+++ #5131 From: Benton Holzwarth Subject: Dan Raymer's Aircraft Design Courses Received this 'e-flyer' from Daniel Raymer for his Aircraft Design courses. Thought some here might be interested. I took in his presentation at Oshkosh a year and a half ago, and thought he was a great speaker. I believe his book, available through AIAA, is well thought of, as well. Also, rather than post the 100k gif course 'flyer' that was attached to the email, I've moved it to my webspace -- www.aracnet.com/~bcgh/oddBits/RaymerClasses01.gif if you'd like to see it. Subject: Dan Raymer's Aircraft Design Courses at National Test Pilot School Date: Thu, 8 Feb 2001 14:18:47 -0800 From: "Daniel P. Raymer" To: Hello, I'm writing to let you know about the Aircraft Design related short courses I will be teaching in the near future. The classes will be held at the National Test Pilot School at Mojave Airport near Los Angeles and are open to the public. For class information and content outlines click on the links below. The popular five-day Aircraft Conceptual Design Short Course (http://www.aircraftdesign.com/shortcrs.html) will be offered from 23-27 April 2001. This is the broad overview course that covers most of the material in my book, "AIRCRAFT DESIGN: A Conceptual Approach" (http://www.aircraftdesign.com/book.html), plus other material of interest to designers and aeronautical engineers. It goes through the complete process of developing, analyzing, and optimizing a new or derivative aircraft concept. The Advanced Aircraft Design Short Course (http://www.aircraftdesign.com/newcrs.html) focuses on configuration design layout and loft. It teaches current or would-be aircraft layout designers the "tools of the trade", from initial loft techniques to the inner workings of CAD systems. It will be offered from 30 April-1 May. Since this is the Monday-Tuesday after the 5-day course, it is possible to take both (with a discount) and spend a weekend in LA or skiing up north. Finally, the three-day Short Course in Aircraft Systems Engineering, Architecting, and Design Management (http://www.aircraftdesign.com/systcrs.html) will be offered 22-24 Oct. 2001. This class considers the "big picture" of aircraft development: Why we are building a new aircraft, what it will do, who wants it and why, what requirements it must meet, and how we will plan and manage the effort. Addressing both commercial and military aircraft, the class also includes such hot topics as Integrated Product Teams, Cost-as-an-Independent-Variable, MultiDisciplinary Optimization, and Acquisition Reform. For further information including price, registration, hotel, and transportation, see http://www.aircraftdesign.com/ntpsclass.html. If you'd like a detailed brochure kindly respond with your mailing address. I would appreciate it if you could post the attached page and pass this email to anyone you think may be interested. Thank you very much. Sincerely, Daniel P. Raymer +++ #5141 From: Ken Beanlands Subject: Airfoil Does anyone know off-hand what airfoil is used on the BH? Even better, what other planes share the BH's airfoil? Just curious about the float capabilities (since none currently exist on floats) and wanted some imperical data to compare with. Some airplanes appear to be great floatplanes on paper but in reality, are not that great. The 180 has done well for years on floats, but compared to a Helio Courier, Super Cub, Rebel or Beaver, it's not even in the same league. A lot of the difference is in wing areas and airfoils used. The 180 has a more laminar airfoil with a lower thickness than the others giving it good cruise performance but compromising take-off and climb performance, especially at gross. Any thoughts? +++ #5142 From: "Todd Chisum" Subject: Re: [Bearhawk] Airfoil NACA 4412 Check out: http://amber.aae.uiuc.edu/~m-selig/ads/aircraft.html#conventional +++ #5143 From: Budd Davisson Subject: Re: [Bearhawk] Airfoil The BH uses a slightly modified 4412 which, obviously, is picked for it's slow speed capabilities. As you may have picked up from some of the earlier posts, it is the wrong airfoil for optimized cruise because at 23 square with the 0-540 the airfoil is a solid 2 degrees nose-down unless the airplane is really loaded. At Oshkosh, when I flew it, we had about 400 pounds of stuff in the back, and the airplane flew airfoil level at exactly the same TAS (155 mph) as when nearly empty. Bob worked out a small linkage change (I think 3/16" longer) in the flaps so that those who want, can reflex the flaps a couple of degrees to load the wing at higher speeds. As the only one in the group who has any flight time in the BH, I'll guarantee you it's gonna be a real hoss on floats! +++ #5207 From: Mark "Mark and Tina Lapierre" Subject: 2 degrees nose down? I've read that the Bearhawk likes to fly 2 degrees nose down in straight and level flight. I've read that this is because of some compromises that had to be made in the wing design to aid the short field performance. There's probably a lot more to it than this, but wouldn't rolling the wing 2 degrees forward on it's mounts reduce parasitic drag by putting the fuselage and more importantly, the empannage in better alignment to the relative wind while in straight and level flight? It would seem that correcting this with the tailfeathers or tucking up the flaps would create some drag as a side effect of curing the problem. Has anyone else looked into this? Is it enough of a problem to even bother with? +++ #5208 From: Russ Erb Subject: RE: [Bearhawk] 2 degrees nose down? We've been around this block before. Let's see if I can summarize. budd started it all in the pilot report on the 260 HP Bearhawk. The 170 HP Bearhawk didn't have this "problem" because it didn't fly as fast. The nose down pitch angle resulted from reducing the angle of attack to maintain level flight at the higher speeds. Adjusting the tail will not solve the problem (I won't bore you with why here). The solution needs to dump lift from the wing to increase the angle of attack. The consensus in the last round was that the best solution without sacrificing short field performance was to slightly reflex the flaps. This is not without its problems, but should be fairly easy to do by adjusting the length of the flap pushrod. Only a few degrees of reflex are needed, and that's about all that are available because eventually the nose of the flap hits the rear spar and won't go any farther. No one has flight tested this idea yet, because The Bob doesn't fly that fast and none of us have a flying example yet. budd has promised to test it (since he started this) when he gets a demonstrator flying. See the archives or the Bearhawk Reference CD for more details from the previous discussion. +++ #5209 From: Corky Scott charles.k.scott@d... Subject: Re: [Bearhawk] Digest Number 330 > The solution needs to dump lift from the wing to increase the > angle of attack. The consensus in the last round was that the > best solution without sacrificing short field performance was > to slightly reflex the flaps.... This solution is in fact what the designer of the Christavia recommends as well. +++ #5576 From: "Float-By Shooter" Subject: Re: [Bearhawk] Structural Analysis Software > You're probably the most knowledgeable as to what Bob was > refering to when he says that he prefers tube and fabric > construction because, among other reasons, the structural > analysis is relatively simple and the software is > reliable. What software does he use? Software? Bob uses software? I think he said the calculations are reliable. Del Rawlins +++ #6412 From: snorttheoneandonly@y... Subject: I was looking at your website and glad to see you include the building process of your Christavia. Very nice site and plane! It got me to thinking about something I had read in the archives of the Bearhawk posts about the building methods of the Thorp T-18 or was it the S-18 derivative? To anyone who might know, is there some very common-sense building technique involved in the T-18 that really makes it a quicker build, and that can be extended to any homebuilt to make the process a bit quicker? I'm doing an internet search to no avail so far, but maybe someone here has some knowledge about the T-18. I'll also send a query to a T- 18 forum if there is one. Kind regards, John Walsh +++ #6414 From: Budd Davisson Subject: Re: [Bearhawk] (unknown) I used to work for John Thorp (my first job out of college) and he was a big believer in "match hole tooling." What this entails is using a strip of aluminum with the rivet pattern drilled in it for each rivet line, then that strip is used to transfer holes from the ribs to the skins, spars to skins, etc. It actually works quite well. I don't know why we don't see more people using it. Factories that aren't using X-Y punches do something similar in that they use big patterns of the skin with drill bushings in the skin so they can be used repeatedly. Then the holes are drilled in the skin. Usually the skin is then positioned on the wing and a centerline drawn on the ribs and pushed back and forth until it lines up with the rivet line in the skin and they are match-drilled. There would be nothing stopping a guy from using a skin template to generate rivet line strips to be used in drilling matching holes in the rivets, but, for the one time guy, match drilling works faster. bd +++ #6417 From: "Bill Cox" Subject: Re: [Bearhawk] (unknown) The T18 group is here. thorplist@yahoogroups.com I built 2 T18s using matched hole tooling and have used an adaptation of that technique since . On the Bearhawk wings I made templates for the rib rivet patterns so that I locate the first rivet and then transfer the pattern from the template. Otherwise I am following Bob's technique pretty closely. Bill Cox #303 +++ #7093 Date: Tue, 07 Aug 2001 12:16:56 -0600 From: Tim tlc2@ Subject: Another Airfoil Site Like the 'Incomplete guide' here's another good site with 1100 Airfoil Coordinates. http://amber.aae.uiuc.edu/~m-selig/ 321Tim >>> 2mar02 #7686-9153 +++ #7750 From: sonny cilley Subject: Re: Digest Number 562 Hi guys, I have talked to alot of folks over the years that I've been involved building to Bearhawk , yesterday I was talking to a tow pilot in Franconia, NH and he knew what the BH was all about and said the only thing he didn't like about it was that it had very narrow landing gear, it kind of surprised me when he said this and I didn't know at that time what the stance of the gear was. but do now. has anyone else heard such a comment. I don't think of it as a problem, just an interesting comment . if it were worrysom to someone, what would it take to widen the stance. thanks, just rambleing on, Sonny # 234 +++ #7751 From: "Bruce A. Frank" Subject: Re: [Bearhawk] Digest Number 562 First let's get into a discussion as to advantages and/or disadvantages of wider or narrower gear. I am under the impression that narrow geared planes have a higher propensity to ground-looping. Long time ago I built my main gear with a 109" wheel center to wheel center track. On a fuselage similar in length and width to the Bearhawk is there any disadvantage to this width track in a tailwheel configuration? Bruce A. Frank +++ #7753 From: "Joe Hemmer" Subject: Re: Main Gear Track Width Speaking from not much personal experience, mostly repeating what I have heard from others, the normal range of gear width is in the range of 1/4 to 1/3 of the wingspan. Yes, definitely narrow track makes for problems with crosswinds, from my personal experience. Luscombe, for example. Extra wide track, such as the Dragonflies with wheels at the ends of the canard, lead to very interesting braking problems. Apparently if you connect the brakes together, no problem. So picking some reasonable compromise between these extremes, your 109 inch gear sounds like it should be somewhere in the ballpark. My Avid will be limited to 7 feet on centers, to be able to fit inside the trailer. Joe Hemmer +++ #7754 From: Budd Davisson Subject: Re: Main Gear Track Width Re: Tailwheel airpane stability The stability of a tailwheel airplane on the ground is driven by a number of different factors, width being fairly far down on the totem pole until the rest are considered. A primary factor is the relationship of the CG to the contact point of the wheels. As a normal rule the angle from the contact pint to the CG should be an angle of around 11-17 degrees back (I'm not sure of the angle, it's been a long time). So the height of the CG as well as it's location back is a factor. The problem is several fold: the further the CG is back, the smaller the amount of angular deflection it takes to get it well off the centerline/ground-track of the airplane. However, when it's located well aft, you can really get on the brakes. The Helio is a case in point. The CG is well aft and you can brake like crazy, but it can be a nasty SOB on the ground. The further forward the CG is, the more the airplane can turn without giving you heartburn, but you have to be more careful with the brakes. Obviously, there's a middle ground for all of this, but like everything else, it's a compromise. The further the tailwheel is back, the more authority it has to control deviations so, although a longer wheel base doesn't actually make it much more stable, it makes it easier to control. The same thing holds true with the moment arm of the rudder. This however is also related to the rudder/fin area. A Stinson 108-3, for instance has a lot of fin and well positioned CG, so it's not very squirrely, but it lacks enough rudder to handle some situations, like a hard left crosswind on take off. That's what brakes are for. What I said about longer wheel bases not effecting stability isn't entirely true. The tailwheel has some drag, so, whether you steer it or not, its drag will be trying to keep the tail from sliding sideways. This isn't noticeable on pavement, but on grass, it is a very real stabilizing factor. Almost like a tailskid. The width of a landing gear becomes a factor primarily when there's also a high CG involved, and the weight transfer in a swerve helps drive the airplane around. A Stearman or a T-6 are examples of this. The aforementioned Luscombe has crosswind problems, not because of its relatively narrow track but because it's light, it has a high aspect ratio so the wing doesn't want to quit flying and because its stall speed is low, so a smaller wind has a bigger effect. Also, although the airplane has a reputation as a ground looper, it really isn't. However, it is one of the few light airplanes that has such a powerful rudder combined with very little rudder break-out forces that it's easy to over control it in yaw. Combine that with a slightly gusty crosswind and you have the makings for problems. In my experience with Luscombes, it'll handle just as much wind as any of its peer group, but you have to be more deliberate with it and fly those long, long wings until it's dead stopped. It is not an airplane that tolerates an approximate pilot very well. It wants specific, measured inputs to counter each outside factor. Just because an airplane has a wide gear is no guarantee it'll be an easy airplane on the ground. Too many other factors come into play. Sorry, I rambled. bd +++ #8029 From: pfflyerz@c Subject: Re: Digest Number 590 > did Bob ever get the plans on his 2 seat design done or is it > still in the works. I saw Bobs 2 seater while at the BBQ. Apparently the wings are done and the fuselage is finish welded, with seats and sticks installed. It is amazing how quickly he can put an airplane together. Pat Fagan #232 Pearblossom CA +++ #8030 From: Bob Romanko Subject: RE: Digest Number 590 I saw the plane at the BBQ as well, and the craftsmanship is excellent. My guess is that he's building the first one as a "proof of plans" and will have the final plans available when he finishes the plane. Based on his track record, that should be in six months (or less). No joke. Planter Bob +++ #8139 From: bearhwk272@a... Subject: "Gotcha List" ( Kevin's Wing List ) First The Disclaimers ( Kit Builders read this for entertainment value. ) 1. Bob did a great job. I have a huge amount of respect for his design of the Bearhawk. ( I am even having fun building. ) 2. I have tried not to "Modify " the Bearhawk. 3. The "Exposure" to these "Gotcha's" is the culmination of seeing... Proto1 completed. Proto 2 under construction. Russ, Pat, Tom's project and a few others as I travel around the country. 4. Most items are documented in the plans, Beartracks, Russ's CD and this forum. 5. I have not passed any of this to Bob nor have I "Actively Discussed" my adjustment solutions until I have actually " DONE IT ". Now I have, so now I will. ( Remember their still not tested.) 6. Mike Meador, If you are out there, you may publish this in Beartracks and present a copy to Bob. ( Run Quick------ Designers Hate Any Tampering with their designs ------- sometimes they even kill the messenger. I know, I suffer from the same illness.) 7. Bob has not approved or disapproved of what I have done. ( Sometimes it is easier to ask for forgiveness than to ask for permission.) 8. I have an engineering background and 20 years in the aircraft component manufacturing arena. Tighten the seat belts and here we go. Wing Spars: 1. I Incorporated 1/2 inch x .032 angles at all vertical stiffener and rib locations on front and rear side of all spars. This adds a little stiffness to the spar and creates a nice finished look. The angles on the back side of the rear spar have one leg trimmed down to clear the flaps in the full up position. 2. Splice joint at Front Spar. If you study the area and the rivet layout it is possible to set up the rivets to do dual duty and hold the splice and the front rib attach angle. 3. Pay attention to the "location and hand" of the angles on the back side of the rear spar. Russ has addressed this, spend a little time and notice that some of the flanges and attach angles are installed "backward" in order to form the pocket at the hinge location. 4. Small aft ribs. Watch the location of the oval lightening hole. Do not get it to close to the rear false spar. I used 3/4" angle instead if 1/2" to attach the false rear spar to the two stub ribs. I am not convinced that if I were to do it again I would put the oval hole in ribs 1 thru 5. Little smaller round I think would be better. Stiffener Angles on Ribs: 1. Stiffeners at rib locations 1,2,5,24 were installed on the side opposite the flange. This creates a nicer finished look and provides a little more clearance in the tank area for working inside the finished tank bay. 2. A really clever builder would understand that the flutes in the flanges of the ribs should be located so that the flute lines up with stiffener. Fuel Tank Area: 1. False Rear Spar is actually the aft tank support. The 5 "Hard Points" for tank strap attachment were increased in size to 1.25" wide X 8" long with the ends tapered to feather out the section change. This adjustment distributes the stresses on the web better. 2. Tank support straps. Made One Inch Wide. Standard width for commercially available anti chafe material, welting or rubber. 3. Tank Support Strap Tensioners. I used 10-32 bolts and .375 rod for the cross tie. This provides a little more edge distance and more full thread engagement. 4. The tank when placed in the tank bay will require anti chafe protection at the location of the strap tensioners as clearance from tank is near zero. 5. Tank must be located accurately and hung from the straps correct or tank will hit the top and bottom skin stiffeners. 6. The tanks support straps that go under the tank should split the area between the tank baffles. Flaps and Ailerons: 1. Really, it is mostly about edge distance, edge distance, edge distance. Be careful when making the hinges. The edge distance from the hinge bolt to the outer edge of the hinge "Lolly Pop" is at the minimum. A little slip and things get to thin. The more I worked with mine the less I liked them. When I remade the hinges I eliminated the "Lolly Pop" and took a straight taper from top to tangent. Added .062 additional edge distance at hinge bolt. Hinge to spar attach bolts were to far out to the ends of the hinge so they were near the spar radius and too close to the edge of the hinge and the edge of the doubler. Moved things inboard about .125 Center to Center. Bingo. Again Russ has visited this area. 2. Ribs to spar attach angles and to spars, be careful you can run out of rivet edge distance where the rib attaches to the spar flange. Tough to get this correct. 3. I added a small 4 in. triangular gusset to each rib location where the rib flange joins the spar flange, similar to the gusset that spans the hinge attach points. Adds a lot of stiffness and unloads the spar web. Not an original idea here, most of the WW 2 stuff has this feature. AREA OF BIGGEST ADJUSTMENTS Flap Actuating Rod Hitting Aileron Cable: As noted in previous posts and some issues addressed by Bob here is the Readers Digest Version. (My Approach) 1. Flap Rod to Aileron Cable had an interference of over 1/2 inch when flaps extended about 30 Deg. OK at Full Up. OK at Full Down My Solution: ( Not All the Reasons Why) a. Lowered the flap torque tube assy toward the bottom of the wing about 1/4 in. b. Lowered the flap actuating support assembly toward the bottom of the wing about 1/4 in. c. Shortened the torque arms at the flap actuating support assembly about 3/16 of an inch. d. Raised the aileron fairlead at the wing root as far as possible. e. Raised the aileron bellcrank about 1/8 in. f. Added a non contacting fairlead at rib # 6. (Cable now runs close to the oval cutout in the ribs, stops slap.) g. Added anti chafe strips to the oval cutout in the ribs. Cable clears the ribs by about 5/16 of an inch. h. Added anti chafe strip to the flap actuating rod. End result is that cable is clear of flap actuating arm. Clearance about 1/8 in. Aileron Actuating Support Area. 1. Mock up your area prior to welding parts. I found ( and noted by others ) that the bellcrank support arm can possibly collide with the rib opening. A little pre planning here can avoid modifying the rib. 2. Be sure that your aileron cable run is parallel to the spar face. Flap and Aileron Actuating Support Tubes. 1. Made my support tubes out of 1.0 dia tube. (3/4 on the plans) a. Allowed me to make the end brackets on a brake. b. Provided the required material to allow a bushing to take a 5/16 bolt for the aileron pulley. (MS20220-3 Deep Groove Control Pulley) c. Wider end brackets allow more clearance for pushrods exiting to controls. Main Spar Aileron Pulley Bracket: 1. The angle of 10 Deg is just not correct. The pulley bracket is rotated from the vertical plane on installation and that causes the plane of the pulley to cant off in the wrong direction when installed. Made mine thrice to get it correct. The bracket needs to change the plane of the cable as it transitions from wing to strut. So...........Yup I am a Happy Builder, greatful that others have passed this way before and thankful that Bob made about a bizillion decisions correctly so I can spend my spare time with the family. Kevin Deutscher +++ #8143 From: "Montee, Dan L." Subject: RE: "Gotcha List" ( Kevin's Wing List ) There is not much I can take advantage of without starting over but new builders should be running to their drawings with a copy of this e-mail and pen in hand. I am building with a friend who hasn't started serious building yet but is helping with some of the machining, etc. On the fuel tank issue I recommended that he take off 1/4" on the height to accommodate amateur GTAW welders like him and me. I am concerned about the warp in the tanks interfering with supports and skins. Thanks for the info regarding interference with the aileron cable and flap rod. This is the most detail I've seen regarding the where, when, and to what the degree the interference represents. This is a concern. Ever since the issue surfaced I've assumed Bob would either eventually issue an engineering change or a disclaimer that the interference was insignificant and that no modification was necessary. I may have missed it but to date I don't recall a comment pro or con on the issue from the designer. At a glance the modification you made to accommodate the interference requires the scrapping of the majority of my wing steel parts and significant clearance modification to many of my nicely Epibond-ed center ribs. Not out of the question but another significant set back for this builder if I have to scrap these parts and start over. Erbman has option # 2 but I'm concerned about the cable sawing it's way through the plastic fairlead and if the rib can handle the load placed on it by the fairlead. Budd, how did you address this issue on the kit? I'm going to soldier on with a hope that a fix # 3 evolves before I close the wings in a year or so. How's that for faith! Dan Montee # 415 +++ #8145 From: "Collin Campbell" Subject: Kevin's "list" I wish to be appreciative for the contribution and respectful for the different experiences and viewpoints that we all might have. I know everyone will see things a bit differently and I'm sure no two of us are alike. The point I want to make is that after completing my wings, I didn't find any of the "changes" or "improvements" necessary. (other that the very slight misalignment of the aileron pulley bracket) I was quite pleased with the way everything went together. I don't think that we should over react and blow things out of proportion. There is no need (IMHO) to start a big ruckus about it. If you have parts already made to plans, I wouldn't change them. The aileron cable thing to me is just simply not a big deal. I mean listen guys, the rudder cables "rub", if you will, in fairleads, from one end of the aircraft to the other. Why are we not also worried about this? I don't think I will worry that the cables will "saw" their way through these fairleads. Doesn't the total time on the two prototypes say anything to us? If there were a problem, don't you think "The Bob" would let us know? Just bond a thin strip of some low friction material of your choice to the flap push rod and get on with it. I don't think rebuilding all your wing steel parts is necessary. Them's my two cents. Not wishing to start any arguements... Collin Campbell #370 +++ #8146 From: "Bruce A. Frank" Subject: Perfection (Was: Kevin's "list") You are correct. To coin a phrase, this is not rocket science. ;-D There is a set of plans, but construction does not call for + or - .0005". One builds to fit. We know the relationship between parts for the system to function properly. Parts from one builders project are not intended to fit another, but they probably can, simply because tolerances do not need to be that tight to produce a fully functional and safe plane. If a cable rubs either bracket another pulley at that point or protect the parts with some anti-chafe material. There was an article a few years ago in one of the magazines about a laid off machinist who decided to build a Long EZ. He re-drew the plans to reflect + or- 1/64" because he was disappointed in the published tolerances. He built his perfect plane. He then sold it to a friend because he felt he wasn't up to precision required to fly the plane correctly. That article was a description of a neurosis, not a project. Build for function, build to fit, build to fly safely, don't get hung up on perfection. Bruce A. Frank +++ #8150 From: Russ and Penny Erb Subject: RE: "Gotcha List" ( Kevin's Wing List ) > 2. A really clever builder would understand that the flutes in > the flanges of the ribs should be located so that the flute > lines up with stiffener. Well, then demote me to just "clever builder". I didn't pay attention to this, and ended up with stiffeners in one position on pretty much each rib rather distorted between the dimple squeezer and driving the rivets. I highly recommend you that you follow Kevin's advice here. Something else I remembered that I don't think has ever been mentioned. If you place a rivet in the center of the main spar flange and then lay out your rivet spacing from there, it is very likely that the next rivet forward of the main spar flange will be positioned right over the capstrips on the front of the main spar. Quite tough to buck rivets there, and the holes you drilled into the edge of the capstrips don't do wonders for its strength. Be sure to watch out for this. Also pay attention to the same problem at the first rivet hole forward of the rear spar. Russ Erb +++ #8493 From: Russ and Penny Erb Subject: Another one to file away... Here are a four more tips that you'll want to file away for future reference. I was reminded of these while visiting Pat Fagan and using his lathe to turn down my tail tie rods. 1. A couple of corrections to Drawing sheet 16A (Fus. Mod. Rear Doors). Near the top of the sheet in the drawing of Section T-T, the note should read "Dim. tapers from point 4 to point 6" instead of "5". Pat said he determined this by inspection of the prototypes. Makes a lot more sense when you see it, too. 2. On the same sheet, the drawing of Section S-S reads "Dim. tapers from 1 to 2 and 2 to 3". I can't reproduce how I came to this conclusion, but I wrote on my sheet that there is no taper from 1 to 2. Since I can't reproduce the reasoning, I'm not as confident of this one. 3. Pat tells me that the 1-1/2" tubing for the axle for the 6.00x6 wheel won't quite fit into the wheel bearings. It will need to be turned down just a fuzz on a lathe. You'll need to this before you weld any of the other parts on. Make sure you have the wheels in hand before making the axle. What a pain to build the landing gear and then find the wheels won't fit! 4. You may want to make the axles a little longer than shown on the plan. Pat built his to plan and has just enough threads to get the cotter pin in. It would have been nice to have a few more. Back to welding... Russ Erb +++ #8537 From: Bob Romanko Subject: Modifications to think about... I just came across this article on AVweb: http://www.avweb.com/articles/profiles/bgriffin/ Bob Griffin's had an exciting career as a mission pilot, and has some suggested mods to the Helio. Look under the heading "Give us examples of your suggestions". I'm thinking that some of these may benefit the Bearhawk as well. I'd like to learn more about his "crash-resistant seat" design. I get a bit concerned when I hear folks yanking a seat out of anywhere and dropping it into an experimental. What good is a full harness if you're sitting in a Yugo seat? Planter Bob +++ #8593 From: Bob Romanko Subject: Bearhawk vs. Aeronca 15AC Sedan? NOT being an engineer, I'm very curious as to why these two planes are so far apart in specs. Both are rag 'n tube fuselages, both are all aluminum wings, both are 4-seaters, both use the same (or similar) NACA 4412 airfoil, and both weigh about the same. In spite of all the similarities, the Bearhawk blows it away in STOL, payload, climb and a host of other specs. Interesting: Aeronca 15 AC Sedan Wingspan 37ft 6in Length 25ft 3in Height 7ft 0in Horsepower: 145.0 Max Speed 119mph 75% Cruise Speed: 104mph Stall Speed: (full flaps) 50mph Gross Weight: 2,050 lbs. Empty Weight: 1,180 Difference: 870 lbs. Fuel Capacity: 36gal=216lbs. Useful Payload: 654lbs. Range: 370nm Take Off: Ground Roll: ft, Over 50 ft. obstacle: 900 ft. Max Climb Rate: 450fpm Service Ceiling: 13,000 ft. Landing: Ground Roll: ft, Over 50 ft obstacle: 1,300 ft. Bearhawk (shamelessly cut and pasted from bearhawkaircraft.com) Top Speed (Vne) 175 mph, TAS Cruise Speed (260 hp) 155-160 mph (60%), TAS Cruise Speed (180 hp) 140 mph, TAS Landing Speed 40 mph, IAS Takeoff Roll 200-500 ft, demonstrated (depends on engine) Rate of Climb @ gross 1,700 fpm Range @ 65% est. 650 mi. Range @ 50% est. 900 mi. Empty Weight 1150-1350 pounds (varies w /builder /engine /prop) Gross weight 2500 pounds Useful Load 1350-1150 pounds (varies w/ builder/ engine/ prop) Fuel Capacity 55 gallons (standard) 75 gallons (optional, w/aux tanks) Wing span 33 ft. Wing Area 180 sq. ft. Length 23 ft. 6 in. Cabin Width 42 in. Cabin Length 9 ft 8 in. (firewall to back of back of baggage area) Engine HP range 150-260 hp Fairly similar dimensionally, but look at the difference in the performance specs. I would think that the performance of the two planes would be much closer, and this side by side comparison serves well to show me just how ignorant I am in aeronautical design. I'm a builder, not an engineer. (As my friend used to comment on the Italians, "They should stick to designing cars and building shoes." No insult to my Italian friends, but I always seem to remember that quote for some reason or another) Can the difference purely be powerplant and prop? Gotta be... Regardless... I'm looking at a plane to buy before leaving (hopefully) for Homer. The Aeronca Sedan seems like a good one to have, but I have my eye on a Cessna 175 Skylark. Yank out the GO-300 and gearbox, drop in the STC'd 220HP Franklin, do the Texas Taildragger mod, and add a Horton STOL kit. I figure for about $40,000 total I'd have a nice zero-time engine all-metal taildragger with pretty decent performance. Something to get by with while the Bearhawk construction proceeds forward. Planter Bob +++ #8594 From: Budd Davisson Subject: Re: Bearhawk vs. Aeronca 15AC Sedan? There are some major differences between the two airplanes: horsepower, frontal area and flaps. The sedan has 145 hp (if I remember correctly) and is something like three-four inches wider and probably taller. You're trying to push a bigger slug (a very apropos term) through the air with much less gun powder. Don't forget the dual struts on the Sedan. Also, folks who modify the Sedan for the bush usually hang big flaps on it, which are sorely needed. Them's my guesses. bd PS Just for the record, the BH is a MUCH better handling airplane in ALL areas. +++ #8595 From: charles.k.scott@d Subject: Re: Digest Number 660 Aeronca 15 AC Sedan Horsepower: 145.0 75% Cruise Speed: 104mph Bearhawk Cruise Speed (260 hp) 155-160 mph (60%), TAS Cruise Speed (180 hp) 140 mph, TAS The difference is in the engine and prop, I'd guess. 145 hp with a fixed pitch prop vs. 180 or 260 hp and a constant speed. Corky Scott +++ #8596 From: "scott anderson" Subject: Re: Bearhawk vs. Aeronca 15AC Sedan? The Sedan is pushing pretty close to a 38 ft wing span. The fuselage is 3inches wider in the cabin than a Cessna 182. The Sedan does come equiped with a Continental C-145. Just looking at her you can tell she isnt the cleanest airplane out there. Oh and she only has one strut. Scott 526 +++ #8597 From: Ian Kerr Subject: Re: Bearhawk vs. Aeronca 15AC Sedan? > cleanest airplane out there. Oh and she only has one strut. what do they do on the other side? +++ #8617 From: "erbman89b" Subject: Re: Bearhawk vs. Aeronca 15AC Sedan? Sorry, P-Bob, I've been off list for a few days (still sitting in a hotel in ABQ). budd and the others who responded are right. It's both a power difference and a drag difference. Just for grins, here's some numbers. Remember that power required (drag * airspeed) varies with the cube of velocity. Therefore, if both airplanes had the same drag, the cruise speed of the Bearhawk would be: (260 hp/145 hp)^(1/3) * 104 mph = 126 mph As we know, the cruise speed of the Bearhawk is more like 140 mph, which tells me (as budd surmised) that the drag coefficient of the Bearhawk is significantly lower. Also note how a large increase in power results in a small increase in airspeed. Russ Erb +++ #8623 From: Ken Beanlands Subject: Re: Re: Bearhawk vs. Aeronca 15AC Sedan? This formula looks like a fairly crude "rule-of-thumb" type. It does nothing to compensate for prop efficiencies. A C/S prop will be much more optomized for any given speed. A fixed pitch prop will only be optimal at one speed (usually somewhere between cruise and climb) I believe that the Sedan has a FP prop and the BH is a CS. If you were to apply this formula to something like Nemisis, it wouldn't even come close. It's FP prop is set to be most efficient at something like 260 mph. If you ever whatch her in a race, she always starts at the back of the pack. As the plane accelerates, the prop becomes a little more efficient and produces a little more thrust and goes a little faster. it will slowly creep up on it's max speed as it works it's way through the pack. Ken Beanlands B.Eng (Aerospace) +++ #8628 From: "erbman89b" Subject: Re: Bearhawk vs. Aeronca 15AC Sedan? No arguments there, Ken. You're right, it is a crude rule of thumb-- that's the best I can do when I'm a full time zone away from my usual operating location. Even so, a well matched fixed pitch prop would probably be optimized for the cruise condition (unless it was a climb prop), and the result would still be similar. You are correct about Nemesis--I've seen it myself. The interesting point is that the Bearhawk will operate right about the point where constant speed prop starts to have an advantage over a fixed pitch prop, so I expect we'll see some of both. Hey, if we carry these discussions to a high enough engineering level, maybe we can get Planter Bob's head to explode... Russ Erb +++ #8870 From: Russ and Penny Erb Subject: RE: Bearhawk wing weight > Does anyone know how much the completed wings weigh? I have quoted a guess before. Based on the highly scientific method of guessing how heavy one end felt while moving each of my completed wings and multiplying by a number somewhere around 2, I came up with a guess of about 150 pounds per wing panel. I would like to know the actual weight, but don't have a convenient way to measure something that big. Of course, I could use a truck scale, but the least significant bit (minimum interval) on those is 20 pounds. Plus that would cost money, and I don't really want to know that bad. Russ Erb >>> 4sep02 #9154-11297 +++ #9641 From: "Bruce A. Frank" Subject: Balanced Control Surfaces(a bit Off Topic?) I see from the conversation here that all of the Bearhawk's control surfaces are balanced. I do not know what the never exceed speed is on the Bearhawk, but I do see that its cruise is higher than the never exceed speed of the TriPacer airframe (which is about 147 MPH). The TriPacer design and thus the V-6 STOL conversion does not have balanced control surfaces. Is there the potential for a higher never exceed speed on the V-6 STOL conversion if we balanced all the control surfaces? Or at least widening the safety margin for potential flutter at the top end of the envelope. Consider also that the early Maule, virtually a knock off of the Piper, has a higher Vne than the Piper. Does anyone know what changes allowed the Maule to specify a higher Vne or was Piper just being conservative in their specs. +++ #9642 From: Ken Beanlands Date: Wed May 1, 2002 6:43 am Subject: Re: [Bearhawk] Balanced Control Surfaces(a bit Off Topic?) Bruce, there are a number of things that can limit Vne. Unless you KNOW what the limiting structure, it is difficumt to guess what it is. For example, the BH as balanced controls, as you mentioned. However, the limiting structural component on the piper maybe something like the windshield or horizontal stabilizer. The BH has a strut stabilizing the LE of the horizontal stab against flutter. Does the Piper? It may also be the control loads onthier hinges. It may also be the drag wires in teh wing (the Fly Baby ended up being speed limited by the drag/anti-drag wires) If Piper arbitrairily picked 145 or 150 mph as the Vne simply because it was a certain percentage above the cruise, they may have designed a lot of the parts to the maximum load imposed by the Vne and no more. Flight testing would have revealed tha actual Vne of 147. Most desighers will layout the flight envelope they want to design for before designing the structure. Having a plane strong enough for a 200 mph Vne with a single component limiting the Vne to 150 mph would mean that the plane was built too heavily. +++ #9644 From: "t18cox" "Bill Cox" Subject: Re: Balanced Control Surfaces(a bit Off Topic?) > OK, is there any DISadvantage to balancing these surfaces? Later (55 and later) model TriPacers had a 170MPH redline. According to my parts manual the spar was changed at #22-2378. That was the beginning of the 1955 production. It's been so long since I looked at the early vs the late wings I'm not sure what the difference was. The control surfaces were still not static balanced. The early models had a flat windshield. That windshield bows pretty badly above 140 even with the little bumper supports near the bottom. Later models used a bubble windshield that looks a lot safer at increased speed. +++ #9649 From: "Bruce A. Frank" Subject: Re: [Bearhawk] Re: Balanced Control Surfaces(a bit Off Topic?) Now that is some helpful info. I am building wings from scratch with the stronger D&E spars along with spar doublers. With my ~37 ft span it is not likely that I could ever push the envelope up to 170 mph even in a vertical dive. My windshield is the thicker bubble type so that is not a limiting factor.. I would bet that one of the changes was the spacing of the ribs. The later models with higher horse power engines had more ribs in the wings (fabric covered). I may have mentioned it before, but I am also creating a wing that is much stiffer both from a lateral and a twisting load point of view. After a lot of research I found that the original Piper spars and the method of wing construction, in craft using larger engines, tended to flex so much under high bank angles that there would sometimes be control reversals. Knowledgeable people told me that several crashes of the Aviat Husky was directly related to control reversal at high bank angles due to the original Piper spec spars. Rather than the standard compression tube between the front and rear spars I am using pieces of skeletonized rear spar material to create a box structure. This change is also intended to help support oversize flaps....I had observed a friends oversize flap's loading actually twist the rear spar.... which bothered him so much that he quit using the flaps. At SNF I also saw a Cub replica, upgraded for the modern market and much larger engines, with square aluminum tube used in place of the drag/anti-drag wires. That is my kind of wing. +++ #9753 From: "Shawn Harrison" Subject: Design Compromises I agree about the looks of the Bearhawk---very nice! As to performance, even for cross-country use, it wouldn't be too bad---faster than the 172s that I will rent. The Bearhawk does seem like an excellent set of compromises for the mission that it is designed to fulfill. For the cross-country "set of compromises," and because I don't see very many backwoods strips in my future, I'm leaning toward a more slippery design. The compromise there, of course, is that you can't land at 35 kts. One question I have: The wing struts, tail wires, and gear leg struts in the bush designs are major creators of drag. I realize these enable a lighter plane. However, I'm thinking out of the box for a minute: If one were to fabricate a bush plane with a light, graphite spar cantilever wing and tail, and spring-steel gear legs that are well faired in, is there any reason that this couldn't be made as durable as the typical strut-based approach? Believe me, I'm not talking about modifying the Bearhawk. But it does seem that, if one were to remove these (and other?) obvious sources of drag, you might be able have a great bush plane that also cruises at 155 mph rather than 125 mph, using Bob Barrows' low-buck 19^2 cruise setting (or 180 mph rather than 150 mph, using a "regular" 23^2 cruise setting). Is there any reason that a bush plane couldn't be made in this manner? I hope this doesn't stir the pot too much. Those who are already building and flying their own planes are way ahead of me. +++ #9757 From: Budd Davisson Subject: Re: Re: Bearhawk muster 2002 #423 > I can see the desire to maintain straight rows particularly when the > skin is not covered by fabric so there is no way to hide such cosmetic > failures, but! > > Is there really a strength issue related to rivets in the leading edge > "D" section? I have a friend who formed his leading edge so that it > fit tightly against the nose ribs. Rather than rivet he proceeded to > use a non-acidic silicone caulk (RTV type) to glue the ribs to the > leading as he pulled it into place. Doesn't the shape of that leading > edge really support itself? The reason for the rivets in the nose ribs is to stabilize the torque box formed by the "D" section and transfer the loads into the ribs. By riveting them, the long torque box is actually cut into a bunch of tiny ones making it much stronger. The regularity of the rivets is mostly cosmetic, the number of rivets determines the strength, so long as the spacing doesn't get so wacky that loads get concentrated som where. Even though the wing depends on the center torque box for most of it's strength, the nose box is still important enough to want to rivet it right. +++ #9760 From: Budd Davisson Subject: Re: Re: Bearhawk muster 2002 #423 > I understand. This whole wing is a torque box. Would the glued method > work? I don't know what kind of glue is available at our level that would have the required strength, producibility and longetivity. If there was one, yes it would work but I wouldn't want to be the pioneer. +++ #9761 From: Budd Davisson Subject: Re: Design Compromises I don't know how old this thread is as i just ran across it, but I'll jump in. The airplane is now a 155-160 cruise at 23 square, which is around 60%. This is without any effort at cleaning up any drag producing areas of which there are plenty. -fairing around gear shock struts -- 2 mph -600 x 6 tires -- 2 mph -wheel pants -- 2 mph -fairing around brakes/axle insection 4 mph -reflex flaps -- 5 mph I make that a very conservative total of 15 mph, so now we're cruising at 170 mph TAS in an airplane with a Vne of 175 mph IAS and we're still at 60% and the airplane is still claw hammer-simple and super durable. Even done in graphite composites, it is highly unlikely you could design a cantilever wing that would be as light as the BH wing because, among other things, you'd have to put a hellacioius carry through structure in the fuselage and composites aren't the super-solution everyone thinks they are. Not to mention the fact, that to tool up and build one would be prohibitive. Glassair found this out when they built the Glas-Star. It started out to be a composite airplane, but they found it wasn't even close to cost effective to do it in composites. Eliminating the BH struts would give maybe 8-10 mph Spring steel gears, especially in tubing fuselages, are also problematic. Many of us, me included, don't like spring steel gears for several reasons, not the least of which they don't let the pilot know exactly what the airplane is doing and you can't damp the rebound as easily as you can on other kinds of gear designs. From a strucural point of view, thelong moment arm of the spring steel gear leg coupled with the narrow mount pad means you really have to be clever and carry lots of metal to keep them from eventually cracking longerons and other mounting points. A Vee type gear spreads the loads more easily and the oil/spring combination in the BH gear makes it easier to absorb the landing shock and still control the rebound. This change would be good for another 8-10 mph. Maybe. And about speed: on a 500 mile trip, which is a LONG trip for an airplane like this, the difference between 150 mph and 180 mph is 33 minutes. It probably depends on your outlook on life, but to get that 33 minutes, you've complicated the living hell out of an airplane and raised the cost considerably. Besides we're all in this because we like to fly, so eliminating flying time is also eliminating part of the reason we're doing this. The practical advantage of speed is a controversial and subjective subject and up to the individual as to whether it's worth it or not. Normally, to a speed increase worth it, it has to be a HUGE increase. A more commonsense approach is to play with fairings as a way of increasing the efficiency of the airplane and speed increases are just a happy byproduct. +++ #9884 From: Budd Davisson Subject: Re: Gear Dimensions/handling > Anybody know the distance between mainmount wheel centerlines on the > Bearhawk. Also the distance from the mains back to the tailwheel? A more critical dimension is the location of the CG aft of the point where the landing gear contacts the ground in a 3-point. If I remember correctly it should be in the 11-17 degree range (Ken B. or Lee Erb, what do you remember?). the farther back the angle, the smaller the angle of divergence it can tolerate before you have to get busy with your feet. The width of the main gear versus the hieght of the CG is also a factor in swerves, but doesn't come into play until you're already screwed up. The BH is Citabria-stable, so no problem and it has a relatively narrow gear-to-span ration, but the CG isn't too far back. +++ #10221 From: Russ and Penny Erb Subject: RE: Glide characteristics > I was wondering what the glide characteristics of the Bearhawk are? First of all, I have not flown a Bearhawk. Having said that, based on a mathematical model of the Bearhawk I created a while back based on published data, the maximum L/D should be around 10.5. While much worse than most gliders, that's equivalent to the measured value for a Cessna 150 that I flight tested once. Therefore, my best guess would be that the Bearhawk glides similar to other typical Cessna aircraft. The aspect ratio of the Bearhawk wing is less but the frontal area is also less. >>> 20may03 #11298-18250 +++ #12860 From: "rodsmith52" Subject: Re: Plans scale > Received my plans from Bob last week, I have a question for anyone. > I notice he uses scales like 1=5 and 1=10 instead of architectural > or engineers scales that I'm familar with. Go to an office supply and get one of those triangular shaped engineer scale rulers. It will have everything from 10 divisions per inch to 60 div per inch. Using the ten division scale on the 1=10 drawing, each division equals 1 inch. Pretty simple huh? For the 1=4 and 1=5 drawings use the 40 or 50 div scale as appropriate and each big division is 1 inch. +++ #15610 From: Russ and Penny Erb Subject: RE: Re: Landing Gear The wire braced tail, just like the strut braced wing, is significantly lighter than a cantilevered tail. For instance, no heavy carry-through structure. Also the vertical fin would have to be beefed up. Going to a cantilever tail would make thicker surfaces, which would probably add as much drag as removing the wires saves. Weight is bad anywhere on an airplane, but is exceptionally heinous when far from the cg, such as at the tail. Then again, maybe that would help balance those big engines. Russ Erb +++ $Id: 6.3-Design-Issues,v 1.6 2003/05/22 04:18:50 bentonh Exp $