kmtranmd

My Feedback: (71)

I set the CG per manual at 145mm for the ESM 88"ws BF109. Plane was very squirrely on maiden flight, acting like it's tail heavy when in fact it's a bit noseheavy at that spot. Please let me know what CG position worked well for you guys.
I'm flying it with Evolution 80cc which gives it good pull but not overpowered.

kenair

My Feedback: (10)

Hi, I don;t have a ESM 109, however the Platt plans for hsi 78" model show his C o G at 5" back of the LE, the Brian Taylor Bf-109 plans that I blew up to 82" ws show the C of G at 5" back from the LE.
I think ESM puts the fuselage plan on the wall and throws a dart to determine their C of G, a buddies Hawker Typhoon C of G was off. I wonder if ESM ever fly their protypes before marking the C of G on production models.
from the Meister site Meister Scale ME109 Platinum
Specifications

• Wingspan: 100"
• CG Location 5" from wing joint
• Fuse length 91"

Cheers - ken

ForcesR

Use the MAC rule to set the CG location, (MAC = 25 - 30%) for a WWII fighter. Measure the wing from the leading edge at the fuselage to the trailing edge of the wing. The total measurement will be the wing cord length. For example the wing cord measurement is 18" (inches), multiply 18 X 27% = 4.86" inches for the CG location. Or 18" = 457.2mm X 27% = 123.5mm for CG location. I do not go beyond 29% MAC for a fighter, I find WWII fighters get very pitch sensitive beyond 29% MAC.

Or use this CG calculator program to find the CG otherwise known as Aerodynamic Center (AC) balance location for flight: Aircraft Center of Gravity Calculator

Roger

kmtranmd

My Feedback: (71)

Thanks for your input guys. But I was hoping for input from guys that flew this bird and found the sweet spot. Otherwise I will have to do my own trial and error.

kmtranmd

My Feedback: (71)

I saw a thread where someone on RCU suggested that 112-116mm is the correct CG location. He did not mention where he was implying the 88inch 50cc class ESM 109 or the 72" size.
Please help if you guys know.

ForcesR

As I mentioned in my earlier post measure the wing from the wing leading edge at the fuselage to the trailing edge and post the chord measurement. Using the MAC calculation method the Aerodynamic Center of balance will be within 2mm of the CG calculator program.Post the wing chord measurement and I will do the calculation for you and give you the sweet spot balance location for flight. I'm very familiar with ESM models and how they give the incorrect balance point measurements for flight. I have never lost a model aircraft to incorrect CG balance point locations when using the MAC 25-30% rule.

kmtranmd

My Feedback: (71)

ME 109 88" has wing cord of 18.5" width at fuselage

ForcesR

Great, 18.5" = 469.9mm X 28% MAC = 131.5mm, you can round that up to 132mm. That will be the Aerodynamic Center balance point, AKA CG for balanced flight at 132mm from the wing leading edge measured at the fuselage. As mentioned 25% - 30% MAC is where WWII RC fighter aircraft will fly safely. Your ME109 at 88" WS will have a MAC range for a safe balance flight starting at 117.5mm to 140.9mm, the sweet spot should be 132mm.

kmtranmd

My Feedback: (71)

I have it currently at 145mm and it flew horrible, very pitch sensitive.
I plan to add 1 lb weight at nose to get to CG 120mm and see how it goes.
Thanks for the calculations

ForcesR

You were lucky to get your ME 109 safely back on the ground, 145mm is 31% MAC, to far aft; 30% MAC is the maximum for a WWII fighter. At 120mm the 109 will fly safely but your landing speed will be a bit high. You can always move the CG back after the first flight if you are not satisfied with it at 120mm. Post the results of your flight at 120mm CG, others including myself will be interested in the post flight report.

kmtranmd

My Feedback: (71)

Ok, I'm adding almost a pound of lead in the nose to get CG 120mm mark. Will fly it in 1-2 weeks and let you guys know.

tevans55

Kmtranmd-
I used the recommended CG on mine and it worked well when properly balanced. I added a significant amount of lead around the inside front edge of the cowl to get it to balance. I also raised the leading edge of the horizontal stab 3/32" because I have found that most of the ESM planes I have built seem to have a small incidence problem. That includes my B-25, two Spitfires and one of my Corsairs. My Bf 109 has flown great right from the first flight but it did take a lot of nose weight.

kmtranmd

My Feedback: (71)

I just flew w CG at 120mm and it was a lot more stable than original position per manual. Less pitch sensitive. May be tail has neg incidence?

tevans55

That would be my guess.

kwik

Hello,
I see there are some good discussions regarding CG here.

Here is a picture of my Meister Scale Platinum 109;



I have flown it with CG at 12.5cm . When landing I feel that I don't have enough elevator to avoid the nose dropping down at the very end before touch down.

Unless, of course I come in and land very fast, which is inconvenient on shorter airfields.

12.5 cm means 23% .
At least when measuring the wing cord at the wing mounting chord as indicated on the picture above.

12.5cm is according to the manual.

Here is my landing on maiden, The bounce after nose dive is maybe 2-5 meters long? but luckily it ended well;



So my plan is to remove some weight up front, ( I have 0.85 kg lead at the moment) and move the CG to 14cm.

Meaning 14/54.3=0.257 or 26%.

Any thoughts about moving cg to 14cm (26%)?

kenair

My Feedback: (10)

How does it fly inverted (at height) - does the nose want to drop down, do you need a lot of down stick to keep it level during inverted flight.
How is the pitch or elevator senstivity?

Nice 109!
landing looked good on the video. Grey plane on a grey day, I see you were up for the flying challenge - good show!