reflex is 7 deg. not 6, as was mentioned. In cruise I have found that the optimum reflex is not the full 7 deg, so I put something under the flap handle to keep it from going the full 7 deg. I would like to see something similar designed for the Bearhawk, it shouldn't take much to implement. Any thoughts? +++ #2240 From: budd davisson Subject: Re: Reflexed flaps I like the idea of reflexed flaps as a compromise mod. It's an aerodynamic "fix", but one that won't compromise the low end performance. The reflex won't have to be as much as the Maule because the flaps are much, much bigger. What you're doing by reflexing the flaps is decreasing the camber of a portion of the airfoil. With the flaps running that far forward, we may find only a few degrees is needed. Also, the amount of reflex shouldn't be a fixed setting because a different amount will be needed for different speed ranges, engines and loads. I could see a big knurled knob mid-way up the flap handle that varies the stowed position and, once you're leveled off in cruise, allows adjusting the reflex to match conditions. Or maybe a ratched situation that changes the stowed position by a degree at a time. That could be a four or five sided eccentric block on the floor with a 1/4" drive ratchet handle and you rotate the block until the right setting pops up. The nice thing about reflexing is its easy to accomplish and easy to research in-flight. +++ #2258 Russ Erb Subject: Flap Reflexions Since nobody else had checked to see if was possible, here are a few thoughts: 1. Checking my CADD drawings and playing with them a while, the maximum reflex available would be about 7.8 degrees before the nose of the flap hits the rear spar. 2. As designed, the flap loads in the full up position are carried by the bumper on the flap drive. Setting the system up for reflex would require the flap cable and thus the flap handle to carry flap loads at all positions except full reflex. 3. Because of interference between the torque tube arm at the wing root and the rear spar attachment, setting the flaps up for reflex may cause the same amount of loss of full deflection at the other end. Fortunately, this would probably not be noticeable. +++ #2261 From: budd davisson Subject: Re: [Bearhawk] Flap Reflexions How about this for an adjustable flap reflex setting: A slight ramp on the floor with a sliding stop that the flap handle rests in As for loads, they aren't very high, but it wouldn't hurt to identify the weak points and beef them up a little. +++ #2262 From: budd davisson Subject: Re: [Bearhawk] Flap Reflexions In re reading your notes about playing with the CADD drawings for reflexing the flaps you mention the up loads are taken by the bumper on the flap drive. That being the case, the ideal situation would be to have that bumper be adjustable. Without going into the drawings and looking, since you've already looked, is that doable thing? It would be much better to keep the drive mechanism unloaded. +++ #2266 From: Russ Erb Subject: Re: [Bearhawk] Flap Reflexions I recommend you look at the drawings. The "bumper" is a piece of rubber hose around the compression tube between the spars that the front end of the pushrod rests against, taking the loads from the flaps through the pushrod and into the compression tube. It's an elegant system, and trying to change it would go against the Barrows doctrine of simplicity, although many of us (note I said "us" not "ya'll") seem unable to leave well enough alone. Another thought would be to provide an adjustable mechanical stop for the horn at the root end of the torque tube. The torque tube would still be loaded, but the cable would not. This strikes me as one of those things that is accessible enough that it can be experimented with after the airplane is flying, and maybe that's the real answer--get it flying, then worry about it. +++ #2271 bearhwk272 Subject: Reflex Flap another concern / consideration While putting down some road miles today contemplating the reflex situation I had a revelation. The previous posted concerns are correct and valid. There is an additional issue in that the current mechanism to retract the flaps is spring return to the stop. If the flap is spring returned into the reflex position the spring force on the flap must be great enough to hold the flap in the reflex position up to Vne. In addition to Vne, spring load must handle the vertical gust requirement without changing position. Yes, the loads are low but there is a Velocity Squared function in there and low and behold the spring is at its maximum retracted position. ie. least force available thru spring and linkage geometry. Somehow I smell a dual cable setup or push rods or electric jack screw........ one change begats another hundred. This is a modification requiring carefull thought and will turn out better and easier if incorporated in the building process rather than a field mod. Would Bob have any interest in performing a preliminary test to determine if there is any benefit to this reflex stuff.? After all he is the only one flying and he does call it PROTO II, not production conforming. +++ #2273 From: Russ Erb Subject: [Bearhawk] Reflex Flap another concern / consideration > There is an additional issue in that the current mechanism to retract > the flaps is spring return to the stop. If the flap is spring returned > into the reflex position the spring force on the flap must be great > enough to hold the flap in the reflex position up to Vne. In addition > to Vne, spring load must handle the vertical gust requirement without > changing position. Excellent point, Kevin. I had missed the jump that the loads would be reversed. My thinking was that in the trail position the cable would be loaded, but missed that at some point the flap won't float up anymore, but would need to be forced into position. We'll see if budd's grand idea includes an answer for that. +++ #2274 From: budd davisson Subject: Re: [Bearhawk] Reflex Flap another concern / consideration Ref: Budd's Last Grand Idea on reflexing I'll call Bob and we'll kick it around. It sounds like the type of thing that could be flight tested with a juried rigged reflex built in to see if it is worth it and then the linkage/stop issues addressed. Knowing his feelings about speed, he'll probably say (very slowly) "Well, I don't know but you can try it if you want," in which case we're back to the get-the-damn-airplane-flying-THEN-diddle-with-it concept, which makes perfect sense +++ #2279 From: budd davisson Subject: Bob's comments on Reflex Flap The final word (?): I just got off the phone with Bob about the reflex flap thing and this is the way he sees it: A. It is probably the most efficient way to fix the wing nose down problem. B. It is EASY to do, his words. C. All that needs to be done is the length of the actuating rod has to change. D. Cut another notch or two in the quadrant for the reflex position(s) He says the spring is plenty strong enough to overcome gust loads. He says he accidentally flew over 100 miles with the flaps at one notch hitting 120 mph (nearly super sonic for Bob) at some points and the flaps didn't move. So much for that discussion. +++ #2291 From: Rod Smith Subject: Wing Incidence Assuming that reflexing the flaps tests out as a viable option, would you recommend any change in the incidence angle. It seems to me that aerodynamically it would be good to go to 0 deg, would this make a big difference in forward visibility during landing. Deck angle should not be a problem for me as I will be on tundra tires. +++ #2294 From: budd davisson Subject: Re:lost comm RE; Angle of incidence Someone asked me a question this morning about angle of incidence and i tried to answer it, but, per usual, my system was screwed up and I don't know if my answer went out or not. Anyway, my answer (which you may already have) is that, no, we don't want to change the angle of incidence. It would bring the tail down for cruise but the nose would be up for flying final and we don't want that. That's a problem with the Husky and Helio Courier. You can't see the spot when you're as slow as you can get on final, so being slow doesn't help you any. Any day now you're going to read a report about some guy going postal and machine gunning his computers. Don't expect any more posts from me after you read that. +++ #2297 From: Tom & Michelle Brant Subject: Re: [Bearhawk] Bob's comments on Reflex Flap Does this mean that Bob is going to test this option? Like you mentioned before it could simply be "jerried" at this point to see if the theoretical turns into actual performance. I agree with your ideas on a knob on the flap handle... A thought on the spring loading also... I trained in the Piper Tomahawk (I know, I know... The Tomahawk and the Bearhawk in the same sentance is a bad omen...) Anyway, the Tomahawk uses spring loading for its elevator trim. ie: It doesn't really have true trim. All the trim wheel does is increase back pressure on the elevator so you (the pilot) doesn't have to hold it there. The only reason I bring this up is to negate the concerns about spring loadings being too much, which Bob already agreed with. My immediate thought when I heard your ideas was of an adjustable knob or ratchet like you mentioned. This thought came about from the Tomahawk which is similar in principal. Hopefully this is something Bob is willing to test so that this discussion can either continue towards a design answer or (if the tests prove it's not worth it) be over with. In any case, it's a good idea. +++ #2318 From: Russ Erb Subject: Steppin' up to the challenge I don't remember if it was in this forum or on budd's pirep for Proto II, but mention was made that the Bearhawk wasn't exactly the easiest airplane to get into. A step would be nice, but it would also serve the additional purpose as a drag-producing device. I had my own experience climbing into Proto I at Sun'n Fun 99. Stand here, throw your leg there, grab this, brace here, pull this, push that, plop your butt in the seat, adjust. Not exactly graceful. I'm confident that my wife (shorter than me) won't be able to do it, or at least won't be willing to do it. Here's my suggestion. It carries a slight weight penalty but no drag penalty: Get a step stool of a suitable height. Tie a line to it. Last person to get in holds the line and pulls the step up after him. In the ideal case, the step would then fold up for storage. By the way, getting out is much easier--throw your legs out and slide down. Gravity does most of the work. +++ #2321 From: budd davisson Subject: Re: [Bearhawk] Steppin' up RE: a boarding step Believe me, getting in the airplane is a stretch and a step is sorely needed. As I mentioned in the pirep, I think a wedge or peg attached to the back leg and sticking straight back would work and would produce little or no drag. then you could put your left foot on that and use it to help get your butt up on the edge of the seat. Once you do that you're okay. My 195's had a retractable step that hinged at the top and a cable attached to the door pulled it in. There's something for the gadget freaks amongst us to work out. It could even be an L'shaped piece of tubing that drops out of the fuselage with alittle handle inside and you pull it up and rotate it 90° to lock it up. At the same time, we're worrying about a miniscule amount of drag, so let's not complicate this thing too much. Getting in easily is more important than the .5 mph saved. +++ #2326 From: Float-By Shooter Subject: Re: [Bearhawk] Steppin' up The one thing that I don't like about a ladder or stirrup hanging off the airplane, is how easy it would be to forget to pull it inside before departure. I like Russ' idea of a stepstool with a string attached, worst case scenario you forget and leave your stool sitting on the ramp someplace, instead of bangin against your fuselage. In the 152 one time I left about 3 inches of my lap belt hanging outside the door, and the resulting noise scared me even more than the time my door decided to open during climbout. Some of the bush super cubs have what looks like a piece of angle iron attached to the gear legs for a step, but they aren't exactly concerned with looks or drag for that matter. +++ #2327 From: Tom & Michelle Brant Subject: Re: [Bearhawk] Bob's comments on Reflex Flap I agree with the comments about not enough down force for cruise. I understand what you're saying about the Bearhawk too, but I think Bobs comments about shortening the linkage should be enough to take care of the problem. My concern is what you had mentioned before about the attatch points and the stresses they would be under with the negative loading of the flap. Surely there is a way this issue can be resolved without too much effort. However, that seems to be the problem with changing something on a design. It doesn't just affect one thing. +++ #2328 From: Bruce A. Frank Subject: Re: [Bearhawk] Steppin' up Would a piece of 4 inch long stream line tube welded, parallel to the ground, to the rear leg of the gear really cause enough drag to noticeably slow the plane? Or maybe a piece of streamline welded to the lower longeron, just behind the lift strut attach point, angled down ending with a horizontal piece (parallel to the ground) similar the what is used on the Defiant (Maybe the Defiant step is not in the plans, but the only one I have ridden is was Bayard DuPont's which did have such steps). +++ #2330 From: mailstuff Subject: Re: [Bearhawk] Steppin' up This is not a laminar flow composite bird. Drag from such a step would be negligible, so make it practical. +++ #2331 From: Pierce Terry Civ 412 TW/TSI Subject: RE: [Bearhawk] Steppin' up The Stinson 108 series uses a piece of streamlined tube down from the lower longeron area with another piece of streamlined tube welded on in what would be a horizontal position in flight. The outboard end of that piece has a flat plate welded on presumably to prevent feet from slipping off. The reason I mention this is that the up tube is not welded to the fuselage. It is slipped up into the next larger size of streamline tubing which is welded to the fuse and pinned there with a bolt. With appropriate access planned ahead of time, you could fly with or without the step on either side as is appropriate for requirements at that time. +++ #2429 From: Benton Holzwarth Subject: re: Flap Reflex > Subject: Reflex Flap another concern / consideration > > While putting down some road miles today contemplating the reflex > situation I had a revelation. The previous posted concerns are > correct and valid. It's been quiet for a day or so, so I thought I'd toss another log on the fire... I've been wading through past posts again and have a pile of 'em I'll comment on as time goes by. My thought on reflex: Would it be as useful to also reflex the ailerons? I can think of a couple ways to do reflexing in the ailerons, none of which are as straight forward as moving the flap's bumper stop. But I guess what got me a little more worked up to consider it was the question of whether, if one were to forget to remove the flap-reflex before landing, would one be flying near stall speed with the outboard section at a greater lift coefficient, and at risk of stalling the outboard section first? If one wing panel were to give out before the other, due to 'stick stirring' that could be bad. Is this a problem, in practice, with other designs that reflex the flaps (only)? Is it just a part of practice to *never* land with the flaps still in reflex on those designs? +++ #2430 From: Float-By Shooter Subject: Re: [Bearhawk] re: Flap Reflex > My thought on reflex: Would it be as useful to also reflex the > ailerons? I can think of a couple ways to do reflexing in the > ailerons, none of which are as straight forward as moving the > flap's bumper stop. I think that since the aileron nose is designed to protrude below the wing when the aileron is up, any benefit to reflexing them would be offset by the increased drag of the aileron nose. The drag is intentional and is meant to reduce adverse yaw. +++ #2432 From: budd davisson Subject: Re: [Bearhawk] re: Flap Reflex The Maule's reflex their flaps 7 degrees and that is the zero-flap, stowed condition and you can't tell any difference when you land it that way. +++ #2451 From: Russ Erb Subject: What? Flap Reflex...Again?! Now relax--there's some actual meat in this post. I've just finished installing the aileron and flap hinge mounts and hinges on the first (left) wing. The records show that it only took a little over 13 hours to drill 26 holes, at an average rate of 30 minutes per hole. It was actually much worse than that--6 of those holes (all in the hinge mounts) took the majority of the time. Why is Mister 3 Sigma so slow? Because these holes are some of the critical holes. Properly positioning the hinge mounts is critical to have the flap and aileron properly positioned (as if that wasn't obvious...). This is not important just to have all of the trailing edges lined up to look pretty, but also to have everything straight so that the airplane will fly straight. Also, since the flap has 3 hinges, all of those must be on the same line or the flap will bind. As such, I consider it time well spent, especially since I'm very happy with the way it turned out. Pretty amazing when you consider that measurements and decisions made over the last four years came together this week and actually fit. Think how many opportunities that was to screw up. As for the title, I have important news. Based on my wing and flap, built to plans as best I could, the maximum flap reflex available would be about -4 degrees. I had previously reported a bigger number, based on the idea that the limiting factor would be the nose of the flap hitting the rear spar. Well, I was wrong. The limiting factor is the flap control horn (flap hinge center, the thing the pushrod attaches too) hitting the hinge mount. Even so, Lee Erb is calculating that we'll only need -2.5 degrees. I plan to make my pushrod such that that is an option. One other thing. While I normally recommend against modifying the design, the area around the hinges on the flaps and ailerons is designed too tight for my tastes. While I was able to make it fit, everything is pretty tight and thus more difficult to work on. If I was doing it again, I would: 1) Widen the cutouts in the nose sections a bit. As it is, the longest bolt I can get in to put throught the rod end bearing is about 1/16" too short for my tastes. This is also needed for #3 below. This will mean moving some nose ribs and also back ribs to suit. 2) In the steel angle hinge pieces that attach to the flap or aileron spar, move the bolt holes closer together, away from the edges of the spar. As I built mine, the bolt holes are right at the edge of the .063 doubler. I would like them closer together so that the .063 doubler had some edge distance. For several reasons I won't go into here, I think mine will be okay, but I would have liked it better with the bolts not so close to the edge. 3) On the same pieces, make the flange a little wider so that the bolt head is moved a little farther away from the side. As it is, I can't get a socket around the bolt head, and have to use an open end wrench in a way it was not intended to be used to tighten the bolt. If you haven't started building these pieces yet, you may want to consider doing this. What I've suggested is not a simple change and will change many dimensions in addition to those mentioned here. You'll probably end up redrawing the whole flap and aileron and part of the wing. On another note, a week and a half ago my composite expert came over and we layed up the fiberglass for my first wing tip. Still much work to be done on that. I may write about that at a later date. +++ #2462 From: bearhwk272 Subject: Re: [Bearhawk] Another Set of Flap and Aileron Mods Russ's comments on the flap and aileron hinge points are consistent with what I am finding, however here are my " fixes ". To obtain additional clearance for the installation of the hinge bolt try the following. On the nose ribs, forming the pocket, drill a hole in the nose rib in line with the hinge bolt CL. The hole should be big enough that the head can be passed thru. Upon hinge bolt installation use needle nose pliers to back the head into the hole. then advance the bolt thru the brackets. Works great. Do the same at the push rod location. No other mods required. ( Russ, you can put these holes in now with a little dremel.) To obtain more meat at the doubler, double the doubler.( Sounds like a Burger add) I made a second doubler that is a .75 wide strap that is attached to the back of the doubler at the top and bottom and secured with the nutplate rivets and a couple of extra rivets thrown in. This also feathers the stress out a little better. Doubler thickness at the bolt location now .125. ( Yes, this to can be added now ) Edge distance not changed but thickness increased, strain lowered. Change the hinge attach bolts to a 12 Point NAS style. This is a little more expensive fastener. The " washer head " is just the right diameter on my brackets. Easy straight socket access with a 12 point socket.( Russ, you can incorporate this now and save the hassle later. ) One last picky point. Have not fully figured out the -4 rivets where the aft ribs join the spar flanges. It is mighty tight to maintain edge distance of 2.5 x D. As required because of the contersunk rivets. I am pondering using -3 and adding a gusset to each aft rib similar to the small ones at the other locations. That method would be much stronger, more conventional. If you think that the -4 rivets at the ends and at the hinge attach pockets are doing anything look again. Comments? +++ #2464 From: Russ Erb Subject: [Bearhawk] Re: What? Flap Reflex...Again?! > How much would you recommend widening them? The flap/aileron hinge cutouts are so tight that a 1/4" would make a world of difference. 1/2" would probably be more than enough. They're basically at zero clearance in several places right now. +++ #6566 From: pfflyerz@c... Date: Sun Jun 17, 2001 7:47 pm Subject: reflexed flaps After reading the Sport Aviation article on the Murphy Super Rebel this month I got reinterested in what it would take to do the same thing on the Bearhawk. Seems to me it could be easily done by simply adding an intermediate "0" stop on the flap control segment. There is another problem though and I don't know what the impact, or the solution to it is. The flaps are held in the "up" postion by the springs on the ground, and by air pressure in flight. The springs can hold the flaps in the reflex position on the ground, but won't air pressure tend to streamline them to the "0" position in flight? There is no apparent force available to hold the flaps in that position tha I can see. Any Ideas? Pat Fagan #232 Pearblossom CA +++ #6568 From: "Bruce A. Frank" Date: Sun Jun 17, 2001 10:53 pm Subject: Re: [Bearhawk] reflexed flaps > The flaps are held in the "up" postion by the springs on the > ground, and by air pressure in flight. The springs can hold > the flaps in the reflex position on the ground, but won't air > pressure tend to streamline them to the "0" position in > flight? I haven't seen how the Bearhawk flaps are actuated, but I gather that with a spring retracting them then the mechanism may be a cable pulling on a bell-crank to extend the flaps. My setup uses a continuous cable loop attaching to two bell-cranks with arms from the bell-cranks to the flaps. The cable continues beyond the fuel tank then makes a 90 deg forward through the rear spar (Piper Super Cub type wing) then through the front spar where it turns 90 deg again to go back to the cabin. The cable loop is a continuous attaching to the flap handle arm in the wing root. This gives me positive actuation and retraction with a notch position for reflexed. -- Bruce A. Frank, +++ #6569 From: "Russ Erb" Date: Mon Jun 18, 2001 8:01 am Subject: Re: [Bearhawk] reflexed flaps Pat--we had a rather substantial discussion of flap reflex back in April 2000. It's all on the Bearhawk CD Version 2 under "Design Modifications". In short, the maximum reflex you will probably get is about 4 degrees because the flap horn hits the hinge mount. We think this should be sufficient to offset the nose down attitude at high cruise speed that budd reported. The consensus also was that there is still enough pressure differential at the flap that it will float to the reflex position. You don't have to modify the flap handle quadrant. You could just shorten the pushrod at the flap. This may mean just adjusting the rod end by screwing it in a few more threads. This would bias all of your flap settings up by that amount. My take on all of this is that I'll get the airplane flying with no reflex first. After I'm happy with that, I can adjust the flap pushrod to see if reflex has the desired effect. Russ Erb +++ #6575 From: pfflyerz@c... Date: Mon Jun 18, 2001 3:45 pm Subject: Re: reflexed flaps > Thanks Bruce and Russ for the thoughts. The consensus also > was that there is still enough pressure differential at the > flap that it will float to the reflex position. I remember the discussion on this subject that went on a while back, but I didn't recall there being any conclusion as to how they would remain reflexed in flight. I kind of figured it would require some positive manner like Bruce described. > You don't have to modify the flap handle quadrant. You could > just shorten the pushrod at the flap. This may mean just > adjusting the rod end by screwing it in a few more threads. > This would bias all of your flap settings up by that amount. I shortened the push rods to get five degrees of reflex at the bottom notch on the flap quadrant, but the second notch is so far away that it causes 4-5 degrees of flap extension, so it would require an intermediate notch for "0". I guess I will wait for someone else to try it to see if a positive up lock is needed. Pat Fagan #232 Pearblossom CA +++ $Id: 2.9-AeroDetails,v 1.3 2001/09/26 04:26:47 bentonh Exp $