# Simulation Program for Rotary Wing Aircraft RotaryWingSim 2.0

#### Jean Claude

##### Junior Member
Juergen,
For your calculations, I think you should only use these NACA data:
- Specific weight (Column D)
- Dynamic pressure (Column H)
- Rotor lift (Column P)
Then, calculate and compare the corresponding results:
- Shaft attack angle (and comparate to column G)
- Rotor speed (and comparate to column I)
- a0 (and comparate to column R)
- a1 (and comparate to column S)
- b1 (and comparate to column T)

It seems to me that your calculations is very consistent (except b1)

Interestingly the lateral disk tilt calculated by my program for case 2 agrees fairly well with the measured value. Perhaps the rotor in case 10 is in a flight state which is not very well captured by the theory.
Yes. Case 2 is to high forward speed, where the induced velocity (and the non-uniformity) is négligeable. Just as your theory!

Could you please also calculate case 2?
My spreadsheet tells me that the autorotation of this gyroplane is not possible beyond mu > 0.5
I assume that in reality the radial velocity can then unload profiles, thus reducing the necessary theoretical attack angle.
It seems to me that this assumption is confirmed by the value of b1 measured higher than theory predicts

Résultat pour les données correspondantes au vol plané n° 1
Le régime calculé du rotor dans ces conditions de charge, de pression dynamique et de masse volumique est 143 t/mn, tandis que la mesure a donné 133.1 t/mn
L’angle d’attaque calculé du disque est 7.2°, tandis que la mesure a donné 1.1° (arbre) + 5° (a1)= 6,1°
L’angle de battement longitudinal a1 calculé est 5.3°, tandis que la mesure a donné 5°
L’angle de battement transversal b1 calculé est 2.8° tandis que la mesure a donné 3.9°

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#### kolibri282

##### Super Member
My spreadsheet tells me that the autorotation of this gyroplane is not possible beyond mu > 0.5
I also had some trouble getting a converged solution for mu > 0.6, it took quite some time fiddeling with initial values until I had (nearly) solved case #2. This seems to indicate that theory is at its limits here. From the pitch distribution shown in naca 515 I deduced the values of 2.68° for the constant pitch angle at the blade root and a washout angle of -0.95°. Are these the values you are using in your spreadsheet?

For your calculations, I think you should only use these NACA data:
- Specific weight (Column D)
- Dynamic pressure (Column H)
- Rotor lift (Column P)
Currently my programs uses physical aircraft data and a prescribed flight state (speed, accelerations) to find a trim solution. I would take quite some changes to be able to prescribe lift and backwards calculate the necessary input for that, so I will probably keep "iterating" input values to get close to a given set of test data

#### Attachments

• PCA-2_rotor_naca-515.png
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#### Jean Claude

##### Junior Member
Juergen,
I entered the pitch values ​​of each of the 11 segments, corresponding to the initial twist added to the dynamic twist (loop manual calculation)
You can see the value in the bottom row.

#### kolibri282

##### Super Member
The PCA-2 used the Goe 429 profile for which, as far as I know, dynamic twist was not an issue. The much larger outboard pitch angles you use very likely explain why your spreadsheet predicts that no auto rotation is possible beyond mu=0.5. As the measured values indicate that mu=0.68 was attained your assumptions would have to be reconsidered. One point is that in case 2 the rotor load is reduced to about half the load value at low speed and therefor torsion, if it exists, is also reduced. naca-515 gives a very comprehensive set of pure rotor test data. You might want to try to reproduce these data with your spread sheet and then proceed to overall aircraft performance.

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#### Jean Claude

##### Junior Member
The PCA-2 used the Goe 429 profile for which, as far as I know, dynamic twist was not an issue. One point is that in case 2 the rotor load is reduced to about half the load value at low speed and therefor torsion, if it exists, is also reduced.

NACA 515 page 183:

So, Juergen, dynamic torsion exists on the PCA2, and I have it always well considered. Not you? Without this, how do you calculate the correct rpm, from false data?

As you can see in my precedent post I have 3.7° at the tip (and 4,4° for glide 10) instead of 1.9° at rest.

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#### kolibri282

##### Super Member
dynamic twist is 0.89 at the tip for 1000 pounds of thrust

This is what I tried to point out for case #2, the rotor thrust is -according to my trim solution - just 1200 lb, so dynamic twist is less than 1°. Also dynamic twist will change during one revolution since the blade load distribution varies. You would have to calculate the lift and drag of a blade for different (about a dozen, better two dozen) postions during one revolution to find out whether you can achieve moment equilibrium for autorotation.

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#### Jean Claude

##### Junior Member
NACA 515 gives a way to estimate the twist of the blades of PCA2 due to thrust. That's what I take into account (linear twist)
Do you neglect it in your calculations? One degree of twist is not negligible relative to 1.9°

At high Mu, the theory is beyond its limits. Radial velocity becomes important. But it is too complicated for me !

Now, observing the curves of report 515, the rotor of PCA2 with a pitch setting at rest to 1.9° could not exceed:
μ max = 0.72 for a thrust giving θ = 3° at tip
μ max= 0.63 for a thrust giving θ = 3.2° at tip
μ max= 0.53 for a thrust giving θ = 3.7° at tip
μ max= 0.42 for a thrust giving θ = 4° at tip

So, μ max is extremely dependent on the pitch θ and one small degree makes all the difference

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