Do bigger scales fly better

[xmech2k]

To expand on that 'feel to fly' statement, I think it refers to something like 'Will my model Piper Cub fly similarly to a full scale cub?' If the wing cube loading #s are similar, they will fly in a similar fashion. Or if your model Cub is way too heavy and has a higher wing cube loading, it might 'feel' more like an F-16!

[kyleservicetech]

Originally Posted by JetPlaneFlyer

Not sure i agree there.

The foamy would fly if it had enough power but it would have to fly at a similar speed to the turbine model, which would appear incredibly fast for a small foamy. But it would actually be no faster in real mph terms than the turbine.
This is because small models (all things being equal) 'look like' they are flying faster than big ones and are 'twitchier' on the controls.

Wing loading determines the actual minimum flying speed and manoeuvrability in absolute terms. Cube loading gives a guide to how the model will 'feel' to fly.

Should have indicated "Small Foamie" with a wingspan on the order of 10-15 inches.

The many many foamie electric jets my club members are flying are hitting 100 MPH as measured by on board speed indicators. Their power input is well over 200 watts per pound of airplane. One guy was running over 80 Amps on a $$$$ motor in his two foot wingspan foamie jet.

[JetPlaneFlyer]

Originally Posted by xmech2k

To expand on that 'feel to fly' statement, I think it refers to something like 'Will my model Piper Cub fly similarly to a full scale cub?' If the wing cube loading #s are similar, they will fly in a similar fashion. Or if your model Cub is way too heavy and has a higher wing cube loading, it might 'feel' more like an F-16!

i think it's important to differentiate between 'feel like they fly in a similar fashion', and 'actually fly in a similar fashion' in absolute terms.

If you have a model cub that had the same wing loading as a full size cub then in real measurable terms it will fly just like the full size Cub.. i.e. it will have about the same stall speed, and will turn in about the same diameter, and (assuming enough power) will have the same top speed and will take off in the same distance etc, etc.

Trouble is that a model that flew like that would 'feel' like a rocket propelled flying brick. Although it was flying at the exact same speed as the real Cub it would 'look like' and 'feel like' it was flying much faster.

On the other hand, if the model and the real one had the same cube loading then the model would in real terms fly much slower and turn much tighter and be generally much more manoeuvrable than the real one. But because the model is smaller this would 'look' and 'feel' much more realistic.

[kyleservicetech]

Originally Posted by JetPlaneFlyer

If you have a model cub that had the same wing loading as a full size cub then in real measurable terms it will fly just like the full size Cub.. i.e. it will have about the same stall speed, and will turn in about the same diameter, and (assuming enough power) will have the same top speed and will take off in the same distance etc, etc.

Trouble is that a model that flew like that would 'feel' like a rocket propelled flying brick. Although it was flying at the exact same speed as the real Cub it would 'look like' and 'feel like' it was flying much faster.

If you run the numbers on a fully loaded military jet fighter, they have about the same wing loading as making a Frisbee out of a cast iron man hole cover.

[fhhuber]

My 22 lb low wing big stick *8 ft span 16 sq ft wing!* will fly so slow the Eagletree and Spektrum pitot tube based airspeed meters will register 0.
This is not hovering... its having the engine at just barely above idle.
(OK... its not electric but this is about wing loading and scale factors and what turns the prop doesn't matter)

My Ultra-Stick 25 E can't even come close to flying as slowly.
Wingspan: 50 in (127 cm)
Overall Length: 41.5 in (105 cm)
Flying Weight: 3.4 lb (1.5 kg)
Motor Size: E-flite Power 25 Outrunner (EFLM4025A) or Power 32 (EFLM4032A)

close to 2X span and 4X area and 7X the weight...

The cubic factor for lift/weight with scale works.

[JetPlaneFlyer]

Sorry, but wing loading, not cubic loading determines stall speed (assuming all other variables are constant).

If you are interested in the physics and maths:

V = √( 2 W g / ρ S Clmax )

where:
V = Stall speed m/s
ρ (rho) = air density kg/m^3 (about 1.2 kg/m3)
g = 9.81 m s^-2
S = wing area m^2
Cl_max = Max Coefficient of Lift
W = mass kg

Or a simplified approximate calculation in ‘old units’ :

Stall speed = 5.25 * √wing loading

speed in mph
wing loading in oz/sqft

[kyleservicetech]

Originally Posted by JetPlaneFlyer

Sorry, but wing loading, not cubic loading determines stall speed (assuming all other variables are constant).

If you are interested in the physics and maths:

V = √( 2 W g / ρ S Clmax )

where:
V = Stall speed m/s
ρ (rho) = air density kg/m^3 (about 1.2 kg/m3)
g = 9.81 m s^-2
S = wing area m^2
Cl_max = Max Coefficient of Lift
W = mass kg

Or a simplified approximate calculation in ‘old units’ :

Stall speed = 5.25 * √wing loading

speed in mph
wing loading in oz/sqft

Ah Ha
I've seen this formula before. So that's where that 5.25 constant came from.

[quorneng]

Interesting post but by the end I do wonder if the OP wished he hadn't asked the question!

[solentlife]

Originally Posted by quorneng

Interesting post but by the end I do wonder if the OP wished he hadn't asked the question!

Think that applies to many threads !!

Nigel

[mclarkson]

I believe we at least established that the answer is, "yes." So many threads fail to achieve any kind of consensus at all, so I'm counting it as a success.

[JetPlaneFlyer]

Originally Posted by mclarkson

I believe we at least established that the answer is, "yes." So many threads fail to achieve any kind of consensus at all, so I'm counting it as a success.

Absolutely.. The answer 'yes' was pretty much arrived at in the first few posts. Some slight topic drift followed, as it does in almost all threads.

[npowell28]

Originally Posted by quorneng

Interesting post but by the end I do wonder if the OP wished he hadn't asked the question!

Ha! That made me laugh. Yes there is a few differences of opinion regarding wing loading and WCL but i think overall i've got my answer. Thanks to everyone that contributed. Very much appreciated.

Right i just need a nice calm day so i can go and see how it flys.

Cheers all