FSX-MS DC-6, B377, C47 - does holding brakes before takeoff help?

[VeryBumpy 272]

On older big prop planes, do you actually get up to speed in a shorter distance if you hold the brakes, rev up the engines then let go of the brakes?

If one does, it must be negligible cause I certainly don't notice it.

[stans 706]

Unfortunately, in FSX it is often not the brakes, but the friction of the tires on the pavement that prevents applying significant engine power before your aircraft begins to move.  In the real world, holding the brakes and applying engine power, but generally not full power, then letting go of the brakes does provide a faster initial acceleration.

[Biggles2010 343]

 

8 hours ago, VeryBumpy said:

On older big prop planes, do you actually get up to speed in a shorter distance if you hold the brakes, rev up the engines then let go of the brakes?

If one does, it must be negligible cause I certainly don't notice it.

Short answer is sometimes yes, but the difference may not be very obvious and there are various other considerations.  The brakes may not hold against full power, and engines can overheat more quickly when stationery, despite the prop thrust.  Full boost for takeoff is usually applied after the aircraft starts rolling, to avoid excess heat buildup and to limit the stress on the engine, with the other very important factor being directional control.  At full power, the aircraft will swing more and it will happen more rapidly on brake release.  With minimal rudder effect until speed builds up, you can quickly have a dangerous situation.  Using brakes to keep straight reduces acceleration and those older aircraft, when loaded, could need a lot of runway distance for takeoff. 

In summary, there were/are recommended procedures for the power settings prior to brake release, and the way that full boost should then be applied. Deviating from those involved risk.

[G550flyer 1,029]

Greetings,

I never flew props, but in general, performance is standard across fixed wing aircraft. There are a couple of things to consider when pondering the effect of power set prior to break release. One is the power setting process. Lets take my heavy jet experience for example. Routinely, there were two options(rolling/prior to brake release) along with line up distance. In heavies, line up distance can be up to 300 feet while in the lighter jets, it can be 100 feet. The rolling takeoff comes in two flavors. There's the rolling and standing rolling. With rolling, as you turn onto the runway, you are spooling the engines to a specified setting to line them up and do a quick check. If everything is good, you pour on the coals. With the standing rolling, your are stopped on the runway. When ready, you release brakes, spool to specified, check the stack and then pour on the coals. Now in the prior to brake release option, you spool to specified, check the stack and then up to takeoff thrust. Once set, you release the brakes. I mention all of these because they will all impact your runway available. Lets talk about the runway available real quick.

Runway available is basically length minus your line up distance. The longer it takes you to get that power set while rolling, the less runway you will have for accel go/stop. Normally, this isn't an issue until your weight is limited by runway available. When you are runway limited, you want all that you can get. Lets say I'm on a 5000ft runway and my weight is limited to 200k because of it. This means that my critical field length or my accel stop is equal to 5000 - line up distance. Better yet, in a balanced field situation, my accel go and accel stop is equal to 5000 - line up distance. In a sense, the accel go is not the critical distance because I should be at 35ft by the end of that distance. Accel stop opens your eyes because that's where you should come to a stop. With those in mind, you can see why people will opt for the power set prior to break release. Now, in general, the accel go or critical field length accounts for the time it takes to set power. The thrust charts may say, power set between 40 and 60 knots or 40 and 80 kts. That's why at the 80 kts call out, you confirm 80kts on both indicators and state "power set". It's those days that are hot/high or if you want that extra safety pad. The times I have set power before brake release is because I needed the max performance. Like, when I flew C141s, we did minimum interval takeoffs. You actually lined up as the jet in front of you started rolling. We spaced the takeoffs with 10 seconds. You rolled on, set power, and when the navigator stated "brake release", you released and chased the other jet down the runway. The air over the runway was full of wake, so you wanted that extra pad. Especially when trying to lift off before or after the jet before you. Other times, I was limited by climb gradient or runway and wanted that extra bit to get off earlier and take advantage of the height gained. You also wanted brake release power when doing a performance check. If the performance check says I should be at 100kts by 1000ft, it's based on brake release power.

Visually, you won't notice the benefit. doing balanced field or runway limited departures, you will always be near the end of the runway at rotate. If you find yourself rotating in the last thousand feet, possibly something was wrong with your data or you took way long to get that power set🤣.

Rick