Seaplane doors

[huntaero]

Here are some pics of our seaplane doors on our Bearhawks,
We had to move the bottom door sil up approx 1.5 inches so as to clear the strut. After all the calculations were done and the wing was installed we had about 1 in of clearance. Used a piano hinge full length of the door at the top. Set up for a sight window on the fwd lwr section, and slider windows in the upper.

Have Fun George Huntington


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[Zzz]

I'm in the process of adding these to my quickbuild fuselage. I've read 2" is what it takes the clear the strut. How did you arrive at 1.5"?

Mounting up the wings to test is a huge effort for me since the wings are stored 30 min away. Curious how people have approached this.

[huntaero]

We calculated the dimension from the drawing and verified it with a mockup, and since have mounted the wings on the first A/C and have approx 1 in clearance, kinda tense for a bit until everything is bolted on.

[whee]

My doors look much like huntaero's but I raised the sill 2" because that's what others told me I needed. When we mounted the wings we had 3/4" clearance which gives room for a 1/2" sill overlap while maintaining 1/4" clearance with the strut. I don't think 1.5" would have worked on my plane.

Give me 6 months Z...I'll fly over and show you

[Zzz]

Give me 6 months Z...I'll fly over and show you

Haha... you'd better make it 10 days... I'm about to cross the point of no return.

[Zzz]

I did mine this weekend, with the help of a friend who's much better at forming sheet metal than I am. I think it ended up a little tall but it should provide some nice overhang of the lexan for a seal.

[huntaero]

Looks good

[svyolo]

I am trying to figure the best (easiest) way to hinge seaplane doors on a QB kit. Welding is an option. I kind of think the kit welded tube hinges might be strong enough. I could also add a 3rd and 4th, but I think the load would end up concentrated on the two outer hinge tubes, and 1 or 2 more in the middle might only make me feel a little better.

I was also looking at making the doors out of 3/4X3/4 X 1/16 AL. My upper and lower steel door frames from he kit weigh about 5 lbs per side. A quick calculation says I can do them in AL for half of that, and for a lot less money and easier to Fab than CF. CF would be a little lighter but 30+ dollars a foot for CF square tube. That might make the extra weight savings outside of my budget. A couple of hundred dollars in price, for a lot more work, and 1/2 pound of weight savings, tops.

[whee]

I am trying to figure the best (easiest) way to hinge seaplane doors on a QB kit. Welding is an option. I kind of think the kit welded tube hinges might be strong enough. I could also add a 3rd and 4th, but I think the load would end up concentrated on the two outer hinge tubes, and 1 or 2 more in the middle might only make me feel a little better.

I was also looking at making the doors out of 3/4X3/4 X 1/16 AL. My upper and lower steel door frames from he kit weigh about 5 lbs per side. A quick calculation says I can do them in AL for half of that, and for a lot less money and easier to Fab than CF. CF would be a little lighter but 30+ dollars a foot for CF square tube. That might make the extra weight savings outside of my budget. A couple of hundred dollars in price, for a lot more work, and 1/2 pound of weight savings, tops.

Best and easiest are not the same here. IMO the seaplane door should be hinged using piano hinges. Mine is done using welded tubes and it works but I wish I had used piano hinges. Also, I’m not sure how the welded steel tubes on the fuselage would play with the welded aluminum tube you’d have to put on your door frame. Using the hinges as is would work if you don’t plan to open the door in flight or maybe even just with the engine running on the ground.

I typically swag aluminum as half the strength for the same weight as 4130. Obviously that’s not exact and the structure will determine the actual strength. In this case the 3/4” x 0.035” 4130 tube weighs 0.267 lbs/ft and the 3/4” x 0.062” aluminum square tube weighs 0.1986. So the aluminum is only 25% lighter and not as strong. If you don’t plan to open the door in flight then obviously it will be fine. Even my steel doors aren’t likely strong enough to open in flight. In fact they are questionable on the ground when the engine is running.

[svyolo]

I wasn't sure about opening them in flight. That is a big barn door to open into the airstream. I remember one guy here saying he opened his, or was planning too.

The kit upper doors are square tube, I think 1/2", the lowers are a mix of round tubing. Together, one upper and one lower weight right at 80 oz. I will recalculate what a seaplane door frame will weigh and repost it here. I thought it was about half. That isn't replacing tube for tube with the lower doors. Just one big door with less tubing than the two smaller doors. I guess I will also calculate how much it would weigh to do the same thing in steel.

[svyolo]

It was a couple of months since I ran the numbers. The seaplane doors will have 14.5 feet of tubing each. 3/4" .049 6061 weighs .22 lbs/ft so 50 oz of tubing per door (80 for the kit doors). I might use 5/8" .035 4130 tube at .28 lbs/ft. 65 oz per door. The AL is $4.50 a foot, the 4130 is $10.50. The aluminum door would be a pound lighter and 75 dollars cheaper (that surprised me).

The cheapest I could find 3/4" CF tube was $30/foot. 500 dollars a door.

I don't know if I need to fly with the doors open, but I would want to taxi with them open for sure.

[whee]

Hmm, I’m pretty sure my plans show 3/4” x 0.035” round for the entire door frame. But my plane is an Alpha. I can’t see a reason to use square tube.

Hard to say without running the numbers but 0.049” is pretty thin for AL and based on my experience with my seaplane doors it’s is not what I’d use. If I was a good AL welder and was building my doors again I would consider 3/4” x 062” AL round.

So far I haven’t been willing to taxi with my door all the way open. I taxi with it partially open but I keep my hand on the handle.

[svyolo]

Lower doors are round tube, upper doors are 1/2" square tube. I can't find the wall thickness on the plans at the moment.

I have some 1/2" .035 square tube (from the skylight) and 3/4" .049 6061. The AL tube is a LOT stiffer in bending than the steel, for nearly identical weight.

The kit hinges are just tubes welded (one side only) on the fuselage. It would be pretty easy to take some .035 and weld it between the hinge tube and the fuselage tubing. That would make the stock hinge point on the fuselage quite a bit stronger.

[svyolo]

I thought I was going to use Piano style hinges but then I started to think how they are loaded. I know they will work. It seems to me that the load on the door hinges as the door is trying to flap in the breeze, concentrates the load in the corners. Piano hinges are great for spreading the load the length of a flexible panel. On a door I don't know if 90% of the hinge (the inner portions) is doing any actual work.

I know the piano hinge will work, and I still might use it.

[whee]

Lower doors are round tube, upper doors are 1/2" square tube. I can't find the wall thickness on the plans at the moment.

I have some 1/2" .035 square tube (from the skylight) and 3/4" .049 6061. The AL tube is a LOT stiffer in bending than the steel, for nearly identical weight.

The kit hinges are just tubes welded (one side only) on the fuselage. It would be pretty easy to take some .035 and weld it between the hinge tube and the fuselage tubing. That would make the stock hinge point on the fuselage quite a bit stronger.

Doors aren’t detailed in the plans on my Alpha. That info is in the Beartracks which specify both haves being made of round tube. But it really doesn’t matter since you are only trying to save weight over what you currently have.

Stiffness isn’t necessarily related to strength but I know you knew that.

I also know that you know I’m just sharing my experience, what I would do differently and what I see when considering your ideas. I makes no difference to me what other builders do.

If you do full lexan or plexi on your doors you’ll gain a full understanding why I suggest going with piano hinges.

[svyolo]

Since I have never even sat in a real tube and fabric airplane, I will take you at your word on the piano hinges!

I am covering my fuselage now and more than likely I will fly with the factory doors. Just trying to see if there is something I need to do now to facilitate changing to seaplane doors down the road. Below the doorsills is all AL and removable so I can raise the door sill easily later.