Weight & Hull strength variations between models

[IrishAl]

Hi. 

 

I have been reading this forum with great interest (and enjoyment!) for months now - thank you to all the contributors.

 

I have a question regarding differences in hull construction between FD models, some of which actually bear the same model name.  I'm trying to identify just what these differences are.

 

The FD USA website states the following (in relation to the lightweight CTLS Club): 

 

‘The weight reduction was accomplished by using ........some lighter parts from the European version of the CTLS.’  

 

This tells us that there are physical differences between the CTLS and the CTLS Club.   Does anyone know what the differences are?

 

In Europe we also have two versions of the CTLS (see www.flightdesign.com, select 'configurator' for models) and they actually have different hulls.  We have a microlight class CTLS (472.5kg) and a 600kg CTLS.  If you look at each model's specification on the website ( see under  ‘configurator’, select the model you want, then select ‘show content’), there is a different description of the hull itself between these models.

 

The lighter version’s hull is listed has having a 'long fuselage tail boom', (which is the extended hull of the CTSW), while the 600kg version has an additional comment that the other one doesn’t have: ‘Improved handling toughness due to reinforced composite layup’.

 

This clearly indicates that (in Europe at least) the actual hulls between two aircraft bearing the same name are, in fact, different. 

 

The description implies that one is less ‘tough’ that the other. Is this also the case in the USA? 

 

I also understand that there are differences in the construction material of the flying surfaces (stabilator, etc.), depending on what side of the pond they’re sold on.  

 

The ambiguity also applies to the CTSW range.

 

The CTSW has now become the CT Supralight (often called CTSL) in Europe – same hull as the CTSW but with the CTLS composite landing gear.  This is now the entry level model and is only advertised in the lighter class of 472.5kg. This suggests to me that all CTSWs may have been built with the lighter-constructed hull.   

 

Can anyone shed more light on this?

 

What I’m really interested to know is if anyone has noticed any material difference in robustness between the lighter and heavier-built models?

 

Alan 

 

[Jacques]

This suggests to me that all CTSWs may have been built with the lighter-constructed hull.   [/font][/color][/size]

 

Can anyone shed more light on this?

Welcome Alan

 

My 2005 CTSW is the 1st SW in Canada and 'limited' to a 560kg MTOW, but is built 'for the american market' . 600kg max LSA .....an empty weight of 300 kg [ the 2005POH take my plane in the CG exemple ]

 

If the plane is made to have a max of 472.kg...(20% less) it's just normal (to me) than a such a CT has a even lighter empty weight.(260..?) A plane has to be able to 'sustain' X times his own weight ( and X is a very safe # at Flight Design ]

 

for the 472kg rule...the Supralight is the best conbination ..with the right landing gear.

CT Maintenance manual 05 rev2.pdf

[IrishAl]

Thanks, Jacques.

The trouble with empty weights is knowing if it's down to a heavier duty air frame or just added extras.

I'm trying to find out if there's two different hulls - one for the USA/LSA market and a lighter one for the European microlight/ultralight class.

Alan 

[Roger Lee]

I believe the stabs were made differently for some areas. And panels were bare bones. We in the US don't really have any experience with the European or other market designs. Hopefully someone from one of those areas will chime in.

[IrishAl]

Thanks Roger.

What parts on the CTLS Club are  lighter parts from the European version of the CTLS?

[Anticept]

You should direct that to dave armando at TopService@FlightDesignUSA.com

[Roger Lee]

I don't know what all parts are different. Just what I have heard from owners here on the forum.

[Tom Baker]

There are only a few CTLS Clubs here in the states, and most of them are on floats. They are said to have a lighter cowling and wheel pants, and maybe some other non-structural items. They are also said to have one less coat of paint. I think 2 coats instead of 3.

[Tip]

When the Lite was introduced, I was told that a coat of paint is 30 pounds.

[Runtoeat]

Hi Al.  Because my 2006 CTSW required reinforcement for the stabilator per FD service bulletin, I've gotten into the construction of this component.  For European "Ultralight" CTSW which is in the 472.5kg class, it appears that the stabilator was constructed of "aramid" fiber while the US CTSW (600kg class) is constructed of carbon fiber.  My limited knowledge of "aramid" indicates this is a "polyester" type material, cheaper and less strength than carbon fiber but supposedly OK for the 472.5kg European CTSW.  I'm not clear if the aramid stabilator saves any weight but it probably is cheaper to produce than it's US carbon fiber brother.  It is noted that there has been a service bulletin released for European "Ultralight" CTSW limiting Vne airspeed due to one documented "flutter" concern.  I'm not sure what the final outcome was of FD's investigation into this. The SB for this is SA-LTUL-CTSW-04.  I believe that the European "Ultralight" and US CTSW have common contruction and components on all other areas but I am not the expert on this.  Note also that there is now the European "Supralight" which has a different stabilator.  I belive this is still constructed from aramid but has a "short width" trim tab and not the "full width" tab found on older "Ultralight".  This is noted in the referenced SB and, new testing of this system indicates there is no speed limiting needed for aircraft which have this later stabilator.

[Anticept]

Aramid (trade name kevlar) fibers are not as strong as carbon fiber in the tensile direction, but it is able to flex and withstand forces better, whereas carbon fiber is brittle.

 

Carbon fiber is extremely strong in the compressive direction, whereas kevlar is horrible for that purpose.

 

TL;DR carbon fiber is super strong and stiff, kevlar is like a super strong rubber band.

[Tom Baker]

The interior of our cabins are laid up with Kevlar to provide crash protection.

[FlyingMonkey]

When the Lite was introduced, I was told that a coat of paint is 30 pounds.

 

A single coat?  That is hard to believe.  I'd guess all the paint on the aircraft might be 30lb, so 10lb per coat.  30lb is really heavy for one coat of paint on such a small airplane.  Most of the guys building Sonex when I was in that community reported 17-25lb for a paint job, depending on how thick and and how many coats were applied.  That was for primer, paint (1-3 coats), and topcoat. 

[IrishAl]

Thank you all for your comments.

 

Dick, thanks for the info on the amended stab. design on the CT Supralight.  Also, I think that (as far as I can ascertain) you're right in saying the CTSW hull is unchanged for the US market.  (Which means the European version operates well within its limits at 472.5kg, notwithstanding the aramid stabilator, of course.)

 

At the back of my question is a concern over the toughness of carbon composite for everyday use - you know, hangar knocks, people leaning where they shouldn't, etc.  

 

The comment on the FD Europe website (‘Improved handling toughness due to reinforced composite layup’) implies that the 472.5kg CTLS hull may be a little sensitive to handling knocks compared to the 600kg model, which has the 'reinforced composite layup'. 

 

I'd love to get feedback on this - do these airframes require more careful handling than metal?  If you drop something hard on aluminium it will dent, but a crack in a carbon tail cone would be a much bigger problem....?  

 

Has anyone suffered damage like this, and what was involved in repairing it?

[IrishAl]

"The interior of our cabins are laid up with Kevlar to provide crash protection."

 

Tom, this is one of the most attractive features of the FD range.  A comparison of accidents (both in number and type) with other composite LSAs suggests a very substantial safety benefit from increased protection in the CTrange.

[Anticept]

IrishAl,

 

Composites are stronger, but with metal there is a dent tolerance. Composites do not have such a tolerance, you need to repair damage because of the nature of delamination and criticality of the core integrity.

 

I did some repairs to mine, and i took pictures. I will throw them up for you.

[Runtoeat]

IrishAl, I can attest to the ability of carbon fiber structures to take a hard knock and only need to have the surface buffed out.  As Anticept says though, there is always the possibility of structural failure resulting from impacts in composites and these can remian hidden unless one knows the specialized methods needed to detect these.  One interesting observation I made when I first was able to see a CTLS is the stabilator trim tab on this airplane only uses the carbon fiber surface for it's "living" hinge. No steel hinges, just the thin carbon fiber surface being called on to flex thousands of times during the life of the plane.  This speaks to the durability of carbon fiber composite structure.  Pretty amazing.

[Tom Baker]

IrishAl, I can attest to the ability of carbon fiber structures to take a hard knock and only need to have the surface buffed out.  As Anticept says though, there is always the possibility of structural failure resulting from impacts in composites and these can remian hidden unless one knows the specialized methods needed to detect these.  One interesting observation I made when I first was able to see a CTLS is the stabilator trim tab on this airplane only uses the carbon fiber surface for it's "living" hinge. No steel hinges, just the thin carbon fiber surface being called on to flex thousands of times during the life of the plane.  This speaks to the durability of carbon fiber composite structure.  Pretty amazing.

The hinge is molded in, but I don't think it is carbon fiber. IIRC it is also Kevlar.

[Anticept]

Images of repairs that I did when I was learning while being supervised by an experienced mechanic. At the time I knew about composites and how to repair them, but I had not much practice. I can do composite repairs pretty easily these days, but I still suck with body work (bondo and paint). Mainly I don't have the right tools for body work, and I don't get much practice (good and bad!).

 

Also, don't do what I did with the square patches, read on down for what I think is a much better method. I did square patches because keeping fibers straight when it comes to circular patches is a pain in the ass, and I figured I would just sand the corners down once it set. Really didn't think that through at the time! Resulted in much bigger paint patches than I expected because, as it turns out, paint is quite soft when compared to carbon fiber and epoxy! In the end, we finally we decided to just paint one big square, which looks less patchy than the little paint jobs we did (there were these two holes, and several paint nicks, someone was tossing stuff up on the wing).

 

Instead, I do a different method than layups now, and it works much better. I will take two pieces of visqueen, put one carbon fiber layer down, some mixed epoxy in the center, and then take a soft body filler spatula thingy and push the epoxy around in the center, and work outwards. It's called a "prepreg" method. After everything is thoroughly impregnated, I'll take a knife or a cloth wheel, and with the visqueen still in place, cut out my patterns *slightly* larger than the repair I need to make. I'll use a cloth dampened with MEK to clean the bonding site. MEK is pretty standard for composite repair because it makes the site CLEAN, and will dry immediately. Key here is use a DAMP CLOTH. Don't let that stuff drip onto the core! Just after it dries, I lay down the repair patch, wait for it to cure, then sand away the now very small edges so that it tapers to the rest of the skin. This allows for a nice smooth transition and looks very nice when finished.

 

EDIT: The circular holes are drilled to remove the damage Since it was only surface damage and slight core damage, I used a potting compound repair method instead of removing the core completely. You have to taper the fiber towards the center (called a scarf repair), because CTs only use a single layer bi-directional cloth around the core in the wing skin surface, so a stepped method doesn't work here. I don't like scarfing, but I do it because I have to.

 

EDIT 2: the white cloth over top of the black one is called a "bleeder" cloth, or Dacron. I forgot to mention what that is for. Basically, epoxy is messy. You only want as much epoxy as needed to impregnate the repair ply, and any extra is just weight and adds nothing to the repair. By laying a bleeder cloth on the repair, you can add pressure to ensure you push air out of the bonding site, it helps keep fibers aligned, and extra epoxy will bleed through, so you will have a nice perfect mix of fiber to epoxy. The Dacron peels off easily after cure.

[Runtoeat]

Anticept, interesting info.  Is that microsperes or microballoons filling the hole?  I imagine it is tedious work to gradually sand down the paint finish to get to the carbon fiber without degrading the carbon?  In the last photo the repaired area is now blended in to where it cannot be detected but there remains a large area where the paint does not match the rest of the wing.  Is this the finished product or do you continue with another coat of paint to get better blend in for the color?

[Anticept]

It's a "dry mix" of microballoons and epoxy. It only offers strength in the compressive direction, and offers NONE in any other, therefore potting compound repairs can only be done in small areas.

 

As for sanding, yes it's a pain, but do it a little at a time. Even with a sanding wheel on a pneumatic dremel, carbon fiber and epoxy are surprisingly strong and resilient. Just keep the dremel moving quickly and let the weight of the tool do the work, taking it down a little at a time. Composites are about patience, or you will end up having to do a lot more repairs.

 

As for the paint: again I suck with body work. I did not polish the paint at all. The experienced mechanic sprayed it on with an HVLP gun. As for the paint matching, never going to happen. There's not much paint on planes, and trying to blend it so you can't see it just is not realistic. Even if you did match, UV will not yellow the new and old paint at the same rate.

[IrishAl]

My friend here has a good solution to mismatching.

He calls it the flying cow.

[IrishAl]

Thanks, Anticept, for that excellent response.

 

I'm surprised that you don't use carbon cloth, which would add strength to the repair and also make a less thick layer, which would mean less sanding to get a flush finish.

 

Is there any particular reason for using polyethylene mat?  

[Anticept]

That's a carbon cloth underneath (notice, round hole, square patch? Again that was a bad idea on my part, added a lot of extra work). I placed a dacron bleeder cloth over top because it helps suck out extra epoxy. It peels away effortlessly when cured, and provides a rough bonding surface for the bondo and paint. In fact, when working with composites you need to keep some 40 or 80 grit sandpaper with you to rough up surfaces for better bonding. Kinda hard to do on scarf repairs though.

 

I edited my post to explain all the things bleeder cloth does.

[FlyingMonkey]

No wonder most airplanes are made from aluminum.  That stuff is easy to fix.