A72 500 Takeoff Trim Help Needed

[ezochi 8]

I was wondering if anyone could help me with how to trim the A72 500 Series that I bought yesterday.

I am using P3D 4.5 and I am having major problems with getting it to leave the runway.
I have tried from and empty to almost full payload.

My first attempt was -2.9 trim and I have tried a variety of settings without luck.

The aircraft either refuses to take off, or, after a few hundred feet, it enters a sharp descent and plunges into the ground.
As a result, I have stopped trying on Vatsim! 😄

I have heard that the ATR 72 can be notoriously difficult when it comes to balance, but surely takeoff must be a bit easier than this.
If someone could give me some pointers, I'd be very grateful.

Many thanks,
Neil

[FDEdev 955]

The FDE has been designed so that takeoff works best with the default neutral trim. Where have you got the -2.9 from?

The Carenado ATR isn't difficult to balance since there is only a single passenger section.

Are you using 15° flaps and the correct speeds? At MTOW VR is 110kts and V2 115kts. 

Edited March 22, 2020 by FDEdev

[ezochi 8]

The trim was in the upper "green" area of the indicator on the main panel. I think placing the cursor over that or something showed a "-2.9" figure. I will need to try again to see what it was.

The first time I tried it was with the default setting and the result was rather ugly.
Flaps are 15% and the Vr/V2 data has been checked. Even at 140, the plane wasn't going anywhere.

The balance difficulty I refewrred to was the real airframe (I should have made that clearer) and I can see that there is only one section for PAX weight.

I'll try again after the long haul now I am doing now is finished.

Thanks for replying so quickly,

Neil

[FDEdev 955]

23 minutes ago, ezochi said:

The first time I tried it was with the default setting and the result was rather ugly.

Flaps are 15% and the Vr/V2 data has been checked. Even at 140, the plane wasn't going anywhere.

How much back pressure did you use? To get the rotation going you need a rather large amount of back pressure.

Using full aft stick isn't a problem as long as you relax the back pressure as soon as the rotation starts.

Did you load the forward cargo compartment as well?

 

Edited March 22, 2020 by FDEdev

[ezochi 8]

Used a fair amount. I'm just using a simple Thrustmaster, but I had it all the way back without even the nose going up.
Even with a climb (on the 6th try or something), the aircraft decided to pitch down and hard.

Forward compartment was about 55% full but I have tried from 85% to 0% with that.

I haven't seen much about trim problems on these forums, so it is obviously not  that much of a problem for other users. At least not to the extent I am having.
I'll have another wee try and report back.

Thanks again,

Neil

[FDEdev 955]

Have you fully loaded the aft cargo compartment before starting to load the forward compartment?

Especially the hard pitch down after takeoff is very strange.  Sounds almost as if the AP is engaged.

 

Edit: Just for testing leave the fwd compartment empty.

 

Edited March 22, 2020 by FDEdev

[ezochi 8]

That will be my next attempt.

The A/P was definitely off. I will have another few trials (fingers crossed it is only one!) and see if I can effect some sort of change.

Best regards,

Neil

[FDEdev 955]

Thanx for your continous testing 🙂

[ezochi 8]

Few more tests and I realised that my thrust readings were only 79% or so.
It appears that the thrust slider on my joystick is not reaching "max" (too much reliance on TOGA switches has kept this problem hidden until this aircraft).

Even though the aircraft had exceeded the Vr speed, the low engine thrust was probably the reason why lift was not happening.
Now, I am airborne even with a 90% load.

Sorry for the cause being as embarrassing as it is and thanks for your help, FDEdev.

Best regards,

Neil

Edited March 22, 2020 by ezochi

[FDEdev 955]

That's not embarrassing at all, and this would have been in fact the next question I would have asked.

Glad that it works for you 🙂

 

[ezochi 8]

You're a kind gent!

Thanks!

[Chock 17,769]

The bit you've heard about the ATR being a bit tricky to balance is true, but not really with regards to trim, it's more to do with ground operations. You may have noticed that the ATR-72, if you see one on the ramp at an airport, has this thing on the tail:

That's a stowable tail stand and it is put on when the aircraft is loaded or unloaded. We take it off when all the cargo is aboard and all the passengers are on board and the airstairs door is about to be closed. It attaches with a little pin a bit like a steering bypass pin, which on that pic is prevented from being lost by being attached with a wire. When not being used, the tail stop is stored behind the cargo curtain at the rear of the aeroplane.

The reason it is necessary to do that, is because of the physical layout of the ATR-72, which under normal circumstances is only boarded via the rear airstairs door. Since that is the case and the aisle is narrow on the aeroplane, passengers tend to bunch up on the rear airstairs and in the vestibule you enter before turning left to enter the cabin, and even then it can sometimes be a bit of a squeeze to get down the aisle to a seat. So that means a lot of weight is on the tail during boarding and disembarking.

Because of this, whenever an ATR-72 comes on stand, the arrival procedure has to be done smoothly and ASAP. Since the ATR has no APU, it goes into 'hotel mode' when it brakes to a halt, whereby engine 1 is shut down, engage 2 has a propeller brake engaged so that the engine can provide power until the FEP or GPU is attached without the danger of a spinning prop. This means it is only chocked on the nose and the port main wheels initially when it arrives and then someone plugs in the FEP/GPU so  the number 2 engine can be shut down (there is a light on the fuselage side which illuminates when the engine is running, but you can hear it anyway.

So, immediately after the number 2 engine is shut down, we hurry to the rear airstairs and someone will go up and into the rear hold, because otherwise they'd never make it past the disembarking passengers, the cabin crew, or one of us lot, attaches the tail stop at that point so that if the thing ends up tail heavy, that will prevent it from tipping fully onto its tail. Meanwhile a truck with a trailer is driven to the rear service door on the starboard side, the door is opened and latched and the person who dashed into the rear hold then hands the bags down out of the rear hold. This gets the weight off the tail ASAP.

Here is a view from the rear hold to the starboard rear service door. Opposite that door is the airstairs door, so you can see why we need to get someone up there quick before passengers block the way when disembarking.

Then what happens, is the person in the rear hold walks through the cabin to the front hold (since hopefully all the passengers are off by then), which can be accessed on both sides of the aisle through cargo nets immediately behind the cockpit door (it's a bit of a squeeze). Meanwhile, the truck and trailer is driven to the front port side and the door to the front hold is opened and stuff is offloaded from that hold too. Theoretically you could climb into the holds through the access doors, but good old health and safety regulations mean you are not supposed to 😉

Loading is the reverse of that procedure. You can get (at a push) about 50 medium sized suitcases in the front and probably about the same in the rear, but less than that typically since some bags are pretty large. A fairly typical load for an ATR-72 will be maybe 20 bags in the front and perhaps 10 in the rear, as they are normally flying short ranged domestic flights, but occasionally they are used for connecting flight, which means they'll have larger transfer baggage on board, and then it can sometimes be a real squeeze to fit all the luggage on board.

Worth noting here is that procedurally, we will try to have the thing fueled before any passengers are boarded because having only one passenger exit under normal circumstances means that in the event of a fire, that would be an evacuation choke point if nobody used the emergency exit doors or got out through the forward hold door. Because of this, when the ATR-72 is being fueled, we put someone on a headset connected to the cockpit crew and they watch the fueler to make sure that if something goes wrong, that person can let the crew know immediately to ensure any evacuation commences quickly. If passengers are boarded whilst the fuel truck is connected to the ATR, the headset person 'announces' 'fuel watch is on', and when fueling stops he/she says 'Fueling complete, fuel watch is off' In reality though, the ATR is so small that you could probably just signal the crew through the window or message port.

When everything is all zipped up, you do a walkaround check and when the passenger door airstairs are closed, you double check that is shut properly and also check that the tail stop has been removed and stowed aboard. Then you get on the headset and the crew will ask to start number 2 in hotel mode, when that's up and running, you can disconnect the FEP/GPU and push it clear, then you can push the thing out off the stand for departure. As the aircraft is clearing the stand, the crew will engage the prop and then they may start number 1 or sometimes just taxi on one engine.

There is no steering bypass pin on an ATR's nose gear, so what i usually do when I've disconnected from it, is hold up the headset wire in lieu of a remove before flight flag and give the crew a thumbs up or a wave to signal they are good to go.

Edited March 22, 2020 by Chock

[ezochi 8]

That is a fantastic piece of insight into the operation behind the scenes. I should pass it on to my Dad, as he often flies in them to EGJB.

I remember the stick on the Flight1 version and was wondering if it appears on the Carenado one. Maybe not.

I hope it won't be long before you are getting the number of aircraft ready for departure that you were before this pandemic.

Thanks again for a very interesting addendum!

Neil

[Biggles2010 343]

It looks like the misfortune for Alan, with his job being suspended, will be very much to our benefit. Seeing how his previous regular contributions have now increased so substantially, he has the makings of a book or two. There is so much that goes on behind the scenes that most people have no idea about, and it makes for interesting reading. Please keep up the stories.