12/22/2009

A Surprise

Have I got a surprise for you.... I'm reminded of a line from a movie a few years back. The movie was "Contact", and the line was from the eccentric old guy, towards the end of the movie, when he says: "Why build just one, when you can build two at twice the cost?" Somehow that seems quite fitting, given this update.

This update is going to be a biggie, and a reveal of something too. I had always thought that the testing process would bugger up the prototype in one way or another. I could not have fathomed I'd be sitting here, with 9 test flights on it including full throttle, high 'g' testing, and not have a scratch on it. However, it did have a problem...weight. Fully fueled and ready to roll, it sat on the scales at 72 lbs. Bear in mind, that I had no finish or no cockpit either. Finishing out the prototype would put it over our AMA limit of 75 lbs. It's a shame really, especially considering that the thing flies great even at this weight.

Last Spring, I heard about the Jet World Masters coming to the US in 2011. I got the news just about as I was getting started on the second plane (Article #2 for those of you following along that know about such names). Not like the whole project hasn't been challenging enough, I decided to see if I could make plane #2 light enough to make the limit of 44 pounds dry. To pull this off, 20 pounds would have to come off the prototype weight. To boot, it would have to be done in 18 months, to be finished in time for the US qualifier, in Fall 2010. It turns out that the prototype was built like a tank, not knowing what I was doing when building it. I did some math, considered doing a lay-up of some lighter weight cloth, thinning down the wood, and refining a bit the lay-up techniques, and figured I could take a good 15 pounds off the prototype weight....but where that last 5 pounds were going to come from, was going to be very, very difficult. Never the less, it was in the realm of possible, so, since March I've been putting in double time trying to pull this off.

Now that I've set the stage for the 2 nearly impossible goals of weight and time, on with the pictures. One thing learned on the prototype, was where the doors and hatches were well suited. One thing that was also missing was proper flanges in where these things were to seat as well. So after some pondering it was apparent, that these doors and hatches needed to be made first. I've also done some experimenting this year with vacuum bagging on some parts making. One thing I learned with this process, was that is was very easy to pull too much resin out of the lay-up. After screwing up several small parts, I changed my techniques a bit when it came time to do the doors and hatches. To do these, I did them in 2 steps. The first step was to do a hand lay-up of the outer part. Then after the outer layer had setup preserving the panel lines and surface detail, I'd put a thin layer of foam in them, and then laminate a thin layer of cloth over that. To pull the foam and laminate layer down, required vacuum at this point. This pic is showing the setup of that stage. I'm also modifying the normal layers here typically used in vacuum bagging. I'm not really worried about pulling resin out, just pinning all the parts together. The white you see around the edges is the 'breather' layer that allows air to travel through when put under pressure.

Once the entire rig is set, I'd start drawing down the vacuum. I watched the vacuum gauge very closely, to seal down the parts, but yet, not crush the foam.

I think my family was thinking either the shop was turning into this mad scientist thing, or I was constructing a monkey trap.

Overall I was very pleased with the results. Here are the 3 nose gear doors being made as one unit, to be later cut apart.

Here's the main gear doors being made. It was learned during flight testing that the previous attempts at gear doors were woefully inadequate, as they flexed heavily under the flight loads and one even separated in flight.

Once the doors and hatches were made, it was on to making the next fuse. This time I decided to make the front and back separately, so that I could do a better job, and have more time to make the lay-ups lighter, while they were wetted out. Also, you can see here on the nose gear mount area, I've taken lightening the wood to the next level, and removed every last bit viewed as not needed.

This show shows closing up the molds prior to seaming the nose section. You'll also note here, that I've added some foam laminate reinforcement areas as well, in the top of the photo.

First results on the nose section are promising. The entire 5 foot long nose section came out at 3.5 pounds, formers included.

On to the aft section construction, and here's showing the top of the fuse, with the equipment hatch, 2 engine access hatches, and the parachute doors, already laid into the mold, getting ready for making the airplane on top of them.

Thin coat of primer down, and now getting started on the glass layout of the top shell. While on the subject of doing the lay-ups, on this plane, I'm using a different resin. It's a high temp resin that looks to have as good or better strength than the West's, but much better heat tolerance. The new resin I'm using now, with just a room temperature cure, is solid up to 325 degrees. This will solve my concerns about a black airplane getting soft on a hot tarmac.

Here we see the bottom aft section, laid up and done. I've cut back the amount of carbon to just the critical areas, in an attempt to shave weight as well. Also, having learned where stuff works well in the plane, I've pre-glued in several equipment anchor points as well

This picture is of the top aft shell, with the formers glued in. You can see here again, now that I know were equipment goes, servo trays and other anchor points are already glued in.

Here's a close up, of the main former area, showing all the work to lighten the load. The entire amount of all the wood in the entire plane, worked out to only 2 pounds. If you look close, you can see they are glued in as well, and with the finest of filets. Also you can see the foam reinforcement between the formers in the flat areas. This was an area of weakness on the prototype, and this solution adds less than an ounce, but is a tremendous help on strength.

Top and bottom aft sections done, it's now time to seam them together. Doing this is an intensive session, that requires much to be done, in a very finite time frame.

Once cured, it's time to crack it open and see how it turned out. I'd wager, not many model shops require multiple block and tackle units to make a model airplane...... :)

Pop quiz.... How many BlackBirds on in this photo? In the foreground, is the new bird, having secured the mid section formers at the break, and doing some fill work, so the seam looks good.

The work on the hatches and doors has paid off and they have all turned out well. One element of this design is that I'm setting it up so that with a few nights work, I can change my gear from the prototype to the show plane and visa-versa, such as engines, tail pipes, landing gear, fuel system, etc. I'm very pleased with the strength of this lighter lay-up, and so far, it's on track to be a solid 15 pounds lighter. I'm still on the hunt for those last 5 pounds. Time will tell if they can be found.... Regardless, the prototype flew great, and really hauled when you stayed in the throttle. One thing that's going to be quite exciting, is if the show plane now under construction comes out at 15+ pounds lighter, it will live up to it's namesake's performance, that's for sure.

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