eta150 wrote:That is what I was thinking, but I technically don't need the same amount of lift (because of the bonus), and I think (correct me if I'm wrong) that the relationship between wing area and lift isn't linear, and I should be able to get enough lift if I use different level of curve. I also don't know how much more time I can get out of a 2:50 + plane.
illusionist wrote:I am getting around 1:30 with my plane. it has a 38.5 cm wingspan and 11 cm chord, 19 cm tailspan, 6 cm tailchord, 3/32 inch rubber motor, and a 20 cm ikra prop. Any suggestions on improving my times? the flight path is very stable and it flies in smooth circles. I am putting in 800 turns. Please help!
Greg Doe wrote:Illusionist,
You actually are getting a fairly good performance for your airplane, and Jeff has already given
you some excellent suggestions, but first let me show you why one airplane out performs
another. Wing loading plays a huge roll in duration flying. Your airplane has a combined wing
and stab area of 547.5 sq. cm. The guy who is going to beat you has an airplane with a combined
wing and stab are of 880 sq.cm. For the sake of this arguement both airplanes weigh the same.
(7 grams we hope!) Your airplane has a heavier wing loading, so it has to fly faster to generate
the same 8.5 grams of lift. Remember we have to include the weight of the motor. You will use
up your fuel faster, so your motor won't run as long, so your flight time is less. If you have time
to build another airplane consider these dimensions. Wingspan 39.9 cm; wing chord 15cm;
stab span 27.9 cm; stab chord 10 cm. Interestingly your airplane's combined wing and stab area
is only slightely more than a "bonus" airplane's combined area would be (ie:smaller wing/larger
If you have relatively good rubber you are only winding to about 55% to 75% of what it
should accept. You should be able to get 1200 to 1500 winds. The extra winds should up your
time a minute or so, if everything else is right. You need to wind a motor until it bursts, so
you know how many winds it is safe to put on. You need to lube your motors, and of course
stretch wind. Jeff Anderson highly recomends a torque meter, which can be helpfull in getting
maximum winds, without exploding motors. Good advice if you have time to make one, or
the resources to buy one. Here is something to ponder; if your airplane dimensions were the maximum allowable in the rules for this year, it would probably be competitive. What you need
is more winds. Even if you had the larger wing and stab that I've recommended, you still need
more winds. Good luck.
jander14indoor wrote:illusionist wrote:I am getting around 1:30 with my plane. it has a 38.5 cm wingspan and 11 cm chord, 19 cm tailspan, 6 cm tailchord, 3/32 inch rubber motor, and a 20 cm ikra prop. Any suggestions on improving my times? the flight path is very stable and it flies in smooth circles. I am putting in 800 turns. Please help!
You didn't say what your plane weighs? If you aren't close to 7.0 gms, that's the first thing, lose weight.
If weights OK, try more turns, so long as the motors don't break, you may be near the limit, but I don't think so. If you are banging the ceiling, wind more and then back off till you stop hitting the ceiling.
If no turns left on landing, thinner rubber or more turns on this rubber.
Try raising the leading edge of the wing or the trailing edge of the tail till you start stalling on descent, then back off a little. Then rematch rubber and prop.
Where's your cg, if not at the rear wing post, or behind, move it back, readjust the wing and stab to stop stalling, and then rematch rubber and prop.
Take and review data every step of the way. Try to repeat each setting twice to make sure some other anomaly didn't mess up the result. Go with what the data says. Be careful about changing too many things at once unless you have someone who can guide you in Design of Experiments (DOE). Note, DOE is NOT experimental method, its a mathematically efficient and correct way of varying multiple factors at once and sorting out the true effects. The basic math to execute DOEs are within a middle school student's capability, theory and correct application will be more of a stretch.
illusionist wrote:<SNIP> my airplane does keep hitting the ceiling, and i don't have a larger place to do some test flights... yes, my plane weighs 7.1 grams
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