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Author Topic: Flaps on a C/L'er vs. R/C'er or real planes?  (Read 6443 times)

Offline Duke.Johnson

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Flaps on a C/L'er vs. R/C'er or real planes?
« on: March 28, 2013, 08:24:39 AM »
This may be to simple for you guys, but here it goes.  Please try not to go to far over my head. 

I have a friend that is a small engine/plane pilot and a R/C'er, he's currently building an ARF Nobler.  He came to me all upset this morning, "The darn *()_&*&%$# instructions told me to hook up the flaps backwards"

When you are flying a real plane level and give it 1% down flaps, your nose will go down (I'm not an R/C'er, but have been told it works the same way on them too.)  We give up elevator and down flaps and the plane goes up.  I thought it most make the plane pivot on the say back half of the wing cord and turn tighter. 

So to all you smart guy, can you explain why we do what we do? D>K

Offline Tim Wescott

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Re: Flaps on a C/L'er vs. R/C'er or real planes?
« Reply #1 on: March 28, 2013, 08:45:38 AM »
Because it makes the turn prettier, and it lets you trim the plane out to fly level easier while still achieving tight turns.  These are entirely different reasons than the usual ones for putting flaps on a plane -- usually you put flaps on an airplane to give it more lift at high angles of attack, when it is going slow.  Here we're putting flaps on a plane to give it controlled lift at zero or moderate angles of attack when it's going fast.

Flaps make the turns prettier because with flaps the wings can develop lift at a lower (or even negative) angle of attack.  Without flaps the wing has to be at high angles of attack, which means that the tail swings out of the corner -- it looks like the thing is fish-tailing.  With flaps you can adjust things so that the plane looks like it is traveling on rails.

I'm not entirely sure why it does the level flight thing -- I think it's because the you can put the center of gravity further forward.  Expert-er folks than me can opine on this one.

If he's seriously interested in control line stunt, and not just noodling around, he may do better with a SkyRay or a Flight Streak.  They're way easier to keep flying after crashes, and you won't be distracted by the complexity of tuning a flapped ship.  I was given this advise by Brett Buck when I was starting out a few years ago, I followed it, and I feel it was an assist to getting me up to where I am now.  Once you know the pattern and you aren't crashing regularly, then move to a flapped stunter.
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Offline Duke.Johnson

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Re: Flaps on a C/L'er vs. R/C'er or real planes?
« Reply #2 on: March 28, 2013, 09:47:38 AM »
Thanks.  He's not too interested in C/L though.  He inherited this plane, and a bunch of other C/L and R/C stuff from his stepfather.  He's an R/C'er and likes to build.  He said he might want me to fly it and then make it a Hanger Queen.

Offline Chuck_Smith

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Re: Flaps on a C/L'er vs. R/C'er or real planes?
« Reply #3 on: March 29, 2013, 05:30:25 AM »


...
When you are flying a real plane level and give it 1% down flaps, your nose will go down (I'm not an R/C'er, but have been told it works the same way on them too.)  We give up elevator and down flaps and the plane goes up.  I thought it most make the plane pivot on the say back half of the wing cord and turn tighter. 

...


Not sure I agree with that. Many planes will pitch nose up when the flaps are extended. It has a lot to do with the wing's downwash angle and how it affects the horizontal tail. My HP had flaps that went both ways, and I used to play with them sometimes using the flap crank to control pitch. Flaps up dropped the nose and flaps down raised it. Since they were on a crank it was like cranking the nose up or down, a lot of fun. The Baron on the the other hand, likes to pitch nose down when the flaps get extended. That's a good thing.
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Offline Duke.Johnson

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Re: Flaps on a C/L'er vs. R/C'er or real planes?
« Reply #4 on: March 29, 2013, 09:04:09 AM »
Not sure I agree with that. Many planes will pitch nose up when the flaps are extended. It has a lot to do with the wing's downwash angle and how it affects the horizontal tail. My HP had flaps that went both ways, and I used to play with them sometimes using the flap crank to control pitch. Flaps up dropped the nose and flaps down raised it. Since they were on a crank it was like cranking the nose up or down, a lot of fun. The Baron on the the other hand, likes to pitch nose down when the flaps get extended. That's a good thing.

That was just an example to start the thread, I really wanted to know about the C/L flaps for my friend.  I don't know enough about it to debate you.  Thanks anyways. D>K

Offline Howard Rush

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Re: Flaps on a C/L'er vs. R/C'er or real planes?
« Reply #5 on: March 29, 2013, 04:57:37 PM »
Duke,

There are two phenomena here: lift and pitching moment.  The main reason people put flaps on airplanes is to increase the maximum lift capability of the wing.  On real airplanes the extra lift enabled by flaps allows lower landing speeds for a given wing size.  On stunt planes with symmetrical airfoils, flaps allow this extra lift in either direction to help maneuvering (a long and interesting story).  A byproduct of the extra flap lift is pitching moment, a torque that tends to rotate the airplane.  In a stunt plane this torque is in the direction that would rotate the airplane in the opposite direction of that which would take advantage of the extra lift provided by the flap.  That torque is easily overcome by putting in opposite elevator.  You just pick the flap/elevator ratio that gives the response you want. 

Chuck mentions cases where the pitching moment from the flaps is overcome by the tail alone without need of additional elevator.  Depending on the configuration, the tail could under- or overcompensate the pitching moment from the flaps.  We don't care much.  We just fiddle with the flap-elevator ratio to make the response come out right.  For any normal stunter, the flaps and elevator move in opposite directions.
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Offline Serge_Krauss

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Re: Flaps on a C/L'er vs. R/C'er or real planes?
« Reply #6 on: March 30, 2013, 02:05:03 AM »
Not sure I agree with that. Many planes will pitch nose up when the flaps are extended.

We had a discussion about this a couple years ago, and two very experienced commercial pilots with time in a variety of aircraft agreed that flaps down raised the nose. It's been a lot of years now, but I'm pretty sure I remember having to put in nose-up trim when I dropped flaps on down wind in my Beachcraft "Musketeer" and then letting the nose down with added flaps and throttling further back. CL planes have their c.g.s forward of R/C and full-sized aircraft, with FF's models' the furthest back, and I suppose the horizontal tail area/TVC have an influence on c.g. placement and therefore initial pitch tendencies with flap deflection in models.

SK

Offline Steve Helmick

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Re: Flaps on a C/L'er vs. R/C'er or real planes?
« Reply #7 on: March 30, 2013, 10:52:05 PM »
For models, think of the flaps as giving a significant increase in wing incidence and an undercambered airfoil. With the elevators deflected the opposite direction (down flaps, up elevator for example), your horizontal tail gets a significant negative incidence and another undercambered airfoil.

The thing that irritates me is effectively having a thrustline that is working against your desired direction of turn, and that is a pretty serious resistance. I always wanted to put a boat u-joint onto a K&B .40 and drive a gimbal mounted prop shaft. I think Howard would say something about control loads and stuff that would go over my head, but about 5 degrees (in the right direction) would make a huge difference in turn radius. I found that out with a combat model that was (inaccurately) built in a dorm room, circa 1965. It was amazing on insides (without slowing down) and really hazardous on outsides.  :-[ Steve
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Offline Howard Rush

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Re: Flaps on a C/L'er vs. R/C'er or real planes?
« Reply #8 on: March 30, 2013, 11:49:26 PM »
Use the motor gimbals instead of an elevator. Electrics would make that easy.  You could skew the axis a little to counter the gyro effect or P factor or whatever.  Let's do it.  I'll put up a combat airframe for the experiment. 
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Online Brett Buck

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Re: Flaps on a C/L'er vs. R/C'er or real planes?
« Reply #9 on: March 31, 2013, 12:06:15 AM »
Use the motor gimbals instead of an elevator. Electrics would make that easy.  You could skew the axis a little to counter the gyro effect or P factor or whatever.  Let's do it.  I'll put up a combat airframe for the experiment. 

    Probably need load cell to sense the thrust and adjust the angle to get something like a consistent response. Otherwise, you are cruising around level with maybe a pound of thrust, then you get into the corner and it goes to 3 - 3 1/2 lbs and triples the pitch torque with no control movement. Given that the thrust is such a strong function of the corner radius, I wonder if its even stable.

     Brett

Offline Igor Burger

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Re: Flaps on a C/L'er vs. R/C'er or real planes?
« Reply #10 on: March 31, 2013, 01:28:51 AM »
For models, think of the flaps as giving a significant increase in wing incidence and an undercambered airfoil. With the elevators deflected the opposite direction (down flaps, up elevator for example), your horizontal tail gets a significant negative incidence and another undercambered airfoil.

The thing that irritates me is effectively having a thrustline that is working against your desired direction of turn, and that is a pretty serious resistance. I always wanted to put a boat u-joint onto a K&B .40 and drive a gimbal mounted prop shaft. I think Howard would say something about control loads and stuff that would go over my head, but about 5 degrees (in the right direction) would make a huge difference in turn radius. I found that out with a combat model that was (inaccurately) built in a dorm room, circa 1965. It was amazing on insides (without slowing down) and really hazardous on outsides.  :-[ Steve
Good stunters have AoA in corner radius aproximately 7 degrees, so the motor thrust line is INSIDE, not outside. However remember of p-factor, if you deflect motor you will get unwanted induced yaw and it will be last thing I want, so if I was the designer of hinged hinged motor, it will make it poit always exactly to the incomming air. The pitching rate is not problem, I can have elevator large enough  :-)

Offline Tim Wescott

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Re: Flaps on a C/L'er vs. R/C'er or real planes?
« Reply #11 on: March 31, 2013, 09:01:12 AM »
    Probably need load cell to sense the thrust and adjust the angle to get something like a consistent response.

Electronic control of the pitch axis?  For shame!
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Offline Howard Rush

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Re: Flaps on a C/L'er vs. R/C'er or real planes?
« Reply #12 on: March 31, 2013, 02:43:57 PM »
Good stunters have AoA in corner radius aproximately 7 degrees, so the motor thrust line is INSIDE, not outside. However remember of p-factor, if you deflect motor you will get unwanted induced yaw and it will be last thing I want, so if I was the designer of hinged hinged motor, it will make it poit always exactly to the incomming air. The pitching rate is not problem, I can have elevator large enough  :-)

We would have linkage with either sign.  Steve, if he does the work on the plane, gets to choose the sign for the first flight.
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Offline Fredvon4

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Re: Flaps on a C/L'er vs. R/C'er or real planes?
« Reply #13 on: September 08, 2014, 11:46:36 AM »
Sorry to bring old topic to the top but as I read this I remembered a guy at our RC field with a vectored thrust plane. It is pusher so maybe not relevant to a stunt ship with a single tractor engine ...but I often wondered how my combat planes might turn tighter if I could figure how to adapt a gimbeled engine mount driven off the bell crank

for reference here is one version of vectored thrust airplane model

http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXDPAX&P=7
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Offline Duke.Johnson

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Re: Flaps on a C/L'er vs. R/C'er or real planes?
« Reply #14 on: September 08, 2014, 12:15:43 PM »
Sorry to bring old topic to the top but as I read this I remembered a guy at our RC field with a vectored thrust plane. It is pusher so maybe not relevant to a stunt ship with a single tractor engine ...but I often wondered how my combat planes might turn tighter if I could figure how to adapt a gimbeled engine mount driven off the bell crank

for reference here is one version of vectored thrust airplane model

http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXDPAX&P=7

Hey Fred
One of our local combat guys coverted a 1/2A with a vector thrust type motor mount.  He hasn't used it in a contest, but has been playing with it.

Offline Tim Wescott

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Re: Flaps on a C/L'er vs. R/C'er or real planes?
« Reply #15 on: September 08, 2014, 12:21:30 PM »
Sorry to bring old topic to the top but as I read this I remembered a guy at our RC field with a vectored thrust plane. It is pusher so maybe not relevant to a stunt ship with a single tractor engine ...but I often wondered how my combat planes might turn tighter if I could figure how to adapt a gimbeled engine mount driven off the bell crank

for reference here is one version of vectored thrust airplane model

http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXDPAX&P=7

I think you'd lose so much forward speed that it would outweigh the advantage in maneuverability.

I'd like to see a Harrier or F-35 (??) in Scale, though, doing a hover as part of its maneuvers.
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Offline Fredvon4

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Re: Flaps on a C/L'er vs. R/C'er or real planes?
« Reply #16 on: September 08, 2014, 12:36:40 PM »
Tim in my hast to write I can see where it might be assumed that the Harrier idea of vectored thrust 0 to 90+ degrees of change would effect airspeed in the extreme....I was thinking more about just pivoting the engine up or down a few degrees in the direction of the turn

Unfortunately in combat, power, weight, simplicity, and strength are all interrelated making a gimbaled motor mount and bell crank Rube Goldberg contraption impractical

Seeing the Delta pusher with vectored thrust fly, I was astounded on the rate of turn for the airspeed, with elevons and rudder alone the craft would just stall and require recovery back to controlled flight

Most of the electric RC guys that have these Ro-Jett type delta planes like to fly them close to or over 200 MPH !
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Offline Duke.Johnson

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Re: Flaps on a C/L'er vs. R/C'er or real planes?
« Reply #17 on: September 08, 2014, 01:46:22 PM »
The one Robert is working on doesn't move but a couple degrees and doesn't sound like it slows it down.. 

Offline Phil Krankowski

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Re: Flaps on a C/L'er vs. R/C'er or real planes?
« Reply #18 on: September 09, 2014, 06:31:22 PM »

Offline Tom Niebuhr

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Re: Flaps on a C/L'er vs. R/C'er or real planes?
« Reply #19 on: September 12, 2014, 12:11:46 PM »
Yes, flaps will cause the nose to pitch up. This will require pushing the stick/yoke forward and/or adding down trim. This is very prevalent in high wing Cessna's.

Coupled "stunt flaps" have been used on full size aircraft to some degree of success. One of the aviation magazines had an article and 3 views of an airplane that used them.

I had a very close personal friend that had a full size "Stits Playboy". That airplane is normally only mildly aerobatic. This one was different. It was highly modified and had a bubble canopy. It had clipped wings and he incorporated coupled "stunt flaps" It worked well and the airplane was flown in Advanced aerobatic competitions and was also flown in air shows.
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