MD 902 Explorer Question

[Trevor KC]

Hi Guys

Just a quick enquiry I was wondering if you could help with. I'm in the middle of an engineering project at the moment and in order to assist with this I am referencing the MD902 RFM. One area I'm having difficulty understanding within the flying control chapters is the collective friction system. I understand the friction release switch and what it's functionality is, what I'm not clear about is how do you adjust the friction: the RFM states it can be adjusted between 5 - 25Ibs. However, I cannot find how this is achieved. The aircraft I have flown - 206B, R22, it is either a knurled knob or a collar on the shaft of the collective lever. Any help would be gratefully received.

Thanks

Trev

[handysnaks]

Trevor, it's a small lever/trigger attached to the collective (underside). The friction is either on or off!

[explorer99]

Trev,

To quote from the maintenance manual:


"The collective friction unit is located below the collective stick assembly under the cockpit floor panel. [It] is an electrically operated series of drum wrap springs that provide friction to a set of drums. The first series maintains friction at the 5 pound resistance level when the pilot releases the friction. The second series applies 25 pounds of resistance when the pilot engages friction. The collective friction unit is linked to the collective stick assembly by the collective friction link.

The collective friction release switch allows the pilot to turn off friction by moving the switch forward or momentarily release the friction by moving the switch aft. The momentary release position is spring-loaded to return to the centre or on position."


In other words, imagine the friction switch as a three-position rocker switch spring-loaded to the centre position and operated by the first two fingers of your left hand under the collective. If you want to apply friction (ie 25 lb resistance), you squeeze the switch backwards, adjust the collective position, then release the switch. If you want to release the friction (ie 5 lb resistance), briefly rock the switch forwards.

In practice it's not perfect; the Tq will tend to drop slightly from the point at which you set it, so I usually pull slightly more power than I want (by about 3-4%) and let it settle. It's certainly a very strange system that initially takes some getting used to but, like most things, becomes second nature after a while.

E99