PT6A-24 propeller brake?

[riggerrob 643]

A buddy claims that they had propeller-brakes on Twin Otter PT6A-24 engines, many years ago when he worked in the Canadian Artic. He vaguely remembers the propeller-brakes as disc brakes installed under a Supplementary Type Certificate.
They installed the propeller brakes after an Eskimo walked through a feathered propeller and got tossed into a snowdrift. He survived with a bad headache!
Considering how many passengers/whuffos/tourists are killed by spinning propellers (one per year), maybe propeller brakes should be installed on jump-planes.

First question: does anyone have numbers on an STC to install propeller brake son PT6A engines?

Secondly question: how much would it cost to install a propeller brake on a jump-plane?

[RiggerLee 61]

I'll be the dick.

Is it worth it? One or two or even ten deaths a year is actually not that many when you look at the number of people involved in aviation. You have to balance it against the weight complexity, matanance, cost, etc. of the installation. You're going to use it on every landing? How long to wear it out. then you're going to sit there while the free turbin spins up again? And of all the places to try to implement such a thing, skydiving? Yes we hot load all the time but 90% of the people out by the plane are or should be contous knowlagable people. The "woofos" near the planes are generally accompanied and corralled by an instructor. Yes there have been accedents, mostly involving a break down in that supervision. There was even one here in texas. A fatality resulting from the violation of a rule is not a reason to rewrite the rule book. It just reaferms the right ness of the current system. The answer is to keep woofos away from props, not to try to make props fluffy and safe with little ribbons on them.

So you'll say that a single life is beyond price. Well... no. If you talk to an actuary he can give you very good numbers for the price of some ones life based on age, income, and a dozen other things. The fact that engions don't have breaks on them attest to the fact that they are not justified and if we just follow the rules never will be.

Don't walk in to the prop. Don't let woofos walk into the prop. Done.

Lee

Lee
lee@velocitysportswear.com
www.velocitysportswear.com

[theplummeter 15]

I'll throw my hat in for not worth it. One malfunction that shuts something down and sends one in will hurt or kill more people than will die walking into a prop. Add in the money for installation and maintenance, and figure that at least one idiot pilot will hot start with the brake engaged and the whole proposition becomes a bigger pain in dthe ass than its worth.

[riggerrob 643]

"... Add in the money for installation and maintenance, and figure that at least one idiot pilot will hot start with the brake engaged ..."

...................................................................................

Sorry, but I a not following your logic??????
How is starting - with the propeller brake engaged - going to damage a free-turbine engine??????

[theplummeter 15]

The PT-6 like most turbines require airflow for cooling. If you were to start one with the prop brake engaged you would lose accelerated air from the propeller, the power turbine not spinning would interrupt outflow, and the higher internal pressure would lead to a higher temperature. If the battery were good and everything else was perfect it would probably be fine, but excessively cold or hot temps along with a forgotten brake and a worn battery are the recipe for turbine blade stew.

[totter 2]

Hey Rob, I think he might be mistaken.
Is he sure that he remembers it as a Twin Otter?
Propeller brakes, or a way to keep the prop from turning with the engine running is more widely used with the larger turboprops in ATRs, C-130s, etc.
Small PT6s just don't have the room internally or when all cowled up.
There is another reason why you would not want a propeller brake on a Twin Otter. The -6 has a time limit for having the prop in feather (i.e. no airflow) because the hot exhaust on the wing will damage the wing permanently. You need the prop blast, even at idle, to help keep the wing cool. Having the prop not turning would have the same effect.
As to starting a PT6 with the prop not turning, both of you are right.
It can be done, just get the hell out of the way once the prop is let go. It does increase the start temp, so if you had a weak battery you could run the risk of a hot start.
Is that a misprint with the engine model? There's no such animal as a -24.

[riggerrob 643]

Hee!
Hee!
Not 100 percent sure he was talking about a PT6A-24. That was 30 years ago, and another company (Bradley) operated the specific Twin Otter.

My buddy did explain that mechanics routinely held onto propeller blades during start-up. It seems - that at minus forty degrees - it take s a minute or so for warm oil to pass from the oil pump to the propeller ... a they preferred oil pressure in propellers before they started turning.
He said that back-pressure was no problem was long as the propeller was fully stopped.
He also said that the primary reason they had propeller brakes, was to AVOID hot starts. Since battery starts were always a risk - at minus forty degrees, they liked to apply the propeller brake to the right-hand (#2) engine, to keep the generator turning and keep the batteries charged ... then they were assured of a routine start on the number one engine. They preferred to shut down the left-hand (#1) engine because it reduced the risk to ground crews loading cargo or re-fueling the airplane.