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dougsnash
Joined: 14 Apr 2008
Posts: 282
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 Posted: Sun Nov 13, 2011 5:07 am Post subject: Zenith-List Digest: XL upgrade video |
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Paul, I'm not sure how much time you have in the 601/650 (or how the 601/650 flys for that matter as I have a 701). I found that in early test flying in my 701 the ball was often not centered. By the time I had 25-30 hours on the plane, I was used to the odd feeling rudder and I had developed a sense of how co-ordinated flight should feel. Now with over 100 hrs on my plane, co-ordinated flight is a non-issue.
If this is a recently completed plane and/or you have limited time on type, you might want to put a few hours on it before deciding on any modifications. Generally speaking, once pilots are used to them, most people don't have any issues with how Zenith aircraft handle.
Doug MacDonald
CH-701 from Scratch
NW Ontario, Canada
Do Not Archive
Time: 08:25:44 AM PST US
From: Paul Mulwitz <psm(at)att.net (psm(at)att.net)>
Subject: Re: Re: XL upgrade video
Hi Tommy,
Pulling the reamer does sound like a good idea. Still, step drilling
with small increments also produces a very nice hole. Drills naturally
go straight and this is really true when taking a small amount of metal
from a relatively large hole.
I too am glad to have finished building and upgrading my XL. It flies
pretty well now, but still has a way to go to finish flight testing.
The issue I am working on right now is a lack of yaw stability. It is
easy to see when you look at the design that there is nothing making it
fly straight except possibly the nose wheel centering mechanism in the
lower gear column bearing. This doesn't work well on my plane, and I
suspect the same is true on many others. The full flying rudder is nice
for control but has no natural "Straight ahead" position like planes
with a fixed vertical stabilizer. I am going to try adding strakes next.
Paul
[quote][b]
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psm(at)att.net
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| Posted: Sun Nov 13, 2011 9:19 am Post subject: Zenith-List Digest: XL upgrade video |
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Hi Doug,
Thanks for the comments. Indeed I only have around 20 hours in type. I am sure you are correct that with enough experience I could fly the plane just fine, but I am the kind of perfectionist that I don't want to deal with this obvious shortcoming in the design that way. I did do some work adjusting the cables so the nose wheel --> rudder pedals --> rudder position in flight allows for a centered ball without standing on one of the rudder pedals all the time (I needed left rudder pedal pressure to get it centered on initial flights.).
There are several reasons I want to fix this problem. First is the fact I have problems landing the plane so the nose wheel doesn't get jerked around when it hits the ground. I also like to touch down with the main gear already aligned with the runway. I have fixed that problem by putting a stripe on the top engine cowl that shows which way is forward, but that will go away if I ever paint the fiberglass cowl. Another issue is I will not be the only person flying this plane. My wife wants to fly it too, and she has a lot less pilot experience than I do. Also, I just want it to be nice to fly.
I have been discussing this issue with a very experienced pilot and builder on my field. We both agree that this is a typical design problem for all airplanes. It is very common for initial designs to be short of vertical stabilizer. This is usually fixed in subsequent design versions by increasing the vertical stabilizer size. In some designs strakes are added to help with this issue. My friend pointed out that this lack of yaw stability is always a problem when floats are added to a land plane. Apparently the shape of the floats puts enough forward bias to the "Center of pressure" that yaw stability is ruined. His opinion is this is usually fixed with strakes.
The issue is worse than usual with the Zodiac XL since there is no vertical stabilizer at all. The Heintz planes (all?) use the same full flying rudder and the XL has no sides on the fuselage that run parallel to the line of flight. Rather, the top down view of the whole fuselage is a diamond shape. This means there simply isn't any natural yaw stability in this design. There is a small attempt to add some with the v-block design of the nose gear lower bearing, but this doesn't work at all on my plane. I spoke to Caleb at ZAC about the v-block issue and he suggested filing down the sides of the V to make it less steep. I'm confident this will make it even less functional in the yaw stability issue.
I considered adding a vertical fin as has been done on lots of planes. This is the kind of feature that extends the full length of the fuselage behind the cockpit to the previous front of the vertical stabilizer. When I looked at the structure of the fuselage top I decided it was not rigid enough for this kind of addition. I did not want to face strengthening the whole fuselage design to support this kind of change. Adding strakes is a lot more straight forward. Using a very simple design that has both strakes connected by a flat plate in the middle the flat plate can be riveted to the existing holes in the bottom longerons and skin. I think this will actually strengthen the fuselage design rather than putting more stress on it. I don't have formal drawings or photos right now, but I have formed the basic part and will install it when I get a burst of energy and the hangar temperature is a little bit warmer than usual for this time of year.
I don't expect a lot from my strakes. I do expect them to add a bit of yaw stability to the design so when the plane is flown with no rudder input it will tend to fly straight. This is actually a requirement of the ASTM LSA standard that the Zodiac XL was designed to meet. Unfortunately, I don't think it ever did meet this requirement. I also expect this to give a little control over landing approach angles with a little bit of forward slip (like most planes). This whole area of interest started when another list member pointed out that slips have no impact on the approach angle. I concluded this is true for small slips but after the nose is offset by 11 degrees from straight ahead then a slip will add drag.
Paul
Camas, WA
XL 20 hours into flight test.
On 11/13/2011 5:05 AM, MacDonald Doug wrote: [quote] Paul, I'm not sure how much time you have in the 601/650 (or how the 601/650 flys for that matter as I have a 701). I found that in early test flying in my 701 the ball was often not centered. By the time I had 25-30 hours on the plane, I was used to the odd feeling rudder and I had developed a sense of how co-ordinated flight should feel. Now with over 100 hrs on my plane, co-ordinated flight is a non-issue.
If this is a recently completed plane and/or you have limited time on type, you might want to put a few hours on it before deciding on any modifications. Generally speaking, once pilots are used to them, most people don't have any issues with how Zenith aircraft handle.
Doug MacDonald
CH-701 from Scratch
NW Ontario, Canada
Do Not Archive
Time: 08:25:44 AM PST US
From: Paul Mulwitz <psm(at)att.net (psm(at)att.net)>
Subject: Re: Re: XL upgrade video
Hi Tommy,
Pulling the reamer does sound like a good idea. Still, step drilling
with small increments also produces a very nice hole. Drills naturally
go straight and this is really true when taking a small amount of metal
from a relatively large hole.
I too am glad to have finished building and upgrading my XL. It flies
pretty well now, but still has a way to go to finish flight testing.
The issue I am working on right now is a lack of yaw stability. It is
easy to see when you look at the design that there is nothing making it
fly straight except possibly the nose wheel centering mechanism in the
lower gear column bearing. This doesn't work well on my plane, and I
suspect the same is true on many others. The full flying rudder is nice
for control but has no natural "Straight ahead" position like planes
with a fixed vertical stabilizer. I am going to try adding strakes next.
Paul
[b]
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