Pros and Cons for Canopy Designs

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wsimpso1

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Hi, I am building fiberglass side-by-side two seater of my own design, and I have to make some choices on the canopy/windshield.

There are several design options out there. I am considering doing mine several ways and am trying to make a decision here. I want to hear what you folks think about each of them. Advantages, disadvantages, lousy features, sexy features. I don't want to bias the discussion with my opinions, at least not yet, so just fire away and I will take notes.

Methods for consideration:

Fixed Windshield, canopy slides fore-and aft (RV8);

Fixed windshield, canopy lifts up on pivot from one side (Bf109);

Fixed Windshield, canopy lifts up on pivots from back (F15);

Full bubble, hinges from one side (Long EZ, Cozy, Brokaw Bullet);

And the non-canopy, Gullwing doors and windshield frame pivoting doors.

So. warm me with your thoughts. If I missed a good option hit me with that too.
 

Metalmaniac

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As an Rv guy, I can't stay out of this one. I'm building an RV7A, side by side. Two options are available. Sliding canopy with fixed windshield or one piece tilt forward. The sliders offer good ventilation during taxi, because you can slide it all the way back and drive around all day looking cool like the fighter piolts. You can then close it up for takeoff and spend the rest of the time staring at a big thick windshield frame and vertical bracing tube running vertically down the center of the windshield. Getting the aft end of the canopy to seal where the bottom meets the top of the fuselage is apparently impossible. Hello wet baggage compartment. They are hard to fit up during building too.
The tilt canopy offers absolutely the finest view forward and up and to the sides as you can get, short of falling out of the airplane. Ventilation sucks, because you can prop it open a tad, but nothing like a slider. It also offers good access to the avionics, because the forward side of the panel is exposed when you open up the canopy. It is apparently impossible to seal the front of this canopy, so you can get wet radios if you fly in the rain. I'm not in the habit of flying in the rain, but when I wash this baby, I'll have to tape off the seam where the front meets the cowling. It's hot in the summer time here in Oklahoma, but I'm not planning to spend all day on the ground sweltering in this thing anyway. I guess I'd rather have that fish-bowl view looking out the windshield than look all hot-roddy from outside. Hey, as an old-timer I know says, it just depends on whether you want it to leak at the front or the back. Whatever you decide on, try to make it something you can get built in this lifetime. Canopies are hard to deal with and very expensive, or can be. Have fun and build something - Richard - Hanger 7A
 

John Slade

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I'm finishing off a Cozy with the side opening canopy. If you go this way, be sure you have a good latching and warning system. There's a lot of suction and an unlatched canopy will "depart the airplane" quickly. I've seen front hinged Cozy canopies (you can get plans from Aerocad or Uli Walter) and wish I'd done mine that way. I don't see any reason why either would be harder to seal than the other.

I also worked on a Velocity with gull wing doors (because the pilot didnt latch the pax door and lost it at 400 ft on climb out.) :rolleyes: I like this configuation except that, on the Velocity it involves some structural issues with part of the strake going up with the door. Much easier to get in - much harder to build.
 

Captain_John

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MM,

I wasn't aware of the potential/propensity that the RV canopies have for leaking. Is it futile to attempt a good seal on the lid?

I have (like many others) been back and forth on this issue myself.

BTW, my RV is back on the short list. I am now gainfully employed and will begin production when my sled sells. It is on ebay now and I have several hot prospects!

It sounds like you went with tip up. Are you happy with your decision? Any remorse?

:D CJ
 

wsimpso1

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Thanks for the so far. There have to be more thoughts, comments, etc on this topic... :

Sliders will leak at the back (I am presuming when flown in the rain);

One piecers will leak at the front when flown in rain;

Make sure that the latch mechanisms are sturdy and have an alarm.

My bird has to open wide to allow things like bags of cross-country skis and snowboards to fit in, so the opening and travel of whatever I pick is kind of big. My thoughts (feel free to chime in any time) run this way:

Fixed Windshield, canopy slides fore-and aft (RV8)
This arrangement is not likely to leak on my radios, but it will require a canopy cover when parked outside. The pressure recovery area will be hard to seal and just has to leak air and water in flight. It will take a two part slide (like a drawer slide) to get the travel, and so far, I have not found anything. The windshield frame and brace does have to be beefy too. I am looking into industrial sources now. Alignment and stability in the wind could be tricky;

Fixed windshield, canopy lifts up on pivot from one side (Bf109)
Same leak paths as the slider, but now I don't have air and water trying to leak in from the pressure recovery area. Rollover structure is in the canopy and out of the way during loading, so it cleans up the view ahead some. It will require a sturdy latch set, but the flop over will be strudy with a cross brace, so that helps;

Fixed Windshield, canopy lifts up on pivots from back (F15)
Same problems as a slider, only worse because it's only one mistake and it is gone!;

Full bubble, hinges from one side (Long EZ, Cozy, Brokaw Bullet)
Hmm, I liked this one until I thought about the high pressure area at the front inducing rain into those expensive radios;

Gullwing doors and windshield frame pivoting doors
Sexy, but compound curves result in having to lap the part inboard of the pivot inside and the rest outside, with the area closest to the joint tricky at best. The roof and windshield arch are one big piece, so rollover structure is solved nicely. A couple of pull pins for the pivots solve emergency egress too.

Now that I have provided my opinions, let's get all of yours on this thread. I really do want a discussion on all of this.
 

Ron

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Canopys

I have a Zenith CH200 with a one piece forward sliding canopy. Like the other guy said with the RV, you can taxi around with it slid open and get lots of ventilation. I have one other advantage. I can unlatch it in flight and it will only slide forward about 3" and you get great ventilation again. And yes it does leak at the back. One disadavantage I don't see anyone mentioning is the GREENHOUSE effect. Don't know where you are located, but here near Detroit it doesn't have to get that hot outside, just a bright sunny day and it's like your under a magnifying glass. The sun just cooks you under that canopy. I've tried different sun shades and nothing seems to work very well. You just roast. Guess that's why I'm building a high wing A/C now.
 

Metalmaniac

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Just a quick clarification to keep things straight, but I haven't started on my canopy yet. I'm still on the wings, so I can't add any real experience here. I just wanted to point out that I did fly one with the tip-up, and sat in one with the slider, and there's no doubt the view is better with the tip-up. I have until fusealage- ordering time to change my mind, but I won't.
And yessir, Capt. John, the leak issue is very real. No reason a guy can't twiddle with it, but the factory guy I met says his leaks like a screen door, and he works for em. Makes you wonder. And they're both hotter than you know what in the summer time. But hey, if we need that much comfort, we'd all just buy a Buick and stay on the ground.
Richard, Hanger 7A
 

Captain_John

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What about using limo tint on the canopy to cut down the rads?

My shaven head would look funny with headset stripe across it and big white ears!!!

:roll:

Seriously now, I am really considering the limo tint. I am currently leaning towards a slider configuration. The thing is like a fishbowl and I would want to darken it up some. I was considering the possibilities of leaving the windshield clear, lightly tinting the sides and DARK tinting the top. What is your opinion?

:confused: CJ
 

Metalmaniac

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I think that's a dandy idea. Can you tint two different shades on one piece and have it come out looking good? I've seen some canopies with just the top shaded with some kind of crap that looked like it came from J C Whitney, pretty un-cool. I don't know diddly about tinting processes but I sure would like to hear more. Also , no doubt you've seen the folding shade some guy markets for RVs. Expensive for what it is and I think doesn't really solve much of the problem.
I like your idea best. Let us know what you find out. I'd be interested.
Richard , Hanger 7A - mounting flap hinges and scratching hairless head
 

Ron

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Canopy tiniting

I've tried some to that rolled tinting film and it DOES NOT work on compound curves. You end up with lots of bubbles and wrinkles. Looks like ****. It won't shrink to fit the curves on the canopy. I once bought this aerosol can of tinting. Glad I tried it on a piece of scrap plexiglass first. The stuff reacted with the plexiglass and you could not see through it. It went all milky but it works great on regular glass.
I finally ended up painting the top of my canopy to match the paint scheme of my A/C. I masked of the area I wanted painted and wet sanded it with 400 paper. When it was dry and cleaned again I just used one of those 3" foam rollers and painted the top of the canopy. Turned out quite well and I don't have the sun beatting down on my head, but you still roast on sunny days.
 

John Slade

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If / when it comes down to designing a custom canopy give Todd a call at Todd's Canopies down here in sunny Florida. http://kgarden.com/todd

I know him well. He makes production and custom canopies for 30 or more aircraft types. If it can be done, Todd'll do it for ya.
 

orion

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Designing a canopy is more a choice pf personal tastes than anything else. The previous discussion has been excellent in going over the various pros and cons. However, as many of you have indicated, designing a good, leak-proof one requires a lot more work. The weather sealing ability requires careful attention to the design of the seals, the return lips and when necessary, channels that collect any water that gets through and direct it out of the airplane.

The latter point can be best illustrated by some automotive sunroofs. In order for these roof openings to stay clean in the installation, they have to be mounted flush with the top of the car. This however often creates a groove or space between the edge of the sunroof frame and the glass, where water collects. If it was allowed to stay there, you'd get wet anytime you open the roof. As a result, many have channels built in leading to drain tubes that take the water and duct it under the skin of the car and out the bottom of the side panels.

The biggest item to keep in mind is that the canopy is a lifting surface, albeit a poor one. In general, there is a bit of dead air space just at the forward root of the widshield. The air then has to accelerate over the top, reducing the surface pressure. Regardless of the design, the hinging and latching mechanism has to be strong and stiff enough to handle this "lift" in a way that results in little or no deflection. If the canopy or door is not stiff enough, the constant motion resulting from flight will reduce the quality of the fit and leaks will start.

Even many production aircraft don't handle this well. I used to own a Grumman, which it was best to park under a roof or at least under a canopy cover. Regardless of what I did or what new seals I installed, it always seemed to leak just a little bit. At least there though it leaked onto the seat, not on my instruments.

In short, research your seal options and for a totally dry airplane, be ready to do a bit more work in this area in order to provide the water a place to go just in case a leak does develop. You may even want to research inflatable seals so when the canopy closes and is securely latched, a tiny pump inflates the seal thus assuring a totally dry interior.

The well sealed canopy also has a secondary benefit, a reduction in drag. Although this is not talked about often, a sigificant contributor to the drag of an airplane is leakage drag - that being the leakeage of slow, dirty air coming out of the various seals and openeing on an aircraft and disturbing the otherwise clean boundary layer. Assuring a well made airplane will address this area to give you just a hair more performance.
 

wsimpso1

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Orion,

Thanks for your reply. I agree that the canopy choice comes down to personal preferences...

Something that seems to be overlooked (I never see it talked about in the books) is that if the frame deflects more than the seal is compressed, the joint will leak. And we see lots of photo's of very flexible components moving around in the airstream. Good examples are RV6's with flaring skirts and the famous Bonanza smile.

I am currently mocking up a gullwing door arrangement. It appeals to me on several counts. The canopy arch and a narrow section of roof and the turtledeck can be made as one piece supplying a lot of rollover structure at relatively low weight and leaving the baggage area accessable. The doors, even relatively large ones, can be made relatively light and stiff as well, which bodes well for sealing. I do plan to use a canopy cover when parked anyway. That only leaves the issues of adequate headroom for ingress/egress, which is what the mockup is about.

One thing that your commentary raised: Gullwing doors are entirely in the low pressure area over the wing, so I doubt that they leak inward while flying. If anything they would leak outward. It occurs to me that I may want to carry a drain tube from the door jamb, but to where? Out the belly, where it will suck exhaust gases and oiley mist while flying? Out the trailing edge of the wing root fairing? How about a flush opening in the surface of the wing root fairing. A check valve that would operate at the pressure differences we will have in flight might be tough to find. I figured that a vent on the belly could just be cut like any other outgoing vent tube to keep it from ingesting gases and mists in flight.

Hmmm. I have been thinking about an inflatable seal powered by squeeze pump like used in blood pressure cuffs. The big issue would be sources for the seals. I was actually leaning towards surgical tubing.

More thinking. I had better go home and set about building that mockup. My Best Man is two meters tall, and has the second largest amount of time in building this bird. He has to fit, so he has spent some time in the mckup before. Then there is the wife (also a pilot), who also has to fit. She is about 14 inches shorter than the Best Man. That is some range to accomodate.

Billski
 
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