Tip weight comparisons.

Yesterday I was asked a question of how much tip weight Matthew was carrying in his latest plane. Well, the question of tip weight is a little more complex than saying, "add this much weight." Different size planes with different size lines will need different amounts of tip weight. Plus, the two wing panels may already be built at slightly different weights (especially with asymmetry), and we have already added weight to the inboard wing with the weight of the leadouts and leadout guide, and to the outboard wing with the weight of the tip box. Since all of this must also be balanced out, the best way to determine tip weight is to turn the plane upside down, hold it by the tail wheel and prop, and then weigh the outboard tip on a gram scale to see how much additional weight the outboard tip carries than the inboard. That, then, becomes the true tip weight.

We trim our planes to give solid pull on the lines in all areas of the circle. Others may trim for the plane to fly considerably lighter on the lines, which could affect the amount of tip weight they are carrying. As such, I would be interested in finding out what amount of tip weight others are carrying on a fully trimmed out competition ship. I am not so much interested in the Flite Streaks as the Noblers and larger size planes that are fully trimmed out to the flyer's satisfaction, and which exhibit no "banging" in the corners. I would like for as many people to respond as possible by weighing the outboard tip as mentioned above, and giving the additional information needed to make it relevant. I will start the discussion by giving the current tip weights for Matt's last three ships, after they were trimmed out to our satisfaction.

Stuka 97: 575 square inches, 46 ounces flying weight, equal panel wings, flying on 67 feet of .015 lines, and powered by a modified 35 FP. 1.6 ounce tip weight.

Stuka 99: 630 square inches, 56 ounces flying weight, equal panel wings, flying on 68 feet of .018 lines, and powered by a modified Magnum .53. 2.46 ounces tip weight.

Stuka 2000: 690 square inches, 61 ounces flying weight, equal panel wings, flying on 68 feet of .018 lines, and powered by a .61 on a pipe. 2.78 ounces tip weight.

OK, your turn. What is your plane, and how much effective tip weight are you using?

>OK, your turn. What is
>your plane, and how much
>effective tip weight are you
>using?
>

OK. my two airplanes:
The Infinity is powered by a PA61, with a 58" span, 60.5 oz, 665 square inches, with a 1/8" wider outboard flap and a 5/8" of assymetry. I am carrying 7/8 of an oz. of effective tip weight (based on counterbalancing).
It flies on 63.5 foot (eyelet-to-eyelet) .018 stranded lines.

The Imitation XL is powered by an OS40VF, with a 55 3/4" span, 63 oz, 645 square inches, with equal-chord flaps with the outboard 1/4" longer span, and 1.5" of assymetry. I am carrying approximately 3/4 oz of tip weight.
It flies on 65 foot .018 lines.

Brett

OK, interesting. Two different degrees of assymetry, two different line lengths, but almost equal effective tip weights. The addition of assymetry would allow you to carry less tip weight and the additional outboard flap would allow you to carry more. (But Matthew's equal panel planes also feature the larger outboard flap.)

I know you like to fly a little lighter on the lines, so my next question to you would be how much do you attribute the lower tip weight to assymetry and how much to the fact that you like to fly lighter on the lines? I know one of the ways Matt increased the "pull" on the lines was to go to additional tip weight--especially with the latest plane.

>I know you like to fly
>a little lighter on the
>lines, so my next question
>to you would be how
>much do you attribute the
>lower tip weight to assymetry
>and how much to the
>fact that you like to
>fly lighter on the lines?

The assymetry is most of the difference. Your tipweights are in the ballpark of most other equal-span airplanes. For this sized airplane, 3 oz is not unusual.

If I add or remove any, it starts rolling in the direction you would think. I have to remove some in low-air-density, and add some in high-air-density situations. It's my guess that this is the result of the symmetrical tail problem mentioned elsewhere.

I would also point out that the yaw trim has a pretty big effect on the amount of allowable tipweight. I think mine is pretty much tangent.

> I know one of
>the ways Matt increased the
>"pull" on the lines was
>to go to additional tip
>weight--especially with the latest plane.

That is a time-honored way of getting more tension, with the expected compromises. It's been my experience that my line tension is in the range of most other top airplanes I've flown. I have a big advantage in that area - I've flown pretty much every airplane Ted and David have built since about 88.

Brett, Len

I guess that I'm a tweener. My effective tip weight on the Intrepid that creates enough line tension and does not cause tip banging is 1.45 ounces. Wing assemerty is 3/4".

The difference here is probably assemetry and the amount of line tension that you desire (expect). Matt flew John Sunderland's plane, and although it flew good and he was comfortable with it, he would opt for more line tension. John flew Matt's plane in return and said it pulled like a freight train. We like that additional pull on the lines and set our planes up for it. Again, it isindividual choice and that was the purpose of this thread. I am still curious as to the amount of tip weigh others are using. Anybody?

What is the effective weight of a large dried-out tube of Ambroid, wrapped around a Ringmaster spar? That's about what I use...

Seriously...the weights so far suggested in the thread generally seem to come out on the high side for a number of applications (equal spans, unequal spans, etc). How do these numbers match the old rule of balancing wht weight of the lines?

When we moved from .015 size lines to .018 size lines, we not only had to add tip weight (more line weight), but we had to move the position of the leadouts farther back (more line drag). In our case line length (68 feet) and lap speeds (around 5.3 seconds) remained essentially the same, so the difference was mostly in the size of the lines themselves. The idea of simply balancing half the weight of the lines goes out the window, however, when one is adjusting for the amount of "pull" he (or she) desires on the lines and when one is adding flap area to the outboard flap, as is becoming more and more a common practice.

>What is the effective weight of
>a large dried-out tube of
>Ambroid, wrapped around a Ringmaster
>spar? That's about what I
>use...

It's the perfect amount. They wouldn't show it on the plans if it wasn't just right, now would they?

>Seriously...the weights so far suggested in
>the thread generally seem
>to come out on the
>high side for a number
>of applications (equal spans, unequal
>spans, etc). How do these
>numbers match the old rule
>of balancing wht weight of
>the lines?

The weight of the lines is not the only factor. What it's for is to balance the other rolling forces of line load and aerodynamics. It's far, far more complex than just a dead weight.

The lines are far from a dead weight. The actual load they apply is nothing like a simple f=ma. The actuall load they apply is related to the weight, but is also related to the line tension, and is far from a constant over time.

The aerodynamic imbalance is an even more complex. We've already talked about the speed differential/assymetry effects a little, but the fore-aft leadout location is also a complicating factor. For instance, if you trim to a bit of outboard yaw, you can stand less tip weight than if you trim tangent or yawed in. The mere fact it's yawed outboard will cause it to also roll outbard-wing-down, which will lead to taking out tip weight. Once you start getting transient in maneuvers from yaw jerks (caused by playing the leadouts off against the aerodynamic yaw, or GP, or differential drag, non-diagonal inertia tensor, etc, etc, etc).

The dynamics of these motions is *extremely* complex - far more so than most real aircraft or spacecraft. That's why you never really finish trimming.

Impact's carry from 16 to 28 grams of tip weight. I trim for NO tip "banging" (roll) at any time.

>Impact's carry from 16 to 28
>grams of tip weight.
>I trim for NO tip
>"banging" (roll) at any time.

Paul, just out of curiosity, what sort of line tension do you have (B17 excluded, of course)?

Nothing significant. A few years ago at the Clovis contest, I flew David's plane and it had more line tension than mine. It always seemed yawed out to me. Later I flew Howard's first Impact, and it did have slightly less line tension (than David's), but it maintained it better throughout. I guess I have gotten too pickey lately, but I can't stand tip banging or yaw out anymore. It is one of those things that just gets under my skin and bothers me until it is gone. My problem only.

Would assymetry have anything to do with this? Al Rabe 20 years ago (or more) convinced me to drop assymetry and we have been flying with equal panel wings ever since. This is why Matt's plane has a lot more tip weight than either yours or Brett's (or Dave's or Ted's) but at the same time it has solid line tension (after finally figuring out the pipe/engine/prop combination) all around. And yet there is no yawing out and no banging in the corners that he nor I can see (we can't notice any from the inside nor the outside of the circle.)

I know the theory of assymetry (inboard wing flys slower than outboard so develops less lift), but up on top assymetry does nothing while extra tip weight still helps. When you start the square loop and climb straight up, assymetry does nothing, while extra tip weight is still working for you. When you start the wingover, assymetry does nothing. When you come out of the clover straight into the wind, assymetry does nothing. Assymetry works when the plane is flying straight and level. When you are flying straight up, straight down, or overhead, its affect is non existant. But in all these the tip weight is still working for you. I, thus, believe that an equal panel wing can be trimmed to give more tension all around with the use of proper tip weight (and a slightly larger outboard flap) than a plane with unequal panels trying to balance the plane with a larger inboard wing and less tip weight.

Your turn. Paul? Brett? Ted? Anyone?

A real beginner here...

But I would agree about equal panel wings. My Jamison is equal panel, and needed a fair amount of tip Wt. (1.1) Oz (36Oz plane total Wt) compared to say... an AA Sr. (.60 oz) (28Oz plane total Wt) Line tension is very consistent on the Jamison, all over. Wing doesn't snap. I was told some weight below the vertical CG is said to help that snap as well, so I added wheel pants right off. Since I didn't fly it without, I can't verify that theory, other that to say, I don't have the problem.

Neat topic
Eric

At this point you are talking about the vertical center of gravity, and that almost starts another topic. This should be balanced--neither too much or too little above or below the point where the leadouts exit. The way to check that is to hang the plane by the leadouts. Then hang a string with a small weight in front of the plane (or have someone else hold both.) Then check to see if the plane is hanging in line with the string. If it leans away from the wheels, you have too much weight on the bottom. If it leans towards the wheels, you need more weight on the bottom. One could, also, move the leadouts up or down a bit at the wing tip to compensate for any imbalance, but this becomes more difficult if you have already installed an adjustable leatout guide.

Right on Leonard. That was the same explanation I was given. With the addition, that low wing airplanes like the Jamison usually could stand more than usual weight offset below the VCG to kind of put the wing back in the middle of VCG, and that this would help keep a what was once a top heavy airplane from the tendency of "snapping a wing" on insides quite so much. (Centrifucal force tipping the top heavy bit outside the circle to snap outboard wing down on a hard inside turn?) Am I on track here?
Eric

>Right on Leonard. That was the
>same explanation I was given.
>With the addition, that low
>wing airplanes like the Jamison
>usually could stand more than
>usual weight offset below the
>VCG to kind of put
>the wing back in the
>middle of VCG, and that
>this would help keep a
>what was once a top
>heavy airplane from the tendency
>of "snapping a wing" on
>insides quite so much. (Centrifucal
>force tipping the top heavy
>bit outside the circle to
>snap outboard wing down on
>a hard inside turn?)
>Am I on track here?
>
>Eric

Centrigrugal force on a top heavy plane would make it lean out while flying upright, and lean in while inverted. It may not make the tip dip, as such, in the bottom corners any more than it already was, but it would cause a lot of "squirrelies", especially at the intersections and in the outsides. You can twist the flaps a little to compensate some, but it will never truly fly correctly without getting that vertical CG correct.

We originally designed our "Das Stunter" design to be built with the option of upright or inverted engine. We built prototypes of both versions. Trouble was, since it was built with the engine thrustline in line with the wing and stabilizer, the upright engine version worked fine, but the inverted version had too much weight below (the opposite of what you were talking about.) We, therefore, abandoned the inverted engine option and it was kitted as a desig for upright engines, only (which was best for beginners anyway.)

>Would assymetry have anything to do
>with this? Al Rabe
>20 years ago (or more)
>convinced me to drop assymetry
>and we have been flying
>with equal panel wings ever
>since. This is why
>Matt's plane has a lot
>more tip weight than either
>yours or Brett's (or Dave's
>or Ted's) but at the
>same time it has solid
>line tension (after finally figuring
>out the pipe/engine/prop combination) all
>around. And yet there
>is no yawing out and
>no banging in the corners
>that he nor I can
>see (we can't notice any
>from the inside nor the
>outside of the circle.)

It's a matter of degree, of course. I suggest that you might want be a little more critical. Seeing this from the outside, particularly, is a pretty difficult task. If you can manage it, I reiterate my suggestion that you get in touch with some more experienced pilots/trimmers to give a second set of eyes.

>I know the theory of assymetry
>(inboard wing flys slower than
>outboard so develops less lift),
>but up on top assymetry
>does nothing while extra tip
>weight still helps. When
>you start the square loop
>and climb straight up, assymetry
>does nothing, while extra tip
>weight is still working for
>you. When you start
>the wingover, assymetry does nothing.
> When you come out
>of the clover straight into
>the wind, assymetry does nothing.
> Assymetry works when the
>plane is flying straight and
>level. When you are
>flying straight up, straight down,
>or overhead, its affect is
>non existant. But in
>all these the tip weight
>is still working for you.

I don't think that's right. Why is assymetry not doing anything overhead? You're still flying in a circle, and drag of equal-span wings will yaw the airplane out due to the extra speed of the outboard even at 0 g's. This will give you more tension in some cases, less in others, but it's one example of those compromises that I was talking about. Tip weight means nothing when you are flying at 0g's.
As soon as you begin maneuvering, the lateral position of the CP and CG will be just as important as any other time, and much more than level flight.

Additional tip weight (or differential lift) causes more line tension by rolling the model to direct the lift vector outboard. I am not alone in suggesting that rolling the model outboard is not what you want for top compeition, mostly because it has to switch directions when you go from inboard to outside, causing a lot of jerking in the lines and driving the coupled roll/yaw into oscillations. This makes the corners harder to control, just like excessive prop diameter. It's a compromise, but in my opinion, you get a net better system by balancing the aerodynamic differential with aerodynamics.

When it comes to line tension, "more" is not necessarily "better", particularly when it causes other problems.

One thing that we are not doing with assymetry is also making the tail assymetrical, which is what I suspect leads us to oversized outboard flaps.

> I, thus, believe that
>an equal panel wing can
>be trimmed to give more
>tension all around with the
>use of proper tip weight
>(and a slightly larger outboard
>flap) than a plane with
>unequal panels trying to balance
>the plane with a larger
>inboard wing and less tip
>weight.

The speed differential that lead us originally to assymetry is still in effect at any time we are flying in a circle. It's my opinion that any time you want tension you would ideally have assymetry. Having said all that, it can be trimmed to an acceptable level for most competition either way.

In a broader sense, it's very tempting to attribute differences in flight characteristics to design issues like assymetry, when in fact these factors are *almost always* overridden by building inaccuracies, variable structural characteristics, and tiny detail differences that we aren't aware of, and trim. How many green box Noblers have been built over the years, and how many flew identically? Not many. Even top builders rarely have 100% repeatable results. Paul can give you examples, but if Paul (whos know to be among the most accuracte builders around) can build 3-4 "identical" Impacts with noticably different characteritics, it tells you that there's something else going on that's a lot more dominant.

The compensation for vertical CG, at least on reasonably normal models. is a classic example. Some designs lift the leadouts 1/8" above the wing centerline to "compensate" for the CG position. The angular correction involved is tan(1/8"/31") or a whopping .23 degrees. Is it theoretically correct? Probably. Does anyone honestly believe that they trim their models to within 1/4 degree in roll at all times? Does anyone think they can tell?

Back on the original subject, I can easily trim my airplane for more line tension, and give up some very small handling difficulties. It's my goal to eliminate the small handling difficulties, because I get adequate tension in that configuration, and the handling quirks make it a lot harder to fly consistently. Others have different plans, but between actual experience and other's comparisons, I have found that almost all consistently competitive pilots (maybe excluding Windy, who runs a tremendous amount of tension with the visible compromises) optimize the controllablility, and use whatever line tension they get as a result.

>Nothing significant. A few years
>ago at the Clovis contest,
>I flew David's plane and
>it had more line tension
>than mine. It always
>seemed yawed out to me.
> Later I flew Howard's
>first Impact, and it did
>have slightly less line tension
>(than David's), but it maintained
>it better throughout.

Just for comparison sake, my line tension is typically a bit less than David and significantly less than Ted. My maneuvering loads are a lot less than all the Trivial Pursuits (and it's innumerable psedonym's). I think Ted's and David's are in the ball park with most competitive guys today, except for Windy, who's airplanes reportedly pull like tractors.

> I
>guess I have gotten too
>pickey lately, but I can't
>stand tip banging or yaw
>out anymore. It is
>one of those things that
>just gets under my skin
>and bothers me until it
>is gone. My problem
>only.

Not at all! It simply can't fly the airplane at all with any yaw motion, and can stand only a little rolling. What is remarkable to me is that some very skilled pilots can't even see it directly.

Part of the the sensitivity to yaw is a function of the airplane design. For instance, some of the Trivial Pursuits (Ted's cream original, and David's foam version) have a bunch of built-in rudder offset, and they yaw around quite a bit. But the side area is small compared to your's and mine, and it's pretty evenly distributed fore-and-aft. As a result, they can yaw around without too much dramatic yanks in the lines or cross-coupling. It's kind of like a combat plane in that respect. If my airplane did that much yawing, it would probably either yank the handle out of my hand, or do St. Vitus' dance in roll and yaw, or both. I suspect the Impact is much closer to mine than to Ted's.

I can live with a little bit of roll sometimes, but usually don't for long. I think my trim is a little more robust than yours. As you've noted in the past, I only rarely have to change anything on the airplane unless I change something in the engine. No more than I fly, I couldn't afford to not have it close when I started. I also no doubt give up something as a result.

I remember watching you and Don out practicing at the 93 NATS, and you were complaining about some trim issue, and wanted to change the tip weight. You pulled out a little sliver of lead so small that I would have just thrown it away, and stuck it in there. Couldn't have been 1/8 oz. I didn't say anything, but I thought to myself that "that's absurd, that little bit's not going to do anything on a 63 oz airplane". Then you flew it and it was dramatically different, even from the outside. Now that's a sensitive airplane!