adding weight?
 

My sig complete minus fuel weighs almost exactly 6 1/2 lbs. However to balance I will need to add 6 oz. (roughly) to the nose. Would it be worth it to buy new engine mounts and slide the engine foward? I have it mounted as per plans. I just think 6 oz. seems like alot. Plus I was happy the plane came in at such a light weight. Be a shame to heavy it up just to balance.

RE: adding weight?
 

You could move the engine forward, but don't be afraid to add weight. 6oz isn't that much

RE: adding weight?
 

What kinda a plane are we talking about??
Can you move your battery or servos forward any further first?

RE: adding weight?
 

You are looking at a whole 5% increase in weight.

RE: adding weight?
 

Sig somethin extra, battery is all the wway front, going to move the uengine foward a 1/4 to 1/2 & try again

RE: adding weight?
 

Here's about a pound and a half of lead in the nose of a P-40 - She flew great!

RE: adding weight?
 

The best thing to do and the most difficult is move anything forward that you can and then remove weight from the tail. You would be surprised what can be done here. On my last project that came out tail heavy, I replaced all the steel hardware in the tail with aluminum hardware. I even made an aluminum wheel collar for the tail wheel. That and moving my RX battery, moving the motor 1/4" forward fixed the CG and the airplane gained no weight.

RE: adding weight?
 

I just added 3 lbs to a ziroli 77" stearman. It was done with 1/4" steel plate cut to cover the firewall. Worked perfect.
Edwin

RE: adding weight?
 

Adding any weight anywhere on the airplane increases the wing loading and stall speed. Always think removing weight first, i.e. nose heavy, remove what weight you can from the tail, second move existing equipment/components to achieve better balance, third and last resort add weight ( if you have already done One and Two above, it will be much less than just adding weight alone.

RE: adding weight?
 

I really don't see adding weight as that much of a sacrilege. I have only had one plane EVER where adding weight caused a problem (And I'd venture to say that I have had more planes than most people). Most planes can easily handle a few extra ounces - In fact, several planes fly better with a little extra beef behind them.

RE: adding weight?
 

You will gain almost nothing by moving the engine that little.

As Mike said, extra weight is a better friend of your plane than any unbalance.

Just in a loop or tight turn, your plane will weight much more than what the static balance shows,.......and will still fly.

Per angle of banking, the wing loading due to centrifugal force (virtual weight of the model) increases as follows:
For a 20 degree bank the force increases in 6%
For a 30 degree bank the force increases in 15%
For a 40 degree bank the force increases in 30%
For a 50 degree bank the force increases in 56%
For a 60 degree bank the force increases in 200%
For a 70 degree bank the force increases in 294%

Easily, your plane can weight three times more during a bank of 70 degree!

Consider this:

http://www.rcuniverse.com/forum/fb.asp?m=10890949

RE: adding weight?
 

I agree that adding weight is much better then flying tail heavy but still consider it a last resort. Lighter will ALWAYS fly better. May be a non issue with a sport pilot but some of us need our airplanes as light as possible. The best airplanes I have ever flown also happen to be the lightest.

RE: adding weight?
 

Keeping it as light as possible works for me, so if there is nothing that you can move around in the fuse to help then shifting the engine forward on the mount gets my vote.

Karol

RE: adding weight?
 

</p>

Note that the key words above is (virtual weight of the model).
If that listing is extended to a 90 degrees bank the force would become "infinity and that is not realistic. .</p>

Those figures imply a non-mentioned condition that the turn remains level in altitude which is seldom achieved by model pilots.</p>

In so called "knife edge" flying without loosing altitude there is no lift provided by the wings and no G force on the wings. The lift is provided by the airstream hitting the side of the airplane and some contribution by the upward inclination of the thrust line. We do not have any "virtual weight" or any weight carried by the wings.</p>

Note that since the air resistance (creating the aerodynamic force) increase by the square of the speed ratio (example: 2 times the speed then 4 times the forces) if then we have 20% more weight we have 20% more lift at a 9.54% speed increase.</p>

How many will notice the difference in their model flight?
Where a difference is more noticeable is the distribution of the masses in a model.</p>

Compare a foam model with most of the weight very close to the CG to a balsa model in which the masses are much further away from the CG. Any acceleration of the masses in axis rotation is slower due to the longer moment-arms. The pilot may notice a slower response to controls using the same amount of surface deflections at the same flying speed. Again it is doubtful that the average pilot will notice.</p>

Just interesting factors to think about.</p>

Zor</p>


</p>

RE: adding weight?
 

I'm not a weight watcher myself, I even have an old school pattern plane, Class C, that was designed to be as heavy as it could be. The designers thinking was he traveled all over the country to compete and in all weather conditions, wind for the most part. Keeping in mind this is a pattern plane, not a 3-D plane. In 1966 3-D was still something seen in a theater.
That being said I still try to keep the weight down during a build, I don't feel that adding weight is a good thing either. On my last build I had no other way to get the proper CG and had to make a formed lead weight and installed it as a nose ring.
6 ounces in a sport plane is no big deal but I still try to CG by moving the gear. A battery pack in the nose like John Buckner shows quite often is just one great way to do it. A heavy spinner or weighted prop nut works pretty well too. Not a first choice but I like them better then just lead weight.
I live and fly in an area where high wind can often just be a normal day. The ultra light planes get bounced around quite a bit. When the wind comes up I just pull out my old daddy Rabbit pattern plane. It's heavy for it's size and it too gets moved around a bit in the high wind but it was designed for it. It's much better then it's light weight cousins when it starts gusting.
The idea of Ultra Light planes came about when ARFs started taking over. They don't have much wood in them compared to a kit built plane so they had to say something. People bought into the Ultra Light thinking and now preach it to others. Myself, I would rather have a bit more weight and a stronger plane. I also can't fly 3-D so it makes very little difference.;)

RE: adding weight?
 

I just have to agree with Gray Beard.

A bit more weight means the ability to tackle the wind and gusts much better and makes it easier to fly in such conditions which are not rare.

I was planning a posting along this line and thanks to Gray Beard to have read my mind http://www.rcuniverse.com/forum/js/f...wink_smile.gif http://www.rcuniverse.com/forum/js/f...sn/biggrin.gif.

Light weight or lighter weight promoters can stay on the ground with no more than 12 oz/sq ft and watch pilots enjoying defying wind gusts with their models in the 20 (2x) oz / sq ft.

Zor

RE: adding weight?
 

Looks like this is going to be a highly debated thread. http://www.rcuniverse.com/forum/js/f...wink_smile.gif


Yes and no. A heavier airplane may appear to handle the wind better but a well trimmed airplane will do a better job. Look at the current crop of pattern airplanes. Lots of side area and 850-950 squares of wing they are among the lightest. AMA rules state a weight limit of 11 lbs. They do however handle the wind very well. This is because of proper setup.

The airplane really does not see wind, all it really sees is airspeed. Yes there are cross winds but most flying sites are set up so you are mostly flying upwind or downwind. So if your airplane is trimmed to fly at a specific airspeed and a gust hits, the airplane reacts to that increase or decrease in airspeed. If the airplane is trimmed correctly, CG, engine thrust, incenence, so that it flies strait regardless of throttle setting then it's going to be disturbed by wind much less. In fact when it is windy we just fly a little faster as to decrease the % in wind induced speed changes.

RE: adding weight?
 

No, it is not a shame. You only add weight (unnecessary weight) to have it balance, precisely. Old folks will tell you that a heavy plane flies better. Also that a extremely heavy war bird flies even better:-) I would not believe that! But, to add weight in order to have the model's CG in place, is a must.

Gerry

RE: adding weight?
 

I would agree with what others said, that 6oz isn't huge. Probably small enough that I would mount the weight to the bottom of the engine mount, with zip ties or something similar and go fly. If you like the way it flies, then make the mounting permanent. It is likely you are going to want to move the CG some any to fit your style of flying and comfort zone anyway, which will involve adding or removing nose weight. Once you are comfortable with how it flies, you can decide if you want to try and remove weight from the tail.

I don't know the ratio of fuselage length in front and behind the CG on the Sig Somethin Extra, but on the last plane I was working with (an Edge 540), it was about 1:3. One inch in front of the CG to three inches behind. A tape measure or yardstick will let you calculate it for your plane. It doesn't have to be to the nearest 16th of a inch. An approximation is good enough. Here is why I point this out. This ratio controls the ratio of weight you will have to add to the nose, or remove from the tail. It is the inverse. For every ounce you removed from the very end of the tail, you could remove three ounces from the tip of the nose and keep the same balance point. So, measure from front where you mount the extra weight back to the CG and from the CG back to where you can remove weight, by changing the tail wheel hardware as an example someone gave. So, if you can save a half an ounce in the tail by putting light tail wheel hardware in place and the ratio from front weight to CG and CG to tail wheel is 3:1, the that half an ounce saves you 1.5oz up front.

This is also why moving the engine forward likely won't have a lot of impact. The math here is greatly simplified for illustration and all the weight is treated as being at a single point. Assume your fuselage is 48" tip to tail and 1:3 ratio in front to behind the CG. Also assume that you are having to add 6oz of lead to the very front to balance and you have an engine that weighs 21oz. You have 27oz in front of the CG balanced by 9oz behind. Now, shift the engine forward by an inch. This changes the ratio to about 1:2.75. You still have that 9oz in the tail that now needs just about 24.9oz in the nose to counter it. Subtract your 21oz engine and you still need almost four ounces to balance. Move it forward another inch and you will still need two ounces to balance and now you have an engine that is two inches further forward than originally designed. That is not a trivial amount.

It is up to you to decide if it is worth the time, effort, and expense to shift weight out of the tail. Hence my suggestion of "balance it with weight in the nose and go fly". If you decide that it is ok with the extra weight, you can also look at getting something useful out of the weight. A bigger battery pack for more flight time, or a slightly larger engine for more power for example.

RE: adding weight?
 

Well I moved the battery to under the tank and it did not help much. Guess the lead it will have to be. I didn't relize it would be such a debate. I can see how a heavier plane will feel more stable , but less agile. Guess it will be the happy medium. The plane will still be under 7 lbs. Plus it's my first build, so if it flies 10', I'll be happy as can be. Thanks all for the replies.

Nick

Oh ya by the way, good idea w/ firewall battery mount. Just not enough room in the sse.

RE: adding weight?
 

It isn't like this is the first one built and put to thread on RCU. Take a look at seamusGs build thread and see what he did. I think it was Jim that had the last good thread anyway?
Jim is a good builder and does a great thread and his planes always come out great looking and fly well. Worth looking at.A little weight is nothing new. Build a plane that the full scale had a rotary engine and then talk to us about adding weight!!Even by using big heavy engines doesn't cure the problem.;) Sometimes it's just the nature of the beast.:D

RE: adding weight?
 

The topic (subject of discussion) here is "adding weight" and its effect on flight if I understand well.

I have some questions to make people think.

Does the plane see a change of airspeed because it is windy?

Does the model airspeed change because the air is tubulent?

What cause turbulence in the air (atmosphere)?

What determine the weight of a model? (Earth gravity does not change where you fly).

If two models are identical but one is appreciably heavier,does it change its control behavior and if it does then how (what has changed)?

What do you mentally visualize by the word "penetration"?

Are you finding answers that satisfy your mind?
Of course no one has to bother thinking.

So what is best?
Always try to avoid a few more grams such as on glue so the model can have more separated pieces in a crash and have a more attractive dance in the air when it is turbulent ___
or ___some more mass, weight and inertia so the turbulent atmosphere has less effect on a heavier weight.

Is not weight another compromise like the whole rest of the design?

Zor

RE: adding weight?
 

Has anybody ever installed the Rx battery next to the engine for CG balancing (over, under)? Or is that too stressful to the battery?

RE: adding weight?
 

The weight of the struts on the tail and the tail wheel could make a lots of difference. On the SE you will have a heck of a time moving the radio gear. A pic of the side vew of the plane would really help!

RE: adding weight?
 

My B-17 model takes 7 pounds to balance, and my Sig kadet LT-40 took 1.5 pounds to balance, flew like a sport plane.

Airplanes that are a tad heavier fly just a little better anyway IMO.

Jason