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Old Oct 07, 2012, 05:38 PM
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Help!
Ballast for a 2m ship

Hi! What would be a good starting point for ballast for a 2m ship (Lil'Bird woodie) and 20 kph wind?

Thanx!

K.
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Old Oct 07, 2012, 09:25 PM
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How much does it weigh now?

My feeling is that it probably doesn't make sense to add less than, say, 20 percent of the total weight, since that only ups your speed by 10 percent or so.

If you can set up your ballast with crushable space in front of it, this may reduce stress on the rest of your airframe. For instance, if there's an open space under the wing, you can put in a piece of relatively stiff PE or EPP foam with a piece of lead in the middle. The lead can take an extra inch or two to come to a stop.
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Old Oct 08, 2012, 04:18 PM
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Thermal or slope? they are very very different.

20 kph = about 13 mph.

Assuming this is for thermal soaring, about 15 to 20% of the gliders weight would be a good starting point. You are trying to balance glider speed with sink rate to be able to get to th ethermals without losing too much altitude. So if the glider was 30 ounces, about 4.5-6 ounces. I have done 10% for lesser conditions but not always enough.

You could go up to 40%. After that I would wonder why you were flying that glider in that much wind for thermal soaring.

Now, on the slope it is a whole different thing. Lift is right there. you can jump in at higher levels and top out higher as long as you are able to land it safely. Adding weight means they land faster and perhps harder.
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Old Oct 08, 2012, 04:51 PM
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Looks like I should get a scale... I don't know how much the plane weighs... I fly on flat land, (desperately) looking for thermals.
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Old Oct 08, 2012, 06:38 PM
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Typical 2M gliders range from 25 to 35 ounces, so that is a big range. But adding ballast starting around 4 ounces and building up in 2 ounce increments can work well.

Best thing to do is pick a day when the wind will keep building.

Fly till you feel you want to try some ballast. Add 4 oz and see the difference.

Then add 6 oz. Then 8, ... till your ballast area is full.

Remember it MUST be centered on the CG. Mess up your CG and you could crash the plane especially if you accidentially shift it rearward.

This is very much a play with it thing. Ballast to taste. I might like 4 oz and you might prefer 8.

On my 3M thermal duration contest gliders I have 2-3 ballast sets prepared so I can add what I think I need. But I typically start around 8.5 ounces on a 60 ounce glider. That is about 15%. my top ballast is around 14 oz or about 25%. I typically don't go higher than that, but some people do. That would carry me into about 20 to 25 mph winds, about 40 kph. However note that that is a molded full house glider with camber and reflex capabilities. It is easier for me to compensate for wind with those controls. A R/E glider only has ballast and elevator trim to help it in the wind.
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Old Oct 08, 2012, 07:20 PM
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The ballast guidelines I learned about use increased wing loading as the measure; not percent of AUW. (for open frame wood construction and flat land thermaling) I suppose it's all just arithmetic.

Although there are lots of variables, my flying coach suggested that 2 ounces per square foot should be enough to make a difference. Adding or removing ballast in one ounce per square foot increments should show the improvement or lack of improvement.

He also said that only weenies who can't fly in the wind use ballast.

Sincerely,
Oscar Meyer
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Old Oct 08, 2012, 11:27 PM
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Quote:
Originally Posted by Riserflier View Post
The ballast guidelines I learned about use increased wing loading as the measure; not percent of AUW. (for open frame wood construction and flat land thermaling) I suppose it's all just arithmetic.

Although there are lots of variables, my flying coach suggested that 2 ounces per square foot should be enough to make a difference. Adding or removing ballast in one ounce per square foot increments should show the improvement or lack of improvement.

He also said that only weenies who can't fly in the wind use ballast.

Sincerely,
Oscar Meyer
I have heard the 2 oz/sq ft rule. That must have been in the day of lead sleds. when wing loading was 12 oz/sq ft and higher.

2 oz on my AVA (about 5.5 oz wing loading) would take about a 35% ballasting or about 16 ounces. I can't even get that into the ballast tube. Max on my AVA is about 12.5 oz. More often I add about 4-6.

2 oz on my Supra would be about 25% ballasting or about 14 oz. That is what I put in in extreme conditions. 6-8 is a more typical starting point. 14 oz is only for the worst wind conditions. I can get up to 35 oz into the Supra's ballast tube but would never load it up that much for thermal soaring. I tried it once, and it flew but it came down pretty fast. But wind didn't bother it at all. On the other hand if you want to fly the Supra on the slope with some high speed, 35 oz might be awesome.

And then there are my DLGs. To go up 2 oz wing loading would mean about 50% ballasting. That ain't gonna happen ever.

That is why I express ballasting as a % of AU weight which also directly translates to % wing loading. Using % of AU weight, the rules carry across all gliders of all sizes and all wing loadings.
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Old Oct 09, 2012, 02:57 PM
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Quote:
Originally Posted by aeajr View Post
I have heard the 2 oz/sq ft rule. That must have been in the day of lead sleds. when wing loading was 12 oz/sq ft and higher.
Ah yes, those old days, walking uphill to school barefoot, in 6 feet of snow,carrying a Windsong and a winch on my back to fly at recess! Seriously, I don't seem to recall much that was above 12oz loading or so. Most was less. But at 12 oz. on a day when the wind was blowing, you'd probably only barely notice an additional 2 ounces if you were alert. I found an additional 8 or 9 oz. very nice on my Easy Glider, which would have been about 2 oz/square foot.

OTOH, I did test fly a European glider for a guy in our club. It was a Robbe or Graupner or something, that had a 16 oz. loading. But I'm thinking that must have been for slope.
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Originally Posted by aeajr View Post
2 oz on my AVA (about 5.5 oz wing loading) would take about a 35% ballasting or about 16 ounces. I can't even get that into the ballast tube. Max on my AVA is about 12.5 oz. More often I add about 4-6.
I made a bigger tube for mine, just for that reason. Used to carry 4 oz. or so even in light air because I liked the way it handled better.
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Originally Posted by aeajr View Post
2 oz on my Supra would be about 25% ballasting or about 14 oz. That is what I put in in extreme conditions. 6-8 is a more typical starting point. 14 oz is only for the worst wind conditions. I can get up to 35 oz into the Supra's ballast tube but would never load it up that much for thermal soaring. I tried it once, and it flew but it came down pretty fast. But wind didn't bother it at all. On the other hand if you want to fly the Supra on the slope with some high speed, 35 oz might be awesome.
I know it seems like it's coming down pretty fast, but if you double the loading, you only come down maybe 40 percent faster. Probably a bit less because of the better Reynolds numbers. On the other hand, your turns will be twice as wide, and your mistakes will cost a whole lot more. Not entirely sure if that's two or four times as much height. I'm guessing the latter. I suspect that the latter two problems are the real issue. Except when you land and you have to dissipate 4 times as much energy!
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And then there are my DLGs. To go up 2 oz wing loading would mean about 50% ballasting. That ain't gonna happen ever.
Might make a whole lotta sense on a really windy day!
I used to put maybe a couple of bucks worth of pennies under the wing of a 2 meter I had. Maybe 20 ounces. Really helped with a flat bottom airfoil when the wind blew. I had another one that was 42 or 43 oz. to start with.
Quote:
Originally Posted by aeajr View Post
That is why I express ballasting as a % of AU weight which also directly translates to % wing loading. Using % of AU weight, the rules carry across all gliders of all sizes and all wing loadings.
Here, we can agree!
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