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Jgrischow,

The flight attitude you are describing is most likely due to inadequate decalage angle. This is the angular difference between the wing and stabilizer incidence angles. This year’s WS design requires about 3.5 degrees of decalage. This can be achieved if the stabilizer incidence is zero degrees (leading edge distance vertical distance from a reference line like the top edge of the motor stick is the same as the trailing edge distance from the same reference line) and the wing incidence is leading edge 1/4” higher than the than the trailing edge from the same reference line (again the fuselage top edge).

This decalage angle will only work though if the other five or six typical trim settings are correct. The other settings, of course, are: center of gravity at about 1.75” forward of the wing TE, left wing washin set to about 1/16” to 1/8”, stabilizer tilt about 2 degrees, tailboom offset for left turn about 2 degrees, thrustline (prop shaft) angled left about 2 degrees and left wing offset about 1/2”.

Use a good propeller like the Ikara symmetrical trimmed. Tie up a 18.5” (or more) motor and wind in 2,800 turns, or more. Back off enough turns to match the ceiling height and fly for 2:30+ in a typical gym.

Brian T.

bjt4888 wrote:Jgrischow,

The flight attitude you are describing is most likely due to inadequate decalage angle. This is the angular difference between the wing and stabilizer incidence angles. This year’s WS design requires about 3.5 degrees of decalage. This can be achieved if the stabilizer incidence is zero degrees (leading edge distance vertical distance from a reference line like the top edge of the motor stick is the same as the trailing edge distance from the same reference line) and the wing incidence is leading edge 1/4” higher than the than the trailing edge from the same reference line (again the fuselage top edge).

This decalage angle will only work though if the other five or six typical trim settings are correct. The other settings, of course, are: center of gravity at about 1.75” forward of the wing TE, left wing washin set to about 1/16” to 1/8”, stabilizer tilt about 2 degrees, tailboom offset for left turn about 2 degrees, thrustline (prop shaft) angled left about 2 degrees and left wing offset about 1/2”.

Use a good propeller like the Ikara symmetrical trimmed. Tie up a 18.5” (or more) motor and wind in 2,800 turns, or more. Back off enough turns to match the ceiling height and fly for 2:30+ in a typical gym.

Brian T.

Thanks for your reply. You obviously know a lot more than I do, but why does this flight pattern only happen sometimes, and other times we get decent flights, with no noticeable difference in settings?

Probably because your airplane’s static stability margin is inadequate. If you supply more data in your next message, I can run the numbers using a design spreadsheet.

Send this: wing and stabilizer width (chord) and length (span), CG location relative to the wing TE, tail moment arm and nose moment arm length (distances from the wing LE and the nose and distance between the wing TE and the stabilizer LE), wing incidence in inches and stabilizer incidence in inches.

Yes, I’ve been flying free flight model airplanes competitively (and reading philosophy) for over 50 year’s.

Brian T.
Academy of Model Aeronautics since 1968 (off and on)

What is a good time to shoot for when flying your glider? In states, our glider flew for 9-10 seconds and we finished with 19th place.

bjt4888 wrote:Probably because your airplane’s static stability margin is inadequate. If you supply more data in your next message, I can run the numbers using a design spreadsheet.

Send this: wing and stabilizer width (chord) and length (span), CG location relative to the wing TE, tail moment arm and nose moment arm length (distances from the wing LE and the nose and distance between the wing TE and the stabilizer LE), wing incidence in inches and stabilizer incidence in inches.

Yes, I’ve been flying free flight model airplanes competitively (and reading philosophy) for over 50 year’s.

Brian T.
Academy of Model Aeronautics since 1968 (off and on)

Forgive the lateness of my reply.

Wing Chord: 9.7 cm
Stab Chord: 6.7 cm
Wing Span: 39.1 cm
Stab Span: 19.7 cm
CG: 4 cm behind wing TE
distance from the wing LE and the nose: 11 cm
distance between the wing TE and the stabilizer LE: 41.2 cm
wing incidence in inches: 5/16
stabilizer incidence in inches: 0

Thank you.

Jgri,

Good job supplying data. Adding up all of the linear fuselagr dimensions supplied your airplane fuselage (including tailboom) is 68.6 cm long, or 27 inches long. This seems very long. Are all of your references to LE and TE correct?

Also, a CG 4 cm behind the TE ( trailing edge) of the wing is very far back from other designs.

Is this your own design?

Brian T

bjt4888 wrote:Jgri,

Good job supplying data. Adding up all of the linear fuselagr dimensions supplied your airplane fuselage (including tailboom) is 68.6 cm long, or 27 inches long. This seems very long. Are all of your references to LE and TE correct?

Also, a CG 4 cm behind the TE ( trailing edge) of the wing is very far back from other designs.

Is this your own design?

Brian T

Measurements are correct. CG has always been pretty far back on our planes relative to what instructions/designs say. Not sure why. My kids are probably using too much glue somewhere.

Design is based off of WLSguy's plans from the Centerville Clinic. Kids follow it as best they can, but probably made some mistakes along the way.

Jgri,

Sorry, in addition to a response to my question above, I need your airplanes overall weight and I need to know if you have any clay ballast added to the airplane to bring it up to the 7 gram minimum. And, if ballast is used, please indicate where exactly it is attached ( ex. 1 cm back from the nose on the fuselage).

Also, what type of propeller and nose bearing are you using exactly and, if you can weigh the propeller, or propeller/nose bearing and send me the weight, that would be helpful.

Brian T

Jgri,

Sorry, last questions, I promise. Length of the motor stick and length of the tail boom.

Once I have the info, I’ll plug it into the design spreadsheet and be able to give you some useful feedback.

Brian T

bjt4888 wrote:Jgri,

Sorry, last questions, I promise. Length of the motor stick and length of the tail boom.

Once I have the info, I’ll plug it into the design spreadsheet and be able to give you some useful feedback.

Brian T

Motor stick is 34.9 cm. Tail boom is 35.1 cm. They are glued together with a 1.5 cm overlap.

bjt4888 wrote:Jgri,

Sorry, in addition to a response to my question above, I need your airplanes overall weight and I need to know if you have any clay ballast added to the airplane to bring it up to the 7 gram minimum. And, if ballast is used, please indicate where exactly it is attached ( ex. 1 cm back from the nose on the fuselage).

Also, what type of propeller and nose bearing are you using exactly and, if you can weigh the propeller, or propeller/nose bearing and send me the weight, that would be helpful.

Brian T

Plane weighs 7.10 g right now. Not sure why; they usually have it at 7.02 ish. They probably re-glued something. I will advise them to take some clay off.

Yes, they use clay ballast. It is right at the CG, so 4 cm behind the TE.

Prop is standard Ikara 15 cm trimmed to 14. Nose/bearing/hook is from FFM. Total weight is .85 g.