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Wingtip weight vs. offset

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Wingtip weight vs. offset

Post  rsv1cox on Thu May 14, 2015 12:54 pm

Which is better? Why and for what aircraft? Novices would like to know.
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Re: Wingtip weight vs. offset

Post  pkrankow on Thu May 14, 2015 2:04 pm

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Re: Wingtip weight vs. offset

Post  pkrankow on Thu May 14, 2015 2:19 pm

A simplified condensed version of what happens:

It is desirable to fly wings level.

1 the airplane sweeps a circle, so the outboard wing moves faster than the inboard wing generating more lift.
2 the weight of the lines pull the inboard wingtip down.

tip weight vs fuselage offset deal with these two effects.

Moving the fuselage is effectively the same as adding tip weight. If you balance the model on the center line of the model (not necessarily the fuselage) then one wingtip will weigh more than the other. Therefore offset of the fuselage is equivalent to adding weight to the outboard tip.

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Re: Wingtip weight vs. offset

Post  Ken Cook on Thu May 14, 2015 3:27 pm

Are you making reference to engine offset? If so, it works but the problem is that the engine isn't flying tangent to the circle. This creates drag and slows the plane down. In addition, whether it may be rudder offset or engine offset, it yaws the plane to the outside. This now creates even more drag and it can also cause problems with fuel delivery. In the older days the plans always called for rudder offset and usually waaaaaay more than needed. In many situations, and I discovered this by accident, the plane flies better without the rudder. I would be flying low level inverted and I would take the rudder off due to hitting the ground. The plane wouldn't crash, but it was noticeably flying better. I would immediately see increased speed. A profile can be very finnicky if the plane has a lot of offset due to the fuel getting pinned in the corner of the tank. The engine will cough and sputter especially at the end of the tank. The tank requires it's rear end to be shimmed off the fuselage. I very rarely put any rudder offset into a plane. If anything I will airfoil the rudder but I glue it on straight.

Wingtip weight is essentially only needed for take off. After that, speed is what generates line tension. This is why too much of the above can do more hurt than good. Older engines like the Fox .35's and the Mccoy .35's need all the help they can get. Flying them on overweight planes especially those that aren't built straight or incidence lines are off just increases the load on the engine and slows the plane down. You want the engine to work only as hard as required.

Too much tip weight can cause issues with the wing dropping. Reason being is if you go into a outside maneuver, the momentum doesn't want to stop on that outboard wing. When the plane is required to go from one direction to another, the weight wants to continue traveling in it's last pointed direction. This can also happen at the top of the circle on a inside loop. If caught on the windy side this can roll the model inboard and cause immediate loss of line tension resulting in a crash. Ken

TO determine if enough tip weight is needed, the model should be flown right side up and inverted and a comparison needs to be made. If the tip is low right side up and also inverted, there's a possibility that more weight is needed to offset the weight of the lines. If it's low or high one way and not the other, it's a warp. I see it many times that flyers mistake a warp and adds more weight to compensate for the wing flying high. It will still fly high and adding more and more weight will bring it down but it can just turn the plane into a slug. Only use enough tip weight. Most profile .35 size models, require anywhere from 5/5-3/4 oz. A full bodied stunter with a wingspan of 54" usually needs a bit more, I generally start with .3/4 oz and go from there. Hold the plane by the prop and just balance the plane on the rudder with your finger tip to insure the wing falls outboard prior to flight. Using the appropriate line size diameter and length is most important. If you use Spectra and Spiderwire, you can remove a bit of tip weight as these lines weigh considerably less than stainless lines. Ken


Last edited by Ken Cook on Thu May 14, 2015 4:11 pm; edited 1 time in total
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Re: Wingtip weight vs. offset

Post  rsv1cox on Thu May 14, 2015 3:32 pm

Interesting. But is wingtip weight a substitute for rudder/engine offset or should they be used together? I don't see how wingtip weights alone prevent the C/L model from turning into you.
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Re: Wingtip weight vs. offset

Post  Ken Cook on Thu May 14, 2015 3:43 pm

Your always going to need wing tip weight. Wingtip weight however goes pretty much along for the ride once the plane leaves the ground. It's not generating the force that keeps the plane to the outside of the circle. Ruder offset and engine offset isn't required to keep the plane to the outside of the circle. The plane gets off the ground, centrifugal force keeps the plane to the outside. Wingtip weight assists until the speed comes up a bit.

Here's what happens when too much weight is installed. https://www.facebook.com/PhillyFliersCL/videos/vb.513140418756097/855485217854947/?type=2&theater

Unfortunately, that really isn't true but it certainly looks funny. ken
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Re: Wingtip weight vs. offset

Post  rsv1cox on Thu May 14, 2015 3:56 pm

Yes, it does give new meaning to the term "knife edge" where C/L is involved.  Looks like he was trying to hover using a third line in his left hand.  Entertaining to say the least.
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Re: Wingtip weight vs. offset

Post  pkrankow on Thu May 14, 2015 5:51 pm

rsv1cox wrote:Interesting.  But is wingtip weight a substitute for rudder/engine offset or should they be used together?  I don't see how wingtip weights alone prevent the C/L model from turning into you.  

No. Tip weight does not keep the airplane on the end of the lines Tip weight adjusts roll, which can prevent elevator input from having a component towards the inside of the circle.

A straight airplane, rudder offset, engine offset, and lead out location keep the plane on the end of the line. Centripetal force (the force to change the direction of the flight into a circle, caused primarily by speed) is the primary reason the plane stays on the end of the line. Adjusting yaw will artificially increase this force.

Fuselage offset is really not changeable. It is a design choice to have the inboard wing longer than the outboard wing. It compensates for tip weight. (we are working with ROLL, and lowering the weight of the entire airframe)

Tip weight is "fixed" (but not really.) The weight is enclosed in the wing and typically not changed as the wing either needs built with an accessible tip weight box, or the wing covering needs opened and repaired. Adhesive weights can also be used on the outside of the wingtip. (we are working with ROLL)

Trim tabs on the wing are used to assist in correcting for warped wings that will not fly level inverted and upright at any tip weight. (again this is ROLL)

Rudder offset is a design choice that can be changed with some difficulty, similar to tip weight. Changing the offset requires cutting and reattaching the rudder. Adjustable rudders exist either using soft steel sheet as a hinge, or some linkage system. Generally this is more trouble than help, especially if the capabilities of the plane are already higher than the pilot. (this is YAW)

Engine offset is used in a similar manner to rudder offset, but is typically (on profiles at least) easy to adjust by adding washers under the engine mounts. The engine offset changes the YAW of the plane.

While we are at it, throw in lead out adjustment. This also changes the YAW of the airplane.

Nose weight/tail weight adjusts the center of gravity location, which changes how quickly the plane reacts to control input. A forward CG is less responsive to control input than a more aft CG. If the CG is too far forward the plane will be very sluggish. If the CG is aft then the plane will be unstable and difficult to control.

CG can also be moved up and down, although this is typically only done with electric power by moving the battery some. vertical CG is used to help balance control response between inside and outside maneuvers.

Phil
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Re: Wingtip weight vs. offset

Post  getback on Fri May 15, 2015 7:07 am

Popcorn Flying I have thought of knife edge in C/L and now I have seen it all >> don't get how he did it though Rolling Eyes
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Re: Wingtip weight vs. offset

Post  RknRusty on Fri May 15, 2015 11:33 am

Tip weight is also needed to counterbalance the weight of the lines and their attachment hardware.

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Re: Wingtip weight vs. offset

Post  gcb on Sat May 16, 2015 9:23 am

rsv1cox wrote:Yes, it does give new meaning to the term "knife edge" where C/L is involved.  Looks like he was trying to hover using a third line in his left hand.  Entertaining to say the least.

The Philly Flyers are noted for being innovative and coming up with fresh ideas and approaches. It would appear that the plane shown was set up for carrier flying where the third line operates a throttle and sometimes applies additional yaw to the plane to keep it out on the lines when flying slow.

As pointed out wingtip weight is used to counteract the weight of the lines and engine torque. As the plane picks up speed it is used to keep the wings fling level and the other purposes are less significant.

When a plane is trimmed properly and under normal conditions neither engine offset nor rudder offset are needed. Consider that the plane is trying to fly straight while the lines are pulling it in a circle which supplies line tension. If you rely too much on engine offset to supply tension, what does the plane do when the engine quits?

But to answer your question, tip weight is used to prevent the plane from rolling in at you and offset is used to prevent the plane from turning in at you.

That's my story and I'm stickin' to it. Huh...  

George
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Re: Wingtip weight vs. offset

Post  Ken Cook on Sat May 16, 2015 9:38 am

We have a picnic which we fly using the 3rd line every Memorial and Labor day which typically brings out all of the members. I can't take credit for the Ring flying like that as it was a concept by Mike Palko. Here's the Ring flying like a Bi-Slob.
https://www.facebook.com/PhillyFliersCL/videos/vb.513140418756097/855087704561365/?type=1&theater

We tie a 3rd line to the tail and pull it in when we want it to hover. The knife edge can end in a disaster if not careful. The 3rd line is tied to the outboard wing tip. If you note, the wing is bending severely. Tomorrow Sunday were having a fun fly at a very old CL club in Reading, PA which we do a lot of demo flying and bring out the new stuff. We've had 7-8 people in the circle flying Bi-Slobs and Ringmaster's. It typically goes well and I hope it does due to Reading being entirely asphalt circles. I broke the cylinders clean off on 2 of my engines there over the years. A lot of fun however and it's stuff like this that makes it even better. Ken
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Re: Wingtip weight vs. offset

Post  getback on Sun May 17, 2015 7:09 am

But to answer your question, tip weight is used to prevent the plane from rolling in at you and offset is used to prevent the plane from turning in at you. wrote:
Well that sums it up for me how bout you Bob ? I will have to learn to build better for now I am so use to putting all in , maybe a least come off the engine offset for now and reduce the rudder input ! I am not as scared as I can't RUN anymore Shocked I can hit the deck though tongue Ken hope things go well at the fly in .
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Re: Wingtip weight vs. offset

Post  gcb on Sun May 17, 2015 9:09 am

Ken Cook wrote:We have a picnic which we fly using the 3rd line  every Memorial and Labor day which typically brings out all of the members. I can't take credit for the Ring flying like that as it was a concept by Mike Palko. Here's the Ring flying like a Bi-Slob.
https://www.facebook.com/PhillyFliersCL/videos/vb.513140418756097/855087704561365/?type=1&theater

Ken

Ken,
Wasn't it Mike Palko and Dan Banjok who teamed up and made that 2X Flite Streak?

George
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Re: Wingtip weight vs. offset

Post  Ken Cook on Sun May 17, 2015 4:11 pm

Yes, Mike was a part of that project. Mike recently married and we haven't seen much of him lately. Ken
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Re: Wingtip weight vs. offset

Post  rsv1cox on Sun May 17, 2015 5:01 pm

getback wrote:   Well that sums it up for me how bout you Bob ? I will have to learn to build better for now I am so use to putting all in , maybe a least come off the engine offset for now and reduce the rudder input ! I am not as scared as I can't RUN anymore Shocked   I can hit the deck though tongue Ken hope things go well at the fly in .

Yes, me too Eric. It's always good to seek opinions when you have a question that you don't know the answer to. Lot's of knowledgable people here to tap into. Guess I will experiment with tip weights. Thanks to all for your responses.

Bob
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Re: Wingtip weight vs. offset

Post  Ken Cook on Sun May 17, 2015 5:16 pm

While I'm not a big fan of weight boxes in Ringmaster type planes or I should say planes that are 39"-42", it certainly is nice to be able to add and subtract. I did things pretty much the old school way early on. This would've been coils of solder, expended Ambroid tubes, nuts, washers, etc. Recently revisiting a old flyer that I built many years ago, I discovered I had 1 oz. of tip weight in this smaller type sport plane. I cut her open and discovered it was glued to the side of the rib. This alone is a bad practice and the weight should have balsa around it's perimeter. If not, the weight and the rib exits the plane. I broke out the rib, cut another and proceeded to cover without tip weight. The plane flew terrifically and this was a huge benefit for the plane in the overhead maneuvers. In any build I do nowadays, the plane get 0 rudder offset. If engine offset is required, installing a washer under the lug is also a bad idea. It stresses the engine lug not to mention it has little to no footprint. They just immediately crush into the doubler. You want a angled nylon engine offset shim or aluminum. Brodak offers nylon versions .

Check the roll on the plane prior to flying even if it's a plane you fly daily. Gear wires get bent, castor goo solidifies on wheel axles and can really sludge up their operation. Roll the plane and make certain it's not rolling into the circle. Stand over the plane facing it head on and make sure the gear isn't bent or the wheels aren't tracking inboard. Test roll on the ground if not sure.
If your planes seem to be coming in during launch, keep the grass short and clear of high weeds. I mentioned this to Rusty that it doesn't hurt to install a friction washer using a piece of fuel tubing in front of your wheel collar to put drag on the outboard wheel. This will keep the plane headed in a outboard direction on take off. Be 100% positive that your lines are the correct size for the plane and your not using lines too heavy. Prior to launch, lift your handle hand with the handle above your head prior to signaling for a launch to be certain your lines are clear and not hooked on weeds or a obstruction. I don't use wire skids on my tails due to them getting caught in the grass or hanging up. I use tail wheels. They can get caught as well but not to the degree a skid does. Ken
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Re: Wingtip weight vs. offset

Post  pkrankow on Mon May 18, 2015 9:07 am

I did entirely fail to talk about ground roll. It is rather important too. Maintaining control on the ground is necessary.

And yes, wedges are superior to washers. Wedges also prevent damage to engine lugs in a crash by providing better support than washers.

Phil
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Re: Wingtip weight vs. offset

Post  gcb on Mon May 18, 2015 10:29 am

I remember using solder, Ambroid tubes (when they were lead), and even a penny or two as wing weight; usually held by a puddle of Ambroid in the wing tip or last rib.

Also used the Ambroid caps to reinforce pushrods until they switched to plastic caps.

My current Ringmaster does have adjustable leadouts and tip weight. Just a matter of preference.

George
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