Flight B/C

[coachchuckaahs]

Hi everyone!

First post on this forum,

I wondered if you guys had any suggestions for winding procedures for low-flight venues. Tryouts for the team at my school has flight tryouts happening in a 15 Ft space (Cafeteria), which is not something that I am normally used to flying (I have been flying at my local gym). I have been following the procedure of using backoff winds to get to my launch torque, but my plane still launches into the air, and even in a full-sized gym, it usually touches the rafters multiple times. I think that it may have something to do with the decalage, but not totally sure where it is coming from. My wing incidence is currently in the sweet spot (If I move it down, there is no climb, up, and it stalls), and I think that my CG is relatively okay.

I am using .87 rubber,

Thank you guys for all the information that you have in these forums!

Pie:

You did not report torque (max and launch) and rubber density (g/in) or loop size (relaxed loop, measure before ever winding it). So it is hard to tell if you have the rubber optimized.

Did you have winds left (at 25' ceiling), or is it running out?

The decalage (incidence) gets adjusted for cruise and letdown. It is a mistake to adjust for climb, as the other portions of flight are typically much longer. It does sound like you are close to correct for your current CG location. You also did not report left wing wash-in, which can have a dramatic impact on climb.

Generally, you should be winding to max and then backing off to launch torque, and the back-off with a non-flaring prop in a low ceiling can be considerable.

Optimize the rubber/prop combo at your 25' ceiling. This means to get the rubber sized such that it just runs out or has maybe half a row of knots on landing, when 25' is reached, with the proper launch torque to just reach the ceiling. In SO it is usually not wise to bang the ceiling a lot, as it can redirect the plane and you only get 2 flights. Now start reducing launch torque to map out a torque vs. altitude curve, for that rubber, prop, and trim combination.

It may take a lot of unwinds to get to a 15' torque value. You may be around 0.2 ox-in, or even lower for that ceiling.

Generally, if the system is optimized at 25', you will need to go to lower launch torque and thicker rubber (by 0.001-0.002") to adjust down. The heavier rubber will slow the letdown, but increase the climb (which is why you need lower torque).

Please see my post just prior to your post, where I talk about rubber thickness. Different batch of SS was probably substantially different thickness, so width had to be substantially lower to perform the same. This is why we prefer to talk loop size or rubber density (g/in) instead of cut width.

If you do not have a torque meter, check out coach Brian's Super Simple Torque Meter build on the NFFS web site. It will be VERY hard to do well in a low ceiling without a torque meter.

Coach Chuck

[FlyingPie]

Hi, thanks for the quick reply!

I have a freedom flight model torque meter (I flew div B but am competing in div C this year) and currently, I have been launching ~.75 oz torque. I have a bit of wash-in on the left hand side, and have been using a loop of May 22 .87 rubber, about 11.5 inches relaxed. and I do have about a knot of winds left. I have been looking into different prop designs for lower ceilings, and have 2 of the Flaring Ikara props, but they haven't been doing well. I think that it may have something to do with the weight and getting the CG right, but for most of the test flights, I have been using a standard Ikara prop.

Thank you for the winding tips, will be experimenting more! I'm really excited for this year!!

[coachchuckaahs]

Pie:

0.75 oz-in is a lot of launch torque on SO planes at any ceiling height (except maybe 60 feet). For a normal gym (say 30-35 feet) with a non-flaring prop you will likely be in the range of 0.3-0.45 to start with. For your low ceiling you will need to back off even more, into the 0.2-0.25 range I suspect. Only your experimentation will tell you, but 0.75 oz-in is a lot of torque.

For C division, with a relatively short tail moment (not as bad as last year), the CG is critically important, and small changes to the CG location will make substantial changes to the flight character. Remember when changing the CG you need to re-optimize the decalage for cruise and letdown.

Also, be sure whatever prop you use will fit in the box mounted to the plane. Last year the 9.5" Ikara was about the largest you could fit in the box for C division, when the plane was angled in the box.

With a full row of knots left, and going to an even lower ceiling, you will want to either go wider on your rubber or pitch the prop down slightly. Obviously, we are talking two variables here (prop pitch and rubber width), so there is a two-parameter optimization. If you are not stripping your own rubber, then you may have to adjust pitch a little between rubber sizes available to you. At some point you will need to determine if you are at an optimum for the rubber/prop combination. Also, the rubber linear density will vary along the piece of rubber you have, so "0.087 width" is not necessarily a constant. Be sure to log your loop length (before any winding, when you make the fresh loop) or the g/in linear density of the rubber before you tie it.

Coach Chuck

[RippyChip911]

Hello:

I am coach here and we have some kits from Freedom Flight Div B planes from last year.

I am wondering if we can use them for this year's competition? Are the dimensions still good for this year?

thanks in advance
Sanjeev

[bjt4888]

Hello:

I am coach here and we have some kits from Freedom Flight Div B planes from last year.

I am wondering if we can use them for this year's competition? Are the dimensions still good for this year?

thanks in advance
Sanjeev

Sanjeev,

Yes, last year’s Freedom Flight Division B kit fits in this year’s box. This year’s box is a fair amount bigger than last year’s, so last year’s Div B airplane will be at a competitive disadvantage to larger airplanes that the new box allows.

Brian T

[jander14indoor]

BUT, the disadvantage is not very large! Until you can fly last years plane to 2+ minutes it won't gain you more than a few seconds (if that) to push to a much larger plane.

I'll note that last years single biggest cause of tiering (and it was still a problem at nationals) was teams pushing the limits on the box size to little, if any advantage.

Jeff Anderson
Livonia, MI

[coachchuckaahs]

Hello:

I am coach here and we have some kits from Freedom Flight Div B planes from last year.

I am wondering if we can use them for this year's competition? Are the dimensions still good for this year?

thanks in advance
Sanjeev

While the allowable plane (box) size has increased some this year, for Div B the increase was only 2cm in length and 2cm in width, same height. So this is not a huge increase in plane dimensions. Therefore I would feel comfortable using last year's kit, especially for Regionals and maybe State, depending how competitive your state is. As Coach Jeff notes, it is far more important to get your plane flying well than to increment the size slightly and still have a poor flying plane.

I should note that the FFM plane design has changed substantially this year. Instead of tip plate he incorporated center dihedral, which allows a notable increase in projected wing span (lifting area). More importantly, the small tip plates on last year's design (to fit box) resulted in needing substantial left wing wash-in to prevent rolling into the circle at high torque. This year's design likely eliminates this wash-in need, which will help the times.

If your school, or your Region/State is highly competitive in flight, you may note differences. If you are middle-of-pack, or your state is less than competitive, there is no need to scrap those kits you already have.

Keep in mind that any plane entered in competition this year must have been built by team members of this year's team.

Spend your time in the gym maximizing the plane's capabilities before spending time and money chasing performance on new kits. Coach Brian's Super Simple plane, based on Chuck Markos design, should get over 2 minutes in a normal gym, for less than $10.

Coach Chuck

[pumptato-cat]

Heya!

Has anyone here used crusty old cya? Wondering whether I should throw away a bottle that's a couple of months old. At what point does CA become "bad" or unusable? I wanted to do some building this weekend but I don't have any other superglue

[bjt4888]

Heya!

Has anyone here used crusty old cya? Wondering whether I should throw away a bottle that's a couple of months old. At what point does CA become "bad" or unusable? I wanted to do some building this weekend but I don't have any other superglue

Cat,

If the CA is fresh when you bought it, and is a good brand, we get about 9-10 months out of a bottle if capped between uses. A good test to see if it’s bad is to bond a couple small scraps of balsa. Hold the bond together for about 10 seconds, if the bond can’t be pulled apart, the glue is probably fine.

Brian T

[coachchuckaahs]

Questions from a Flight Group on Discord:

1. Do I add decalage to climb more?
2. What can I do if the blowers are on or the air is noisy?

Answers and some discussion:
1. No. The basic trim (decalage and CG) are set for cruise and letdown. While the plane may climb more with excess decalage, it will stall or mush on letdown and you will lose a lot of time.

Adjust your trim by running low torque flights so you can observe cruise and letdown at eye level and make adjustments. If you move CG forward, you will need more decalage, and vice versa. At each CG location, re-adjust the decalage. Then re-adjust the launch torque and rubber width to get climb to your desired altitude. Then check the stopwatch, comparing like-altitude flights after re-optimizing decalage for CG. The C division planes especially are sensitive to CG location and decalage, so you will want to experiment with this. However, don't be tempted to increase climb with decalage!

Once your plane is trimmed, higher torque at launch should increase climb. If it does not, you need to fix other areas of trim, not decalage. First, is it a rubber issue, or rubber winding issue? Are you winding per Coach Brian's demo on Freeflight.org? Wind to near max torque (breaking torque) and then unwind to launch torque.

Second, does the plan roll in (left) at high torque? If so you can add a little left wing wash-in to help prevent this. This should be used in moderation, because wash can add a lot of drag. Some kits last year needed a lot of wash. Do not just add wash because it is what was needed last year. Adding wash is a strong compromise.

Third, does the plane dive without rolling in? It may be motor stick flex causing this. Consider adding a post at the midpoint (1/16" square basswood works well), and then truss the motorstick with Kevlar thread (strong sewing thread can be used in a pinch). We typically have a post about 1" tall. This can help control vertical motor stick flex.

Note: On F1D planes designed for very high ceilings (salt mines), some motor sticks are designed to twist at high torque, inducing wash-in during the climb that then goes away for the cruise and letdown. This is probably beyond what is needed for SO.

2. If blowers are on, or low ceilings are expected (ceiling touches likely), you want to INCREASE stability.

Stability is NOT a lack of stalling. A stable plane can still stall. Stability is adjusted by moving the CG relative to the wing, or relative to the center of lift. To gain stability, move clay forward, add clay to the nose, or move the wing back. Moving the wing back will shorten the tail moment which may make trimming more difficult. If you have a well-trimmed plane that needs to be more stable, you will move the CG forward, and then add decalage to lift the nose. This increases stability, but also increases drag. A necessary evil in many SO venues.

Stability is the ability to recover from external disturbances, such as rough air or ceiling touches. Lowering the decalage, as suggested by one in that forum, will speed the plane up but does nothing to add stability. Move the CG forward (which also will speed the plane up), and then slow it back down by adding decalage.

Any plane, stable or not, can be made to stall by adding decalage. The stall is not an indicator of stability.

If your plane touches the ceiling and dives to the floor, it needs more stability. If your plane touches the ceiling, drops a few inches, and then continues on, it may be too stable. What is wrong with that? It will be flying with more drag and therefore less efficiency.

There will be a decent range of CG's with useable stability. Now you need to explore that space to see the impact on the stopwatch, vs the risk of disturbance. Move the CG 2mm, then re-optimize the decalage for acceptable flight in letdown. Then adjust the launch torque to get to the intended altitude. Then adjust your rubber width (and/or prop pitch) to use up most of your winds. Then compare the duration to prior combinations. Don't compare without getting to the same altitude and using the winds effectively.

Note also you CAN try different decalages at the same CG to see what speed for forward flight is most efficient. Some planes, notably the short coupled planes, may "mush" instead of stalling, and it may not be as obvious. But the stopwatch will tell the story.

Coach Chuck