+ Reply to Thread
Results 1 to 13 of 13

Thread: Affordaplane A-plane

  1. #1
    Registered User
    Join Date
    May 2005
    Location
    Moore, Ok.
    Posts
    20

    Affordaplane A-plane

    Ok. So I plan on building the Affordaplane A-plane. This is a question for you design/Engineer types out there. The main fuselage frame material is 2x2 aluminum square tubing (t-6 of course). My question is this: is square tubing a better choice than round? I'm told that square tubing would buckle if it got bashed, whereas round tubing is more structurally sound and would be less likely to buckle if it was bashed. Also, this design calls for foam ribs with aluminum cap strips. I've never heard of using foam ribs and it kinda scares me. Can anyone shed any light on the safety and structural effectiveness of using foam ribs? Also, since I'm a big guy (6'4, 300 lbs.) I know I'll need more than 40 hp, so I plan on putting in about 60 hp, which will weigh about 10-15 lbs more. Any suggestions on an engine mounting system, or is it best to let the engine mfg. suggest one?

  2. #2
    Super Moderator orion's Avatar
    Join Date
    Mar 2003
    Location
    Western Washington
    Posts
    5,945
    Assuming you're comparing square tubing that has the same height and width dimensions as the round tubing has diameter: The characteristics are that for a given material thickness, the square tubing will have more material per foot and as such, will be heavier than the round. Structurally though, the square tubing will be stronger and due to the cross sectional characteristics (larger cross sectional moment of inertia), the square tubing will be more stable and resistant to damage than the round material.

    The argument that a square cross section may be less stable is correct but only in very limited cases where the material gauges are very thin. For instance, most of us are familiar with an empty pop can being able to support our weight, until one just barely touches a side. If the pop can was made from the same gauge material but was made square instead, it is feasible that the square can might not be able to supprt the weight as well as the round one due to the fact that the flat walls would be less stable than those of the round shape.

    This however does not apply to the tubes used in the airplane since the ratio of gauge to wall height is substantially different.

    Now, that being said, I would suggest that you use the search function at this site for other posts regarding this particular design. According to several other writers, there seems to be a question of the viability and safety of this particular design. Several other posts herein discuss this in a bit more detail.

    Regarding the foam, for a lightly loaded wing in an airplane that has a relativley mild operating envelope, the loads within the structure are not all that high and as such, it is feasible that the use of foam ribs can be justified as long as the gauge and spacing were well designed and as long as the skin adhesion to those ribs is also good.

    But keep in mind that even if the airplane was well designed, it was most likely designed specifically for a limited weight and loading - subjecting the airframe to any higher loads is a recipe for disaster. This is especially the case if you compound the problem and add power that the airplane was not designed for.

    As such, I'd recommend two possible options. The first would be to have the airframe re-evaluated and/or redesigned for the higher weight, loading and power you migh anticipate installing. Only then can you feel confident that the structure will be able to withstand your anticiapted flight envelope.

    The second option would be to just do a bit more searching and find an airplane that is designed for your height and mass.

    Being 6' 4" and a few years ago over 300# myself, I can relate. Even today at about 230#, I still consider most homebuilts a shoehorn and a gallon of goose grease sort of fit.

  3. #3
    Registered User
    Join Date
    May 2005
    Location
    Moore, Ok.
    Posts
    20
    Great feedback! Thanks. I was talking about round tubing of equal size vs. square. According to the specs, the max pilot weight is 250 lbs. According to others I have cooresponded with, the A-plane consistantly comes in at around 300 lbs. empty weight after customizing. I will search the site for those other posts. I intend to dig as deep as I can, and get as much info as I can, as I want to be completely satisfied that the frame and wing can support an extra 50 lbs. of pilot weight. My gut feeling here is it won't be a problem, but I want to be absolutely sure.

  4. #4
    BDD
    BDD is offline
    Registered User
    Join Date
    Apr 2005
    Location
    WI
    Posts
    388
    A 50 pound weight difference is a fairly big discrepancy with an ultralight where the heaviest component of the plane is probably the pilot. The rated "G" loads maneuvers could not be done and the FAR 103 landing speed might not be met. Just things to consider, that's all.

    Square tubes should be stable against side force and buckling while under compression because of the higher moment of inertia (as was mentioned). I also like the way they can be joined by gussets and with simple cuts vs. the elaborate shaping that is required when welding round tubes together. I saw part of a frame once that consisted of small, square aluminum tubes adhered together with gussets and a British made aerospace epoxy. The joints seemed to be very strong. I would think that due to the superior stability of square tubes that an overall lighter fuselage could be built with smaller tubes than might be required if round; overcoming the initially heavier seeming weight of square tubes.

    The foam rib with an aluminum (or wood in some instances?) capstrip is a way to produce a very light rib. The capstrips would act like the flanges of a beam or the top and bottom chords of a truss and would take bending stresses. The foam rib would take shear loads like the web of a beam. You would need to make sure that the foam and adhesive don't age or deteriorate, that the foam isn't overstressed in shear, that the adhesive is also good for the shear flow between capstrip and foam web, etc. The way they connect to the wing spars would also be important. The bending loads and torsion would be transmitted to the spar by the capstrips, not the foam, etc. The foam could transmit vertical shear loads.

    Ribs like these could be easily built and tested to find out how strong they really are. You would also need a smooth foam surface to glue the capstrips to.

  5. #5
    BDD
    BDD is offline
    Registered User
    Join Date
    Apr 2005
    Location
    WI
    Posts
    388
    With foam ribs there could also be an effect of "creep" due to "long term" loads. Either the adhesive could "creep" (if it is somewhat "plastic" like some hardware store epoxies) or the foam could take on a permanent distortion (it certainly seems possible).

    You would want to make sure that foam ribs like these always return to their unstressed shape after loads of a typical realistic duration are applied.

  6. #6
    M51
    M51 is offline
    Registered User M51's Avatar
    Join Date
    Apr 2005
    Location
    MI
    Posts
    27
    If the foam ribs are constructed in a similar fashion to the Lazair ultralight, The rib is also wrapped in a criss-crossing pattern with fiberglass tape over the rib and capstrips. There are many Lazairs around here, most built in the eighties and flown many many hours. Not one rib has shown any distortion, or failed from flight loads. The fiberglass tape really makes the rib very strong, and is key in distribuing the loads to keep the rib assembly from creeping or allowing permanent distortion to set in as it is subject to stress.

  7. #7
    BDD
    BDD is offline
    Registered User
    Join Date
    Apr 2005
    Location
    WI
    Posts
    388
    Is the fiberglass tape literally woven fiberglass reinforcing "tape" that comes in rolls which gets epoxy resin applied?

  8. #8
    M51
    M51 is offline
    Registered User M51's Avatar
    Join Date
    Apr 2005
    Location
    MI
    Posts
    27
    I used to own a Lazair a few years back, but never had to replace the rib tape. It was applied to the ribs by the factory. Looking through some Lazair archives, I believe it is just glass yarn filament tape. The rib and tape is painted for UV protection as the wing covereing was clear tedlar. I think the tape used has a 380 lb tensile strength per inch. Lazairs do require wing recovering every so often, but I believe the filament tape lasts quite a bit longer. Will have to check with the locals about what they use, and if they have ever needed to replace the filament tape during a recover of the wing.

  9. #9
    BDD
    BDD is offline
    Registered User
    Join Date
    Apr 2005
    Location
    WI
    Posts
    388
    Is this the packing tape that you see? I'm not familiar with another product, besides the fiberglass cloth rolls or "tape" that I mentioned.
    If so, the U.V. resistance of the tape plastic and it's adhesive would be an issue.

  10. #10
    M51
    M51 is offline
    Registered User M51's Avatar
    Join Date
    Apr 2005
    Location
    MI
    Posts
    27
    I'm not sure of the actual tape, but is most likely some form of packing tape. As I said, the completed rib is painted after it is wrapped with tape to provide UV protection for the foam and tape as well. The wing does require recovering every so often as the tedlar and its tape is UV resistant, but not UV proof. It is easy to replace the filament tape if needed at the same time, but it long outlasts the tedlar. I doubt Dale Kramer (the designer) thought there would still be many of these flying some 20 yrs later, as they are ultralights after all. Don't know what life span he would have expected for the rib tape, but a couple here still have the original tape.

  11. #11
    Registered User Aviatrix's Avatar
    Join Date
    Apr 2005
    Location
    Phoenix, Arizona
    Posts
    135
    Ultrabuzzard,

    I'm going to be starting on an Affordaplane in the next month or so, as a "Warm-up" to the 2 seater "Sport Pilot" plane I'll be working on over the next few years.

    I've got an engine question in the Ultralight section, and it seems since both you and I are fairly "big" people, we will probably have some of the same questions.

    One "mod" I've heard talk of is to use thinner, and slightly smaller diameter tubing for the fueselage/tail boom, and to make two of them, in a "box" style, which tapers at the tail.

    Supposedly the weight difference is neglible, but there is a strength benefit to be had.

    I've also heard talk of using aluminum ribs.
    I am not Kirk, Spock, Luke, Buck, Flash or Arthur frelling Dent. Im Dorothy Gale from Kansas. -
    Cmdr. John Crichton "Farscape"

  12. #12
    Registered User
    Join Date
    May 2005
    Location
    Moore, Ok.
    Posts
    20
    I've had email correspondence with Dave Edwards on this. His view on mods is mostly about reinforcing the wing, and he said basically that the fuselage is over designed and the extra weight on that is not a big problem. My thoughts on mods center around the wing attachment, as in adding an extra pair of attach points, as well as beefing up the rib structure (using foam ribs) by adding fiberglass tape to wrap across the ribs from the root to the tip in a criss-cross fashion, as well as wrapping the ribs edge with tape and resin, top and bottom. My main concern is compensating for the added stress on the wing that comes with the added weight. I believe that adding the fiberglass tape and resin along with the extra wing attachments will be sufficient to reinforce the wing. I will be using a 60-65 hp engine on my plane. That should be more than enough for my weight. (I'm also working on losing about 50 lbs. lol)

  13. #13
    Registered User Aviatrix's Avatar
    Join Date
    Apr 2005
    Location
    Phoenix, Arizona
    Posts
    135
    Heh,


    Yeah, I'm going to try and get back down to 190. That way I can use some of that "spare gross weight" to fully enclose the cockpit of the Affordaplane. I'm thinking a little bit of sheet metal and plexiglass cant weigh more than 10-15 lbs.

    Plus, if I can pull it off the engine I'm thinking of using is maybe 50lbs. Not sure how that copares to a Rotax, but 50lbs seems light to me.


    I'll be keeping an eye on the wing mods.

    My interest in the "box" fuselage was to be able to cover it, and apparently the tail boom as listed in the plans cannot handle the stresses if it's been completely covered.
    I am not Kirk, Spock, Luke, Buck, Flash or Arthur frelling Dent. Im Dorothy Gale from Kansas. -
    Cmdr. John Crichton "Farscape"

+ Reply to Thread

Similar Threads

  1. 2-seat version of Affordaplane or similar?
    By Pete in forum The light stuff area
    Replies: 6
    Last Post: December 5th, 2013, 09:20 PM
  2. Affordaplane Plans
    By UltraBuzzard in forum Hangar Flying
    Replies: 33
    Last Post: January 30th, 2012, 05:56 PM
  3. Seaplane vs land plane speed difference
    By Holden in forum Bush / Float flying
    Replies: 32
    Last Post: June 18th, 2008, 01:29 PM
  4. Looking for the right plane
    By Chris m in forum Wood Construction
    Replies: 7
    Last Post: February 13th, 2005, 07:26 PM
  5. Light Sport Plane Options
    By jimboe in forum General Experimental Aviation Questions
    Replies: 3
    Last Post: June 29th, 2004, 12:27 AM

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts