Should I bubble my doors ??? Kitfox-4-1200

[rogerh12]

Howdy All;

I finally finished my seat install in my model 4, complete with new looking (but used) custom seat pads.
I have two new metal door frames, the kind with two lateral braces, which I can build doors with, but also purchased a couple of finished doors off a salvage model 4 for just $25 each.

I put the salvage doors on and my wife and I got into the kitfox (in my garage) and closed the doors. Well, it was kinda tight (not that I expected it not to be), so I was wondering about the bubble door options. Here are my questions:

1) With the bubble doors, do I still use my stock metal frame, and if so what happens to the two cross braces?

2) Will it give me elbow & hip room too, or just shoulder room?

3) Are they more fragile, being made of one large piece of plastic?

4) Can I still use the stock door struts?

5) Can I used the tight fit of the kitfox to get my wife to lose weight?

Thanks in advance

Roger

[Av8r3400]

1-yes. They become handles and are nit in the way.
2-yes.
3-not at all. Door rigidity is the same between my two examples.
4-yes. The weight is very similar.
5-that would be a very dangerous game to play.

[HighWing]

Roger,
If this was my project and I was determined to use a somewhat heavier engine, I would pay a great deal of attention to any mod that could concieveably add weight. This is one problem often found with imaginative folks - me included. My first Model IV with Rotax weighed 704 lbs. I just "had to have" lots of little things which added lots of little ounces resulting in lots of added pounds. Again, my best buddies same era Model IV weighed exactly 100 lbs. less than mine - 604 lbs. This time, I am putting a few of the same things on my project (fairings etc), but I weigh everything before and after the mod to see what I am getting into. My thoughts are into how to make the things I want weigh as little as possible like the three ounce jury strut fairings and the seven pound (both wings) lift strut fairings.. This way, I can do a mental cost benefit analysis. I have no experience with bubble doors, but the LP windshield I mounted on a Series V had to have weighed nearly three times the weight of a Polycarbonate windshield.
Just remember this. There has been much talked about on the VW engine and the performance expectations. Anything you do that increases the flying weight unnecessarily risks the performance you are expecting. There have just been too many stories in the past on auto conversions gone bad because of heavy finished products. Keep it light! If you have questions on whether or not you need it, you don't!

Lowell

[rogerh12]

Lowell'
Thanks for the input, I have already added some weight to the plane. Aero dynamic strut fairings, Tri-gear configuration and Grove Spring gear, not to mention over strength Matco WT600XT wheels (that I got new for 1/4 new price - thanks to ebay), so weight is a real consideration. I plan to keep the interior and panel very simple though, but he main issue is my weight at 250 lbs. (I weighed 150 lbs when I was 19 !!!!) So perhaps my Kitfox weight issue is best addressed via the Jenny Craigs Forum instead?
Oh, one other thing, whats this " LP windshield" you referred too?
Roger

[Paul Z]

Simple answer. Yes!

Question #5. I refuse to articulate for fear I might deviate from the true and given course of rectitude. In short I will not answer for fear I might DIE!

[HighWing]

Roger,
LP Aero Plastics is the company that makes the acrylic windshields and the bubble doors. The windshield on the Series V was almost 3/16" thick vs. the .090 for the heavy Polycarbonate and the .040 that was used on everything but the speedster. I would presume because of the nature of acrylic that the bubble door would be much thicker than the Polycarbonate and consequently heavier likely by a factor of two or three times. For your airplane the .040 would be fine. I put 900 hours with a .040" windshield on the first IV and changed it once, mostly to clean up the scratches that developed over the years - it never failed. It would vibrate a bit during redline dives, but held firm otherwise. One more thing about the bubble doors that is not often mentioned is that the door won't open as high due to the outward curve of the glass and the underside of the wing. Getting in and out can be a bit more challenging for us older guys - speaking only of myself.

I realize other opinions will vary, but if you are already flying an 800 lb. airplane the difference is a small factor relatively speaking. If you are trying to get to the ideal low 600 lbs. for the performance the IV is known for and already committed to an engine that might add more than a couple of pounds, a little just might turn out to ba a lot.
Lowell

[rogerh12]

Lowell;

Thanks for the info. Fortunately I do have a spare set of completed doors I can use to flight test the kifox. If weight and climb performance is not a problem, i can then create another set of heavier bubble doors to add comfort, so I am covered both ways.

Thanks again

Roger