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Bonnet gas struts

Rhodyspit75

Jedi Knight
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Has anyone here ever seen gas struts used in place of the factory supports on a Bugeye bonnet. I have them on my Spitfire and they work great.
 
Good morning Rhodyspit75. Did you go forward with installing gas struts on a bugeye? Gads, they sure need them - not that I can't curl 40 pounds, I'd just refer not having to.

Anyone out there put gas struts on a bugeye bonnet?
 
In theory, it could be done. However, it would require mounting the gas strut in the middle of the outer tube. This would require fabricating a mount with a pivot. Take a look at how the stock telescoping props allow the top portion to slide down beside the foot box.
 
In theory, it could be done. However, it would require mounting the gas strut in the middle of the outer tube. This would require fabricating a mount with a pivot. Take a look at how the stock telescoping props allow the top portion to slide down beside the foot box.
Let's just say it is complex - that part I get. So, I took some pictures and tried to depict what the bonnet strut does when it is down, and what a gas strut might do. As I said, it is complex, or very simple, one or the other.

This is a shot with the bonnet closed, depicting the bonnet strut (in white) as just the line between its upper and lower pivot points. In reality, as you point out, the strut extends farther down beside the foot-box panel. But, for simplicity, I've just shown the length between pivots. As you can see, it the bottom part of the bonnet strut would be parallels to my blue line, which is meant to represent the collapsed gas strut.

Closed Bonnet.JPG


The next photo shows the strut locations with the bonnet open.

IF I did the math right, the gas strut dimensions on the two photo's are correct. Hopefully.

Open Bonnet.JPG


Lifting the bonnet from closed takes roughly 40 pounds. The gas strut would not be exerting all of its force vertically (unfortunately). When closed about half of the gas struts force would be in the vertical direction. But, with the off-set bonnet hinge point, more than half the gas strut force would assist. I didn't try to work that one out. Likewise, when the bonnet is open about 90 percent of the gas strut force is vertical.

Figuring about a 3 to 1 ratio of gas strut force to required lift, I'm thinking a total of 120 pounds of strut force. Of course, gas struts have more force when compressed, which helps to compensate for the less than vertical force vector with the bonnet closed.

I also note that the gas strut will be pushing the bonnet forward when closed. With that in mind I am thinking of using a 50 pound gas strut on each side. When compressed the 29.49" strut below from McMaster-Carr > McMaster-Carr < has a 65 pound force. The 29.49 inch long strut looks like it would be a good fit.
Gas Struts.JPG


My thought is to reduce the effort to open the bonnet, but still rely on the existing struts to hold it open.

I envision leaving the existing strut's upper pivot point where it is and adding the pivot for the gas strut just behind it. The lower pivot location would be set to match the extended length of the gas strut and set up so the gas strut doesn't foul the existing strut when the bonnet is closed.

Seem reasonable?

Stephen
 
Did you check the clearance between the bonnet and the footbox?
Also, most bugeye bonnets are a bit tweaked because of the placement of the props. Will gas struts make this worse if they are strong enough to hold the bonnet open?
 
Excellent feedback. Thank you.

It looks like there is plenty of room between the edge of the bonnet and the footbox - especially given the gas strut is less than 3/4 inch in diameter. Flip side, as part of my installing seals around the front wheel arches (to keep road debris and water from getting thrown up by the wheels into the engine compartment) I have added HDPE slides to keep the outer fenders from rubbing things as the bonnet is opened and closed. You can see one of the slides just behind the wheel opening - sort of looks like a delta wing aircraft. These also assure the bonnet edges wouldn't foul the gas struts as the bonnet opens and closes. Because, as you point out, these cars are all a bit tweaked.
 
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