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Forum: Rotorheads
17th Jun 2019, 11:43
Replies: 1,480
Views: 1,553,406
Posted By AMDEC

Losses of yaw control on helicopters

I fully agree that the number of accidents should be related to the number of flight hours. I was not able to find the information.

I do not say that the helicopters that have the largest number...
Forum: Rotorheads
17th Jun 2019, 07:16
Replies: 1,480
Views: 1,553,406
Posted By AMDEC

Losses of yaw control on helicopters

The reproach that can be made about the article in "Pilot" is not what is said of the Cabri, but that it is presented as a problem of the Cabri only. A small look in accident reports databases.(and...
Forum: Rotorheads
26th Apr 2019, 10:50
Replies: 1,480
Views: 1,553,406
Posted By AMDEC

Loss of control in yaw is not specific to the...

Loss of control in yaw is not specific to the fenestron. I looked into accident reports coming from different Aviation Investigation Boards. Between 2010 and 2016 (seven years) I have 9 on the Cabri,...
Forum: Rotorheads
24th Apr 2019, 10:35
Replies: 1,480
Views: 1,553,406
Posted By AMDEC

Fenestron Stall

The Fenestron Stall problem is in the name. The British Army thought that the fenestron stalled and asked to add pedal into the turn when unanticipated yaw started. It can be found in the CAA paper...
Forum: Rotorheads
30th Nov 2018, 12:36
Replies: 1,173
Views: 532,291
Posted By AMDEC

...with no advanced warning, he felt the nose of...

...with no advanced warning, he felt the nose of the helicopter drift right. He initially corrected with left pedal; however, the nose continued to drift right.

This is very similar to what AAIB...
Forum: Rotorheads
30th Nov 2018, 05:11
Replies: 1,173
Views: 532,291
Posted By AMDEC

Failure ?

Unless I missed something the AAIB report does not tell that a failure occurred...
Forum: Rotorheads
10th Nov 2018, 14:57
Replies: 1,173
Views: 532,291
Posted By AMDEC

Why look for a TR failure ?

Statistically there are many more accidents due to unanticipated yaw -- so poorly named as LTE -- than due to TR failures. Looking at the initial yaw, there is no abrupt acceleration. If it is a TR...
Forum: Rotorheads
18th Sep 2018, 10:07
Replies: 38
Views: 4,149
Posted By AMDEC

Vibration issue

Do not think about it. It would be a perfect shaker.
The flapping motion of the blade induces some vertical force at the flapping hinge that directly varies with the flapping angle. If you sum the...
Forum: Rotorheads
17th Feb 2014, 07:39
Replies: 40
Views: 14,372
Posted By AMDEC

Cat A vs Class 1

Cat A and Cat B are defined in certification rules.
Class 1, 2 and 3 are defined in operational rules.

Class 1 and Class 2 performance require the helicopter to be certified in Cat A (and...
Forum: Rotorheads
7th Feb 2014, 07:42
Replies: 13
Views: 2,164
Posted By AMDEC

Simple formula

Try this

n = 0.2 ρ b ℓ R UČ / Mg

where
· ρ is the air density in kg/m3 (1.225 in ISA SL conditions)
· b is the number of blades of the main rotor
· ℓ is the average chord in meters
· R is...
Forum: Rotorheads
5th Aug 2013, 09:01
Replies: 38
Views: 4,540
Posted By AMDEC

The ball is a sideslip indicator on a symmetrical aircraft only

In the helicopter axes (where the ball is actually installed) aerodynamic forces are balanced by inertia forces. The ball only sees inertia forces, but they are a view of the opposing aerodynamic...
Forum: Rotorheads
13th Apr 2013, 20:41
Replies: 1,886
Views: 845,784
Posted By AMDEC

Taxi rollover

Not counterbalancing the tail rotor thrust by some main rotor moment can lead to taxi rollover. This has nothing to do with dynamic rollover which occurs in flight when the landing gear hits the...
Forum: Rotorheads
29th Sep 2011, 19:08
Replies: 41
Views: 7,539
Posted By AMDEC

Froude theory (cont)

220 lb asks for 2.2kW. It is only the minimum power required to produce the momentum and lift that weight (assuming 100% efficiency). The drag of the blades and the antitorque are additional power....
Forum: Rotorheads
29th Sep 2011, 07:06
Replies: 41
Views: 7,539
Posted By AMDEC

Froude theory

Froude theory tells that with a 10m diameter rotor you need at least 7.5kW to hover 500lb and more than 12kW for 700lb. The burden is less on the second crew member but still challenging !
Forum: Rotorheads
28th Mar 2011, 11:52
Replies: 12
Views: 3,575
Posted By AMDEC

Increasing the airspeed on a fixed-wing aircraft...

Increasing the airspeed on a fixed-wing aircraft allows to reach higher load factors, sometimes beyond the structural strength. This is why some fixed-wing aircrafts have g-limitations.
There is...
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