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