HobbyKing.com New Products Flash Sale
Reply
Thread Tools
Old Dec 29, 2012, 08:31 PM
R2R
Registered User
R2R's Avatar
St Johns, FL, USA
Joined Nov 2009
608 Posts
Discussion
Ballast Use: How much do you use in what conditions and why?

I got the green light to attend a few nearby contests this winter and spring, so I spent some time over the last couple of days installing a ballast tube in my Sapphire and cutting some ballast rods. They are 5/8" diameter steel.

3 1/2" x 5 oz
5 7/8" x 8 oz
9 7/8" x 14
15 1/8" x 22 oz

The tube is rolled fiberglass with a blind nut epoxied to it and the aft-end sealed off. (Thanks to the personal stash of a great vendor/fellow RCG'er for that one and another one to be installed in my RES!! ) In the tail boom the tube is epoxied to the tail floor with a piece of foam wedged above and epoxied to tie everything in. At the forward end of the tube, it is glued to the hardwood dowel cross-brace on top and to a 1" diameter dowel that is glued to the fuse floor. The front of the dowel is also epoxied to my servo tray. A #6 screw will lock the ballast into place, screwing down into the blind nut into the dowel. The forecast is for 9MPH winds tomorrow, so I should get the chance to try out the lighter weights.

It was very timely receiving my Model Aviation this month. The excerpts on how the Masters use ballast was super interesting, especially JW's comments on Max LD to wind speed in marginal lift conditions and D.Hobby's comments. What I got out of it was that, both tune ballast using thermal activity as the overriding factor, while still keeping in mind wind speed. Seemed a little more concrete/systematic than what Dave Thornburg has captured in Old Buzzards.

I have never used ballast, so I can't offer any personal experience; how much do you all use for certain situations and why?

Allan
R2R is online now Find More Posts by R2R
Reply With Quote
Sign up now
to remove ads between posts
Old Dec 30, 2012, 07:20 AM
F3B
satinet's Avatar
Warwickshire, England
Joined Sep 2006
5,510 Posts
What's your glider like?

Ballast is realitive to the weight and characteristics of the model imho.
satinet is offline Find More Posts by satinet
Reply With Quote
Old Dec 30, 2012, 07:37 AM
R2R
Registered User
R2R's Avatar
St Johns, FL, USA
Joined Nov 2009
608 Posts
satinet,

It is 64.4 oz @ about 9.5 oz/sq-ft loading without ballast. SD7037 airfoil. 120" wingspan, fullhouse. I'm not sure what other characteristics ...
R2R is online now Find More Posts by R2R
Reply With Quote
Old Dec 30, 2012, 08:30 AM
F3B
satinet's Avatar
Warwickshire, England
Joined Sep 2006
5,510 Posts
sounds like a pretty floaty model.
Hard to say isn't it. try and bit and see how you go. A few ounces won't drastically effect the sink rate.
satinet is offline Find More Posts by satinet
Reply With Quote
Old Dec 30, 2012, 08:35 AM
Red Merle ALES
Curtis Suter's Avatar
United States, Mt, Helena
Joined Apr 2002
5,564 Posts
I have never flown that airfoil that light. I used to fly it at 12 oz sq/ft and it was great! Camber changing is real important with the SD7037 too. I can't wait for your test results.

Would you happen to have a small GPS receiver that can export NMEA data?
If you do and would like to accomplish some trailing edge L/D testing send me a PM.
The weather isn't conducive for me to accomplish that for a few months or more!

Curtis
Curtis Suter is offline Find More Posts by Curtis Suter
RCG Plus Member
Reply With Quote
Old Dec 30, 2012, 09:29 AM
R2R
Registered User
R2R's Avatar
St Johns, FL, USA
Joined Nov 2009
608 Posts
satinet, I will give it a try, hopefully this afternoon, when it warms up a bit outside! Thanks.

Curtis, I don't have a GPS receiver, but thanks for the offer! Didn't know people were flying the SD7037 at 12oz/sqft.
R2R is online now Find More Posts by R2R
Reply With Quote
Old Dec 30, 2012, 10:44 AM
Registered User
Joined Feb 2006
579 Posts
Quote:
Originally Posted by satinet View Post
sounds like a pretty floaty model.
Hard to say isn't it. try and bit and see how you go. A few ounces won't drastically effect the sink rate.
If the ballast is centered on the CG, there should be no need to change the elevator trim. Under those conditions, the plane will glide along essentially the same glide path independent of the weight of the plane. Increased ballast will result in increased speed down that glide slope. The L/D (lift/drag) will remain nearly the same.

Under the conditions described above, the speed of the plane will be proportional to the square root of the weight. Doubling the weight of a plane will increase the speed by 41% (sqrt(2)=1.414...). Adding 6 oz. of ballast to a 60-oz. plane will increase the speed by 5% (sqrt(1.1)=1.05...). Increased speed means both a higher horizontal speed and a higher vertical speed (rate of descent). If thermals are strong, the increased rate of descent isn't a problem. The increased horizontal speed means that it easier to find new thermals and also easier to come upwind to land.

Increased weight also means the plane will be tossed around less by wind gusts.
williamson is offline Find More Posts by williamson
Reply With Quote
Old Dec 30, 2012, 12:26 PM
Registered User
Joined Jan 2008
4,443 Posts
R2R:

I fly DLGs, and ballast is a big factor in those. How I use it is this way: when the turbulence makes the airplane difficult to control, I add ballast. It's not a function of wind speed, primarily.

The advantage of ballast is the higher speed at which the airplane will fly, for a given L/D (a lot of folks will climb all over this, but that's my point of view). The price of ballast is increased sink rate, which is sometimes a heavy price to pay in windy conditions when thermals may not be as strong.

I had a pair of Taboos a couple of years ago, and experimented with ballast quite a bit. They both weighed 8.7 ounces or so. I could easily load as much as five ounces of ballast, but not only did they fly faster, they also broke in less-than-perfect landings. I realized that three ounces was the practical limit - less might not make the airplane more manageable, more increased the probability of damage. I routinely flew those Taboos in winds approaching 20mph with two or three ounces of ballast. I fly a pair of Blaster 3s now, and have a 2-ounce ballast stick. They weigh right at 10 ounces, and simply don't need more.

It's a personal preference, but I install ballast so that the CG is unchanged. Makes it a lot easier to put in and take out - no requirement to re-trim for ballast.

Good luck, and have fun at the contest. That's the best place to learn.

Yours, Greg
glidermang is offline Find More Posts by glidermang
Reply With Quote
Old Dec 30, 2012, 01:36 PM
R2R
Registered User
R2R's Avatar
St Johns, FL, USA
Joined Nov 2009
608 Posts
williamson,

That looks like a nice formula for estimating speed gained by adding ballast. My ballast system is set up so that the CG doesn't change regardless of the amount added. Hopefully no trim adjustments will be needed.
R2R is online now Find More Posts by R2R
Reply With Quote
Old Dec 30, 2012, 01:48 PM
R2R
Registered User
R2R's Avatar
St Johns, FL, USA
Joined Nov 2009
608 Posts
Greg,
Interesting methods of deciding when and how much ballast. I can see the advantages of being more resistant to turbulence, in addition to better speed. Like you, my ballast system is set up so that the CG doesn't change regardless of the amount added.
R2R is online now Find More Posts by R2R
Reply With Quote
Old Jan 19, 2013, 11:29 PM
Proud member of LISF and ESL
LI, New York, USA
Joined Mar 2003
24,371 Posts
Supra - 8 to 14 ounces
Ava 9 to 12 oz
Radian - 4-6 ounces
Easy Glider 4-9 ounces
Spirit 4-12 ounces
aeajr is offline Find More Posts by aeajr
Reply With Quote
Old Jan 20, 2013, 06:41 PM
R2R
Registered User
R2R's Avatar
St Johns, FL, USA
Joined Nov 2009
608 Posts
Quote:
Originally Posted by aeajr View Post
Supra - 8 to 14 ounces
Ava 9 to 12 oz
Radian - 4-6 ounces
Easy Glider 4-9 ounces
Spirit 4-12 ounces
Thanks for posting, Ed. From the looks of your weights, I am probably fine with my first 3 sets of ballast (5-14 oz) and probably won't ever need the 22-oz setup.

I flew the 5-oz set last weekend. The wind was only about 5-9 mph and the lift was weak, but I wanted to get a feel for flying with the ballast. It was interesting to see the difference in speed in thermal turns and the momentum while landing. I would deploy flaps on final, and the plane's glide path/pitch was the same as without ballast, but the speed was higher and it just wanted to maintain the trajectory. I found that I have to flare earlier than usual -- took about three times to figure it out (yeah, I'm a little slow that way with piloting), one time flaring much too late and unintentionally dorking at about 30 degrees, tail stuck in the air, nose buried.
R2R is online now Find More Posts by R2R
Reply With Quote
Old Jan 20, 2013, 06:53 PM
Proud member of LISF and ESL
LI, New York, USA
Joined Mar 2003
24,371 Posts
Dependng on the plane I would typically not put ballast in till we are around 10 mph for the light ballast and build up from there.

Ava, Radian maybe a little sooner.
aeajr is offline Find More Posts by aeajr
Reply With Quote
Old Jan 20, 2013, 08:22 PM
Registered User
R.M. Gellart's Avatar
Joined Nov 2005
3,551 Posts
From my Sapphire days, I had a solid steel wingrod I used for ballast, it added 16oz, and that was my start point. I would probably wait till 12-14mph of wind. Remember, that when ballasting, you need to make a significant difference in loading on an airfoil like the 7037. Your 5 and 8oz bars, I am guessing you will not even notice the difference, but the 14 and 22oz bars will be useful. Your install is very nice.

The new airfoils, and current very light airframes, ballasting has changed a bit since those days and when we flew 7037's alot.

Marc
R.M. Gellart is offline Find More Posts by R.M. Gellart
Reply With Quote
Old Jan 20, 2013, 09:03 PM
Proud member of LISF and ESL
LI, New York, USA
Joined Mar 2003
24,371 Posts
I have always looked at ballasting as a % of of the unballasted weight.

At 15% I can tell the difference.

For a Radian at 28 oz that is about 4 oz
For a 60 ounce Supra that is about 9 oz

I have rarely every felt the need to ballast more than 25%

Again for the Radian that would be 7 oz
for that 60 oz Supra that would be 15 oz

If I have to ballast more than 25% I better be flying for a world championship because those conditions must be wicked!

I ballasted my Supra at 60% once, just for testing. She flew just fine into a 25 mph wind. Clearly the sink rate was higher but I was able to push right through the wind to find lift that I probably would not have reached at 25%. But the sink rate was certainly much higher. And it landed fast.

Naturally your smileage will vary.
aeajr is offline Find More Posts by aeajr
Last edited by aeajr; Jan 20, 2013 at 09:08 PM.
Reply With Quote
Reply


Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Discussion So if Romney pays 13% in taxes, how much do you pay? LVsoaring Life, The Universe, and Politics 110 Aug 21, 2012 10:04 AM
Discussion How much do you carry in spare parts ? old4570 Electric Heli Talk 11 Aug 08, 2012 04:27 PM
Question how much overlap do you use with lam film?? grfcon Slope 5 May 01, 2012 04:47 PM
Discussion how much line do you store on your winch webdragon Thermal 17 Apr 21, 2012 07:40 PM
Radio Control for UAV, What do you use and how much range do you get ???? JettPilot UAV - Unmanned Aerial Vehicles 17 Apr 14, 2009 12:47 PM