Canopy frame design

Discussion in 'Aircraft Design / Aerodynamics / New Technology' started by Scheny, Sep 2, 2019.

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  1. Sep 2, 2019 #1

    Scheny

    Scheny

    Scheny

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    My project has a 3mm Plexi window over a carbon frame, with the form of the window already fixed, but the rest of the details are still out for discussion.

    I have watched a video () where a guy is asking Mr Jonkers about their new JS-3 glider. Apart from the stunning details they added to this plane, it has some very interesting remark about new findings in crash safety they incorporated to their canopy frame design and I would like to know who has more background about it.

    Most of you will know how a glass/carbon canopy normally looks like in a Diamond DA40 or a Cirrus. The JS-3 however does not have the frame be positioned by the profile in the fuselage going around the frame, instead it has 2 pins per side which are holding it in place while its freely floating on top. If I understood correctly, this improves closure under heavy buckling conditions. The closing mechanism seems to drive bolts through this pins, so it is attached to the fuselage at all four points.

    What do you think about this design? Can I have a rectangular cross-shape carbon frame, glue the Plexi on it and have it flat mounted to the fuselage with only a seal between, or should there be a profile added to it instead?

    Also, what kind of locking mechanism do you prefer? My favourite is the Diamond. I will attach a drawing later on.
     
  2. Sep 2, 2019 #2

    BJC

    BJC

    BJC

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    I’m not a sailplane pilot, but I have a strong preference for a canopy release system that allows opening or jettisoning the canopy with a single hand with a single motion. (That may be possible with the JS3, but I didn’t see that feature.)

    As relates to the Vne / flutter thread, about IAS verses TAS verses the actual flutter speed, note that the Vne, in IAS, reduces with altitude.


    BJC
     
  3. Sep 2, 2019 #3

    Scheny

    Scheny

    Scheny

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    Thanks BJC! I forgot to mention that it will have a BRS installed, so no reason for jettison capability. It is also powered, not a glider. Still, the cockpit has much resemblence of a glider cockpit (see my avatar).

    I concur having single lever is best, this is what I love in the Diamonds. They are only locking at the rearmost part, but as you mentioned the Vne topic: the DA42 in the NG version (increased weight & speed) I flew last Thursday had some vertical pins added in the front door frame which were not there in the original DA42.

    As my Vne will be lead by a "3" (~300kt), I take your advice serious. Any glider builder here with advice about frame cross-section? @BoKu @Topaz
     
    Last edited: Sep 2, 2019
  4. Sep 2, 2019 #4

    BJC

    BJC

    BJC

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    Even with a BRS, I would want jettison capability.

    Is there a BRS that is rated for 300 knots?


    BJC
     
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  5. Sep 2, 2019 #5

    Scheny

    Scheny

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    The GRS 6 473 SD Napkin can handle 220kt which is exactly cruise speed. As the design weight is only reached at MTOW with AUX fuel and directly after take off (turbojet burns a lot in the climb), there is a lot of margin. So, most of the time it should be able to handle up to 250kt before failure, of course without any guarantee of survival. As there is no better version available, everyone trying to push the Vne by emptying testing is welcome to do it above open water and without me inside :rolleyes:. You need at least MCT to reach and maintain 300kt, so not possible to exceed 250kt by accident.

    As for jettison, there are not many use cases except toppled and burning, which is a low risk with Jet A1. Still, I will consider it.
     
  6. Sep 3, 2019 #6

    pictsidhe

    pictsidhe

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    Ditching in water may have you scrambling to get out. Now is the time to add easy egress options!

    A BRS manufacturer may well be able to tweak max opening speed by adding or altering the slider. Worth asking rather than just blindly ordering a stock model. It would slow deployment speed at all speeds, so not something they'd offer for the much more common slower aircaft.
     
  7. Sep 3, 2019 #7

    BJC

    BJC

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    BTDT. Still have the scar on the top of my head where I busted through the canopy.


    BJC
     
  8. Sep 3, 2019 #8

    wktaylor

    wktaylor

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    Concur.
    A good/reliable emergency release/partial-release system... or canopy break-out system... to ensure You are not trapped in an on-ground crash scenario is wise. Any 'stuck' canopy, door etc, can make an otherwise survivable crash disastrous with post-crash fire, water-immersion, impaling, quick-rescue, etc.

    WARNING.
    Be very cautious about how the HOW any part of an aircraft is deliberately jettisoned... especially a canopy/door... and under what conditions. This should be last resort to BAIL-OUT.

    Reason... a randomly jettisoned canopy, with a low energy departure from over the cockpit is likely to tangle-with/destroy Your vertical/horizontal stabilizer... and/or may be a hazard to Your CAPS system if jett'ed at the wrong-time. As I recall, loosing a canopy in flight in several homebuilts was a 'death sentence'... the lost canopies either struck the stabilizers or grossly affected the aerodynamics causing loss of control.

    NOTE.
    I've worked for years on military aircraft with ejection systems. Dealing with the canopy is a very critical aspect of survival. Most military acft canopies are thruster-jettisoned to take them safely away from the airframe... the 'others' are deliberately left in-place for thru-the-canopy ejections. In at least 2-instances that I'm aware-of, the thruster-jettisoned canopy failed to move as intended and then struck/severed the one of more of the stabilizer surfaces. The fact that the pilots were in moving ejection seats, a second behind the canopy, saved their butts!
     
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  9. Sep 3, 2019 #9

    flyboy2160

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    Because two friends of mine were killed trying to bail out of aerobatic airplanes and because I've seen problems getting out of overturned planes, I took bailout and rollover provisions as high priorities in designing my plane.

    My final canopy design candidates were car door designs, with one door on each side that extended to the centerline of the plane. The baseline design is 'normal' opening car doors, the other is suicide doors.

    My intention for the suicide door was to allow it to be cracked open in flight, swing fully aft, and then be retained in that open position. It could even be opened this way at low speeds in preparation for a rough emergency landing.

    The trick will be to engineer a motion snubbing device to slow the violence of the wind-aided opening. I've already run CFD with the suicide doors fully open - the plane is still stable in pitch.

    I've considered retaining the normal car door with an ejection leash before it hits the empennage.

    p.s. And yes, I know this sounds like it should be added to the famous cartoon:

    [​IMG]
     
    Last edited: Sep 4, 2019
  10. Sep 4, 2019 #10

    Scheny

    Scheny

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    Here is the Diamond frame cross section that I promised:
    upload_2019-9-4_10-7-20.png

    As for the things you mentioned before:
    • Roll-over protection: Already included in the architecture. Only point I am unsure is, whether the roll over will protrude above the head (low clearance and risk of head injury during sitting down), or be behind the head as in a glider
    • Jettison: single release lever unlocking all pins already foreseen, single hinge at the front (less risk with inadvertent opening), have to evaluate jettison for the hinge
    • BRS: of course I will ask them about a custom riser, but this is still way too early for the current phase of the project. In addition a BRS is always a compromise between height loss during opening and maximum speed. I don't think it makes sense to tune it for a speed run that normally won't occur. Cruise speed is around 220kt and while it is possible to reach 300kt, you should not, as this implies potential flutter and intense stress on the engine. For comparison: European cars are built for 130km/h (max speed on most motorways). No one designs the brakes and gears to work best at higher speeds.

    My questions are:
    • does the rectangular cross section of the Jonkers make sense, or is the one in the picture still the state of the art?
    • two locking pins at the rear of the canopy (hinge at the front), or four locking pins at the bottom of the canopy in the corners?
     
  11. Sep 4, 2019 #11

    BJC

    BJC

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    I have no direct answers, but will mention some things that I would consider wrt your questions.

    Cross section would depend on at least two things: whether or not I planned on sitting on the sill when entering and exiting the cockpit, and how I planned to seal the canopy frame to the sill. Sealing will be important at your target speeds.

    Locking pin size, number and placement would depend on the maximum load on the canopy, which will be significant at a Vd of 333 knots / Vne of 300 knots. The glider’s Vne seems to be about 130 knots; big difference in loads verses your’s. It also would depend on the arrangement for jettisoning. I would want it to lift clear of my face and head before it began moving aft. The sailplane people have a neat system for that. Someone here likely can point you to a description, as well as the forward end lifting force.


    BJC
     
    Last edited: Sep 4, 2019

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