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