Flight B/C

[pumptato-cat]

As for approximate flight times for this year, you can get a pretty good estimate by first knowing your best typical flight average propeller revolutions per second (RPS) from last year. And then use the rubber motor max turns equation (on the NFFS website already linked in this forum). I did this type of calculation in my demonstration flight for the "Super Simple Div B Airplane flying video" on the NFFS website. Look in the description for this video and you'll see all the specs for my winding and my calculated RPS. The RPS we got on the stock FF kit (with stock propeller with pitch adjusted) last year after extensive testing and improving of CG, decalage, rubber density and prop pitch, was 7.0 RPS (for 24 ft flights of about 3:10-3:15; best flights with a flaring prop were 3:30 at 22 ft last year). So, an 11" 1.49g motor with two black rubber o-rings is .0622 g/in (approx) and will take about 1,300 turns at about 88% breaking turns. A good trim might allow 150 backoff turns and 150 turns remaining for 25 ft climb height flight. This would mean 1,000 turns are used to fly the airplane. Divide this by an RPS of 7 would give a flight of 2:22. Even better trim and a flaring propeller would get the flight closer to 3:00.

Good questions. Keep them coming!

Brian T

Okay, thank you so much! I'm back with another question: Why did so many planes that medaled at nats last season use stock Ikaras? I heard that most planes in Division C used them--so what was the advantage over balsa props, or was it simply a coincidence?

[bjt4888]

As for approximate flight times for this year, you can get a pretty good estimate by first knowing your best typical flight average propeller revolutions per second (RPS) from last year. And then use the rubber motor max turns equation (on the NFFS website already linked in this forum). I did this type of calculation in my demonstration flight for the "Super Simple Div B Airplane flying video" on the NFFS website. Look in the description for this video and you'll see all the specs for my winding and my calculated RPS. The RPS we got on the stock FF kit (with stock propeller with pitch adjusted) last year after extensive testing and improving of CG, decalage, rubber density and prop pitch, was 7.0 RPS (for 24 ft flights of about 3:10-3:15; best flights with a flaring prop were 3:30 at 22 ft last year). So, an 11" 1.49g motor with two black rubber o-rings is .0622 g/in (approx) and will take about 1,300 turns at about 88% breaking turns. A good trim might allow 150 backoff turns and 150 turns remaining for 25 ft climb height flight. This would mean 1,000 turns are used to fly the airplane. Divide this by an RPS of 7 would give a flight of 2:22. Even better trim and a flaring propeller would get the flight closer to 3:00.

Good questions. Keep them coming!

Brian T

Okay, thank you so much! I'm back with another question: Why did so many planes that medaled at nats last season use stock Ikaras? I heard that most planes in Division C used them--so what was the advantage over balsa props, or was it simply a coincidence?

Cat,

Good question. We never fly the stock 24 cm Ikara. Even with the 24 cm modified Ikara flare (modified as shown in the 2015 forum so that it actually flares) we usually gain 10-15 seconds. With a balsa “Bill Gowen” flare prop at maximum diameter to fit in the box we gained another 10 seconds. This flight time gain was less than we typically get as the super inefficient airplane configuration that resulted from the “box rules” did not benefit as much as usual from a flaring prop. We would have easily won nationals last year if we could have qualified to go (my best whole 23 event team place last year was 4th at Michigan States; we won both B and C by large margins in Flight though).

With your experience prop building, definitely build your own. I like the Gowen carbon hub as it is quite resistant to breakage and fairly easy to tune for flaring stiffness.

Brian T

[pumptato-cat]

Ah, got it, thanks! I keep forgetting that nationals isn't the best teams in the nation; rather, it's the best teams from each state. So I suppose it might've been a coincidence?
I'll definitely be building more props--I already have the supplies and the building is pretty easy. It's hard deciding what to build, though(what diameter? What pitch? What blade shape? There's 1294021948 more variables I'm forgetting). I guess I'll just try things until they work.
It's a pity that individual competitors are limited by their teams

[bjt4888]

Ah, got it, thanks! I keep forgetting that nationals isn't the best teams in the nation; rather, it's the best teams from each state. So I suppose it might've been a coincidence?
I'll definitely be building more props--I already have the supplies and the building is pretty easy. It's hard deciding what to build, though(what diameter? What pitch? What blade shape? There's 1294021948 more variables I'm forgetting). I guess I'll just try things until they work.
It's a pity that individual competitors are limited by their teams

Cat,

Diameter would be the maximum you can go and still fit in the box. This is a little tricky to estimate, so if you build 1/4” bigger than works, you can always sand 1/8” off each blade tip to fit. Pitch would be all in the range of 1.4-2.0 pitch/diameter ratio (after building, you can wet and bend some to add or remove a few degrees of pitch) and a good start for blade shape would be a tracing of the front portion of the Ikara flaring prop or a half ellipse of 1.625” chord and 4.25” blade length. Hub can be either a simple 6” stick of 1/16” square basswood or the Gowen carbon rod hub.

Did you get my Scioly.org PM regarding this question?

Brian T

[hchharawalla]

Hi Coach Brian and Coach Chuck- this is my first time trying to coach and help my kids out in Flight, and I appreciate all the fantastic NFFS resources so much! This event no longer seems as terrifying to comprehend . I think I get that the main area for improvement is good prop design and trimming.

I was comparing Gowen's Finny to the SuperFinny design and his flight notes (https://indoorarchive.github.io/0811/4855.html), and after seeing some great planes last year I was curious about something. How much time and payoff is worth experimenting with larger wing chord lengths? And at what stage would it be recommended to try? It seems to be a trend I've noticed in some planes with high flying times.

[bjt4888]

Hi Coach Brian and Coach Chuck- this is my first time trying to coach and help my kids out in Flight, and I appreciate all the fantastic NFFS resources so much! This event no longer seems as terrifying to comprehend . I think I get that the main area for improvement is good prop design and trimming.

I was comparing Gowen's Finny to the SuperFinny design and his flight notes (https://indoorarchive.github.io/0811/4855.html), and after seeing some great planes last year I was curious about something. How much time and payoff is worth experimenting with larger wing chord lengths? And at what stage would it be recommended to try? It seems to be a trend I've noticed in some planes with high flying times.

Hch,

Glad the new NFFS website content and config were helpful! The indoor freeflight community likes to say that it's all about the prop and the rubber and the rest is just along for the ride. This assumes a reasonably good design though. And yes, Bill Gowen's designs are very good.

It is worthwhile experimenting with larger wing (and stabilizer) chord with the "fit in a box" rules. You'll want to have a fair amount of gym time (with blowers off) to do this as well as testing different propellers/rubber match. The teams that I coach usually build variations we want to test right from the start of the season as it can take some time to get trim, propeller variations and rubber matching done for each design variation.

Brian T

[coachchuckaahs]

Hi Coach Brian and Coach Chuck- this is my first time trying to coach and help my kids out in Flight, and I appreciate all the fantastic NFFS resources so much! This event no longer seems as terrifying to comprehend . I think I get that the main area for improvement is good prop design and trimming.

I was comparing Gowen's Finny to the SuperFinny design and his flight notes (https://indoorarchive.github.io/0811/4855.html), and after seeing some great planes last year I was curious about something. How much time and payoff is worth experimenting with larger wing chord lengths? And at what stage would it be recommended to try? It seems to be a trend I've noticed in some planes with high flying times.

I agree with Brian's direction here. First step is to get in the gym with something decent. Our first year we were in the gym with the equivalent of Brian's "super Simple" design, and taking lots of data. We then built 12 planes, and eventually probably 25 props.

With this year's rules (and last year), much less is defined on the layout of the plane, so experimenting with larger chord is certainly on the table. You do not indicate if you are B or C division. In B division, there is plenty of room to experiment. In C, because of the fairly short tail moment (better than last year), you could run into stability issues. As you make larger chords on the wing and stab, you end up with a shorter effective tail moment, which makes a more troublesome plane to trim (sensitive to very small changes).

Once you have a basic layout, build it and fly it. Work first on getting it optimized with a commercial prop, if you have any available. Once trimmed, change things such as CG, and retrim. Adjust torque until you get to the ceiling, or nearly so, and then compare times to see what was better.

As far as props, I would not get too hung up on perfection here. We typically, on years we went to Nationals, built 25-35 props adjusting flare, shape, pitch, etc. This year we add in diameter as a variable, but the box will set your limits on that. We did "Bucket props" where you form the prop shape on a cone or cylinder, and eventually made our own prop blocks. Bucket props can be a very close approximation to a helical pitch progression prop.

We still use the Ikara shape, forward of the spar, with nothing behind, for our planform. Even in LPOP we use that, slightly enlarged on a copier. The LPP has a diameter limit of 12", so we used that experience to benefit last year's Div B props, whereas C div we used the stock Ikara flaring prop size. We used 1/32" C-grain wood for the blades, and did not bother to thin them as we needed mass up front anyway. We did make some with A grain, but they proved to be too flexible (over-flared), which would result in poor climb after the initial burst.

Be sure to keep detailed logs for your flights. You may even want to start a second log for props, with columns for each variable you can control on the prop. Adding prop building adds a number of variables. and that experimental space needs to be explored carefully and systematically. You can only do this with good logs.

We used the Basswood spars for simplicity, and could wet the inner part of the spar, twist it a bit, and dry with a heat gun to make pitch changes. With the Gowen prop hub, you could make small pitch changes by wetting the blade near the spar and bending it slightly, at the risk of changing your airfoil of the prop. When we did those hubs we typically made multiple props with identical features except varied the pitch over a range.

Coach Chuck

[coachchuckaahs]

New video posted: Super Simple Torque Meter, https://www.youtube.com/watch?v=HccYaD_AjQg, with a document with the dial and details at https://www.freeflight.org/wp-content/u ... eMeter.pdf

If you have read much in this forum, you have seen all of the coaches preach using a torque meter. Coach Brian, with support from the NFFS Youth Development Program, has developed a simple TM build using paint stir sticks and a guitar wire. He built his for $0.95,, having only to buy the guitar string! The length of the wire is chosen to give good accuracy for 2.0 oz-in on one full turn.

You can also purchase TM's from most kit suppliers for under $20, which if you order with a kit should not add to the shipping costs.

Coach Chuck

[pumptato-cat]

Ah, got it, thanks! I keep forgetting that nationals isn't the best teams in the nation; rather, it's the best teams from each state. So I suppose it might've been a coincidence?
I'll definitely be building more props--I already have the supplies and the building is pretty easy. It's hard deciding what to build, though(what diameter? What pitch? What blade shape? There's 1294021948 more variables I'm forgetting). I guess I'll just try things until they work.
It's a pity that individual competitors are limited by their teams

Cat,

Diameter would be the maximum you can go and still fit in the box. This is a little tricky to estimate, so if you build 1/4” bigger than works, you can always sand 1/8” off each blade tip to fit. Pitch would be all in the range of 1.4-2.0 pitch/diameter ratio (after building, you can wet and bend some to add or remove a few degrees of pitch) and a good start for blade shape would be a tracing of the front portion of the Ikara flaring prop or a half ellipse of 1.625” chord and 4.25” blade length. Hub can be either a simple 6” stick of 1/16” square basswood or the Gowen carbon rod hub.

Did you get my Scioly.org PM regarding this question?

Brian T

Thank you! That helps a lot--just saw your PM, sorry!

[randomdogonapc]

Hi everyone!
While I'm waiting for our kits to arrive, I decided to try and document as much useful trimming and design advice from last year's and previous flight forums. Flight forums are always super full, so I wanted to thin down the amount of reading I would have to do. Does anyone know what years of Flight/Wright Stuff had rules closest to the designs we're seeing this year? I know the Wright Stuff rules from past years were a lot stricter, but as far as I can tell 2019 and 2020 seasons were both restricted to monoplanes, while 2021 allowed for biplanes? I feel like most trimming advice from the monoplane seasons will hold up to the 2024 season, but I also don't want to go through hundreds of pages of forum posts. Thanks in advance!