Flying With An Open Canopy

Discussion in 'Aircraft Design / Aerodynamics / New Technology' started by GESchwarz, Apr 23, 2012.

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  1. Apr 23, 2012 #1

    GESchwarz

    GESchwarz

    GESchwarz

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    I am soliciting knowledge on how to safely open and close a sliding canopy in flight. My design is a tandem seat much like the RV-8. What sort of forces can I expect to encounter as I manually open and close a sliding canopy? What sort of latch, handles, and locking devices work well? Are there existing designs that work well? What devices can be employed to reduce aerodynamic loads and noise while the cockpit is open?

    I have seen a sort of vortex generator that flips up that I suppose reduces buffeting of the canopy.
     
  2. Apr 23, 2012 #2

    TFF

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    The Grumman Tiger family can be opened only a few inches. Too far back and your not going to close it if not slamming all the way back, and the drag is very high, to where you wish you did not do it. I have never heard of an RV flying with it cracked. I dont know if it is true or wives tail but I here if you get a Grumman Yankee into a spin you suppose to throw it back to let the drag help straighten you out. WWII planes are large and can handle the drag of an open canopy. RV8 and a P-51's cockpit are about the same size where one plane is 40% bigger.
     
  3. Apr 23, 2012 #3

    Rick McWilliams

    Rick McWilliams

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    Flying with an open canopy is a novelty. I have flown four airplanes that can operate with the canopy open, Ercoupe, Super cub, Varga Kachina, and Yak52. The cockpit turbulence is very forceful. Above 80 knots a helmet is needed to keep your headset in place. The Yak 52 has sliding segments about 24 inches long in the canopy. The force is about 15 lbs, motion is awkward. I am pretty sure that my wife would not be able to operate it in flight. The Varga has a lateral slide and fold opening. The Ercoupe side windows slide into the sides of the fusealge. The cub windows hinge up to the wing, and down to the fuselage side. It can be rather pleasant flying a super cub on floats with the doors off in hot weather.
     
  4. Apr 23, 2012 #4

    bmcj

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    It doesn't really answer your question, but may shed a little more light on the thought process...

    The 2-place training gliders we use have side hinged canopies that can be easily opened (fully) and closed inflight; granted, the cruise speeds are only around 55 mph or less, much slower than you are talking about.
     
  5. Apr 23, 2012 #5

    djschwartz

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    I am using a latch from a T-6 on the updated canopy mechanism for my Stephens Akro. The T-6 latch gives a good handle to hang on to while opening or closing the canopy. A heavy gauge stainless steel slotted angle, custom fabricated for this purpose, give the T-6 latch something to drop it's locking pin into. I also made a new rear slide. The "T" track is sailboat jib track from West Marine. The car is made of aluminum with delrin slides. A rod end bearing attached to the canopy frame cross bars is pinned to the car.

    IMG_0168.jpg IMG_0167.jpg
     
  6. Apr 23, 2012 #6

    autoreply

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    I've witnessed several gliders landing with open canopies. Especially with a sliding canopy, a serious degradation of control (airflow over the tail) seems unlikely. A disintegrating canopy though might degrade control a bit.

    As for the forces, look at the pressure (Cp) plot of an airfoil. You have a lot of underpressure over the aft part. Extending that to a sliding canopy, it will pull upwards and backwards hard. Very hard.

    The spoilers are a good idea. I have one on my motorcycle, check out the picture:
    http://82.170.178.163/Public/IMAGE_521.jpg

    Even at 120 mph, that tiny spoiler is enough to deflect all the air over your head. A spoiler on the wind screen might be enough to completely avoid any buffeting, especially when it's adjustable (tilt fwd/aft).
     
  7. Apr 23, 2012 #7

    Jay Kempf

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    Nice insect collection! I've been to that movie. The only thing on a motorcycle that has you wishing for a rainstorm so you can clear your faceshield. Epoxy should be made from bug guts.
     
  8. Apr 23, 2012 #8

    GESchwarz

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    Thanks for the inputs. So I gather that an open cockpit could be fun if only flying at nothing more than freeway speed. VG’s can do a good job of knocking off the buffeting and maybe even reducing drag.

    I like the latch that Schwartz has, but I was thinking of a center-line mounted 90 degree twist lever that would actuate two pins, one on each canopy rail (port and starboard), that way I could use either hand. I am also concerned about jamming the canopy if I am applying force only on one side; the asymmetric loads could cause the canopy to twist or rack. The cables would be of the solid throttle cable type with a return spring assist.
     
  9. Apr 23, 2012 #9

    djschwartz

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    I do not like overhead latches lined up with ones head. I was nearly killed by that in the Stephens when the canopy came loose on takeoff. Fortunately it was only a small "flip" latch with no real handle and I was wearing a helmet and was left with a gouge on it instead of my skull. A larger handle would likely have knocked me silly and I would have crashed. This is one reason I've gone to the side handle. The Pitts S1 typically has a center handle but it's only a piece of plastic tubing over a small braided steel wire that runs along the front edge of the canopy and pulls pins on either side of it at the rails. This works fine for the very small, light canopy on a Pitts S1 but would not be adequate for something the size of an RV-8.

    FWIW, when the canopy departed the aircraft I never did notice the buffet; however, I had so much adrenalin in me by then I probably wouldn't have noticed a small nuclear explosion!

    If your canopy and track mechanism on a single seat or tandem aircraft is flexible enough that it would jam or be difficult to actuate with a side handle then you should not attempt to fly with it open.
     
  10. Apr 23, 2012 #10

    orion

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    Having owned several I can comfortably say that the two place Grummans can fly with the canopy all the way open. Noise is of course increased but turbulence is actually pretty minimal. Opening and closing the canopy on the small two place airframes is no big deal and does not induce any slamming or heavy loads on the track. The drag penalty reduces cruise by about eight ten mph but the airplane is fully controllable, even to stall. There does seem to be a very slight decrease in horizontal tail performance with the canopy open but again, not detrimental. Best air speed for open canopy is the maneuvering speed.

    And yes, the open canopy for spin recovery is a rumor but I have never heard of a case where this was actually verified.

    The four place Grummans do have about a six inch limit however most owners I've known have flown them at Va fully open. It is however a larger surface than that of the two place airframes so some caution is generally advised so as not to over-stress the rails.

    Most of the limitations I've seen on open canopies have to do with canopy shape. The Grumman sliding canopies have only minor curvature extending through this part of the cockpit enclosure and so the air tends to flow past with only very minor surface pressures. This also holds for the four place airframes. Similar characteristics can be seen in examples like that of the T-6 and the Beech T-34 and the Kachina - the openable parts of the canopy are straight so subject to low air loads.

    Something like an RV-8 would have dramatically higher loads due to the surface's curvature.

    The bottom line is simply that if your canopy is relatively straight and so subject to relatively small aerodynamic loads, flying with it open should present you with minimal issues (but test very carefully anyway). If however it has a higher degree of curvature, you'll have to run some calculations to see if the integrated pressure distribution could cause damage to the attachment or to the canopy itself.
     
  11. Apr 24, 2012 #11

    Rick McWilliams

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    The pressure distribution on a closed canopy is predictable. The flows around an opened canopy are much more difficult to estimate.
    I wonder how they designed the doors on the flight designs LSA. These are large, highly cambered, and of light construction.
     
  12. Apr 24, 2012 #12

    fly2kads

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    The Thorp T-211 is another example of an aircraft that you can fly with the canopy open. Of course, it too is side-by-side.
     
  13. Apr 24, 2012 #13

    GESchwarz

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    So what you're saying is that so long as the canopy in burried in the boundary layer the airstream doesn't know it's open. Am I getting that right?
     
  14. Apr 24, 2012 #14

    orion

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    Partly but it also should have as little fore-aft curvature as possible. An RV-8 canopy is pretty much airfoil shaped and thus has a low pressure field distributed over it just like a wing section. If you open it and it allows air to flow over and through it, it could take part of the pane with it as it breaks away.

    Notice that on the T-6 the openable part of the canopy is perfectly straight fore-aft so when you slide it back, it presents no camber to the airstream.

    T-6_n.jpg
     
  15. Apr 24, 2012 #15

    autoreply

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    It's not so much the boundary layer, but the pressure field on the canopy that's the problem in fwd/aft forces. A low canopy will have relatively low forces acting backwards, thus like a thin airfoil. The boundary layer is only problematic in turbulence/buffeting inside the canopy and that can be helped with a spoiler, much like the one on my motorcycle or what many modern cabrio's have.
     
  16. Apr 24, 2012 #16

    GESchwarz

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    Okay, I can see that I will have to go back to the drawing board. Thank you.

    Also, the crash hazard of a handle located at centerline or anywhere in the "nogen zone" has to be considered for relocation, or design it in such a way that I wouldn't mind wacking it with my head. I just think that if I'm pulling on one side it could jamb, but maybe that's because I don't have any plex installed yet, which will give rigidity to what I have now which is just the canopy frame.
     
  17. Apr 24, 2012 #17

    djschwartz

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    However, the P-51D and many others have bubble canopies that can be opened in flight. Even the rear opening portion of the T-34's canopy is a highly curved bubble. That certainly does require a more robust track and actuating mechanism than a flat canopy like the T-6 or Yak; but, at the speeds we fly, especially in the pattern where it would be most desirable to have the canopy open, it should be possible with appropriate design. Your caution about making sure the design is robust enough is well put. When I lost the canopy on the Stephens it went straight back and smashed itself on the tail. Being an unlimited aerobatic ship, the chrome moly steel tail held up well, some cuts in the fabric and one bent brace wire. Had it been a more conventional sport plane I suspect the damage would have been much worse.

    FWIW, the forward attach on the Stephens canopy are roller bearings at the bottom of each side of the canopy frame directly under the front bow. These roll in steel "C" channel welded to the top of each longeron with the open part of the "C" facing outward on each side. Thus the front of the canopy frame is well supported and restrained through its entire travel while still able to actuate even with a substantial load on it. The track mechanism at the aft support also maintains its restraint over the full travel of the canopy. The original rear support was a pair of telescoping tubes. When the canopy was open and the tubes extended the rear of the canopy could move around quite a bit.

    BTW, I'll second your comments about flying the Grummans with the canopy open. It works just fine. Lots of fun, get to pretend you're a Navy pilot on approach to a carrier. Just remember to flare!
     
  18. Apr 24, 2012 #18

    GESchwarz

    GESchwarz

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    And that's the whole point, to make the flying experience more fun.
     
  19. Apr 25, 2012 #19

    DaveK

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    This is a bit of a tangent, but the design I have been working on has a forward sliding canopy. The question I have is if this came unlatched or wasn't latched would it slide open due to the low pressures at the front, or would it stay shut. I know some of the Jodels have this type of canopy and at least one glider had the whole nose slide forward, but I can't seem to find any real world info on this.
     
  20. Apr 25, 2012 #20

    Rick McWilliams

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    The acrobatic Zlin 242 has a forward sliding canopy. Early versions allowed opening in flight 6 inches. Opening force is low. The canopy tracks are very robust. I think the POH was changed due to the risk of activating the canopy release. A peculiar problem is starting the engine with dew on the cowling and the canopy open. Wet and cold.
     

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