Johng

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Well, another one has come & gone. The weather was unseasonably cool for Florida in April, which worked to everyone's advantage. It was 48 deg on Sunday morning, but at least 80 by noon. It never did clear 80 by very much the whole week & weekend - which was absolutely great. It also allowed the planes to perform relatively well, compared with some of the 90+ days I've been thru.

With this year's minimum span requirement, the planes generally had plenty of wing area, which mostly resulted in good handling planes. There were very few airplanes that got off the ground that didn't have a very good shot at making a qualifying landing. There was very little attrition among the pre-qualified competitiors as well. That means flight rounds tended to stay lengthy throughout the weekend, with so many planes staying in the contest.

In general, the long wings resulted in airplanes that glided very well - too well. Many teams did not include drag devices for landing, resulting in very flat glides to landing and much difficulty in hitting the strip. Well, I flew for two teams, and I had my hands full getting them down anyway.

I did fly for the 3rd place team, Ecole de Technologie Superieure from Montreal as well as the University of California, Irvine. Both had good planes. The team from Auburn won, in their first year sending a team to the competition.

So, let's start with a picture of me flying for ETS. This one made the paper as well as a pretty decent article in the Olando Sentinel at :
http://www.orlandosentinel.com/news/...dlines-volusia

Johng

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OK, so here's a picture of the 3rd place ETS team greeting the 2nd place team at the post-award photo session. Also, a runway photo of the winning Auburn team.

Johng

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Paul, I have 48 Mb of pics lemme know how I should send them to you.

Johng

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Here's an interesting airplane. Relatively high chord, low aspect ratio wing. It could fly at walking speed, with payload. But it just didn't have the excess power to climb. THe pic is taken at it's max height for the round, flying downwind, carrying 18 pounds. I do remember that this plane was built with an empty weight of 18 pounds, which is 8 pounds more than the top teams. This basic design, built to those lighter weights, would have been very competitive with the top teams.

Tall Paul

John, I've recently changed to Adelphia Cable modem.. transfer rates have been as high as 3Mb/sec! About 80x faster than the fastest I ever saw with Earthlink DSL.
Probably several files works best.
800x??? images, as anything more is just too large.
.

Johng

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OK, Paul, I'll send 'em in 10 MB chunks.

Here's a ground picture of the "low rider" plane. It doesn't look like it ought to be 18 lbs. It's a fine "ground effects" machine. It basically got up to one wingspan off the ground and wouldn't go any higher. The slow speed ability of this plane is unbelievable. On Saturday morning, we had a wind of 5-7 mph, this plane took off with about 10 lbs of cargo and turned into the wind, and essentially hovered in one 10' high spot for 3 or 4 seconds. We were all waiting for it to flip or nose over into the ground when it just turned downwind and completed a circuit at that height. I could not believe it.

It seems that most of these planes had lift in reserve. They were operating on the back end of the drag curve so that the successfull ones would take off and then have to gain speed before really getting a decent climb rate. This is what you'd expect when building a DA100 sized airplane and putting a .61 on the front. Some of the failures occured when they would lift off then decelerate and sink back to the ground.

Johng

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Have a look at a couple of the "more imaginitive" but less successfull designs. The "sorta-biplane" got part way thru it's qual flight without much directional control at one point rolling nearly inverted and recovering. It later tried to get me on takeoff when it yawed sideways out of control. Compare the forward and rear vertical surfaces and you can see why. It did not end up qualifying.

The twin is an unsuccessful entry in the open class. It lifted off and rolled up into a left knife edge which it flew for a few seconds. A better pilot may have saved it. Maybe it was just too far out of trim to save. It was a jaw dropping sight to see it ripping along just above the ground in knife edge before it finally gave up.

Johng

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Here is a regular class entry from one of the Brazilian teams. They did some excellent open-bay construction on both their regular and open class planes. The clear covering is really a beautiful thing. If you look close, you can see some spanwise line patterns in the covering. At first, I thought it might be some sort of fiber-reinforcement. But upon closer inspection, I found that the clear skin is just packing tape, put on in spanwise strips. It really does the job well.

MikeSell

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Soooo...Do you have a picture of the one that lifted the most weight?

Johng

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Geez Mike, after posting all over the place about your son's team, the attempt at subtlety is pretty amusing. Cedarville consistently does well because they stay within themselves designing airplanes that fly and lift, not lifters that try to fly.

Have fun with the practice plane. SAE planes make good float planes too.

I must say though, with no planform restriction, I have no idea why the stab was made so small. Makes for an unforgiving CG range. Even so, it's a fine design without any unnecessary bells & whistles.

Here ya go.

Johng

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Mike, I can e-mail you 1600x1200 originials too if you want.

Tall Paul

That itty-bitty thing lifted 50 pounds?????

SST

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Gross flying weight was over 50#. The airframe wt. was, I think, 17.5#. I think the reason he's fishing for pix is because his digital camera isn't back home from the contest yet and we haven't seen any pix or video yet...He and I threw that practice plane together from the team's specs (and I must admit a lack of enthusiasm for the size of the horizontal stab myself) in a couple of weeks of 5-hour nights in the basement of a quonset hut. Neither of us had ever used a foam bow much before, nor had we ever built anything of this size or glassed a wing before, however I had patched a few boat hulls, but the technique is different.

BTW...They flew that thing with HS81s!

Tall Paul

I wonder about the small horizontals on last year's planes and this year's. With the area restriction ancient history, I'd go for a large horizontal if only to make the plane easier to fly.

MikeSell

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Thanks, those are the first pictures I've seen of their completed plane. SST, my son and I built the practice plane but SST still has not seen it in its completed form. My cameras are still at Cedarville.
I asked my son about the small horizontal as well a questioning him about them not making it full flying. He told me that the calculus programs they ran on the plane said it would have plenty of surface. I had many other questions about the design also but it was not my design. I was only volunteer labor.
When all was said and done he told me that the horizontal was more than enough but the rudder need all the throw he could program or build in. He said that the planes behaved similarly but not the same.

Johng

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Well, obviously, he was right, in that it didn't really need more surface area. It worked fine. I would've just been more conservative in that the larger tail gives a wider CG range, which could be usefull if you want to fine tune the CG location wrt the landing gear, or something along those lines.

Another common holdover on some planes that Cedarville didn't do is the tubular tail boom. What's with that? There was one plane, as always, that had an empenage that was only flying loose formation on the wing, being at the end of a too-flexy tailboom. After a couple wobbles toward the crowd line, we had to pull it's safety approval until they put bracing wires on that thing. Once they did, it was a better flying plane with loads more carrying capacity.

BTW - here's a snap of the Cedarville practice plane retired to the trailer:

Johng

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Just to stir things up, they announced next year's requirement as a maximum 60" wingspan. Discuss.

MikeSell

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I almost didn't recognize it hanging upside down like that. The tail boom I used was a piece of an old antenna, I just didn't want to use that much balsa and I was sure that it was strong enough. Since I had to finance the practice plane I tried to keep costs as low as possible.

SST

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Is that the only requirement? No little caveats?

Johng

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AFAIK, the rest of the rules haven't been published. I'd go on the premise that just the wing requirement has been changed. Same engine, same cargo volume.

I'm thinking a couple of massively cambered & slotted wings, staggered along the fuse. Perhaps the gap of the forward wing acts as a 'slot' to energize the air over the rear wing.

You could do quite respectably in next year's competition by taking a 120 stick, and fitting 2 clipped wings to the fuse.

Tall Paul

First thought is biplanes or 2nd, tandems...
Or possibly a delta, just to be odd.
Maybe make the biplane glider of that m.a.c. thread a little larger...

taylorcraft1947

Johng

The formula for the horiz-stab said that about 100 sq.in. would be sufficient, but we gave it 150 just to be safe. There was no problem with the CG, we moved it all of the way from 25% to ~34% on the last flight. The only problem I had was that the plane flew so slowly that I would partially loose authority on the rudder. The formulas predicted that the takeoff and climb speed would only be ~23Kn. We do plan to compete at west, and we will probably try 35 pounds. There was a major mistake in the predicted payload (we predicted gross, not payload), and our presentation was not what the judges wanted, so we will fix the errors and try again. There was still some capacity on the last flight, and I hear that there are not so many trees in Fort Worth.

the pilot for Cedarville
taylorcraft1947

Johng

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Well, not that I'm defensive about the flying site or anything, but there was 1000 feet of clear space in either direction from the runway for anyone willing to fly the centerline instead of being in a hurry to turn over the trees. I did not understand the approach of the Brazilian packing-tape team in some of their attempts at the north end of the runway. Multiple variations on turning into the trees instead of climbing straight ahead. I would bet the heat in Ft Worth in June will be a bigger problem than the trees here ever were. We got lucky with the weather staying around 82-83 for highs each day. On Sunday, the temp was 48 degrees when I got to the field. That's unheard of in April in FL. Usually the high in April is around 90 and the humidity is up higher - much less air to work with there. Those conditions are what you are likely to see in TX. The weather.com average high for mid-June in Ft. Worth is 92. Be ready to fly early in the morning.

As for the stab size, like I said - the Cedarville design obviously worked fine. I just don't understand why teams did not make them bigger - being as there no longer is a planform area restriction. More control authority, more CG range, more dynamic damping. There's not a minimum or maximum stab size, just that as the stab area goes to zero, so does the variation in allowable CG.

SST

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More drag...

Johng

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Well, I guess that's a reason. Not a good reason by any means, but a reason.

The added drag by doubling the size of the stab, if any, would be negligible.