F3J ballasting tips

[Gary B]

Realising that the top guys might not want to give any secrets away are there any rules of thumb or tips for ballasting?!!

 

All I have is the reasonable advice from George Stringwell's excellent 'Thermal Soaring' book to raise the wing loading by 1 ounce per square foot for every 3 mph wind above calm.

 

On the first day of Radioglide F3J (Sunday) I was flying a very light glider and did badly with it, I got the impression that the wing wasn't 'working' but it could have been down totally to my ineptitude on the sticks!!

 

Ballasting for model gliders seems to be more about the ability to penetrate in to wind where it is used in full-size gliders to improve the glide ratio at higher cross country speeds used when thermals are strong.

 

Cheers

 

Gary

 

 

[EssexBOF]

Tend to agree with Pete on this. George Stringwells book was written some time ago now think the late 70s/80s, when things were different. Built up wings no 4 servo wings and the sections E193 etc were thicker and more draggy.

Some 3 years ago I built a new wing for my 2 metre Watts Up electric glider, after not having great success with it at the Nats in 2010 when the usual Nats weather of wind and occasional rain, ment even with ballast it did not perform well.

So I built a new all sheet covered wing with the section thinned down from MH32 to MH30. Fitted with full crow breaking which allows camber change the model was a revelation when flown in wind, which was just as well as the following year at Cottesmore, the wind was blowing at 25mph, but I flew it with no ballast, just using the camber change to penetrate or soar.

It will also perform in light wing conditions where there is thermal activity only losing out where there is little if any.

That said when flying in Portugal recently, Richard Frederick flying a Pike Perfect was flying with 500grams of ballast and said he can increase this to 650 grams and the model performed well, with wind speeds of 22 knots

Brian

Barcs 230

[Peter]

First rule of ballasting is that there are no rules!

 

Just remember the old adage 'ballast to the strength of the lift and not to the strength of the wind'

 

RG day 1 had light winds but strong lift (and sink) so there was no point in using a light plane because you needed to be able to move around the sky quickly to find the right bits to fly in. Modern wing sections are much thinner than in George Stringwells days and have camber changing ability so have a much greater speed range compared to the good old E193 but the wing loading of modern moulded models is also much lighter than the 'holy grail' of 8oz/sq ft of yesteryear so ballasting is still necessary to move fast without excessive height loss.

 

RG day 2 was very windy and ballast was necessary just to penetrate but there was also strong lilt (well sometimes!) and that had to be followed downwind with the ability to return back upwind. If there had been no lift then the minimum ballast just to penetrate would have been the correct choice. As it was with strong thermals the ability to follow a thermal downwind and return back required lots of lead.

 

Mind you if you got it wrong you were on the ground very quickly - lots of time for a re-flight!

 

Peter

[satinet]

Hi Gary

 

My basic rule when flying in higher windspeeds ALWAYS was/IS NOT to add ballast but to fly my heavier back-up model with a thinner wing section AND with better penetration instead

IMO Ballasting is for increased performance in disciplines such as F3F, no amount of ballast can "cure" a poor lift situation, in F3F more weight plus good lift equals more speed, not better penetration, that is ultimately limited by the design of the model

IMO ballasting-up thermal soarers ruins their "feel" in the air it is FAR better to change models to one that better suits the conditions

For me, that's why we had a spare in the first place - not to replace a broken one but to provide an alternative that better suited the conditions

 

Hope this helps

 

Pete

BARCS1702

That is based on two pretty big assumptions though - 1) that you have a heavier backup model. 2) that the model you use "normally" doesn't have a thin wing section already (unlikely).

 

What modern f3j soarer has a thick wing section? You would have to take your f3j pretty seriously to have a backup model specifically for heavy air. Not a bad idea, but probably doesn't apply to most of us. 

 

Penetration is a pretty wooly word used to describe the speed models fly through head wind (a ground factor obviously). Adding ballast increases the speed at which the model flies at its best glide ratio - ergo it "penetrates" better.

 

  I think it's rather contradicatory to say have a heavy backup model but not use a lighter model with ballast when the two basically add up to the same thing. Like I say bearing in mind that there are no current f3j models specifically designed for high winds from an aerodynamic perspective, that I am aware of.  If your wing can't structurally take the load then yes maybe a heavier layup is the order of the day.

 

Personally I don't feel like adding 300g say to a 3.5m+ model is going to have a drastic effect on its ability to stay up for 10 minutes. It's a really small increase in wing loading. Even 650 grams on a pike perfection probably isn't more than a couple of ounce increase in the wing loading.

 

By the rule of 1ounce per 3mph you would have to increase the wing loading from say 8oz to 15oz in a 21mph wind.  How many f3j models have enough ballast to double weight of the model!?

 

Ballast certainly is a tricky one, no doubt.  It's hard to predict the lift and the wind. I guess that is what flying is all about.

[Gary B]

I suspected that there would be differing thoughts!!

 

I realise George Stringwell's book is very old and applies to 'floaters', I don't bother ballasting my classic gliders, if it's windy I don't fly them! At 20 mph he suggests increasing the wing loading by 5 ounces per square foot.

 

I do have a choice of two heavier back up models and my plan was to swap between the light and heavy gliders to save messing about with ballast but it seems like the light glider is a tad too light if there is some wind (like RG day 1). I will shortly have ballast for the light glider so I can experiment at my home field.

 

My full size glider (a Schempp Hirth Mini Nimbus) could carry 125 litres of water in the wings on a good day, it did calm the bouncy handling down, made it a bit ponderous in roll and went like a rocket in a straight line. The latest big span ships carry enormous amounts that give the tugs a hard time, I've been on the other end of the tow rope and the low climb rate does make you sweat a bit! 

 

The amount of ballast carried was based on the predicted thermal strength and some guess work, better into wind penetration was an added bonus. 

 

Looks like a lovely day, think I'll go out and bungee my Veron Vortex!!

 

 Cheers

 

   Gary

[satinet]

I  must admit I don't really understand f3j ballast strategy. To me if you add say 150g to a 4m model the change seems incredibly small.

[ThermalBoy]

Ballasting for F3J is something of a black art and everyone seems to have their own prefered approach.

 

Ballasting isn't just about increasing penetration though. Often pilots will put a small amount of ballast in just to improve how the model handles.Yes, ballast really can improve the feel/handling of models in certain conditions/circumstances. Primarily it can be used to dampen/smooth out the models response to inputs and prevailing conditions. Smooth/Precise flying is often the difference between staying up or landing.

 

For me personally its really important to be able to move around the sky quickly and efficiently,  inparticular I need to be sure that I can get back to the field when I have travelled a long way downwind with a thermal. If you dont make it back welcome to the big zero for that flight, game over. As to how much to use in really windy weather like Monday at RadioGlide. All I can say is that I couldn't get any more in but the conditions overall meant that allthough it was very windy it was condusive to finding decent lift.

 

I am currently sorting out my new 4m Maxa's. Part of the testing program was to see how they perform in windy weather fully ballasted. Que, lack of wind of course! We decided however to fill the things up with full ballast (approx 800g) and put them up on the winch in fairly calm conditions just to see how they felt. The big surprise was that despite this big increase in overall weight they still handled well and could thermal out from very light lift extremely well.

 

In summary the right ballast solution is always going to be the one that best suits your flying style, comfort levels and the plane you are using. Try using different amounts in different conditions to see what suits you and the model best and take notes of the wind strength vs ballast used and what the conditions were like. That way, in the future you take a lot of the guesswork out of the "How much ballast to use" question.

 

Colin

[Gary B]

Thanks Colin, I think you got it there.

 

I was flying my Xplorer at 2.4 kg on Monday and it was just holding station, I should have tried it on Sunday as well, probably would have done better.

 

Got a few weeks to practise and tweak things before Interglide, see ya there.

[satinet]

what were the old skool 3m model like from back in the "day"?

 

I just wonder how things were when models were a lot heavier and a lot smaller. I guess they also had wing sections that were less good at moving around the sky. As a newcomer I kind of find it surprising that everything seems to be about weight when people are talking about f3j models. 

 

My X2 has a 3.8m wing with a fair bit of camber and not much weight in it (about 1900g).  I was surprised that it moved the around the sky pretty well, although I have only flown it on a low wind day and not in hooley.  I did find with the X2 that it sinks a lot more slowly than models I am used to (f3f/f3b) when not in lift. How much is down to the design and how much is the weight,  I don't know.

[satinet]

I think Gary's post says that he was flying at Radio Glide just gone.

 

I don't think it is all about glide ratio in f3j and not slow sinking.  Otherwise the models would not be so light (and getting lighter) and the designs would be more biased towards having a fast L/D (i.e like an f3b model). 

 

I think with a full house model you can trim for best L/D and minimum sink - i.e by using flight phases and camber settings.  I honestly don't see how you can fly around in min sink mode all the time in a 20mph wind regardless of the era your glider was designed in.  I don't really see why using ballast to increase the weight of a given model is a bad thing. 

[satinet]

I know what min sink and best l/d are Pete. Are you seriously thinking I don't . My point was you can trim for both with flight phases. It's hardly a choice of one or the other. I don't think most people do their actual thermal turns at min sink speed.

I still don't understand why flying a heavier model is okay but using ballast is not.

[satinet]

Hi Tom

 

It's probably that I'm not explaining myself properly

 

Trimming for glide angle means trimming for the greatest distance you can acheive for your model considering its total weight and its span

Modern models are getting lighter because total weight effectively  establishes its potential power to weight ratio i.e how much it will sink because of its weight in dead air ( not in lift or sink) given the efficiency of the wing section in providing best lift/drag performance

 

With  min sink you are trying to stay up as long as possible more or less in one place, its akin to hovering flight

 

Glide angle is trimming in such a way as to minimise the height lost in order to cover the greatest distance (thus enabling a larger search area for the good air you are looking for) 

 

Is that a better explanation?

 

Ballast would increase the model's total weight which would in turn affect the model's performance potential in such a way as to decrease its ability to cover greater distance given that it's span and the efficiency of the wing  is/are effectively a constant

 

So, good for F3F but not for F3J........

 

Sorry if that doesn't explain what I mean

 

Pete

BARCS1702

 

Sorry that is not right.   Ballast doesn't decrease your ability to cover distance at all. What would be the point of that. In f3b distance where the whole object of the excercise is to cover distance we use a lot of ballast. Typcially I was flying over 1kg of ballast last season in distance. 

 

here is an interesting interview with serveral f3j world champions. Note their thoughts on ballast (they all use it).

http://www.modelaviation.com/rcsoaring-jan2013

[Gary B]

Interesting interview, will have to read it in more detail!!

 

It seems to me that there are two reasons for using ballast in model gliders, the first is for more efficient travelling between thermals and the second is being able to hold station into wind or return from downwind which is not a consideration for full-size gliders. George Stringwell bases his ballasting section only on the second consideration.

 

I have uploaded a polar curve diagram diagram as it might help visualise things, unfortunately it is a single curve for a hypothetical unflapped glider, there would be many more curves for different flap settings and wing loadings (ballast).  

 

Point A is the stalling speed 

 

Point B is the minimum sink speed, flying slower than this is inefficient. In full-size gliders we do thermal at this speed, just above the stall, in turbulent conditions we would fly a bit faster for control. With a model we fly a bit faster as well as the cost in height of an accidental stall outweighs the slight loss of flying at a higher speed (something I need to remind myself!!)

 

Point C is the best glide angle speed.

 

At speeds above best glide the curve drops away sharply and the glide angle penalty for not carrying ballast is high.

 

With ballast onboard (increased wing loading) all the three points move to the right, increased stall speed, increased min sink speed and increased best glide angle speed. The practical effect is to increase the thermalling speed (typically from 45 knots to 50 or 55 knots) and to increase the best glide speed (Mini Nimbus best glide was 40:1 at 60 knots, with water onboard this went up to 75 to 80 knots).

 

Flaps modify the curve in two ways, positive flap reduces the min sink rate airspeed and stalling speed, negative flap (reflex) flattens out the curve at higher speeds typically needed between thermals. Out of interest the flap settings on the Mini Nimbus were '0' degrees for cruise/best glide, +6 for weak or turbulent thermal circling and +10 for strong thermals (this was too much and they reduced it to +8 on later ones). The negative flap settings were -4 and -7. Exactly which flap to use was marked on the airspeed indicator, cross country flying was a two handed job, right hand on the stick controlling the speed and left hand on the flap lever pumping the flaps up and down. 

 

GB

 

[thermaldoctor]

Nice article Tom. An interesting read.

 

Benny has to make you laugh though but that's just how he is. He turned up well after everyone else in South Africa, didn't do any macho hand throwing and soaring away or even practice flights I don't think. He spent a lot of time sleeping and didn't even bother to fly the pre-contest either. 

 

Then he went and won the whole thing. And also won in 2008 and was runner up in 2010. I think he does a bit more practice and flying than he lets on but the majority of his success is mostly down to absolute pure talent and understanding.

 

Also notice there is not one defined answer on the best ballast solution for F3j 

[satinet]

Nice article Tom. An interesting read.

 

Benny has to make you laugh though but that's just how he is. He turned up well after everyone else in South Africa, didn't do any macho hand throwing and soaring away or even practice flights I don't think. He spent a lot of time sleeping and didn't even bother to fly the pre-contest either. 

 

Then he went and won the whole thing. And also won in 2008 and was runner up in 2010. I think he does a bit more practice and flying than he lets on but the majority of his success is mostly down to absolute pure talent and understanding.

 

Also notice there is not one defined answer on the best ballast solution for F3j 

 

Reminds me of myself*........

 

*In the field of eating pies and drinking tea.

[Gary B]

Well...!!

 

Just flown Interglide, it was very windy on both days.

 

I chose to only fly my 3.5 Xplorer all weekend, its basic weight is 2.4 kg, wing loading of 10 oz sq ft and I can't put ballast in it.

 

At 20 knots plus wind speed at operating height it could just hold station with a couple of clicks of down in 'cruise' flap. Thermal flap had it going backwards and out of the standing lift.

 

Some pilots were penetrating forward and climbing better than me, they seemed to have longer wings. Quite wacky as the site is very flat but pushing forward seemed to work (Tywell is the same?!).

 

Tom mentioned ballasting light gliders earlier, I could have ballasted my Tragi higher than the Xplorer but might have lost the wings on the launch! My Xplorer must have been made from recycled F1 car tubs as it laughs at full power winch or pulley tows!

 

My Tragi is too light, I fly it with nine aluminium slugs in all the time now and it is much better.

 

My first experience with ballast was with a Middle Phase on Bishop Hill, Portmoak in Scotland, used a spark plug socket to fly in 40 mph wind. Not enough, I recovered the socket from the wreckage half a mile downwind!

 

 Great fun

 

   GB

[Austin]

I chose to only fly my 3.5 Xplorer all weekend, its basic weight is 2.4 kg, wing loading of 10 oz sq ft and I can't put ballast in it.

 

 

Gary, of course you can ballast the Xplorer, it will take another 600 grams with the standard brass bar??

[satinet]

Or 1.5 socket wrenches.

You're better off buying a 3kg f3j glider though obviously. ;)

[Austin]

How does 1.5 socket wrenches work, do you mean a long bar of something?

 

Gary's model used to be mine and it was specially made by NAN, triple carbon wing and can take any wind. If its 2.4 without ballast you can get it to 3kg with, so unless its over the legal wind limit the model is going to be spot on for those conditions.

[satinet]

I was just joking Austin.