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Re: Nationals results

Posted: June 3rd, 2010, 3:47 pm
by leetx
MMP

Amazing flight. From the initial climb, it is obvious that your plane flies well. It climbs softly and slowly -- qualities that only the best planes have. Just the kind of behavior that's needed to last 5+ minutes. Again, congratulations.

leetx
SO coach

Re: Nationals results

Posted: June 3rd, 2010, 6:13 pm
by jgan96
calgoddard wrote:MMP - Thanks for posting the amazing video of the 2nd place flight at Nationals. Congratulations to Marie Murphy. I was amazed that the plane did not go "dead stick", i.e. run out of winds, until near the end of the flight.

Also, in further answer to another post, it was very smart to launch the plane from full extension of the arms overhead.

You know the reasons why, but I want to explain to others.

In very high ceiling hight flying sites, you wind to max torque, and don't back off so the plane will climb as high as possible. Many planes experience some motor stick bending and/or stab twist at the beginning of the flight. This can cause positive stab incidence, wide turns, lack of adquate wash - in, etc. You want max altitude at launch in case the plane initially flies in a downward path before the toruqe bleeds off. There is little chance the plane will hit the ceiling so launching from max height is not a problem.

Also, at very high launch torque, the plane can experience prop stall, and "hang" on its prop, i.e. dangle nearly vertically. Max launch height can allow the plane to experience this event yet not touch the ground and still recover.

In low ceiling height flying sites, you often back off torque to get a "no touch" flight, i.e. one that does not hit the celing. You launch from a kneeling position to get the maxium available flying height and there is little chance the plane will experience motor stick bending that will give positive stab incidence and a downward trajectory on launch.



Ah, I knew that!! <_>

Thanks for the info. If i ever make it to nationals, I can use that. Unfortunately, I don't think thats happening... :(

How is stab twist/stick bending caused? High torque?

-Jason

Re: Nationals results

Posted: June 3rd, 2010, 6:28 pm
by MMP
Thanks guys.... we couldn't have done it without the great information on this forum. It has been a very rewarding experience for kids (and coaches as well) to see how science works and to learn to work hard for good results. We have been in constant progressing path for the last two years in wright stuff, and we had seen pretty much every problems you experts pointed out.

eta150, I believe I witnessed your ill-fated flight, which was very surprising (and hurting) to me as well. Did you fly another plane or did you have to quickly fix it for second flight?

Re: Nationals results

Posted: June 4th, 2010, 4:23 am
by eta150
That was the first time it had ever happened...I repaired the plane in less than a minute, but then the next 2 rubber bands snapped at low torque. I only got off that first flight, which lasted less than eighteen seconds, as compared to my consistent four minutes. It's okay though, because I won every other competition I entered, even against JC Booth at Solon, my biggest moment of pride. I wound up in 54th at nats.

Re: Nationals results

Posted: June 4th, 2010, 10:44 am
by calgoddard
Here are replies to the questions posed above, mamley, "How is stab twist/stick bending caused? High torque?"

The prop hanger and the rear motor hook place the wound rubber motor below the motor stick, causing it to bow. This is because the rubber motor pulls on each end of the motor stick similar to the forces exerted by a bow string when a bow and arrow are used to shoot an arrow. The bowing on the motor stick is very difficult to see, but since the tail boom extends many inches from the end of the motor stick the effect is accentuated, often resulting in positive stab incidence when you usually want about one degree of negative stab incidence.

The higher the torque, the more the bending, depending on the stiffness of the motor stick. The amount of bending of a solid motor stick depends on the nature of the wood, mostly the lbs per square foot and the cross - sectional area. Solid motor sticks should be carefully selected by weighing them individually and testing them on a stiffness measuring device. A couple of dowel pins inserted in vertically extending planar piece of hardwood will suffice to hold the inner end of the motor stick. A weight can then be hung on the free end of the motor stick and the deflection measured using graduated markings on the surface of the hardwood.

The same rubber motor torque temporarily causes the motor stick to twist around its longitudnal axis, causing the stab tilt to disappear or even go in the opposite direction to that desired. This can cause your plane to fly in a wide circle at launch, instead of the smaller circle desired, and can result in the plane hitting the wall.

Motor stick twisting can also tempmorarily remove wash - in, i.e. the designed - in lower trailing edge on the inboard side of the main wing. The motor stick twists between the main wing posts, causing them to change their relative angles and inducing an undesired warp in the main wing. Removal of the wash - in could cause the plane to spiral into the floor at launch.

Rolled motor sticks are less suspetible to undesirable motor stick bending and twisting. However they require considerable time and skill to build properly.

Re: Nationals results

Posted: June 4th, 2010, 10:54 am
by eta150
I never had a bowing issue, but mine twisted at nationals to the degree that it started turning the opposite direction. It was such a large gym that this wasn't a problem. Not that it mattered though.

Re: Nationals results

Posted: June 4th, 2010, 10:56 am
by lllazar
eta150 wrote:That was the first time it had ever happened...I repaired the plane in less than a minute, but then the next 2 rubber bands snapped at low torque. I only got off that first flight, which lasted less than eighteen seconds, as compared to my consistent four minutes. It's okay though, because I won every other competition I entered, even against JC Booth at Solon, my biggest moment of pride. I wound up in 54th at nats.


Wow, now that's depressing...im really sorry, sadly with Wright Stuff gone next year you won't get a chance at redemption....

And helicopter could never take Wright Stuff's place...

Edit: Btw, how do u get a plane to move so slowly? I don't really understand the physics in this event, but it's really cool.

Re: Nationals results

Posted: June 4th, 2010, 11:10 am
by eta150
lllazar wrote:
eta150 wrote:That was the first time it had ever happened...I repaired the plane in less than a minute, but then the next 2 rubber bands snapped at low torque. I only got off that first flight, which lasted less than eighteen seconds, as compared to my consistent four minutes. It's okay though, because I won every other competition I entered, even against JC Booth at Solon, my biggest moment of pride. I wound up in 54th at nats.


Wow, now that's depressing...im really sorry, sadly with Wright Stuff gone next year you won't get a chance at redemption....

And helicopter could never take Wright Stuff's place...

Edit: Btw, how do u get a plane to move so slowly? I don't really understand the physics in this event, but it's really cool.

They go so slow mainly because of the wider props and high wing angles of incidence. If you can use a thinner rubber band with lower torque, it also keeps the plane moving slowly and adds to time. High lift wings coupled with broad props and lower thickness rubber make for a slow, long-flying plane.

Also, thanks, but I really can't be disappointed with two nationals medals.

Re: Nationals results

Posted: June 4th, 2010, 11:47 am
by jander14indoor
eta150 wrote:
lllazar wrote:
eta150 wrote:<SNIP>Edit: Btw, how do u get a plane to move so slowly? I don't really understand the physics in this event, but it's really cool.

They go so slow mainly because of the wider props and high wing angles of incidence. If you can use a thinner rubber band with lower torque, it also keeps the plane moving slowly and adds to time. High lift wings coupled with broad props and lower thickness rubber make for a slow, long-flying plane.

Also, thanks, but I really can't be disappointed with two nationals medals.


NO, no, planes don't go slow because of wide props or thin rubber. They go slow because they are light and have lots of lift (big wing, optimum angle of attack (so you have it partially right))! That ALLOWS wide props, thin rubber, more turns, slower longer flights. Not the other way round.

You put wide props and thin rubber on a heavy, low lift plane and it won't fly slower, it won't fly! To get it to fly you HAVE to give it more rubber or lower pitch prop to get more power which means faster , but shorter flights!

Flight speed is a direct function of weight and wing lift. All else is tuning to maximize this!

PS, congrats to EVERYONE who medaled at nationals, the level of competition at nationals is consistently amazing. Two is definitely impressive!

PPS, don't underestimate helicopters!!

PPPS, WS WILL be back, probably in two years, C level.

Jeff Anderson
Livonia, MI

Re: Nationals results

Posted: June 4th, 2010, 12:37 pm
by calgoddard
Jeff:

Our team is looking forward to the challenge of the Helicopter Duration event next year.

Last year's trial event rules were very clear, and well thought out. The parameters were just right to allow students to experiment and arrive at a good design that can stay in the air over one minute.

Thanks for spear heading the Helicopter Duration trial event.

We have plenty of good rubber and balsa just waiting to be used :)

Re: Nationals results

Posted: June 4th, 2010, 1:18 pm
by MMP
according to the tentative 2011 events list here:
http://soinc.org/sites/default/files/uploaded_files/2011Chart5-30-10.pdf
Helicopter is only for division C, but not B ?

Re: Nationals results

Posted: June 4th, 2010, 1:57 pm
by smartkid222
That is correct. Bottle rockets is its equivalent in division B.

Re: Nationals results

Posted: June 6th, 2010, 9:38 am
by jgan96
lllazar wrote:
eta150 wrote:That was the first time it had ever happened...I repaired the plane in less than a minute, but then the next 2 rubber bands snapped at low torque. I only got off that first flight, which lasted less than eighteen seconds, as compared to my consistent four minutes. It's okay though, because I won every other competition I entered, even against JC Booth at Solon, my biggest moment of pride. I wound up in 54th at nats.


Wow, now that's depressing...im really sorry, sadly with Wright Stuff gone next year you won't get a chance at redemption....

And helicopter could never take Wright Stuff's place...

Edit: Btw, how do u get a plane to move so slowly? I don't really understand the physics in this event, but it's really cool.



WS IS GONE NEXT YEAR?!?!?!?!?! !@#$%^&* !@#$%^&* !@#$%^&* !@#$%^&* !@#$%^&* !@#$%^&*

I was hoping to coach the team for community service and skipping school... :lol: Anyway I loved building and testing the planes, and I was hoping in 2011 our team might make it to Nationals with WS. :cry:

-Jason

Re: Nationals results

Posted: June 6th, 2010, 9:39 am
by jgan96
calgoddard wrote:Here are replies to the questions posed above, mamley, "How is stab twist/stick bending caused? High torque?"

The prop hanger and the rear motor hook place the wound rubber motor below the motor stick, causing it to bow. This is because the rubber motor pulls on each end of the motor stick similar to the forces exerted by a bow string when a bow and arrow are used to shoot an arrow. The bowing on the motor stick is very difficult to see, but since the tail boom extends many inches from the end of the motor stick the effect is accentuated, often resulting in positive stab incidence when you usually want about one degree of negative stab incidence.

The higher the torque, the more the bending, depending on the stiffness of the motor stick. The amount of bending of a solid motor stick depends on the nature of the wood, mostly the lbs per square foot and the cross - sectional area. Solid motor sticks should be carefully selected by weighing them individually and testing them on a stiffness measuring device. A couple of dowel pins inserted in vertically extending planar piece of hardwood will suffice to hold the inner end of the motor stick. A weight can then be hung on the free end of the motor stick and the deflection measured using graduated markings on the surface of the hardwood.

The same rubber motor torque temporarily causes the motor stick to twist around its longitudnal axis, causing the stab tilt to disappear or even go in the opposite direction to that desired. This can cause your plane to fly in a wide circle at launch, instead of the smaller circle desired, and can result in the plane hitting the wall.

Motor stick twisting can also tempmorarily remove wash - in, i.e. the designed - in lower trailing edge on the inboard side of the main wing. The motor stick twists between the main wing posts, causing them to change their relative angles and inducing an undesired warp in the main wing. Removal of the wash - in could cause the plane to spiral into the floor at launch.

Rolled motor sticks are less suspetible to undesirable motor stick bending and twisting. However they require considerable time and skill to build properly.



Ah, thank you. Very interesting to know.

-Jason