Does ballast help or hurt roll response?

[Skycruiser]

I've been having a 'discussion' with a flying buddy about this. If you ballast an R/E model up, does it affect roll response when one wing hits lift? I know it's flying faster, so it'll respond faster to control inputs, but if a wingtip clips a thermal, will that tip be lifted faster? Slower? No different?

Assuming no cg change when adding the ballast of course.

Nick

[target]

If you dont ballast in the wings (as some moldies do) then it won't make a big difference. This is assuming you don't get crazy and double the weight of your plane with ballast.

Ballast properly done WILL make your plane less prone to a little turbulence.

R,
Target

[rdeis]

Assuming no cg change and no roll moment of inertia change, not much difference.

[scaflock]

As long as it kept on the CG and secured down tight it won't make any real change from my experience. This is assuming that you don't overload it for conditions. Just remember that you're thermal flying not going nutz on a slope in 30+ mph winds.

[Skycruiser]

If you dont ballast in the wings (as some moldies do) then it won't make a big difference. This is assuming you don't get crazy and double the weight of your plane with ballast.

Ballast properly done WILL make your plane less prone to a little turbulence.

R,
Target

Well yes, I know that it makes the plane less prone to turbulence, esp. in pitch, but if the roll response hasn't changed shouldn't it be just as sensitive to turbulence on the roll axis?

[fnev]

“Well yes, I know that it makes the plane less prone to turbulence, esp. in pitch, but if the roll response hasn't changed shouldn't it be just as sensitive to turbulence on the roll axis?”

You are absolutely right if the CoG has not been affected and the added mass IS exactly (and concentrated) at the CoG. And in that hypothetical case your glider will have the very same response to turbulences or control surfaces input except for the changes linked to the new flight attitude (higher angle of attack due to the added mass) therefore new aerodynamic equilibrium.

The problem is the way the added mass is distributed in respect to the CoG. This will have an influence on the inertias on the three aircraft axis. If, for example, your ballast is a cylinder with its center at the CoG and its main axis parallel to the “X” axis of the aircraft the roll inertia increase could be considered as negligible while the pitch and yaw inertias will be affected (increased).

[target]

You are absolutely right if the CoG has not been affected and the added mass IS exactly (and concentrated) at the CoG. And in that hypothetical case your glider will have the very same response to turbulences or control surfaces input except for the changes linked to the new flight attitude (higher angle of attack due to the added mass) therefore new aerodynamic equilibrium.

The problem is the way the added mass is distributed in respect to the CoG. This will have an influence on the inertias on the three aircraft axis. If, for example, your ballast is a cylinder with its center at the CoG and its main axis parallel to the “X” axis of the aircraft the roll inertia increase could be considered as negligible while the pitch and yaw inertias will be affected (increased).

I disagree here on both accounts, to some degree.

Both of you gents are over-thinking this.

First of all, the plane probably ISN'T going to fly "with a higher angle of attack, due to the added weight". It's simply going to fly a bit faster to generate the needed extra lift. That is why you will have better upwind penetration. I don't re-trim my plane when I add ballast.

As for the the plane being just as sensitive to gusts from the side with the added ballast, again, I don't think so. The plane should show lift just a little less (it should be flying a bit faster, right?), but it's been my experience that with added ballast, the planes are less sensitive to turbulance, because any added weight is below the center of mass of the plane.

My suggestion is to "Just try it" and decide through your on "real world" experiences, not theory on a chat site.

Regards,
Target

[cvanscho]

Good post, Target.

No changes in trim and settings (including mass) have simple, linear outcomes in a plane: there are too many interrelated causes and effects (such as the plane speeding up to maintain lift when ballasted). The best approach is (as was said) to try it and see..

[tom43004]

Adding weight never increases roll response. It always decreases roll response. How much decrease depends upon where you add the weight.

With that being said, yes we're probably overthinking it. Just go fly.

Tom Siler
Columbus, OH

[cvanscho]

Adding weight never increases roll response. It always decreases roll response. I'm sorry, but I cannot agree.

[SmokinJoe101]

With that being said, yes we're probably overthinking it. Just go fly.

Tom Siler
Columbus, OH

It would not be RCG with out the OVERTHINKERS :eek:

sj

[tom43004]

**Overthinking alert** :P

More weight = more mass to disturb when initiating the roll, even if the weight is placed on the axis of rotation. If you are seeing increased roll response while ballasted, it's because of increased airspeed due to ballast causing the controls to produce more force for a given deflection. If you could achieve more airspeed without ballast (with reduced camber or even trim) you would see even more increase in roll response.

Tom Siler
Columbus, OH

[Kiesling]

**Overthinking alert** :P

More weight = more mass to disturb when initiating the roll, even if the weight is placed on the axis of rotation. If you are seeing increased roll response while ballasted, it's because of increased airspeed due to ballast causing the controls to produce more force for a given deflection. If you could achieve more airspeed without ballast (with reduced camber or even trim) you would see even more increase in roll response.

Tom Siler
Columbus, OH

I agree

[schrederman]

However ... more speed means more responsiveness to control inputs. Your rolls will be crisper with increased airspeed. This will overcome any mass differences for the most part. Full scale have a VNE speed, (velocity never exceed). They also have a maneuvering speed, which will be lower. Maneuvering speed is the max speed at which one can move the controls at full travel without over stressing the airframe.

So, with ballast and the extra speed, your model will not show lift indicators quite as well, but will respond a little quicker to most control inputs... from my experience at least...

Jack

[Libelle201B]

If you build really heavy, (epoxy only) you will more than likely not have to worry about ballast. Better control response, better penetration on windy days ect, will be built into your bird. This way you can show up at the field and argue at length that the need to add BALLAST is a myth .

[rdeis]

On my old Shuttle I'd add ballast in the wing spars with the *intention* of damping roll. Not response to control inputs, mind you, just sensitivity to turbulence in very difficult air.

Ballasted up like that it would behave reasonably well on days where I'd otherwise have had to go home.

[schrederman]

I just can't believe someone would admit to having flown a Shovel... er... Shuttle...:D

[target]

No way man! How can adding ballast ever be a good thing?? :rolleyes: :D

I'm kidding, or course.

On my Ceres, when the air is very turbulent, I add the wing ballast with one or more slugs outboard, to help dampen unwanted roll upsets while flying.
I can neither confirm, nor deny if this helps, but I know that it doesn't hurt me enough to make me want to not do it...

For your R/E plane, maybe just try 10% increments of the unballasted weight, being careful to keep the CG constant, and see what you think.

If you don't like it, you don't have to use it. Some planes may not benefit much from ballast, because they aren't designed to fly in windier conditions.....

That being said, when I was a lad, I had a Marks Models Wanderer that weighed 24 oz, and it got maidened in 18-20kts of wind on a slope, and did fine, so long as I didn't want to fly upwind faster than pretty slowly. For that particular condition, 6oz of ballast would have helped, I'm sure!

Good luck,
Target

PS. Make sure the mounting for the ballast is substantial!

[rdeis]

I just can't believe someone would admit to having flown a Shovel... er... Shuttle...:D

Hey- I dug a lot of holes with that nose! (Still have the wings around here someplace..)

[target]

I thought that those things were pretty cool looking, even if a bit ugly.

They seemed to fly fine in super light slope lift (2M).

Target

[rdeis]

Flew fine in thermal lift, too. I scored my first 5 minute flights with it, and learned to fly in turbulence with ballast.

I think I got my first couple of 3m landings with it, too, but learning to land on a spot with that nose and no spoilers was tough..

A most unique (and really big) 2m ship- fun for the kid at the time.