CH. 3, EPOXY!... epoxy?

[marbleturtle]

Okay... since there's no Ch. 3 in the chapter specific sections, I'll ask this here! Everyone was raving about the MGS epoxy system, and it is recommended in the plans. But the plans also say to only use the Safe-T epoxy or RAE for mixing with dry micro... is this correct or is this an older section of the plans that haven't been updated?

 

Any Cons about using the MGS?

 

Thanks!

[John Slade]

The comment about dry micro is probably a left over.

I used MGS for everything without any problems. Using different epoxys for different tasks would be a pain.

[marbleturtle]

That's what I thought. Thanks John.

[marbleturtle]

I just read the part about no starter on the motor... I'm not going without a starter!

[John Slade]

Again - old information. I don't think there's a Cozy flying without a starter.

 

But what's this got to do with epoxy?

[marbleturtle]

uh... well... nothing.

 

Okay, how about this... there are two types of hardener, which do you use in the hardener side of a pump? Do you mix the hardener types for whatever you use most often and then not use the pump for really fast or slow mixes?

 

I definately want to go with the pump, but that was something that I couldn't find an answer for.

 

Oh, and does MGS have a milder oder than the others?

[John Slade]

>there are two types of hardener, which do you use in the hardener side of a pump?

 

A mixture of each depending on how fast you want to cure. Start with about 50/50 and work from there. Use all slow on you're first BIG layup.

 

>Do you mix the hardener types for whatever you use most often and >then not use the pump for really fast or slow mixes?

No. Use a fairly small amount of 50/50, then dump in some more fast or slow to change the ratio.

 

>Oh, and does MGS have a milder oder than the others?

MGS has practically NO odor at all. By the way, having used both I'd probably use MGS 285 rather than 335. It seems a little better at staying liquid, then curing at the cure time.

[GregL]

The MGS 285 system has a Tg of 195 to 230 deg F (Wicks catalog). It would seem that in addition to the fluidity comparison temperature resistance be also desirable. Since I'll be stuck with white finish, I'd want as much temperature resistance as possible. Maybe I could try the Light Blue that Dick Rutan painted his Long EZ?

[John Slade]

>The MGS 285 system has a Tg of 195 to 230 deg F (Wicks catalog).

Right. My thoughts there were that both MGS 335 and 285 have tg values way above the stuff most EZ's were built with so either formulation will definately do the job on that score. The difference in cure behavior is subtle, but it's there.

 

Perhaps you'd get away with a light blue. Personally I LIKE white.

[marbleturtle]

I've seen white, yellow, light blue... does anyone know if silver or if a metallic based white (ie: pearl white) stays as cool or cooler than white? I know the metal surface of my silver car seems to stay cooler than the white surface of my wife's van... although this is totally unscientific.

 

I would like to do something a little different like pearl white.

[buzzard]

Here's a picture of a Berkut painted silver. The plane is in England I believe. Looks pretty good to me.

[John Slade]

Yes, it does look nice, but how would it stand up in AZ?

keep in mind - they don't get much sun in UK. Why do you think I moved to FL?

[jperryfly]

The pearl white requires a base coat/clear coat and the pearl or metallic is in the clear coat. This makes it difficult to repair. It's not worth it for me. I hear PPG is really good has anyone else used it recently? That's what I used on the LZ but that was 10 years ago.

[JakeC]

One other thing to consider is, with silver, you would have to have one perfect surface in order for it to look good. I was thinking about the same thing but with the moldless construction I'm not sure I could get it that perfect. What do you think?

 

Jake

[marbleturtle]

This looks pretty straight to me...

[JakeC]

Sure does. Thanks for the pic.

 

Jake

[marbleturtle]

Does anyone remember what Nat said at the Oshkosh Cozy Dinner about a plane that had warped wings because it was sitting in the sun and the epoxy softened? I think it was in reference to a dragonfly where the wheels were on the tip of the bottom wing and the wing was in compression... that it wouldn't happen to a cozy because its wheels are mounted to the fuselage and the wing tops are in tension while on the ground.

 

Just curious. Maybe I should go with the higher temp MGS epoxy. I am thinking about retracts, which mount the wheels to the wings. This would put the top of the spar and strakes in compression, but the wings would still be in tension... I think.

 

Any thoughts?

[Dave Clifford]

Retracts; Add $8,000 or more to the cost of the plane, add another 100 pounds to the plane and lower its gross weight, add hundreds of hours extra build time for the cool looking things, you MIGHT gain 3 knots if your lucky. Oh, don't forget the high probability of a gear-up landing.

[marbleturtle]

Oh Clifford... *sigh

 

Those are tired old arguments. I'll save a little time and space by just directing you to: http://www.geocities.com/plmjohnson/retractable_gear.htm

He does a good job of reviewing common misconceptions about retractable gear, specifically directed toward the Cozy.

 

You might even check out...

http://www.infinityaerospace.com (although this site would obviously be pro-retractable)

 

And its not the "cool" factor since not I nor anyone else would be able to see the plane with the wheels retracted. Its simply a matter of common sense if you examine the number of high performance aircraft that use retractable gear. (I'm talking rear gear for the Cozy since the nose gear is already retractable... don't forget to put the nose gear down!) It would appear that the positives outweigh the negatives.

 

I think the benefits of higher payload, longer range, higher speed, added safety (gear up emergency off field landing is safer than flipping over the main gear) are worth the extra expense.

[Dave Clifford]

Go for it then!! Let me know how things work out.

[dust]

We both,clifford and I, opted for the auto extend option on wilhemson's nose gear, 90 knots = nose gear extension.

 

It's not if but when

 

Are any cozies flying with retracts?

[Jim Sower]

MT,

Phil Johnson's web page does indeed make the most thorough and rational case for RG. Saves a lot of fuss and bother when someone gets all shrill and starts spouting unsupportable numbers to just refer him to the link. Nat has a penchant for exageration and fuzzy extrapolation when the subject comes up (understandable given his agende - liability and all).

 

I have heard lots of rumors around delivery problems with Infinity. I know the manufacturer of Q2000. I'll touch base with him and see what he has to say about that.

 

For my own part, I aim to go with Infinity and Mazda turbo 13B. The naysayers exagerate shamelessly and have no valid data to back up their claims of marginal advantage. Truth be told, there aren't many data points. Velocity has a lot, but how exactly to apply that data to Cozys is an open question. Time will tell. In any event, I aim to be one of those data points.

[marbleturtle]

Well... I did fall under the category of not wanting gear based on the common arguments expressed earlier. But after reading Phil's site and a few others, I am convinced that there are real benefits to retractable gear. But the benefits are only evident when the aircraft as a whole is set up to take advantage of it. Like when you upgrade to a higher horsepower engine but keep the propeller that was optimized for the lower horsepower... you won't see an increase in speed.

 

Its the same with retracts. If you don't adjust your prop to work against less drag (similar to adding power), the aircraft will not see an increase in speed. If you put a Ferrari body on a truck chassis... it will still only top out at 100mph even if the horsepower is the same.

 

This brings me back to the question I had before. The only thing I've heard or read that makes me re-think the idea of retractable gear is what Nat had to say. He made a remark in reference to epoxy under the heat of the Sun and whether or not it softened at high temperatures and distorted the wing. He said that the only case he knew of wing distortion was a dragonfly that had the wheels at the outer edge of the lower wing. He also went on to say that wheels on the outer edge of the wing put the sunny side of the wing in compression. Apparently when the wing is in tension, if the epoxy does soften, the glass fibers stay straight because they are being pulled straight. Under compression, the fibers are being bunched together and could theoretically malform.

 

After considering it more, since the infinity retracts are attatched to the spar (not the far tips of the wing), I believe that the top of the wing on the Cozy would still be under tension out from the spar, not compression. The top layer of the spar would be under compression, but not exposed to the same heat that the top of the wing would be.

 

I wanted to know if anyone else has considered / researched the possibility. I still might not do the retracts due to the net expense difference of $3000, but I'm certainly leaning toward it. As for the rotary engine, the turbo 13B or 20B is a given for me. No way I'm using anything else.

 

As for delivery problems, JD did say it took 6 months longer for a subcontractor to do the work he needed, but he said he is now back up to speed. Have you ordered a set yet? How far along are you?

 

About the SQ2000... is KLS still in business?

[Jim Sower]

MT,

The sagging Dragonfly is well known. As you said, it had wheels at the wing tips and all the weight putting the spar caps in compression (pretty much as if he was pulling 1 G in flight). It was the heat and [low?]Tg that did him in. A Cozy retract OTOH would be loading the spar box, not the wing. Further, you have epoxy available that has better Tg than that Dragonfly (the expensive MGS). Also, the spar box lends itself to strenuous post cure. If you checked out the temp limits of the foam used (it's NOT wing core foam) you might find that you could "bake" it to a pretty high temp. In any event, shaped like it is, you could put it in the sun under a black plastic "tent" with a thermostat controlled fan to ventilate it. You could also cut your spar box just a tad deeper and beef up the spar cap a couple of laminations of tape. And wrap the box with a couple of opposite wound spirals of Uni. All told, it's probably a non issue, and more than adequate compensation is readily available.

 

As to performance, a turbo 13B would have to be over propped from here to yonder (or have a CS unit) This is because if you turbo normalize to 15k', you'll be making 250-300 kts true which will require a a prop pitched at about 150" or so. Your performance envelope would be so wide as to make for a totally TOTALLY stalled prop on T/O but a plane that would HOWL at altitude.

 

As for KLS, I haven't heard from Stan for a while so I don't know. The Q2000 part of the opertion seemed to be a little thin, but he's building a sort of Maule(?) STOL heavy hauler for missionarys and the like that operate in primitive places.

 

I'm nowhere near mounting the gear yet. Particularly as regards finances. Got plenty of time in that department before I have to make a firm decision.