A few words on aircraft construction

[FastEddieB]

I did not want to hijack another thread, so I thought it best to start a new thread on this topic.

 

Without going into a lot of detail, someone keeps referring to metal airplanes as somehow inferior and composite airplanes as somehow "better", or at least aerodynamically different.

 

This is a crock.

 

In my 35 years of flying, I've owned a handful of planes.

 

One metal, with riveted semi-monocoque construction (Cessna 150)

 

Two metal, with bonded construction (Grumman AA5 Traveler and AA5B Tiger)

 

Two tube and fabric (Citabria 7ECA and 7GCBC)

 

And two composite (Cirrus SR22 and my current Sky Arrow)

 

Plus I have many thousands of hours in other planes of each type.

 

There is virtually nothing in the method of construction that informs one as to how an aircraft will handle. Nothing.

 

I really don't think one could fly different aircraft "blinded" and say what the construction is. A Bellanca Viking and a Beechcraft Bonanza and a Cirrus SR22 all use differing construction, but there are just too many other factors (control type and linkage, airfoil design, power, configuration and the like) to say anything meaningful about how any of them will handle, based solely on construction method.

 

I'll stipulate that composite is probably the future, but this is largely because the traditional methods (riveted aluminum and tube and fabric) are highly labor intensive, while a Cirrus fuselage or wing, let's say, can be laid up and cured in far fewer hours involving far fewer parts. It had been promised that composite should result in lighter airframes, but this has not been realized in practice - Google "Beechcraft Starship" for an example of unfulfilled promise. Maybe carbon fiber and nanotube construction will eclipse everything else someday, but that someday remains in the future.

 

Anyway, I just wanted to clear that up. Some of the strongest opinions and most absolute statements on this forum come from members with very little experience or knowledge of the things they're posting so positively on.

[Ed Cesnalis]

The nameless poster takes it a step farther, he not only claims that a 'carbon ghost' flies differently than a metal design but that the advanced carbon design calls for different technique, namely a need for speed, little or no need for flaps and to give up full stall landings.

 

I agree with Eddie, the material and construction method does not dictate results though the CTs clean egg shape is easy to achieve with composites and I suspect the cantilevered wing is easily done with the carbon fiber spars.

 

I strongly disagree with the often repeated contention that using flaps and doing full stall landings are a sign of a pilot that has not yet transitioned. I elect to do full stall landings with flaps not as a crutch but as the obvious method to achieve landings at minimum speed.

 

The design could rely on Lopresti speed mods to clean up drag on a metal plane or carbon fiber lay-ups either way how do you get to giving up flaps and adding speed when you have a slippery design? That's just backwords. The more slippery the design the greater the need to reconfigure to a high lift high drag configuration that will support steeper approaches at slower speeds, a better view of the runway, and landing at minimum speeds.

[Doug G.]

My only comment to this is that my experience is very limited (Cessna Skycatcher -162 and CTLS) it seems that the parasitic drag is certainly less on the CTLS. Much of this is due to not having wing struts, and some due to the lack of rivets. This does lead to a small difference in the flight characteristics. I would not go nearly so far as the unnamed poster.

[Ed Cesnalis]

Doug,

 

I'm sure your right, if we group aircraft by SLSA category we would find many stronger similarities than if we grouped aircraft by construction method. SLSA have light wing loading, speed range and stall speeds in common which factor in heavily.

[FastEddieB]

Doug,

 

Sure. Like I said, composite is likely the future, and having more seamless structures is one advantage.

 

But prior to composites, some metal planes utilized flush rivets and could by quite slippery. Grumman wings are aluminum, but with bonding, nary a rivet to be found. and even tube and fabric planes can be made quite aerodynamic.

 

I get your point, but still don't think a pilot who did not know the construction method of a CT could discern it from its flying qualities.

 

But it's an interesting thought.

[Doug G.]

I agree Eddie, only I have never had the chance to fly the H1. lol

Most of the metal GA planes I have been around and that I would compare to the CT don't have flush rivets, and do have wing struts - assuming they are high wing. I would imagine that fabric in some cases would have very low parasitic drag.

But, no, I doubt you could easily tell the difference.

[sandpiper]

If aluminum and rivets are so bad, how come my RV-12 neighbor out climbs and out runs me??

[FastEddieB]

And, as a reminder, in aircraft design everything is a compromise.

 

Take wing struts. Getting rid of them to reduce drag seems like a no-brainer.

 

But when you remove the support they provide, you usually have to add structure, and weight, to accomplish that goal.

 

Parasitic drag increases as the SQUARE of the increase in velocity. So it's FOUR times greater for any given structure as you go from 100k to 200k, let's say.

 

So, the added weight to get rid of struts makes little sense in a Cub or a Cessna 150. On a Cessna 210 it starts to make sense.

 

In the middle ground it can go either way - the Cessna 177 got rid of them and was designed to replace the strutted 172. Turns out the marketplace preferred the tried-and-true strutted 172.

 

My 100k Sky Arrow is composite, yet has struts. I think both it and the CT are in that middle ground. It's certainly highly commendable that the CT got rid of the struts yet still kept a farly low empty weight - much below my Sky Arrow, incidentally. Credit where credit is due!

[Ed Cesnalis]

... how come my ... neighbor out climbs and out runs me??

 

Your not a young man John

[Jim Meade]

Rivet heads on the back part of a slow moving wing are not going to be a big parasitic drag feature, as I recall. Some wings have a smooth leading edge that is either bonded or uses flush rivets and the top of the wing uses headed rivets. Fairings, such as wheel pants, can make quite a difference, as we know in that flying wires are more draggy than some bigger struts that are more aerodynamically shaped.

 

[FlyingMonkey]

Sure. Like I said, composite is likely the future, and having more seamless structures is one advantage.

 

I see seamless construction as a mixed bag. Of course the lack of fasteners and their associated drag is a boon, and potentially the construction can be faster, too.

 

However, the lack of seams and panels means that maintenance can be complicated. If you have to get inside a CTSW wing for some reason to maintain or fix something...what do you do? You might be able to get in there by pulling the wing and going in through the root, but your work space is going to be *severely* limited. With a metal wing you can drill out a bunch of rivets and pull the whole wing skin off fairly easily, giving you all the space to work you could possibly need.

 

I'm not saying one is better or worse, just that the advantages are also simultaneously disadvantages in some cases.

[sandpiper]

Your not a young man John

 

Leave it to CT to get at the heart of the matter. :unsure:

 

Struts on a high wing are very handy. They give something to push on making ground handling easier.

[Tom Baker]

I see seamless construction as a mixed bag. Of course the lack of fasteners and their associated drag is a boon, and potentially the construction can be faster, too.

 

However, the lack of seams and panels means that maintenance can be complicated. If you have to get inside a CTSW wing for some reason to maintain or fix something...what do you do? You might be able to get in there by pulling the wing and going in through the root, but your work space is going to be *severely* limited. With a metal wing you can drill out a bunch of rivets and pull the whole wing skin off fairly easily, giving you all the space to work you could possibly need.

 

I'm not saying one is better or worse, just that the advantages are also simultaneously disadvantages in some cases.

 

They have or you can make inspection covers for the CT. You just cut the hole, do the work, and bond the cover back in place. It is just a different way of doing it for composite. Doing the composite work might even take less work time, but you can't just work straight through because of needing to allow cure time.