I built a RV3 this winter, with a scale sliding canopy. The latching system works fine on the ground with a 14x6 prop at 9400 rpm. What I am curious about is: When flying at WOT will the force trying to rip off the canopy be greater than the force of the prop blast --will it be more, less, or the same?

I think, repeat think, you're probably fine. The reality is that if the airplane is accelerating, then there is an inbalance of forces. At some point, drag will grow (square of speed) to the point where it balances thrust and the airplane accelerates no more. Certainly at terminal velocity there will be some level of pull (friction drag) on the canopy in excess of what it experiences at full throttle on the ground. However, since that prop likely puts out a fair amount of blast, if it appears to be holding well, then you're probably ok.

Will there be more force on the canopy in flight than when sitting on the ground with the engine running? Yes.

When the airplay is plugging along at say 70mph in the air, the canopy is feeling that over every bit of it. Plus whatever prop blast that is faster than that other air will add to what the canopy is feeling. Will all that air actually work to pull the canopy open? Depends on how the latch works to hold the canopy closed. There is probably going to be negative pressure on the canopy but it just might pull the latching tighter. If you're using a proven design for the latch mechanism, don't sweat it, but play it smart.

First flights on the airplane, cut out the additional worry that the canopy might pop off. You already got enought to sort out. Your focus needs to be clearly about flying the airplane. So tape the sucker closed and get the important stuff done first.

After you've gotten the airplane flying good, then sneak up on the question of latching adequacy. Only use a little bit of tape and see what the canopy does. If there's negative pressure working hard enough to cause problems, the tape will reduce the severity of the results. With luck, bad and good, you'll see the joint opening where it's not supported. And can beef up what needs it. With good luck only, nothing will show because the latching is working. Just don't do any terminal speed dives or such.

Nobody can really answer your questions with any hope of accuracy, because none of us have any idea what the mechanism is or how well it's installed or what it's made out of or how fast your airplane might fly or how fast you'll probably fly it or if even if the sucker fits tightly or not.

But one thing is certain. The canopy isn't seeing any force on the ground just from some prop blast compared to what it'll see in the air.

BTW, it might be some value to do a little experimenting when you're trimming out the new airplane. Put some fairly weak tape pieces on the canopy and see if they're pulled off. If they are, and the canopy doesn't go with them, the latching is working ok. If they aren't, then maybe the canopy isn't really seeing much negative pressure.

Good luck and let us know how it turns out.

And keep in mind that if you built it once, and it didn't stand up in service, you're probably the most knowledgeable person to do an effective redesign and repair.

Thanks, will keep all this in mind. To defeat the system or unlatch, the canopy must be squeezed in at the front. I don't think there would be any forces in the air that would do this?