It has been a while since I posted an update. A couple of weeks ago, while the correct my receiver extension cord was still in the mail, I tested the plane out at the local baseball fields. It had recently rained an one of the fields had flooded, so I had a chance to test how the plane would perform dirt, grass, and water takeoffs. The results left somethings to be desired. Initial tests indoors were promising, however when taking off on grass the added friction was enough to tilt forward on to the skids, in spite of the 8 degrees of inclination of the propeller. On water the plane would taxi great, but then as you would accelerate for takeoff the plane would again tip forward and the prop would catch the water and slow down. Conventional wisdom insists the step on the floats should be inline to just behind the CG, then again very little about this craft is conventional.
On the infield the plane would effortlessly slide around on low throttle (I took the time to tweak the throttle curve to widen this sweet spot). One nagging issue that kept happening as the plane went faster is the left plane would consistently veer left. At first I assumed it was just a trim issue, although after trying to correct for this, I think it was more likely result from the torque of the prop causing the left skid to drag more.
Then again most ground effect sleds I've seen are single prop don't seem to have that problem. Also, it is probable the elevons are to close to the CG to bring the nose off the ground, nevertheless I did find another way to get fully airborne.
Part of the transition from the dirt to the grass made a natural ski jump that would launch the air. The jumps being sudden and unpredictable and my flying skills being what they are I would end up crashing the plane into the ground only seconds later
. I could have practiced a few hand launches, but at this point my batteries were staring to run low, both cross bracing wires had detached, and I need to replace the bent prop.
To quote Millennium 7*, based on initial design criteria the final result could best be described as a "successful failure". A few notable lessons:
1. If I want to make a plane actually fly, I'll need to build a trainer and take the time to practice flying. No shortcuts.
2. She can really take a hit! Besides the bent prop and the cross brace wires detaching from the tail I mentioned, the rest of the plane took half a dozen crashes without any noticeable damage (no new creases, wrinkles, tares, glue seams that cracked open). Why post new pictures because it looks the exact same?
3. Propeller damage is still the Achilles heel. Future designs will be ducted props/BDFs. All made easier by...
4. Twin mid-mounted props are indeed the way to go.
5. It is difficult to design a plane to takeoff on grass AND water. I might avoid the added complication of making every design amphibious until I can make them fly better.
6. Designing a sled that skims along in cord-dominated ground effect is easy; making one fly stable in span-dominated ground effect (0.2-1.0 wingspan) is more of a challenge. (At least I am in good company, ProjectAir released a video of his latest GEV the same week I tested my plane to similar results)
Without sticking to an established design or doing the complex calculations that require would wind tunnel testing, I am kind of throwing darts at a dart board. Going forward I will need to conduct more careful research and glider tests. The next design I have in mind is an origami-style build that will look similar to the Mayfly with twin mid-mounted A-motors either paired to HQ3x5x3 or HQ4x4.3x3 (testing needed).