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Author Topic: How is Tip weight measured?  (Read 1511 times)

Offline kevin king

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How is Tip weight measured?
« on: April 04, 2022, 02:52:20 PM »
When i read that someone has 1 and a quarter ounce tip weight are they refering to the weight of the lead or the weight of the outboard wing measured with the plane on its back and a scale underneath the wing tip? It seems we should have a standard. Also how much do you lighten the outer wing tip block, as in how much should be carved out? I just dont want my wingtip weight box to break out of the tip when screwing the cover on, and it would seem to me the lead would put alot of stress on the wing tip as well when the plane is in flight.

Online Ken Culbertson

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Re: How is Tip weight measured?
« Reply #1 on: April 04, 2022, 04:33:49 PM »
When i read that someone has 1 and a quarter ounce tip weight are they refering to the weight of the lead or the weight of the outboard wing measured with the plane on its back and a scale underneath the wing tip? It seems we should have a standard. Also how much do you lighten the outer wing tip block, as in how much should be carved out? I just dont want my wingtip weight box to break out of the tip when screwing the cover on, and it would seem to me the lead would put alot of stress on the wing tip as well when the plane is in flight.
to answer two of your questions, it is the actual weight.  I have never heard it quoted any other way so I assume that would be the standard.  I do not hollow my outboard tip block and I use the heavier of the two on the outboard.  I never have nor have I ever seen a tip weight box come out.  I have seen clay fly off.

Ken
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Offline Dan McEntee

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Re: How is Tip weight measured?
« Reply #2 on: April 04, 2022, 04:44:20 PM »
When i read that someone has 1 and a quarter ounce tip weight are they refering to the weight of the lead or the weight of the outboard wing measured with the plane on its back and a scale underneath the wing tip? It seems we should have a standard. Also how much do you lighten the outer wing tip block, as in how much should be carved out? I just dont want my wingtip weight box to break out of the tip when screwing the cover on, and it would seem to me the lead would put alot of stress on the wing tip as well when the plane is in flight.

    The weight that is referred to is the weight of the lead or whatever you are using for tip weight. Some guys will just do a static balance of the model so the outboard wing tip is just a bit heavier than the inboard and it will drop when trying to balance the model laterally. Some will take the flying lines they will be using , coil them up and set them on the inboard tip, and then add weight to the outboard until it balances laterally. I usually put about 3/4 to 1 ounce in the outboard tip for initial flights and then adjust from there. Many guys weigh their ribs and such and put the heaviest ribs in the outboard wing when building, and the same with tip blocks. I don't like to get too carried away with that theory, as I have a couple of models hanging on the wall right now that have no tip weight in the outboard tip but have a 1/4 to 1/2 ounce on the inboard tip! I think it's best to have a sturdy box built into the wing, just inside of the outboard tip rib in front of the spar. Make it big enough to hold more weight than you think you will need just in case. I think 1/16" ply is more than good enough to build the box, and epoxy it to the spars and tip rib, and make the cover to contour with the airfoil. It will still function as it is supposed to and take any stress off the tip block. There have ben several other methods of installing tip weight used through the years, but I think this is the most simple and easiest to use.
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Offline kevin king

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Re: How is Tip weight measured?
« Reply #3 on: April 04, 2022, 05:14:59 PM »
Thanks for clarifying gents

Offline Tim Wescott

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Re: How is Tip weight measured?
« Reply #4 on: April 04, 2022, 05:15:45 PM »
I never have nor have I ever seen a tip weight box come out.  I have seen clay fly off.

Well, you just don't crash hard enough.

@Kevin: people are talking about the amount of weight that they've added to the outboard tip.

From experience, I put in "that's about right" tip weight in and then I go fly, adjusting the weight per Paul Walker's trim chart.  "That's about right" is whatever the plans say, or about 1 1/4 or 1 1/2 ounces for a "40 sized" stunter, less for smaller.  For that first flight more is better, but it's one of the first things that you want to start adjusting when you trim.  If you have equal or nearly equal span wings, the elaborate technique I've heard is to put your full line reel at half-span on the inboard wing, and an empty line real at half-span on the outboard wing, then put in tip weight until the plane balances in roll.  I think I'll stick with starting out heavy and doing short flights until it's right...
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Online Brett Buck

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Re: How is Tip weight measured?
« Reply #5 on: April 04, 2022, 08:14:29 PM »
When i read that someone has 1 and a quarter ounce tip weight are they refering to the weight of the lead or the weight of the outboard wing measured with the plane on its back and a scale underneath the wing tip? It seems we should have a standard. Also how much do you lighten the outer wing tip block, as in how much should be carved out? I just dont want my wingtip weight box to break out of the tip when screwing the cover on, and it would seem to me the lead would put alot of stress on the wing tip as well when the plane is in flight.

     Unfortunately the "standard" is how much you put in the box/tube. This generally means almost nothing because you have no idea how much lateral imbalance there is when you start.

   My suggested, quasi-meaningful suggestion is to, when you want to measure it, is to instead balance the airplane laterally with temporary weight on the inboard wing tip and measure that, i.e. counterbalance the airplane. This method allows a reasonably comparable measurement from airplane to airplane, because it includes the effect of any existing out-of-balance that might be present, like "heavy outboard panel" on purpose, the leadouts,  and the engine and tank on a profile.

    On my original Skyray 35, I had about 3/8 ounce in the tipweight box. When I counterbalanced the airplane, I had to stack 1.76 ounces of weight to balance. The difference - the tank and engine was all hanging out on the outboard side, and that had the effect of shifting the CG to the right.

    Brett

Online Brett Buck

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Re: How is Tip weight measured?
« Reply #6 on: April 04, 2022, 08:46:00 PM »
I never have nor have I ever seen a tip weight box come out.  I have seen clay fly off.

   Both my 1995 airplane and my 2006 airplane had multiple stress cracks around the tipweight box from hard maneuvering. On the 2006 airplane I had to cut off the wingtip and reinforce it. These appeared within 6 months. This from repeated 13-14 G corners and the weight of the box +~ 3/4 ounce of lead. The 2020 airplane has stub spars on the box and is glued firmly to the wingtip cap to help spread the load.

     You cannot underestimate the loads and the fatigue that you get over time with modern-quality cornering, almost everything tends to fatigue and break, particularly in the wing.

     Brett

Offline Matt Colan

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Re: How is Tip weight measured?
« Reply #7 on: April 04, 2022, 08:52:07 PM »
I have seen clay fly off.

Ken

Me too! Wonder who that happened to recently?  LL~
Matt Colan

Offline Matt Colan

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Re: How is Tip weight measured?
« Reply #8 on: April 04, 2022, 08:57:27 PM »
   Both my 1995 airplane and my 2006 airplane had multiple stress cracks around the tipweight box from hard maneuvering. On the 2006 airplane I had to cut off the wingtip and reinforce it. These appeared within 6 months. This from repeated 13-14 G corners and the weight of the box +~ 3/4 ounce of lead. The 2020 airplane has stub spars on the box and is glued firmly to the wingtip cap to help spread the load.

     You cannot underestimate the loads and the fatigue that you get over time with modern-quality cornering, almost everything tends to fatigue and break, particularly in the wing.

     Brett

This is really interesting. I have yet to have that happen and build pretty flimsy tip weight boxes. Ive always figured it’s not a structural piece so I put almost no effort into making them strong and just sandwich the box between the top half of the tip with a couple small scrap pieces of balsa and/or filed a notch in the top half of the tip for it to be CAed to
Matt Colan

Offline Dave Hull

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Re: How is Tip weight measured?
« Reply #9 on: April 04, 2022, 11:58:22 PM »
I watched an expert flyer "tuning up" for the summer season. He seemed pretty happy with the trim during his first flights, but as the day progressed he thought he was going backwards and would have to start trimming all over again. As he finished up the practice session and he was cleaning up his plane he noticed that the tip weight box lid was missing....

If you think something is getting worse, you might be right?

Offline Trostle

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Re: How is Tip weight measured?
« Reply #10 on: April 05, 2022, 12:11:43 AM »

I have seen clay fly off.

Ken

There is still a clump of clay underneath the outboard wing tip of the airplane that won the 1970 Nats/Walker Cup.  That airplane was built before I knew anything about tip weight boxes.

Keith
« Last Edit: April 05, 2022, 12:10:57 PM by Trostle »

Offline kevin king

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Re: How is Tip weight measured?
« Reply #11 on: April 05, 2022, 02:09:00 PM »
I watched an expert flyer "tuning up" for the summer season. He seemed pretty happy with the trim during his first flights, but as the day progressed he thought he was going backwards and would have to start trimming all over again. As he finished up the practice session and he was cleaning up his plane he noticed that the tip weight box lid was missing....

If you think something is getting worse, you might be right?
I always use clear packing tape over the wingtip weight box cover. Nobody wasnts to be hit by lead travelling at 60 mph 😁

Offline L0U CRANE

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Re: How is Tip weight measured?
« Reply #12 on: April 05, 2022, 02:35:12 PM »
My approach is sort of like Ty's in reply #3, just a bit more complicated.

Figuring the fuse centerline in level flight is just about the mid-point between inside and outside 'g' roll load variations, I 'static balance' the model about the centerline. full weight of lines, reel and clips, etc.  halfway from centerline to leadouts equals half the weight at full distance. (  (The flyer carries the other half of line weight in level flight). Brett and Howard both advise this isn't accurate - too many other conditions. I agree, but it seems a reasonable start point. Final trimming always follows in-flight flight observation. (At my 'humble' level, it's good enough) ...And there's no need to weigh anything.

How to do it? With he model upside down on a cushioned flat surface. Place the reel, with  flying lines and clips on it, on the inboard panel halfway from centerline to the leadouts. Balance the reel and clips weight with an empty identical reel plus clips the same distance out on the outboard panel. Add tipweight until 'balanced'. I put BBs in the weight box to find an approximate match.

This works well! For one very light profile, it actually found how much INBOARD tipweight it needed!
\BEST\LOU

Online Brett Buck

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Re: How is Tip weight measured?
« Reply #13 on: April 05, 2022, 03:59:05 PM »

This works well! For one very light profile, it actually found how much INBOARD tipweight it needed!

   Exactly. The Skyray - a pretty small airplane with a pretty heavy engine and muffler, and only 30 ounces total, ended up with about 1 full ounce worth of static imbalance with no tip weight at all. I don't intentionally build the outboard wing heavier (bad idea in general, since it also makes the outboard wing stiffer, unless you are careful) but even then, it has an entire ounce of built-in tipweight. Fortunately, it also has equal-span wings, which generally requires more tip weight so I ended up needing 1.75 ounces worth of lateral CG shift.  If it had an inch of asymmetry, I can easily imagine that I would have to have put at least some weight on the inboard tip, and I have seen that necessary on multiple occasions.

   Brett

Offline L0U CRANE

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Re: How is Tip weight measured?
« Reply #14 on: April 06, 2022, 01:36:00 PM »
... forgot to mention... I generally do this before finishing, while a tip-weight box is easily available. The difference, if any, in lateral weight caused by the finish is small.

I refer things to the fuselage centerline as it does several things: it is usually a 'keel' dividing airflow left and right of the line along which the mass of fuselage, engine and tailfeathers rest on wing lift.

And I use my early LINE* type program (or should I say 'APP' these days?) to estimate panel structural asymmetry for the dynamic conditions. Seems to work fairly well - I never saw "hinging" of a model built to it. Of course, my stuff was/is smaller and lighter, and I never cornered as violently as is now the rule.

Hoping my balance and other foot problems continue to improve. I'm still not confident about backing around in a small circle for about 8 minutes with a model trying to pull me off balance.
\BEST\LOU


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