Wright Stuff B

[retired1]

Read this carefully and then come back with specific questions.
https://www.soinc.org/sites/default/fil ... iad5.0.pdf
If that is a bit much for a beginner I would buy the Freedom Flight kit. Dave is not advertising it on his site, but he has started kit construction. It is a complete kit for 2 planes that if built correctly will be very competitive if you practice a lot.

[bjt4888]

For those of you that are looking at modifying Bill Gowen's Finny09 design to match this year's rules, here are a few design modification suggestions:

1. Increase the motor stick length to 13" or 14" instead of 12". It is likely that with the light wing loading and small propeller in this year's rules the optimum motor length will be 14" to 16". A slightly longer motor stick, with the rear hook mounted near the end of the stick and not with the plan designated 10" nose to rear hook distance, will make it easier to load a longer motor without "knot chains" poking out and rubbing on the motor stick. Of course, it is possible to load a long motor on a short motor stick (as with the AMA A-6 event), but it is likely to give you a better result if the stick is a little longer. A 14" stick will give you about 13" hook-to-hook, which works pretty well with a 15" - 16" loop motor.
2. This long, thin motor won't require such a beefy motor stick. 3/16"x3/8" of 8lb cu ft wood will give you a 2.0 gram stick before adding hook, nosebearing and tissue tubes.
3. Although 4 lb cu ft wood for the stab and 5 lb cu ft wood for the tailboom will help locate the CG correctly with the 1.5" nose. You can build the stab with 8 lb cu ft spars and 6 lb cu ft ribs and, with a careful job of covering, it will still only weigh about .36 grams if you skip the tip plates. A single vertical fin of about 2.5" base, 2.5" height and 1.5" top (swept to look nice) can be substituted for the twin tip plates. This fin should only weigh about 0.1 grams even if constructed of 8 lb wood (recommended for durability).
4. You could shorten the tailboom to 11" for a length overall of 25" (with 14" motor stick) and cut the tailboom from easier to obtain 6 lb cu ft wood and it will only weigh about 0.5 grams.
5. With a wing weight of 1.5 grams and a prop weight of about 1.6 grams, this will give you an all up weight of about 6.3 - 6.5 grams, allowing 1 - 1.2 grams of ballast that you can move around to vary center of gravity.
6. Probably you'll find that a nose length of about 2.5" will be required (instead of the 1.5" shown on the plan) to give the correct center of gravity if the ballast is located about 4" from the nose. This ballast location should be a good compromise to all CG adjustment in both directions.
7. If you find the drooped tail boom intimidating, you can build with a tailboom that has a bottom surface parallel and in line with the bottom surface of the motor stick (easy to construct). This will create about 0.7 degrees of positive stab incidence, which may require another 1/16" of wing incidence to counter.
8. Offset of the tailboom about 2.5 - 3.0 degrees will help greatly with the left turn as will the recommended stab tilt (maybe about 3 - 4 degrees). These two trim settings, along with the 2.5 - 3.0 degrees of left thrust offset and possibly about 1/16" of left wing washin (and the plan amount of .75" wing offset), should create a controllable left turn circle of about 20 ft - 25 ft.

Of course, the wing dimensions and the stab dimensions and the propeller diameter need to be adjusted to this year's rules.

Good Luck

Brian T.
AMA since 1972 (off and on)

[bjt4888]

A few more:

9. Overlap joint for the tailboom to motor stick (overlap 1/2", so the tail boom is actually 11.5").
10. 12 lb cu ft wood for wing spars. A little tougher to withstand possible rough handling.
11. 1/16" wood for the stab ribs.
12. Harlan SO thrust bearing. It has the "pigtail" now and fits the .020" shaft without modification.
13. Cover with Ultrafilm.

Have fun and do lots of test flying.

Brian T.

[bjt4888]

In my recommendation for mods to the Bill Gowen Finny09 above, #3 refers to a fin constructed of 8 lb wood that would weight 0.1 grams covered. Sorry, I wasn't very clear in this direction. The fin is not constructed of sheet wood (note "covered"), but is constructed of 8 lb. 1/16" square sticks and covered with ultrafilm. A sheet wood fin of 1/16" 8 lb wood would obviously be way too heavy.

Brian T.

[jander14indoor]

I'd like to propose some additions and alternatives to Brian T's suggestions on changes to the Finny09 design

For a beginning team I'm not sure I'd lengthen the motor stick, so many students have trouble with bending already. Even with thinner motors I suspect you should keep the stick robust and short is better. Not much performance difference to offset bending motor issues.

Don't lock on the indoor covering. With the weight budget on these planes you can use lightweight grocery/shopping/produce bags or dry cleaning bags. Make sure you test and select the lightest available. Yes it is a weight penalty, but only around 0.5 gm and you'd only need to reduce the ballast to offset that. And they are free, though you are trading money for time. Note, there are a lot of heavy bags out there, avoid those, and especially avoid Saran Wrap or other food grade plastic wrap.

Prop hanger. The Harlan is good because it allows you to change props. Another alternative is wire pigtail prop hangers you make yourself. There is a good video on line showing how to do it. No real benefit of one vs the other than the opportunity to again trade time for money if that is important.

I'd shoot for a weight without ballast of closer to 7.0 gm and allow for less ballast. Then not use ballast to balance (other than minor adjustments) but build to balance. Build your whole plane except attaching the wing tubes. Assemble the whole plane less the wing, attach prop and a 1.5 gm motor. Find the balance point of this assembly. THEN locate the wing tubes and wing based on distance from this balance point.

If you are covering with store bags, you may not want to use denser wood for the tail. It could run your cg too far back. Manageable if you find the balance point as suggested, but the nose may get a little long.

To help hit a target weight, consider developing a bill of material listing each part, its size and density to give a target weight for each part. Add it up and target 7.0 gm. Don't forget to allow for glue.

Jeff Anderson
Livonia, MI

[MysterySkye04]

So, has anyone created a working plane yet? I know it's a bit early, but I would like to know how everyone's plane is doing My planes have been horrible, but now getting better. (I'm just a curious kid, my bad)

[Sciencevale]

We have been looking for rubber bands and can't find any. Where are you guys getting your rubber bands?

[Unome]

We have been looking for rubber bands and can't find any. Where are you guys getting your rubber bands?

I frequently hear than Tan Super Sport Rubber is the best in the business (and possibly the only one in the business of actually making rubber, since apparently a lot of other companies just sell their rubber repackaged). Don't quote me on this though, it's just hearsay from reading a lot of posts.

[bernard]

We have been looking for rubber bands and can't find any. Where are you guys getting your rubber bands?

I frequently hear than Tan Super Sport Rubber is the best in the business (and possibly the only one in the business of actually making rubber, since apparently a lot of other companies just sell their rubber repackaged). Don't quote me on this though, it's just hearsay from reading a lot of posts.

If you buy rubber from FAI Model Supply, chances are it's not the size you're looking for. Flyers buy bulk rubber and cut it to size using rubber strippers (usually $150-200). Need rubber of a certain size but don't have a rubber stripper? Order through the Freedom Flight website.

[Sduvall01]

How do you find the center point of gravity on your plane? Also what are good places to buy your propellers?