Instructions for building plane without kit?

[bjt4888]

Kyle,

So the wing incidence is 2/16", which equals 1/8". This wing incidence amount creates 1.67 degrees of positive wing incidence angle (inverse Sin of .125/4.3).

Is the tailboom exactly in line with and parallel to the bottom or top edge of the fuselage?

What amount of wing incidence is recommended by the kit instructions?

Brian T.

[Kyle_Guo]

Kyle,

So the wing incidence is 2/16", which equals 1/8". This wing incidence amount creates 1.67 degrees of positive wing incidence angle (inverse Sin of .125/4.3).

Is the tailboom exactly in line with and parallel to the bottom or top edge of the fuselage?

What amount of wing incidence is recommended by the kit instructions?

Brian T.

The tailboom is parallel with the top of the MS. There is a 3 degree left offset. The kit recommends the LE to be 1/4" taller than the TE but that stalled way more for me so I gradually decreased incidence.

[bjt4888]

Kyle,

Good job verifying the tailboom.

First let's define some terminology. I believe (based upon over 50 year of doing this) that you need to move the wing incidence angle back to 1/4" and move the CG forward to about 1.5" forward of the wing TE. Move the CG forward first by shifting the clay as far forward as possible. If this doesn't get the CG to 1.5" fwd of the TE, shift the wing back in 1/4" increments, checking the CG with each shift, till you are at 1.5" ahead of the TE.

Currently, you are flying with 0.58 degrees of decalage and with the CG behind the Neutral Point. The very low amount of decalage angle is why the airplane sort of trims out with the CG so far back. Decalage angle is the difference (meaning = subtract) between the wing incidence angle and the stabilizer incidence angle. The wing set at 1/8" incidence measurement is creating a 1.67 degree wing incidence angle. The stabilizer at 1/16" incidence measurement is creating a positive (meaning leading edge up relative to trailing edge of the stab) is creating a 1.085 degree incidence angle.

Your current decalage angle is 1.67 - 1.085 = 0.585 degrees. This airplane needs between 2.0 and 3.0 degrees of decalage. Your current settings of .058 degrees of decalage and CG behind NP will result in a high degree of instability and erratic flight behavior. This may explain the strange shifting you see during the turn.

Again, as I mentioned before, the settings above are a starting point. You will need to fine-tune by test flying. Use my previous recommendations for fin-tuning and removing stall.

To answer a previous question; yes you need about 1/16" to 1/18" of left wing washin. See the kit directions for recommendations for creating the washin. All other flying surfaces must be completely flat (even a 1/16" twist in one half of the stabilizer or in one of the winglets must be corrected). You can correct slight warps by heating the wood by breathing on it, or very slightly wetting it, and bending at a very localized spot, usually bending 3x or 4x more than you want to correct, and holding for about one or two minutes. This bending method should help straighten any inadvertent warps out of other flying surfaces.

Please make a checklist out of this email and checkoff each recommendation and do them all. Doing a portion of what I recommend will not give you a portion of success. This is what makes this such a great science experiment. Lot's of things to measure and adjust correctly and lots of data to collect and verify in order to achieve success.

Brian T.

[Kyle_Guo]

"Finally, you need the angle of attack of the left wing to be slightly higher than the right wing. This is called wash in where the tip of a wing is twisted to a slightly higher angle of attack than the root (center) of the wing. If your tip angle of attack is less than at the root its called washout. So, build the right wing flat and the left wing so the tip of the leading edge is raised about 1/8 inch higher than the trailing edge. This will require you to crack the front spar so it can bend at the root and reglue it." - jander14indoor
Should I just do that and make the LE of the left part of the wing tilted up so that the LE is 1/16 taller? (measuring from the end of the LE to the end of the TE) The FF kits this year do not address how to create wash-in. They told you to make the wing completely straight and there would be a natural warp that would help the flight, not naming it or telling you how to make it if your wing was actually just flat. I will be putting all the clay at the nose and making the CG 1.5" front of TE. If this all works, the plane will not dive directly for the ground when I wind more than 1400 winds.

[bjt4888]

Kyle,

1/8" left wing washin is a good starting point.

Be sure to increase the wing incidence to 1/4" also.

Reread my previous posts regarding fine tuning CG and wing incidence.

Also reread my previous posts regarding winding, back off turns and launch torque.

Brian T

[bjt4888]

Kyle,

One small word of warning regarding measuring stabilizer incidence angle. Be sure you actually measure with a long straight edge to be sure the tailboom is parallel and in line with the fuselage top line (or bottom line; same thing). It may be that it was your intention to attach like this, but tailbooms are difficult to attach accurately as they are thin and flexible and it is often the case that the tailboom angle is not as planned after it is glued in place. If your tailboom is angled up or down even 1/16" or 1/8", this must be verified and taken into account in order to determine a logical wing incidence angle to create the starting decalage angle. I always measure my tailboom angle after I glue it in place.

Also, some notes on measuring rubber. You mention that your rubber loop is 18" or 18.5". Was this measurement taken before it was wound for the first time, or after one or more windings? The reason that I ask is that it appears that the rubber you are using is thinner than you think it is. Here is how I am arriving at this conclusion. An 18" loop is 36.5" of rubber strip (approximately 0.5" is bound up in the knot). Subtracting the weight of the one o-ring you are using (if you are using the black rubber O-rings from the kit) leaves you with 1.49 - .04 = 1.45 grams of rubber. 1.45 grams divided by 36.5 inches gives a result of .0397 g/in. The "benchmark" rubber that most of use for stripping thinner rubber is 1/8" or .125" and this thickness rubber weighs on average .0833 grams/inch. If you divide .0397 (your rubber density) by .0833 (average density of 1/8" rubber), you get a result of .4766. Multiply this ratio of .4766 times .125 and you get 0.0596 inches thick. This is different than the .065" that you indicated. I'm guessing that the kit came with this rubber in a bag labeled .065". As rubber density varies over its length, it happens that stripping 1/8" rubber into rubber that you may call .065" will actually produce varying densities. For example, the rubber we got from the Freedom Flight helicopter kits that is labeled .085" varies between .057 g/in and .052 g/in. This variance is not due to anything that Freedom Flight Models is doing. They are doing a perfect job of cutting to width. This variance is due to density variation of the rubber strip. This is why competition modelers always discuss rubber by referring to density and not to thickness in inches.

All this being said, the rubber you have is perfectly fine to use, you just need to be aware that it is a little on the thin side and this would guide you with respect to what propeller pitch might be optimal and what maximum winds you should expect and what turns remaining to expect.

Have fun and good luck,

Brian T.

[Kyle_Guo]

Ok, I'll remove the 1/16 shim from the stab and I'll use my other packet of 0.065 rubber. Im pretty sure that's right because I ordered that separately.
Just to be sure, I crack (not cut) the LE at the offset point (3/8" in right of the center) then I add cement and angle it up? It seems a little risky doing that and I feel that using 2 diagonal supports on the wing would be better. The LE support would push the LE up and the TE support would keep the TE from going up with the LE. I will try that and see if it works.
The front prop ring on the motor stick described before broke so I will have to use another balsa stick and add the prop ring to it. Note: this one may be heavier by 0.5 gram or something, will that affect the CG being 1.5 front of the TE? I will remove enough clay to the plane is 7.6 g.

[bjt4888]

Kyle,

I'm not suggesting that your remove the 1/16" shim from the LE of the stabilizer. I'm suggesting that you use a straight edge to verify that the tailboom is parallel and in line with the top of the motor stick. If it is not, then you can compensate by adjusting the wing incidence more or less in order to achieve about 3.0 degrees of decalage angle.

Brian T.

[Kyle_Guo]

Because of the new Motor stick, the plane weighs 7.86g without clay. I think this is because The previous motor stick was cut (instead of being a rectangular stick, I shaved off weight, turning it into a triangular stick (cutting off an edge)). The current MS weights 4.03g (I don't know why the FF kit MS are so heavy). The tail section weighs .98g, the wing weighs 1.87g, and the reinforced prop weighs .98g. I have removed the shim on the Tail boom (You said you didn't tell me to do this and I misunderstood your question about that shim as if it weren't supposed to be there. Will I need to adjust the incidence of the wing to compensate for the straight stab?) and it is horizontal and parallel with the MS that I checked with a protractor. I made it balance (without clay because it was really heavy) at 1.5 in front of the TE and the LE is 4 15/16" behind the tip of the MS. Is this about correct? Will it change when I shave off wood to lose weight? I remember an early estimate for the LE placement was 5 1/2" back. I think this is very close to that estimate. I have made the LE on the left side 1/8" taller by a combination of cracking the LE and diagonal supports. Is this all correct? if it is, I will shave off the extra 0.36- 0.26g of weight somehow and move on to testing and adjusting it.

[bjt4888]

Kyle,

You should set the wing incidence to 1/4" for a starting point. Sounds like you have a good starting point for testing once you do this. Read my previous posts to understand adjustments you may need to make during testing to change the CG and then possibly the wing incidence to eliminate stall or, possibly, to induce stall and then eliminate stall.

Brian T.