hitman5363

I balanced my on the wing mounting carbon rod and with out the wings mine is 7.5 ozs. Tail Heavy. I do not see how anyone could be nose heavy. I am using DLE 20RA and both servos on the tail plus I made a solid wood motor mount. I am basically ready to break in the engine. Only thing I am lacking is deciding on Spinner.....but may go with a heavy prop nut for the needed weight up front.

tailskid

My Feedback: (34)

I just got my computer back.....I'll do some measurements tomorrow and post them....remember I have the Fun Fly Sbach 300......but the 'numbers' of my plane and yours are very similar - in fact I bet the same factory built both!

But in the meantime: http://www.rcgroups.com/forums/showthread.php?t=2209319

hitman5363

Still have to cut cowling for exhaust...break in engine and final balancing. Also close up holes in sides from tightening up "L" bracket bolts for landing gear. The tachometer is mounting in the canopy so I can see it from behind the plane.

hitman5363

More Photos

JoeMamma

Hi tailskid,

Thanks for the attempt at helping us all, but...........

The Fun Fly Sbach is an 11 pound plane with a 73” wingspan and the Troy Built Sbach is a 9 1/2 pound plane with a 69” wingspan. With the larger wing on the Fun Fly, the chord of the wing at the fuse would probably be wider/longer so the CG location would probably be different between the two different Sbach versions.

After reading and studying your review, the airframe appears to be similar in some respects, but very different in others. The one big difference I noticed about the Fun Fly edition is it’s set up to use a muffler canister. The Fun Fly version of the Sbach would have been perfect for me as I had originally planned on using a small 30 size gasser for power. My club has a noise limit so a muffler canister would have worked out great.

Again, thanks for the attempt.

Joe M.

JoeMamma

hitman5363,

Lookin' Great ! Looks like you are about done.

Appears you are using a separate choke servo ?

Where will you set your initial CG at and how did you determine its location ?

Joe M.

hitman5363

yes a servo for the choke.

Well I thought I read in this thread the CG should be around 4 7/8.....dead center on the wing rod from leading edge is 5 inches and the Aero Plus 20cc SBACH that the manual was downloaded on this thread has that plane at 4 inches. I use the wing rod as my balancing point and have it a little nose heavy from there.......once you fuel it up it will be even more nose heavy but once you burn off that fuel you'll be back at your balance point.....that's how I intend to start off at least.

Bcolici

Im not home to take measurements, perhaps this will help with cg.
http://adamone.rchomepage.com/cg_calc.htm
If you run the numbers please post it here.

JoeMamma

Hi Max,

Thanks......that's a real nice chart.

I have never needed to do this, but I think I'll lay out the wing and fuse after dinner tonight and using your supplied chart see what I come up with. Stay tuned.

As I had mentioned earlier, I had looked at quite a number of assembly manuals of different Sbach models in the 65" to 75" range. The CG specs. varied up to 3+ inches between each manufacturer. That (in my opinion) is a large variation.

Sorry, but back to my venting.......grrrrrrr.......none of us should need to be doing any of this just to determine the CG. A big thanks again to Troy Built Models !!

Joe M.

Bcolici

You're welcome and thank you for taking the time to do it.
You'll be done with dinner and putting the numbers in way before i get home.
I hate the late shift. It interferes with my morning flying.

JoeMamma

First off, I have never attempted to determine a CG setting, so bear with me. Also found out it is very difficult to take measurements on a plane that is all finished up. Having swept back wings and a swept back horizontal stab sure doesn’t help either.

My first big problem when taking dimensions was determining whether or not to include the ailerons in my overall measurements. Same-O for the elevator halves.

Looking at the chart, I really didn’t know if the dimensions were to be taken with or without any considerations to the ailerons or elevator halves.

Using the chart ? I took all the necessary measurements from the chart in two different ways. The first set of measurements was taken as if the ailerons and elevator halves were not installed. The second set of measurements were taken as if the ailerons and elevator halves were installed.

Another problem came up when determining where to take dimension “Y” (“Y” from the chart). Should dimension “Y” be taken at the sides of the fuse where the wing chord is at its widest, or at the center of the fuse as shown on the chart. Again, I took two different measurements.

I then pulled up the chart, plunked in my measurements 4 different ways and clicked OK each time. Also, according to the chart, I used the 10% Static Margin (fudge factor).

My final CG location ? Depending on which of the 4 different measurements you look at, the CG, taken at the leading edge of the wing where it meets the fuse should be between 4.01” to 5.13”. So, until I hear from one of you guys that has done a flying-type CG test, it looks like my initial CG setting will be about 4 5/8”.

Also, my initial elevator setting will be low at about 1/2” with a lot of exponential added, probably 60-70%. Reason for my low elevator setting ? On at least one occasion (first flight) on a 3D type plane many years ago, the elevator was overly sensitive and consequently the plane was out of control from the onset. After fighting it for a while, I finally pile-drived it into the ground.

Don’t know if you guys have ever done a flying CG test before. If not check out Ken Myers write-up at http://www.theampeer.org/cg/cg.html Once there search for The CG Dive Test:

This particular dive test is the one CG flying test I always perform on a first flight. This dive test will get you “into the ballpark” for subsequent CG testing. After performing the dive test I make any weight adjustments. On the next flights I then try a climbing CG test and also an inverted CG test. Also, search the net for CG flying tests for more info.

Joe M.

Bcolici

Joemamma , I would say to include the ailerons and elevators in the measurement.
As far as where to measure for the wing root chord or half span,Im not sure either. I would think at the sideof fuse.
I sent an e-mail to the site for the calcuator regarding your questions.
I will post back when I hear something.

Bcolici

Here's another. http://www.friendlyflyers.org/cg-calc.html

race60

My Feedback: (1)

I have preformed every CG method I can think of on this 69" sbach and I came up with one conclusion. Anything from 4-1/4 to 5.0" is acceptable for this model. At this point I am more concerned with the excessive amount of holes in the fire wall. Hopefully I won't blow all the covering off the airframe in a power dive.

Bcolici

Joemamma 4 5/8 Im getting as well for cg starting point.

Race60 close up the holes with material of your choice.
Im going to use some liteply and fasten accordingly.

hitman5363

Like I said.....5" is the exact middle of the carbon wing rod....so 4 5/8 to 4 7/8....is perfect for balancing......I like my OLD Fashion way better.....all that equation BS makes my old head hurt....

Bcolici

But you didn't say how you came up with that.
How did you come up with that? just curious to maybe learn something.

hitman5363

How did I come up with the 5 inch number. Easy, since the wings insert partially into the fuselage it is really easy to measure from where the leading edge will be in the inserted area and back from there to the center of the carbon fiber wing rod is exactly 5 inches.

Many many times I have used the manufacturers CG measurement and then once out in the field flying I did not like the performance of the model so I went back to my old method of balancing on the wing rod.....(using a string with a loop in each end that is put over the wing rod).... and moving forward from there to find the perfect spot.

Not scientific at all....basically just balancing the model

JoeMamma

Designed wing tube location ?

I could be wrong, but I believe the designed location of the wing tube really doesn’t have too much to do with an initial CG setting. It may be close, but.........

I have a large number of planes with wingspans up to about 117”. Because I have too many toy airplanes (that’s what she says), I keep the mass confusion out of this old brain by keeping a detailed log book for each model.

I just took a peek at my recorded CG settings for a number of planes. I then took a quick measurement on a number of the actual wing tube locations. I then did a comparison of the actual wing tube locations versus my recorded CG specs. Some of the wing tube centers are off by as much as 2” (for and/or aft) versus my recorded CG figures.

Again, I could be wrong, but I believe if the actual CG setting on any model airplane that happens to come out at the center of the wing tube, that it’s just a coincidence.

I’m no aerodynamics engineer, but I think a 5” CG location on a 69” tapered seems a little tail heavy to me.

Joe M.

hitman5363

Look at post above....I was 7.5 ozs tail heavy..........at 5 inches........ I do not believe the.. CG for this plane is 5 inches.....more like what you all got...between 4 5/8 and 4 7/8......I ONLY use the wing root balance for ROUGH estimates..........sorry, but I am extremely OCD.......but I am not going to use that overly mathematical equation to figure out where this plane will balance. I will make it NOSE HEAVY to start and work back from there until I find the EXACT PLACE where I like it.....bottom line.

hitman5363

OK, this one is simpler.....

Bcolici

Similar method to a Vanessa cg rig but not quite.
I posted a link somewhere here if you're interested.

rekit500

DO NOT USE 5"!!! Holy ****, what a handfull on elevator! I never moved the stick more than enough to tell that it even moved and I was all over the sky. Thankfully it only needed 1 click of elevator and 1 click on aileron. Wife shot some video but haven't looked at it yet. Will post more later. My email quit notifying me of posts a week ago so I thought no one was posting, Missed some stuff. I was tail heavy at 4 7/8, moved my batteries up far as I could. Got to 5" and figured with 10 oz of fuel I'd be ok. Oh hell no.........got it down, actually decent landing

JoeMamma

Thanks for the warning. Joe M.

rekit500

Adding 1 pound of lead to get to 4.5". Going again tomorrow.