Balancing a plane; is it better to move the engine farther forward or to add weight?

"what is the best balancing solution; move the engine forward and add less or no weight, or mount it all the way rearward and add more weight?"

hey Rusty,
If engine is moved forward that should require more tail weight, as it will now be nose heavy, likewise if engine is moved aft it will become tail heavy. I guess it would depend on how off it is, I would rather have a slightly longer nose movement then a chunk of lead in tail.

P.S. I'm still recovering...slowly. Wow, who would of thought, maybe it will be ok, Jan 1

If it was balanced for a Tee Dee and you're adding a heavier engine, the new engine will need to move back.

Mark Boesen wrote:...P.S. I'm still recovering...slowly. Wow, who would of thought, maybe it will be ok, Jan 1

Yeah boy y'all took a lickin' for sure. Those big ol Nebraska boys ought to be a good match for the Bulldogs.

I suppose I should have made my question more hypothetical, rather than about a specific plane. I will re-ask this afternoon and try to better explain what I want to know.

Hi Rusty
I think (so do most of my hoppo's) that adding weight to a plane should be punishable by hanging. drawing,
quartering, then the miscreants entrails should be......
Seriously though, if you can move components around to effect the same balance point change
that should always be the first port of call.

"should be punishable by hanging. drawing,quartering, then the miscreants entrails should be......" - John (buried at tow water mark in the ocean)

John Boy is displaying a repressed pychological reaction to the Mel Gibson film "Braveheart".

Be calm, son. It'll be alright now. Take several deep breaths and try to relax.

RknRusty wrote: So my question is, what is the best balancing solution; move the engine forward and add less or no weight, or mount it all the way rearward and add more weight? Or is it six of one, half dozen of the other.

I think I understand your question: What’s the lesser of two evils, nose length or tail weight? Nose length.

If engine is moved forward that should require more tail weight, as it will now be nose heavy, likewise if engine is moved aft it will become tail heavy. I guess it would depend on how off it is, I would rather have a slightly longer nose movement then a chunk of lead in tail.

I am stuck by the weather for painting on a build based on some sketchy instructions (Zinger). I ended up strapping the tail assembly, wing, and motor to a stick with some pins and rubber bands, then moving the wing and motor to suit the balance. I ended up with a somewhat long nose compared to what I expected. Fitting the covered wings into the fuselage with the motor pinned on has proved to balance very near where it should. I expect little trouble getting the balance perfect after paint and assembly.

I also just completed a remote control franken-plane based on a SPAD fuselage and a Tower40 wing. I haven't flown it yet, but my neighbor (who gave me his old tower 40 I promptly crashed) is quite impressed by the build and looks forward to giving it a maiden flight for me.

I am currently of the opinion that balance is more important than weight distribution, and maintaining low weight will make for a better flying model. Concentrating mass at the CG is of benefit, but not always practical.

Locating variable items like fuel or heavy items like batteries (especially for electric flight) near the CG if possible is probably more beneficial than trying to bring the motor back.

I have recently had the jumping bean balance problems you have helped me with, but I have also had a platter extreme that a few repairs made it uniformly too heavy to fly.

Phil

Yes, I'm interested in the lesser of two evils.
Here's the hypothetical situation; you build a beam mount type of CL plane and want maximum aerobatic capability(smallest possible loops). For this reason, you mount the engine all the way at the back of the beam but find it to be slightly tail heavy.

Option #1 is to leave the engine rearward and add nose weight to balance it. But we know adding nose weight reduces aerobatic capability.

Option #2 is to move the engine forward to balance it. But we know moving an engine forward reduces aerobatic capability.

Which option will yield the tightest loops?

EDIT: I posted this before reading Phil's last post.

Rusty,
You’ve proposed a very interesting question that might take several paragraphs to answer, but to be brief and pick one I’d say #2 to avoid the weight.
It would really boil down to the design and all the aerodynamic parameters associated with it. The tightest turns would probably be something like a combat ship with a carbon fiber tail boom, longest, lightest movement vs. shortest nose.
Back in the ‘old’ days many airplane designers thought a ‘short coupled’ (see All American) model was more responsive, now we know that a longer tail movement is actually better. Having a long nose is often times a necessary evil (to be avoided if possible) to balance out plane ( see Cox Hyper Viper, Spook, Sig Banshee, SV-11) but still fly very well.

a lot of your (two scenario only) question has to do with wing loading, and any lift from the stab/elevator.

The answer is obvious from ALL the basic combat designs.

All up weight vs. engine power, coupled with very SHORT moment for fast and tight turns. Wing average chord, lift, and tail area are critical.

So a lot of your answer is bound to type wing (flat, symetrical, semi symetrical, etc), chord (wide, thin, flat), and Over all length of tail to CG ratio (moment or angle of attack incedence)

IMO Your posted flying habits, your desire to have quick turning and stable aircraft, suggests, moving BOTH engine nacel and tail towards the CG and adjusting power and weight to ballance. You might conside adding wing length to adjust wing loading lower....Seems someone here just did that with tip cap and alerion additions...but I forget who

Spot-on, guys. Thanks for the answers. That's what I was fishing for. I haven't tried anything yet so this is all academic right now. I could have just commenced experimenting but this plane given to me is really nice and I hate undoing and redoing and uglying it all up. JP is a great experimenter, so thanks for the encouragement on that, Jim.

Mark and Fred, I have just recently realized from y'all's previous posts and videos that it makes good sense to have a longer light tail boom. Back a couple of years ago I chopped my Stuntman23, and put its big ol' feathers an inch and half behind the wing and it became my funnest flyer; the short coupled method. I renamed it from Green Death to The Chopper. That was in my pre-real-wing era. So there is some truth to the short tail method. But like the answers on the front end, there are different ways to splat a cat. One of these days I'm gonna get one of those combat planes, like the Sonic Chicken or something.

Since the holes are already drilled on this Streak(I should call it the Streak II), I'll see how it balances there first. I'm thinking he chose that location so his wedge tank fits. I'll mine your answers and come up with a plan. On my first streak I put the engine in the back of the beam and packed 3/4oz to the nose and it flies great. I think the AUW is around 8oz. So anyway, my main purpose here is only to improve on what works great anyway. I'm interested to compare the two planes, one I built versus one someone else built.

SuperDave wrote:"should be punishable by hanging. drawing,quartering, then the miscreants entrails should be......" - John (buried at tow water mark in the ocean)

John Boy is displaying a repressed pychological reaction to the Mel Gibson film "Braveheart".

Be calm, son. It'll be alright now. Take several deep breaths and try to relax.

HighjACK ALERTT

We don't mind the Scots Dave they allow us this from time to time..

Seriously though back to the weight thing....
One of the newbies at our club turned up a couple weeks back with some bits and pieces he's had laying around for 20 years.....
I got the plane with it's MDS 40 flying OK(ish) but with the onset of the FFFFFFFFFrrrrr coold weather
it only had 2 throttle positions (on and off) so not much good for teaching him to fly on the buddy.
He also had a new thunder Tiger GP42 in a box so I chucked that on.
Even tho the 42 had slightly more capacity it weighed only 345grams against the MDS' 530,
this allowed the lead on the tail to be removed and has totally transformed the way it flys
from an old dog that wanted to sink all the time to a very pleasing airplane.
I realise removing 7 oz's of weight from an R/C model is an extreme example compared to Rusty s dilemma but it
illustrates how unnecessary high loading is a baaaaaad thing.