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  1. DaveD

    Articles / Blog - Ultralight Design Concepts

    So for three years I quietly wrote a design column for Sport Pilot Mag here in Australia. I didn't really publicize it on this site as it was basically "Aircraft Design for the Uninitiated" and I figured if you hung out on this forum it was probably pitched a bit below your level (I deliberately...
  2. DaveD

    Grumman G-73 Crashes in Swan River

    This happened in my back yard (so to speak) yesterday. It was during the Australia Day Celebrations so there's lots of video. Looks like a stall-spin (or at least it would have been a spin if there was more altitude)...
  3. DaveD

    404 Error on old Posts

    I just did a search for "solid core wings" but clicking on several of the resulting threads produced a 404 error. Have we lost some of the older stuff? I went back to the "New Posts" section and that is working fine so I don't think it's a connection problem at my end. Thanks Dave
  4. DaveD

    Worked Example - Plywood Gusset

    So it took me a whole lot longer than I expected, but here it is. I've put it in a new thread in the optimistic hope that others will do similar things so in future a quick search for "Worked Example" will find them all! I’m interested to hear people’s feedback, there’s definitely room for...
  5. DaveD

    Posting Example Design Calculations on HBA

    I've thought this on several previous occasions but the current discussion on gusset design in other threads has spurred me into action. There's few more useful tools than having a worked example to look at when you are trying to design something. We certainly have the expertise within the...
  6. DaveD

    Wing Design

    I've seen this type of wing on model gliders but it doesn't seem to turn up much on full size aircraft. It would lend itself to composite construction, probably a bit fiddly for metal/wood construction. Gliders seem to prefer a straight trailing edge (Schuemann wing?) Are there any full size...
  7. DaveD

    Minimum Composite Thickness/Layup

    I'm suprised there isn't already a thread on this, but I couldn't find one specifically. Digging around in other threads I found a few suggestions for minimums but there is obviously a degree of personal preference. Here's what I've come up with: Glass (GRP): Billski mensions 3×7oz UNI...
  8. DaveD

    Inline engine mounted on its Side

    Inline auto engines invariably have the crank at the bottom as this is most convenient for a car transmission, but planes typically need the prop near the top for visibilty and prop clearance. I was looking at the airtrikes website and noticed some photos of installations of Geo and Honda Fit...
  9. DaveD

    Peery - Aircraft structures question

    I just want to make sure I'm not missing somthing! Here are diagrams 10.1 and 10.5 from Peery's Aircraft Structures Book. Fig 10.1 is supposed to show the notional loads on a wing at four "corner" points on the flight envelope (points A,B,C & E on the Vn diagram). I assumed the arrows in 10.1...
  10. DaveD

    Vacuum Resin Infusion with Cores and Carbon Pultrusions

    So I've been busy in the shed trialing my newly acquired Resin Infusion tools. The plan was to make a composite beam for a few reasons: 1) I can test it to see if it is as strong as the calculations say it will be 2) Good way to practice with the new equipment and methods and get some...
  11. DaveD

    How is this Composite wing Assembled?

    I originally posted this inside another thread, but it is really a separate topic so I'm reposing here with a more relevant title. I was having a look at autoreply's composites presentation and saw the attached picture which triggered a lot of questions about how it was constructed (see the...
  12. DaveD

    Horizontal Tail (for a twin boom pusher) - In propwash or Out?

    I guess this is really an 'H' tail vs inverted 'U' tail question. First up there seem to be both types out there: The Sadler Vampire has most of it's HT in the propwash as does a Cessna 337. The Scaled Composites (& Northrop Grumman) Firebird has a inverted 'U' tail clear of the propwash as...
  13. DaveD

    Flap Blow-back

    I just came across an article which mentions "flap blow-back". From what I can tell this appears to be an automatic system which partially retracts the flaps if they are extended and VFE is exceeded. It sounds like a good idea. Is anyone familiar with this system? Do any GA size planes use it...
  14. DaveD

    Ultimate Loads and Factors of Safety

    I've got some questions about factors of safety, and how these are dealt with when designing in composites. But first some “thinking out loud”: Taking at FAR23 as a starting point there are limit loads and ultimate loads. Limit loads being the maximum loads the structure can expect to see in...
  15. DaveD

    One Wing Spar or Two?

    The discussion over on on the Tail Boom Attachment thread has got me thinking about the relative merits of two spar wings. My original thinking was that you could get more torsional stiffness for less weight with a two spar wing (but I haven't done the calcs yet to check, so I could well be...
  16. DaveD

    Tail Boom Attachment, any thoughts?

    Ok, so I'm trying to think through how to attach the tail booms to the wings. What I've come up with so far is this: Treat the tail boom a bit like a fuselage attachment where the spar carries through the bending loads without transferring them to the structure. A picture paints 1000 words...
  17. DaveD

    Flaps on non-tapered untwisted wings

    I thought that one of the main benefits of an untapered & untwisted wing (beyond simplicity of construction) was that the stall develops from the center section and then spreads outwards thus maintaining aileron authority during the stall (or if you prefer - avoiding tip stall). I've used the...
  18. DaveD

    Pitching Moment Coefficient Question

    I'm planning on using a GA37A315 (Riblett) Airfoil for my wing and have been running some analysis on XFLR5 to generate some design data. The Cl and Cd plots come out pretty much as expected but the Cm does not. Between -5 and +5 aoa I get a fairly constant value of -0.05 but by 15deg aoa the...
  19. DaveD

    Retractable Gear - Design

    I've been thinking about retractable gear, are there any design considerations I have missed? The vital ones: 1) It should be self-locking (not requiring power) in the lowered position and an indication should be provided to the pilot that the gear is down & locked. 2) It should be...
  20. DaveD

    Composite Sandwich - Help!

    I'm looking for some decent reference material on composite sandwich construction/analysis. The major texts appear to be as follows: MIL-HNBK-23A - Sandwich Structures H G Allen - Analysis and Design of Structural Sandwich Panels Dan Zenkhert - An Introduction to Sandwich Construction F J...