Flight B/C

[bjt4888]

Thank you so much for the advice!!!
I've seen on past designs that the Horizontal stab is attached by two posts and tubes, similar to the wings on this year's FF design--except this year, you just glue the stab to the motor stick. How would I adjust this? I used duco cement, and have no idea how to slant the stab. In the instructions, it says, "offset the rudder to the left by angling the Tail Boom", but there isn't a tail boom?.. It's just a motor stick.. Am I misunderstanding something here? If not, how would you suggest adjusting angle of the stab? (it's glued to a piece of balsa that is glued to the motor stick) Thanks!
(also, we reserved a warehouse for flying with no AC! will update my previous post when we get some good flying in )

Cat,

A stabilizer mounted on posts is not necessary for Science Olympiad. This type of design does allow for stabilizer incidence adjustment, but you’ll get enough adjustment of decalage angle with the adjustable wing posts (decalage is the difference between the stabilizer incidence and the wing incidence angles).

Stabilizer tilt is the angle I was referring to and is shown in the diagram on page 12 of the FF kit directions. Before attaching the stabilizer, you could sand a nice even 2 degree angle on the top surface of the fuselage stick where the stab is mounted. Tilt affects turn mostly in the latter portion of the flight and the stabilizer skew (effectively causing rudder offset) has more affect during the higher power early portion of the flight.

Yes, there is no tailboom for this year’s FF design. Think of the portion of the fuselage where the stabilizer mounts as the tailboom.

Take video of your full flights. Have the camera off to the side so that we can see the airplane in its full flight pattern. I’ll attach a sample video a little later tonight.

Brian T

[Maxout]

I'm not sure why we're still not using adjustable tails, especially since FF used to have them. I've got the Div. C kit on my desk and it requires you to tack glue the stab in place. You might try using the dental bands to hold it in position initially. This year I switched to an adjustable tail on the Stinger because people had so much trouble with indicence settings last year. The problem with putting incidence into the wing mount is that it couples pitch adjustments to the thrustline so you're chasing two adjustments at once. All that said, the FF kit is a proven design and will likely fly fine for you. If you do run into issues, save some of the excess carbon rod and wing mount tubing and use that to make an adjustable stab mount.

-Josh

Thank you so much for the advice!!!
I've seen on past designs that the Horizontal stab is attached by two posts and tubes, similar to the wings on this year's FF design--except this year, you just glue the stab to the motor stick. How would I adjust this? I used duco cement, and have no idea how to slant the stab. In the instructions, it says, "offset the rudder to the left by angling the Tail Boom", but there isn't a tail boom?.. It's just a motor stick.. Am I misunderstanding something here? If not, how would you suggest adjusting angle of the stab? (it's glued to a piece of balsa that is glued to the motor stick) Thanks!
(also, we reserved a warehouse for flying with no AC! will update my previous post when we get some good flying in )

[coachchuckaahs]

I agree with Josh. We always have adjustable stab, but that's just the way we are used to doing things! It does add more items you can record in your log!

Adjustability is good, if you maintain control of your variables and understand what you are doing!

On older SO planes we would add rudder and tail tilt adjustments by wetting the tailboom a little (bottle of water, splash onto fingers, rub boom), bend/twist, and heat with a mini heat gun. Incidence we adjusted with stab posts. This year we anticipate using the entire stick as Motor Stick, so I would be hesitant to adjust rudder with bending stick, as you are inducing a bend in the loaded (compression) stick. Twist, for tail tilt may still be OK.

Coach Chuck

[pumptato-cat]

Thanks everyone!! How do you guys log angle incidence/washin/other angles? I'm not sure how to measure this(or sand a 2 degree tilt to the stab...)
Currently, my plane is flying ok(not the best but not good), but I'm eyeballing things and after changing the stab angle, my times dropped by 30-60sec.. I want to be able to measure precisely..

[coachchuckaahs]

Generally we measure incidence as height in mm from the MS/TB to the lower edge of the wing or stab leading edge and trailing edge. So that gives 4 measurements, for what is essentially two data items (Stab and Wing incidence), or could even be one item (decalage). But it is simplest to record all four. Note: This approach assumes that the TB and MS are straight and in line with each other. Even with an angled tailboom it is still a repeatable measurement, as long as your TB material is not changing shape (too flimsy)

For stab tilt we just eyeball/estimate in terms of cm difference between the right and left tips, relative to the wing. We usually do not record this, but it could be recorded (probably should be). One could make a simple protractor device that you hold along the wing, and rotate a pivoting edge while you sight from the front or rear, until the rotating part aligns with the stab. Then record the angle difference between the wing and stab.

Wing wash looks to be fairly important this year. We have always looked from the front to see the relative difference in tilt between the LE and TE of the wing, expressed as cm at the tip, when either the other tip lines up or the center at wingpost lines up. I think center at wingpost more appropriate. We have just estimated, but again you could express as an angle by using a simple protractor sighting tool.

I commend you for putting more thought into these "minor" adjustments that we tend to ignore. If it is adjustable, it should be measured and recorded. We have not been diligent in doing this, but in some cases these adjustments may have large effect, like wash-in this year on some designs.

Coach Chuck

[bjt4888]

Pumptato-cat sent me a PM through this forum that included a video of her flight. Below are the recommendations I sent to her that I thought the others on the forum might find useful as the kit she is using from Freedom Flight is likely to have similar fine tuning needs for most students.

Cat,

I am also going to post this in the public Scioly.ofg forum (without your video or your questions) as other students might be able to use this info.

Let’s start with the flight video. In both flight videos you shared, the key things to focus on first are as follows:

1. The airplane circles are a little too small
2. The airplane climbs a little too quick
3. The airplane stalls; especially noticeable during the last part of the descending portion of the flight and more noticeable on the two-minute flight than the one minute flight (this might be due to the reattaching of the stabilizer reduced the overall decalage angle; angled the stabilizer LE up slightly maybe).

Also, key to focus on is your note that the CG position is 5 cm forward of the TE and the kit recommended starting CG setting is 5.4 cm forward of the CG.

So, this airplane design is very sensitive to CG placement. A little too far forward and the airplane will dive steadily to the ground. A little too far back and you’ll get tight circles throughout the flight, too fast climb and steady stalling towards the end of the flight.

Your first fix is to move the wing back on the fuselage about 1/8” and fly (which will move the CG forward an almost not measurable amount). See if the circle size gets a little large and the climb rate is a little less and the stall during the last portion of the flight is gone. If all of these don’t improve, then move the wing back on the fuselage another 1/8” and fly again. If this improves the above three flight characteristics, good, if the airplane dives and rolls to the left, move the wing forward again the 1/8". The kit recommended starting setting for CG location is 2.125” from the TE, or about 5.4 cm. Since you're at 5.0 cm, moving the CG forward a little makes sense. This will result in a kit recommended nose length of about 2.5” (end of fuselage stick to the LE).

The next most important parameter to work on is getting full turns and torque on the motor. Once my teams have performed a first “safety check” flight with about 50 winder turns (15:1 ratio winder) to make sure that the airplane doesn’t dive or stall too much and that the circle size is reasonable, they immediately begin winding to full max torque and turns for every flight thereafter. You don’t really learn anything from partially wound motors. Once fully wound, you control height of the flight by backoff turns and reduced launch torque (reduced from the fully wound torque). You only need to go back to performing the 50 winder turn "safety check" flight if you have a major adjustment of a setting or if you have crash damage to settings and want to see if you got them back to where the were when the airplane was flying well.

A .094” wide rubber strip is really .0624 gram/inch rubber on average. You should be calculating density in grams per inch of every motor and you will discover that in a bag of .094” cut rubber there is over 5% variance in density between each motor cut from the bag. This is too much variance to not be taking data on. You may get good flights (best duration) from .063 g/in and much worse duration on .060 g/in and these two densities could be the variance in one bag of cut .094” rubber.

A fully wound .0624 g/in motor (about 15” long and 1.98 grams with two black rubber o-rings) will take 110 winder turns (again 15:1 winder and this 110 is 85% of breaking turns using the equation I posted earlier in the forum). The first use of a new motor you will get a little less than this; maybe 100-105 and later uses will get a few more turns (at the same torque) for each use. Beginners that I teach the correct winding process to sometimes might get fewer turns, like 90-95, till they learn the process (see my video). The motor will have about 1.2 – 1.4 inch ounces of torque when fully wound. The next step is to backoff (reverse winder turns) to reduce launch torque to a safe level. Backoff turns to get this launch torque might be between 15 and 20. Keep the launch torque pretty low for the first “full winds” flight; maybe 0.28 – 0.30 inch ounces. This flight should get you about 8-12 ft of climb height. If this is the climb height you get, the next flight (again, wound to 100 – 110 winder turns and 1.2 – 1.4 in oz) will be backed off a little less giving you a slightly higher launch torque; maybe 0.32 – 0.34 in oz. See if this launch torque gets you another 3-5 ft of climb height. I’m estimating climb height, but you get the picture, you’ll get 2-5 ft of additional climb height for each increase in launch torque of about 0.02 – 0.04 in oz. Continue this process for each flight till you are as close to the ceiling as you feel is safe.

The next step in the trim process is to vary the pitch of the propeller maybe 2-3 degrees (increased, in the case of the Ikara symmetrical prop). Higher pitch will reduce climb rate and open up the circle size and may require slightly thicker (more density and shorter) motors for best duration. We test pitch diameter ratios between 1.4 and 2.0. Too much pitch will inhibit climb rate too much and will reduce durations. You determine this by testing lots of pitch angles. See the kit instructions for how to twist the Ikara propeller hub with needle nose pliers to change the pitch.

Your stabilizer tilt looks fine; looks to be about 2-3 degrees. Don’t change it again yet, but do measure it (see picture in the Google Drive I linked).

The “planes wings” uneven you mention (left wing tip down right tip up) is called “roll”. Rolling can be reduced (sometimes) by increasing left wing washin slightly. However, as this airplane kit design does not have the typical longer left wing than right wing, it will probably roll some and this is not a concern. If I were you, I would not increase left wing washin at this point in trimming as this setting also increases climb rate and you need to see how the CG fix affects climb rate, stall and circle size first. Flat wings during climb is not super important. I will sometimes trim an airplane deliberately to roll (impeding and reducing climb rate) during the start of the flight with the roll gradually disappearing in the middle to end of the flight. This is a common trim for very low ceilings.

After the CG fix and using full torque/turns winding on the motors, you could then try slightly more left wing washin. Remember this setting change will likely cause the airplane to climb faster and higher, so reduce launch torque for the initial flight after this change so that overall climb height is safely short of the ceiling.

For you other questions about how to measure:

1. wing/stab incidence – see picture in the google drive; measure just under wing TE to a reference point like the fuselage bottom edge; do the same for the wing LE and take the difference between these two measures. For example, our design has a measure of 1.75” for the TE and 2.0” for the LE for a wing incidence of 0.25” (take the inverse sin of 0.25 incidence/5.0 wing chord measure and see that this is 2.87 degrees)
2. decalage – difference between the stabilizer incidence angle and the wing incidence angle. Since the stabilizer is mounted on the fuselage top edge, the stabilizer incidence is zero degrees. So, the decalage angle is the wing incidence angle
3. rudder offset – use a straight edge held against the fuselage side and a ruler to measure the offset amount of the center rib relative to the fuselage side. Calculate the angle in degrees with inverse sin of the triangle formed by the length of the rib and this offset measure.
4. launch angle – this is not important unless I am misunderstanding what you are asking. Add detail if you would like to describe this question more
5. washin/washout – done by eyeball sighting from the front of the airplane like the picture in the kit instructions. The exact measure is not that important. The effect of washin (too little causes roll to the left and poor climb; too much causes too large left circles and excessive climb rate; way too much might make the airplane fly in a straight line)
6. Propeller pitch angle – buy the pitch measurement tool from Freedom Flight and see the picture in my google directory
7. Stabilizer tilt – See the picture in my google directory. With the airplane assembled and on the workbench, block the wing so that it is level and parallel to the workbench and measure the height of each stabilizer tip from the work bench and take the difference between these measures. Convert this measure to degrees again by taking the inverse sin of the measure over the stabilizer span (ours is inverse sin of 0.375”/11” = 1.954 degrees).

Keep asking good questions!

Brian T

[Frost0125]

Hi!

I am a longtime scioly student, but this year I decided to tackle building events because a lot of my team's graduating seniors were builders. I have tryouts for my team Dec 14, and I am looking for either a kit to order for flight/ a beginner-friendly way to build a plane. I am a very beginner builder, and am currently taking AP Physics, so I have a tiny bit of base knowledge. What kit would anyone recommend that would get here in time for my tryouts with time to work on the plane before/would you recommend a kit over building it from scratch?

[coachchuckaahs]

Frosty:

In the short time you have, and not having built a plane before, I would recommend a kit.

Keep in mind that Flight is NOT ABOUT DESIGN OR BUILDING. It is a FLIGHT OPTIMIZATION EVENT. You will need to spend far more time flying than you did building in order to do well. Once you have built you are probably 10% of the way there (to competition-ready).

As far as fast builds, I highly recommend the Laser Cut Planes kits. They are self jigging and really go together fast, and are known to fly well. I believe J&H's cheaper kit (all wood, not carbon) also has similar build approaches with interlocking ribs and spars, and would not be a bad option,

I like the carbon approach because we are in a very dry climate, and when going to a wetter location with an all-wood plane we experienced some warping. The carbon eliminated that for us. But, the all-wood kits are cheaper and faster to build.

Start scheduling the gym time ASAP!

Coach Chuck

[joshdaposh]

Hello, I have questions about my Wright Stuff Plane (I have built it using the Freedom Flight Models kit).

1. What really makes the difference between a 1-3 ranking national-level plane and a 4-10 ranking national-level plane? Is it how the plane is built? I doubt it because of the size limitations and most of the teams competing have won at the state level anyway to prove that they are competitive... Is it intricate little additions or removals? Or is it that the 1-3 place planes just had more winds in them?
2. I'm having trouble understanding how to trim my broad flaring-style propellor from Ikara. I heard that people sand it and trim it using small cuts but where...how... From testing it on my FFM plane, I noticed that my plane just dives straight down which probably means my propellor is way too heavy.
3. If a plane has a slow climb at the beginning of the flight will it have a slow descent on the way down? Is there a quick way to test the descent of your plane without having to fully wind it and see it climb and wait a couple of minutes for it to come back down?
4. How do we know which rubber thickness is going to maximize our performance? I've heard that thicker rubbers provide more power but fewer winds than thinner rubber. Wouldn't the obvious choice be to use a thin rubber then? I use a 0.94 rubber but I'm wondering if I should go down to like a 0.6 thickness or just remain at the 0.94.
5. If I just used my propellor out of the box would I be losing any performance from that? I noticed that people tend to change the pitch of their 24cm ikara propellor but what benefit does that have compared to just using it out of the box?
6. I noticed that some people tend to shim the trailing edge of their horizontal stabilizer to create more climb but wouldn't that lead to stalling as the plane descends down?
7. Finally, what CG is optimal for such a big wing for the 2023 FFM Division C kit?

[bjt4888]

Hello, I have questions about my Wright Stuff Plane (I have built it using the Freedom Flight Models kit).

1. What really makes the difference between a 1-3 ranking national-level plane and a 4-10 ranking national-level plane? Is it how the plane is built? I doubt it because of the size limitations and most of the teams competing have won at the state level anyway to prove that they are competitive... Is it intricate little additions or removals? Or is it that the 1-3 place planes just had more winds in them?
2. I'm having trouble understanding how to trim my broad flaring-style propellor from Ikara. I heard that people sand it and trim it using small cuts but where...how... From testing it on my FFM plane, I noticed that my plane just dives straight down which probably means my propellor is way too heavy.
3. If a plane has a slow climb at the beginning of the flight will it have a slow descent on the way down? Is there a quick way to test the descent of your plane without having to fully wind it and see it climb and wait a couple of minutes for it to come back down?
4. How do we know which rubber thickness is going to maximize our performance? I've heard that thicker rubbers provide more power but fewer winds than thinner rubber. Wouldn't the obvious choice be to use a thin rubber then? I use a 0.94 rubber but I'm wondering if I should go down to like a 0.6 thickness or just remain at the 0.94.
5. If I just used my propellor out of the box would I be losing any performance from that? I noticed that people tend to change the pitch of their 24cm ikara propellor but what benefit does that have compared to just using it out of the box?
6. I noticed that some people tend to shim the trailing edge of their horizontal stabilizer to create more climb but wouldn't that lead to stalling as the plane descends down?
7. Finally, what CG is optimal for such a big wing for the 2023 FFM Division C kit?

Josh,

If you haven’t already done so, you’ll want to read all the earlier posts from me, Coach Chuck and Jeff Anderson in this forum. Several of your questions have already been addressed.

Here are some additional thoughts:
1. Good rubber motor winding procedures, a good propeller and rubber well matched to the propeller and airplane trim are the critical success factors for the event. Also, lots of practice and testing of slight changes in propeller pitch and rubber density. See previous posts for a video of me winding a helicopter motor from a couple years ago. As noted in earlier posts, any reasonable airplane design will do. Airplane design is only 10% to 20% of the event.
2. The broad flaring Ikara weighs about 2.4 grams and the symmetrical Ikara is about 2.0 grams. So, to keep the CG the same, you’ll need to move the wing forward on the FF kit if you install a heavier propeller. “Dives straight down” sounds like the CG is too far forward (I say this based upon over 200 test flights by my students so far this year). See here for sanding and trimming the Ikara flaring prop for better performance https://scioly.org/forums/viewtopic.php?t=6085&start=70 and here https://scioly.org/forums/viewtopic.php?t=6554
3. You have to fully wind to determine a particular motor, trim, CG and prop and prop pitch effect on the climb, cruise (this is the mid portion of the flight where the airplane stays at the same altitude for 30-40 seconds) and let down (this is the name for the descent).
4. (and 5.) Determine rubber thickness (actually density; see previous posts) is done by lots of test flights. The FF kit comes with three rubber widths (again calculate the density of every motor) try them all with the stock prop and stock prop pitch. Then increase the prop pitch 2 degrees and test all three again. Then increase by 2 degrees and test all three again; etc. Longest flight duration (if rubber winding is consistent) is your best rubber. .06 rubber is not going to be any good on the FF kit with the 24 cm prop. Stick with what came with the kit and calculate rubber density of every motor.
6. Shimming the TE of the stabilizer has only a slightly different effect than raising the LE of the wing. As the FF kit has an adjustable wing incidence angle and doesn’t have an adjustable stabilizer incidence, stick with the wing incidence. Yes, an airplane with too much decalage angle (see my previous posts for definition) will stall. Test small changes in CG location and small changes in wing incidence to see their effect.
7. The starting point CG for the FF 2023 kit is 2.125” forward of the wing TE. Start there and test changes after you have first determined your best propeller pitch and rubber width (density). Moving the CG forward will require more wing incidence and will generate higher lift and higher drag and is probably not the way to go (but test it). Moving the CG back in 1/8” increments (and probably reducing the wing incidence if stalling, is probably a good direction to test. Again, work on the propeller pitch variations and the rubber density first.

Have fun with your airplane and do lots of test flights.

Brian T