Flight Times

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Re: Flight Times

Postby jcollier » March 6th, 2010, 1:44 pm

The rules have made the state and national wing a little more interesting this year. Last year, my son's first good plane wanted to rocket out of the gym, so I thought it might be worth the effort for him to try the bonus wing. Comparing best flights, he would have needed about a 50% bonus to make it worthwhile. I would think a well constructed and trimmed, 7 gram Freedom Flights or Leading Edge plane would be pretty tough to beat with a bonus wing. If I was going to try, I would try a similar reduction in stab cord, but keep the max span.

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Re: Flight Times

Postby jander14indoor » March 6th, 2010, 6:47 pm

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.


Actually the relation between lift and area is linear. BUT, its not that simple. The relation between SPEED and lift isn't linear, its squared. So to lift the same 8.5 gm with a wing half the size, you need to go sqrt(2) faster or 1.44. But you aren't finished there. You have to consider drag. It also follows speed as a square, so it will take twice the energy (1.44 squared) to fly at 1.44 speed increase. SO, as a first order approximation, you'll fly half the time on half the wing.

Of course the trouble is, who's to say that you have to stop at a 15 cm wing? Why not 16 cm, or 17? Then the bonus is less than half the competing wing. Of course low aspect ratio wings tend to have higher drag than high aspect ration. Enough? Ahh, that's why its an experiment.

If a competitor knows the answer, don't expect a straight answer. Your fellow SO students are nice and all, but...

And as a mentor, well, that's an exercise left for the student...

Jeff Anderson
Livonia, MI

mg
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Re: Flight Times

Postby mg » March 7th, 2010, 8:24 am

Hi!
I won MN state tornament yesterday. It was a rough day. My plane flies three minutes, and my practice flights were 2:35 all day. When it came time for the event I used a .093 rubber band thinking it was a .088. I over wound the rubberband, and crashed my first flight. I then relized the rubber band mistake and wound the .088 less only getting a 2:08. To my suprise I won by 3 seconds. See you at nationals!! :D

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Re: Flight Times

Postby jcollier » March 7th, 2010, 10:48 am

Congratulations! Now you get to fly in that great big space. :D

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Re: Flight Times

Postby jcollier » March 10th, 2010, 2:51 pm

Middle Eastern PA Regionals tomorrow. I will be supervisor for WS. Hope we get a bunch of planes that can fly well this year. :D

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Re: Flight Times

Postby hammy » March 10th, 2010, 3:14 pm

Right now me and my partner are getting about 1:32 at the most making some new ajustments though.

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Re: Flight Times

Postby sydneenicole902 » March 11th, 2010, 9:28 am

most times in our regional competions are like 1:20. This year WS at Auburn was in like a regular room. If was so bad we placed 9th with only 12 seconds because most of the planes crashed. In our school gym we can get like 2 minutes without going into the rafters.
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Re: Flight Times

Postby jcollier » March 11th, 2010, 2:53 pm

Well, the words for the day at our regionals was power stall! A few teams that are going to States had impressive trim flights, then had fairly major problems with their official flights. The winning time was 2.06.6. If Wright Stuff was not rotating out of the lineup, I think I would see if I could invest in Freedom Flights kits. Saw a whole bunch of them today.

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Re: Flight Times

Postby illusionist » March 20th, 2010, 4:47 pm

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!
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Rule 7d. "Event Supervisors are allowed to break any competitors' devices" -bearasauras

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Re: Flight Times

Postby jander14indoor » March 20th, 2010, 6:58 pm

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.

Jeff Anderson
Livonia, MI

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Re: Flight Times

Postby Greg Doe » March 21st, 2010, 12:03 am

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
stab).

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.
Greg Doe
Smyrna, TN

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Re: Flight Times

Postby Littleboy » March 21st, 2010, 10:24 am

What would be a top flight time for state in MI?

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Re: Flight Times

Postby illusionist » March 21st, 2010, 12:52 pm

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
stab).

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.
Greg Doe
Smyrna, TN

thank you so much, this should help, but also, 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
2012-2013 Building Event Captain
Rule 7d. "Event Supervisors are allowed to break any competitors' devices" -bearasauras

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Re: Flight Times

Postby illusionist » March 21st, 2010, 12:54 pm

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.

Jeff Anderson
Livonia, MI

thank you very much for the suggestions. my cg is right in front of the rear wing post, and my plane weighs 7.1 grams.Could you further explain DOE? My regional competitions in a week, and I'm a little worried about my times...
2012-2013 Building Event Captain
Rule 7d. "Event Supervisors are allowed to break any competitors' devices" -bearasauras

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Re: Flight Times

Postby jander14indoor » March 21st, 2010, 4:29 pm

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


If you are banging your plane off the ceiling with that few winds on that motor, it is WAY to fat. You really need thinner rubber and to wind harder.

And the problem isn't really with the ceiling height, you are climbing to fast due to the motor being too strong. While low ceilings limit flight time, there are ways to compensate so its not as bad as most people think. Last years planes would do 3 minutes in a 25 ft gym (expertly flown). This years planes will beat that.

As to explaining DOEs, dang, not easy. Probably best to get a local expert to help, but I'll see if I can write up something coherent in less than a page and post it later. I've used them lots at work to solve difficult technical problems. I've set them up for others to execute. But teaching concisely is SO much harder. OK, enough complaining, I brought it up, I'll try to explain it in a follow on note.

In the mean time, you may not need such a powerful technique. Seriously, your motor is too fat. I've been flying on motors less than 0.080 inch wide 1500-1800 turns with last years plane and its smaller tail.

Jeff Anderson
Livonia, MI


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