Brakes Aren't Holding

[GuiLaMon 0]

I am using Aerosoft's interactive checklist to get my Twin Otter (Extended) into the air.

When I get to the Propeller governer and autofeather testing portions, when I advance the power levers as instructed, my plane starts to advance forward despite my parking brakes being on. Also, on occassion, my plane tends to tip back onto it's stern when the throttles advance in a parked position.

 

What should I be doing to avoid these occurences.

[Herman 1591]

IRL, you'd never rely on the parking brake alone to hold the aircraft still while under more than idle power, especially on run-up. Feet always on the toe brakes to hold, and at runup power, full braking is the norm. Of course, if you're using physical rudder pedals with toe brakes, make sure they're correctly calibrated. By the way, many require the two brake axes be reversed, so be sure to test after calibration.

 

Not sure about your second issue. What you describe would be normal if you're in beta/reverse thrust. If you're on the brakes with power on (especially a lot), and then reduce power quickly, the oleo in the nose wheel strut will de-compress some and let the nose pitch up a little. Not enough to put the tail on the skid though.

[MarkHurst 173]

4 hours ago, GuiLaMon said:

What should I be doing to avoid these occurences.

 

I have this too. There used to be a hotfix that changed the checklist script for lower RPMs during the power-on tests, but that disappeared during a forum reorganisation. No matter, going through the checklists makes no difference anyway so once you've done it once it's pretty pointless.

[GuiLaMon 0]

Thanks guys for your replies. I'll see what happens with the toe brakes applied! On a similar note, how do you keep a float plane in place when toe brakes and parking brakes (in my mind) would be somewhat ineffective? Excuse my ignorance ... this is a new adventure for me.

[Herman 1591]

As you thought, on the water, there are no brakes. To come to a stop on the water, you use the beta range with the power levers (throttles). Simplistically, beta is the range aft of zero thrust and into reverse.

[GuiLaMon 0]

Hey, thanks Herman. So, if I wanted to follow the checklist provided for the Twin Otter, there is a pretty extensive section on engine runup and testing. In that scenario, as I had learned from not applying the toe brakes on land craft, no doubt my float plane will insist on moving forward. So, to keep it from sailing away during runoff, who does one stay stationary to complete the tests?

[Herman 1591]

Most can be done in beta. I don’t remember any more which tests require full RPM, but generally, those aren’t done on the water, even on a long lake like Lake Washington. IRL, I used to do Twin Otter floatplane checkrides on Seattle’s Lake Union for an operator and even for a check ride, we just did limited run-ups.

[Aerosoft Team [Inactive Account] 51558]

10 hours ago, GuiLaMon said:

Hey, thanks Herman. So, if I wanted to follow the checklist provided for the Twin Otter, there is a pretty extensive section on engine runup and testing. In that scenario, as I had learned from not applying the toe brakes on land craft, no doubt my float plane will insist on moving forward. So, to keep it from sailing away during runoff, who does one stay stationary to complete the tests?

 

It will not, lol. Most of the time you have enough room on water of course.

[MarkHurst 173]

13 hours ago, GuiLaMon said:

So, if I wanted to follow the checklist provided for the Twin Otter, there is a pretty extensive section on engine runup and testing. In that scenario, as I had learned from not applying the toe brakes on land craft, no doubt my float plane will insist on moving forward. So, to keep it from sailing away during runoff, who does one stay stationary to complete the tests?

 

I guess you could face it up against the dock, although in real life than might be frowned on!

[Aerosoft Team [Inactive Account] 51558]

Normally they are only done completely at the first flight of the day. If I remember from my (very limited experience) they did them pointing into wind in open water.

[Herman 1591]

10 hours ago, Mathijs Kok said:

Normally they are only done completely at the first flight of the day. If I remember from my (very limited experience) they did them pointing into wind in open water.

Mathijs is right about facing into the wind helps. When you're familiar with the aircraft and know what you're doing, the high power checks can be done pretty quickly, and by holding full back pressure, you maximize water drag, which also helps.

 

Another point is that unlike a piston engine, where you'd always do at least a mag check before the second and subsequent flight of your day, turbine engines are much more reliable than pistons. For a PT-6, the governor checks (and fuel-topping checks depending on the dash number of the engine) are the ones most pilots worry about the most. If you think about it, the run-up checks are about the prop and related accessories. A runaway prop or worse, one that goes into beta in flight, especially in a twin, do more to wreck your day than a simple engine failure.

 

Mark, you're right about nosing up to the dock. That's a no-no.