Instructions for building plane without kit?

[Kyle_Guo]

Kyle,

I should explain the NP and CG spreadsheet calculator a bit more. The spreadsheet has data entry cells for the stabilizer and tailboom as separately weighed items. Since you supplied the weight of the two together (no problem with this) I had to estimate each part's separate weight and enter it into the spreadsheet. Also, the spreadsheet wouldn't be able to adjust for a motor stick that might be slightly heavier on one end or the other.

Also, the calculator spreadsheet is originally designed for very light international class models and I do find that it calculates the CG slightly forward for heavy models like WS. I like to use the calculator even though it has this slight variance as a way to determine a good general range for the weights of the various parts for WS (which tells you what dimensions and wood densities might be best) and i like to build about 1.0 gram underweight and then use the clay ballast position to get the final CG correct.

Try attaching the clay to the nose of the airplane on the top of the motor stick and moving the wing forward about 0.5" and remeasure the CG. If it is not at 1.5" from the TE, repeat the process (move the wing forward again about 0.5" and measure CG again). Repeat this process until you have the CG at 1.5" forward of the TE.

Also, a bit of experimentation may be necessary for both the CG and the wing incidence. Some have found that the particular configuration of this year's WS model have made the NP calculators a little imperfect for determining ideal CG. My guess is that the combination of a very large wing with relatively highly cambered airfoil and a very small stab seems to make the airplane behave as if the NP were further back than the calculator predicts. This means that the ideal CG may also have to be further back than 1.5". Here is how you would determine this. If in your first test flight with full power (it's difficult to determine much during the initial, low power flights; remember full power means winding to 85% or 90% of maximum turns and torque and backing off to a safe launch torque to keep the airplane off of the ceiling) if the airplane does not gently stall all the way through the flight (especially during the descent) then either the CG is too far forward or the wing incidence and decalage angle are too great. Since the 3.3 degrees of wing incidence and decalage angle are almost certainly too much for this airplane, the best thing to test is the CG. So, again, if the airplane is not stalling, move the wing forward about 0.5", measure the change in CG and record in your flight log and fly it again. If still not stalling, move the wing forward 0.5" again and record CG in the log again. I would think that you would start stalling by this flight (if you weren't already stalling on the first flight). Once you have a plane that is gently stalling and have found a good working CG in this way, you can try removing a small amount of wing incidence (maybe about 1/16" lower LE) to see if this removes the stall. If this does it, you have a perfect setup. Mark the wing posts at the point they enter the tubes with something you will remember (like a red pen mark) and mark the final CG with a red pen.

Once the above trimming steps are completed, best possible flights will be achieved by experimenting with increased pitch on the propeller and varying motor thickness.

Let me know how it goes.

Brian T.

I see a possible problem. Does the leading edge have to be at the 5.5" mark? I have a balsa strip in which has the 2 plastic tubes that the wing fit onto. The balsa strip is connected to the MS by 2 very small rubber bands (called orthodontic bands in the FF kit). In order for the bands to hold it onto the MS, the strip is slightly longer than the 11 cm wing chord. The LE only starts 6/32" after the strip and I have been measuring nose length from the start of the strip. Should I measure nose length from the start of the leading edge?
"the spreadsheet wouldn't be able to adjust for a motor stick that might be slightly heavier on one end or the other." My motor stick is slightly heavier at the tip because of the propeller mount ring at the front and the fact that 2/3 of the "inner balsa stick" that keeps the outer strip (for length) from warping under pressure is at the front. If I have interpreted this right, I should ballast the nose, and go forward 0.5" until the CG is 1.5" forward of the TE. Then I should test the plane to see if this is right and make adjustments and determine if the CG is farther back than 1.5" and get the incidence right.
You said "gently stall all the way through the flight" does that mean throughout the WHOLE flight the plane will be dropping and climbing back? How much loss of altitude is a gentle stall?
" Since the 3.3 degrees of wing incidence and decalage angle are almost certainly too much for this airplane, the best thing to test is the CG. So, again, if the airplane is not stalling, move the wing forward about 0.5", measure the change in CG and record in your flight log and fly it again. If still not stalling, move the wing forward 0.5" again and record CG in the log again. I would think that you would start stalling by this flight (if you weren't already stalling on the first flight). Once you have a plane that is gently stalling and have found a good working CG in this way, you can try removing a small amount of wing incidence (maybe about 1/16" lower LE) to see if this removes the stall. If this does it, you have a perfect setup" So move the CG forward till just stalling and reduce the incidence until stall is just removed.

[Kyle_Guo]

Kyle,

Sorry, I didn't want to give you lots of things to consider all at once, but i will be pretty busy for the rest of the day and wanted to comment on a couple of things that I think I noticed in the picture of your airplane. First of all, congratulations on constructing a very nice airplane! Please don't take these comments as criticism in any way. I just want to see if I can help.

I am guessing that the fuselage, tailboom and stabilizer on your airplane are from the Freedom Flight Kit. If this is so, did you attach the nose bearing hanger exactly per the directions? I tried to zoom your picture to get a good look at this attach point as it appears to be a little delicate. However, I could not zoom you picture without it going out of focus. It looks like your nose bearing is projecting forward of the motor stick a little. This joint needs to be very strong in order to take the torque force of the rubber motor and in order to withstand the airplane possibly bumping into walls and ceiling obstructions. If you want me to inspect this joint, take a close-up picture of it from the side and post in the wiki.

One other thing, it may be just a slight distortion in you picture due to the angle of the camera relative to the wing, but it appears that your wing tips are splayed out to the side slightly. Maybe the wing tip plate vertical components are not exactly 90 degrees to the wing spars. If this is so, and if the wing spar lengths are close to the 45 cm allowed by the rules, the wing span as measured at the top of the tip plates (tip plate to tip plate) may be greater than 45 cm. It may be the case that not all judges will catch this, but the proper way to measure a wing with tip plates (or dihedral,or really any wing) is from the wing tip to the wing tip. Double check that the wing span measured from tip of tip plate to tip of tip plate is not greater than 45 cm.

Also, per your previous question about changing the fuselage motor stick length in order to lengthen the tail moment arm. I wouldn't bother with this. Increasing tail moment arm length in order to allow reduced decalage angle and reduced drag is a very minimal factor compared to the other trimming items I mentioned in my last post.

Brian T.

The fuselage, stabilizer, and tail boom are from the Freedom flight kits. I found making my own would be very similar to the FF ones since its the only one I know how to make from experience so I just used an extra MS. I decided to make my parts so that they could all be swapped onto a freedom flight MS. The nose bearing was pretty strong, the angle of offset was also correct but it was tilting down maybe 1-2 degrees and the fact that it wasn't pushed fully in nagged at me until I decided to cut the current part off and redo it (not affecting the length of the MS because the nose bearing is attached to the shorter one that is used to be slid to desirable length). There is a no distortion of the wing tip plates. The angles were off by less than or equal to 1 degree though and the length from the top of the plates was 44.8 cm and the length of the wing bottom was 44.65 (approx it was in between).

[bjt4888]

Kyle,

When shifting CG back during testing in order to induce stall you will not notice the stall too much during the climb phase of the flight as the power output of the propeller will likely be "pulling" the airplane right through the stall. A fully wound (and backed off) motor, if the launch torque is correct, will cause the airplane to "cruise" for 25% or more of the total flight. If you haven't already observed this, you will see the cruise start as the climb ends and the cruise will usually be five to seven circles at almost exactly the same altitude. During the cruise, the propeller thrust is less than the climb and the flight speed is lower and any tendency to stall will be obvious. Stall can be extreme if the airplane CG and decalage angle are far away from ideal. This would be evidenced by a nose then nose down flight attitude every four to 10 feet with each up and down getting more extreme until the airplane noses into the ground. Your airplane should be pretty close to proper adjustment with the 1.5" CG ahead of LE and if you properly measure wing and stabilizer incidence at 3.3 degrees (or so). So, the stall you should see in the cruise and let down portion of the flight should be a gently nose up then nose down attitude every 8 to 10 feet (3 to 4 times in each circle).

Yes, you should measure distance from nose to LE and not distance from nose to wing mount fixture when we are discussing wing position on the fuselage.

Your other statements in the previous post tell me that you are starting to understand the concepts of this pre-flight adjustment pretty well.

When are you going to flight test? Do you have a torque meter? Do you understand stretch winding and maximum turns and motor turn back off to launch torque?

Brian T.

[Kyle_Guo]

Kyle,

When shifting CG back during testing in order to induce stall you will not notice the stall too much during the climb phase of the flight as the power output of the propeller will likely be "pulling" the airplane right through the stall. A fully wound (and backed off) motor, if the launch torque is correct, will cause the airplane to "cruise" for 25% or more of the total flight. If you haven't already observed this, you will see the cruise start as the climb ends and the cruise will usually be five to seven circles at almost exactly the same altitude. During the cruise, the propeller thrust is less than the climb and the flight speed is lower and any tendency to stall will be obvious. Stall can be extreme if the airplane CG and decalage angle are far away from ideal. This would be evidenced by a nose then nose down flight attitude every four to 10 feet with each up and down getting more extreme until the airplane noses into the ground. Your airplane should be pretty close to proper adjustment with the 1.5" CG ahead of LE and if you properly measure wing and stabilizer incidence at 3.3 degrees (or so). So, the stall you should see in the cruise and let down portion of the flight should be a gently nose up then nose down attitude every 8 to 10 feet (3 to 4 times in each circle).

Yes, you should measure distance from nose to LE and not distance from nose to wing mount fixture when we are discussing wing position on the fuselage.

Your other statements in the previous post tell me that you are starting to understand the concepts of this pre-flight adjustment pretty well.

When are you going to flight test? Do you have a torque meter? Do you understand stretch winding and maximum turns and motor turn back off to launch torque?

Brian T.

I am going to test in my school gym after school tomorrow for 3-4 hours. I have a torque meter (made from brass tubing, a printed dial, and piano wire) but I don't know if it's accurate (Is a torque meter just a twisting piece of piano wire that has a hook for rubber?) When I have winded 1500 winds, the torque is 0.35 in-oz. That seems very little since the dial goes up to 2.5 in-oz. And when I flew at 0.35 in-oz it didn't come very close to the ceiling ( is that normal? this was before the CG was set correctly with the correct nose length) I haven't tested for maximum turns yet and I am going to break a rubber loop tomorrow and wind to about 90% of that. I have no experience with de-winding back to launch torque because I don't know what the suitable launch torque is for my plane. I have never had the problem of the plane going too high as it usually just goes 3/5 the way up the gym, circles a few times, then slowly comes down with many stalls on the way back (during a short testing session on Saturday).

[Kyle_Guo]

Kyle,

When shifting CG back during testing in order to induce stall you will not notice the stall too much during the climb phase of the flight as the power output of the propeller will likely be "pulling" the airplane right through the stall. A fully wound (and backed off) motor, if the launch torque is correct, will cause the airplane to "cruise" for 25% or more of the total flight. If you haven't already observed this, you will see the cruise start as the climb ends and the cruise will usually be five to seven circles at almost exactly the same altitude. During the cruise, the propeller thrust is less than the climb and the flight speed is lower and any tendency to stall will be obvious. Stall can be extreme if the airplane CG and decalage angle are far away from ideal. This would be evidenced by a nose then nose down flight attitude every four to 10 feet with each up and down getting more extreme until the airplane noses into the ground. Your airplane should be pretty close to proper adjustment with the 1.5" CG ahead of LE and if you properly measure wing and stabilizer incidence at 3.3 degrees (or so). So, the stall you should see in the cruise and let down portion of the flight should be a gently nose up then nose down attitude every 8 to 10 feet (3 to 4 times in each circle).

Yes, you should measure distance from nose to LE and not distance from nose to wing mount fixture when we are discussing wing position on the fuselage.

Your other statements in the previous post tell me that you are starting to understand the concepts of this pre-flight adjustment pretty well.

When are you going to flight test? Do you have a torque meter? Do you understand stretch winding and maximum turns and motor turn back off to launch torque?

Brian T.

You mean shifitng the CG forward right? not back. You said to shift it forward in posts before I am going to test in my school gym after school tomorrow for 3-4 hours. I have a torque meter (made from brass tubing, a printed dial, and piano wire) but I don't know if it's accurate (Is a torque meter just a twisting piece of piano wire that has a hook for rubber?) When I have winded 1500 winds, the torque is 0.35 in-oz. That seems very little since the dial goes up to 2.5 in-oz. And when I flew at 0.35 in-oz it didn't come very close to the ceiling ( is that normal? this was before the CG was set correctly with the correct nose length) I haven't tested for maximum turns yet and I am going to break a rubber loop tomorrow and wind to about 90% of that. I have no experience with de-winding back to launch torque because I don't know what the suitable launch torque is for my plane. I have never had the problem of the plane going too high as it usually just goes 3/5 the way up the gym, circles a few times, then slowly comes down with many stalls on the way back (during a short testing session on Saturday).

[bjt4888]

Kyle,

Read my comments carefully. Based upon information I have received from other teams, this year's WS airplane sometimes behaves as if the Neutral Point were further back. So, it is possible that you will need to shift the CG back (which means that the nose is lighter) from the 1.5" ahead of TE that the design spreadsheet recommends.

Read my earlier posts that describe a detailed set of flight tests. Also, it would help you immensely to read the previous year's wikis. Jeff Anderson, Calgoddard, myself and several other coaches and experience competitors posted extensive information on flight testing, building flaring propellers, propeller pitch adjusting and selection of motors. There is even a video posted of an international competitor winding.

Brian T.

[Kyle_Guo]

Are you sure you got my data all correctly entered? When I followed your recommendations of putting ballast at the nose (.28g) and moving the wing up 0.5" until the CG is 1.5" in front of the TE (moved up 2 times from 5.5"). I set the LE 1/4" higher than the TE. When I flew with 1800 winds, the plane turned at a ~5-10 foot radius and dived into the floor with a 3-second flight. Anything I did didn't stop this result. I tried raising the LE as high as I could, I tried removing the ballast. The only thing that would get the plane into flights of more than 3 seconds was putting the wing back at 2.5", removing the ballast, and setting the wing posts to what they were when I was testing on Saturday but that only gave me a 24-second flight. Do you know what the problem was with the plane?

[bjt4888]

Kyle,

Reread my previous comments about left wing offset and left wing washin and reread my testing post tht describes in detail how you should wind. The cg was correct at 1.5" ahead of le.

Brian T.

[bjt4888]

Sorry, i meant to type 1.5" ahead of TE in the last post. Also, did you check stabilizer incidence is zero?

[bjt4888]

Kyle,

I'm going to reply again to encourage you; and push you a little. You're doing very good work on a difficult project and I congratulate you. You may already be doing this, but if not, I want you to consider converting my posts or recommendations in to lists of items to complete. When you complete an item that I recommend, check it off the list. If you are not understanding an item, be sure to ask a question right away.

It is likely that inadequate left wing washin is causing the airplane to roll quickly to the floor. Also, you will note in the Freedom Flight kit and in the Finny 09 plan that there is left wing offset. Both of these settings are critical. Since you don't mention checking the stabilizer incidence, I mentioned again above.

The likely reason that the airplane flew a little when you moved the wing forward again, is that this adjustment made the nose of the airplane very very light (CG way too far back) which would result in such an extreme "nose-up" capability that the lack of roll control (inadequate left wing washin and offset possibly) becomes insignificant to the ability to fly for a short duration. With this type of setup, a very short flight would result in a large stall (which is deceptive to observe since the airplane is under full power) and a quick landing.

Also, you mention launching at 1,800 turns. If left wing washin and offset and wing/stabilizer decalage angles are correct, as well as correct propeller thrust line offset, stabilizer tilt and tailboom offset, it should only take about 1,000 turns on a 1/16" motor to give you a good first test flight. 1,800 is too much for the first flight. After the first test flight has demonstrated that the setup is safe (smooth 25 ft diameter climbing circles followed by smooth descending circles to about 15 ft height) you should be winding to about 85% maximum turns, which is about 2,200 or 2,300 turns for 1/16" rubber, and about 1.1 in oz torque and backing off turns, maybe backoff about 180, till torque reduces to 0.30 in oz torque for your next flight (as I already mentioned in an earlier post).

Brian T.