Canopy anti-bulge


Help Support HomeBuiltAirplanes.com:


New Member
Jan 21, 2012
Greenacres, WA (SE Spokane) at SkyMeadow Airpark (
With greater speed comes canopy bulge. Over-complicated mechanical systems using many parts to stop the bulge are completely unnecessary.

The chief design problem is how to get an anti-bulge pin on the canopy to seat into the fuselage since the path of motion of a descending canopy is curved. Pins don't slide into a curved slot...but an egg can!

Affix half an egg to the bottom of the canopy. Drill out a round hole in the fuselage sill where the egg nests as the canopy closes. The nested egg prohibits the canopy from bulging.

An anti-bulge system with NO moving parts! :)

It's easy to design complicated Rube Goldberg contraptions but hard to get a design titrated down to only the necessary and sufficient elements to get the job done. You know you've succeeded in the design when it meets some standards: Does it work? Is it robust? Does it have a long service life? Is it least expensive in price and time to build? Is it simple? Is it beautiful.

The egg anti-bulge system works efficiently, simply, reliably and well. It is robust to damage, doesn't hardly cost and builds quickly.

Use a wooden "Easter Egg" which can be bought at almost any cutsie store. Ask your wife where to get one. Aircraft Spruce doesn't carry wooden eggs!

Here's a solution: NO moving parts in this anti-bulge system.

See my "Egg" album.


Well-Known Member
Aug 20, 2007
Evansville, Indiana
What aircraft are you talking about?

Thicker material would be my first suggestion if you're having a problem with a canopy bulging outward when exposed to high speed (define "high speed"). Not to mention that there is the added benefit of the canopy being more resistant to impacts from birds with the increase in density. If the wind is buckling this, then anything bigger than a starling is going to get up close and personal if it hits the canopy.

My other suggestion would be that such a problem is a sign that the canopy seal is not adequate if you're getting bulging.


Well-Known Member
Mar 2, 2003
Western Washington
Bulging due to higher speeds has been an issue for quite a few airplanes. The most common fix is to incorporate several latching points around the periphery so that the frame is locked in position. Actually, the suggested method of using egg shaped or hemispherical locking protrusions is excellent (we're using something similar in our work) in that it does lock the frame without requiring an extensive latching mechanism. In the case of our race plane project the canopy frame is a fairly massive graphite laminate but despite being well over an inch thick around the periphery, there would still be a noticeable bit of movement if it was not properly constrained.

Most airplanes in our market have issues due to bulging. The Glasair windscreen for instance had a continual habit of cracking around the periphery bond. Their canopy door frames also bulged despite a fairly nice structure and a two point lock.

It almost seems like designers sort of ignore the canopies and windscreens, somehow thinking that just any mounting will work.