Su-25T Warnings

[Horns]

There's this thread

https://forums.eagle.ru/showthread.php?t=190912

where neofightr discusses how the USN has its pilots do carrier landings, among a variety of other topics.

 

Actually, here's the relevant bit, since there's a lot of stuff to dig through to get to the relevant bits (much is worth reading, but there's a lot of off topic with respect to landing).

 

 

 

 

 

 

 

The condensed version is that when flying the final approach you use the stick to control not your pitch, but your AoA. The throttle you use to control your altitude above or below the glideslope. Horizontal alignment you correct as needed with roll and yaw.

 

A natural question is, "but if I'm controlling altitude with throttle, how do I control my speed?"

 

Mostly the answer is that you don't need to worry about it. If the plane isn't overloaded with fuel and stores and is in landing configuration (part to full flaps and gear down), the speed will pretty much take care of itself if you're keeping reasonably close to glideslope.

 

It may feel odd if that's not the way you're used to doing things, but it does seem to produce consistently good results, which is very desirable when landing an airplane.

 

I'm sure somewhere there's an official number for the Su-25T, but in the absence of knowing what exactly it is, I find that keeping the needle on the AoA gauge at about 10 works fairly well.

 

Unlike a carrier landing, it is advisable in a Su-25T to flare (in the increase AoA sense not the deploy countermeasures sense) in the last few hundred meters just before landing. In terms of amount, just enough to get your decent rate to the 0.5 to 1 m/s range at touchdown.

 

The idea of landing according to the AoA on approach is intriguing, I have been adjusting pitch to control speed and glancing at the AoA gauge, but a stall would be a bigger problem than a little extra speed, and maintaining some AoA means I'll be losing some speed anyway. When I know I'm cutting it fine on AoA I will try using that as my main reference. Thanks :)

[Ironhand]

The idea of landing according to the AoA on approach is intriguing, I have been adjusting pitch to control speed and glancing at the AoA gauge, but a stall would be a bigger problem than a little extra speed, and maintaining some AoA means I'll be losing some speed anyway. When I know I'm cutting it fine on AoA I will try using that as my main reference. Thanks :)

If you want to have some "fun", take a clean aircraft up to around 4K meters (mainly to give yourself some room). Slow to roughly 400 km/hr indicated and stabilize your speed. Trim for level flight. Once you're there, check your AoA. Now, with your hand off the stick, s-l-o-w-l-y decrease your throttle in increments, and watch what happens. You'll notice that the AoA and airspeed will remain virtually the same. You will simply be losing altitude (control altitude with throttle or, rather, rate of descent or ascent) while the a/c holds the AoA and airspeed.

 

Now advance the throttle slowly in like manner. You'll see pretty much the same in the opposite direction. Your descent will slow and you'll return to level flight, then transition into a climb. The climb portion is a bit more problematic because, if your rate is above 5/sec you'll start slowing. But, anyway, it's a great way to see that AoA controls airspeed, while throttle controls altitude (ascent/descent rate).

 

Another neat thing is that the -25T has positive dynamic stability. Once trimmed for a certain AoA in level flight, it will return to that AoA and level flight on its own if disrupted. From level trimmed flight, flick the stick slightly back and let it go. Your nose will come up and then drop. It will then go through a series of oscillations that gradually slow (each oscillation is slightly less severe) and you'll end up in level flight once again at that AoA without touching the stick.

 

I would try this stuff in a clean aircraft in a mission with no wind so that you can keep your hands completely off the stick once trimmed...except for that last of course because you'll have to use the stick initially to induce the oscillation. But, anyway, you can see that the -25T has positive stability. It wants to return to stable flight whether that flight is level, a sustained descent, or a sustained ascent (within reason).