TFDi Design 717

[ShawnG 1,823]

1 hour ago, Christopher Low said:

I do not understand the flight characteristics of this aircraft. When I make a turn at low speed, the nose starts to drop. So far, so good. However, the speed increases, and the nose never rises. It just keeps on pointing down. The PMDG 737NGX and 747-400 hand fly superbly at low speed with gear and flaps down, and the nose starts to rise as air speed increases during a turn. They are both very stable, and behave exactly as I would expect. However, the 717 is currently a complete mystery to me.

I really wish that I could learn to save my money, and concentrate on the aircraft that I already have

 

two different aircraft.  different wing positions, tail styles, and engine placement.  Also the 717 uses leading edge slats, which have a differing effect when extended than traditional trailing edge flaps.  I'm sure there are plenty who know more about the technical detail than me, but iirc slats only provide more lift at higher angles of attack.  so, if you are hand flying, you will need to adapt to the realities of the aircraft.

[Christopher Low 5,332]

Quote

Why would you assume that a t-tail/rear-engine aircraft would have the same flight model as low elev/wing-engine aircraft?  Different is not always bad

I tried flying the aircraft again. Smooth climb out after take off, and I started a left turn. If I kept the bank very shallow, the aircraft continued to climb, and the airspeed remained reasonably steady. If I increased the bank angle to one that I would be using normally to enter the pattern (and that's not steep), the airspeed started to increase quite significantly (130 > 170 knots), but the nose did not rise. I then levelled out, and gave it one notch of up trim. The nose slowly started to rise, and the airspeed (eventually) started to drop. It fell back to 130 knots, but the nose continued to rise.

Is that what should happen in a T-tail rear engine jet like the 717? If so, then I need to stick to flying the 737 and 747!

[branks737 29]

I only bought this bird last week and it's really growing on me, despite being a diehard 737 person. I think one of the best aspects of this plane is hand flying it. There are some issues with it ( check their forums to find out), but it seems the Devs are always improving it. Ive only had it for a week and I've  got no dramas completing flights despite my minimal knowledge on its systems. Ive been reading the tfdi manuals which is limited,  but also reading MD11 material on the web. Ithink for the price it's a great addition to the hanger

[Christopher Low 5,332]

Another test......

I set the aircraft up roughly on a final approach path (with gear down and full flaps), with the nose pointed slightly down The speed was around 145 knots. I then increased the engine power to maximum. The airspeed increased to over 210 knots, but the nose continued to very slowly drop. The aircraft never pitched up at all! I can understand an initial pitch down due to increased thrust from engines that may be slightly above the CG, but surely the nose should start to rise as the lift increases? This never happened. It just continued in a dive towards the ground.

Is this how the aircraft should behave??

[branks737 29]

2 minutes ago, Christopher Low said:

Another test......

I set the aircraft up roughly on a final approach path (with gear down and full flaps), with the nose pointed slightly down The speed was around 145 knots. I then increased the engine power to maximum. The airspeed increased to over 210 knots, but the nose continued to very slowly drop. The aircraft never pitched up at all! I can understand an initial pitch down due to increased thrust from engines that may be slightly above the CG, but surely the nose should start to rise as the lift increases? This never happened. It just continued in a dive towards the ground.

Is this how the aircraft should behave??

Are you checking your stabiliser trim settings?

[Christopher Low 5,332]

Stabiliser trim is preset to a specific value, but the pitch of the aircraft should surely still respond to airspeed? I have tried a range of settings, but the overall behaviour remains the same.

[branks737 29]

I haven't noticed this. I'll do some tests when I get home from work

[Christopher Low 5,332]

To be fair, I am basing my comments on what I expect an aircraft to do with a change in airspeed (all other things being equal). The PMDG 737 and 747 behave exactly as I would expect, but maybe it is different for a T-Tail jet with engines at the rear? The Quality Wings 146 is a T-Tail jet with engines on the wings (so, a sort of "halfway house"), and that behaves the same as the PMDG aircraft.

[branks737 29]

4 hours ago, Christopher Low said:

Stabiliser trim is preset to a specific value, but the pitch of the aircraft should surely still respond to airspeed? I have tried a range of settings, but the overall behaviour remains the same.

Yes your right, advancing full throttle from idle whilst in the air does nothing to pitch

[Christopher Low 5,332]

Is that a technical issue that needs to be addressed, or just a quirk of the aircraft? It seems rather odd behaviour to me.

[JRBarrett 3,038]

17 hours ago, Christopher Low said:

I tried flying the aircraft again. Smooth climb out after take off, and I started a left turn. If I kept the bank very shallow, the aircraft continued to climb, and the airspeed remained reasonably steady. If I increased the bank angle to one that I would be using normally to enter the pattern (and that's not steep), the airspeed started to increase quite significantly (130 > 170 knots), but the nose did not rise. I then levelled out, and gave it one notch of up trim. The nose slowly started to rise, and the airspeed (eventually) started to drop. It fell back to 130 knots, but the nose continued to rise.

Is that what should happen in a T-tail rear engine jet like the 717? If so, then I need to stick to flying the 737 and 747!

That is exactly what a real aircraft does when hand flying and executing a turn. As you increase the bank angle, the amount of lift acting on the  wings decreases. You have to counter the tendency of the nose to drop by increasing back pressure on the yoke. The  steeper the turn, the more back pressure you need. The nose will not rise by itself in the turn - you, as the pilot, have to provide the necessary up elevator input.

Now, if the nose drops when flying on autopilot, that’s a different matter...

[Christopher Low 5,332]

Quote

That is exactly what a real aircraft does when hand flying and executing a turn. As you increase the bank angle, the amount of lift acting on the  wings decreases. You have to counter the tendency of the nose to drop by increasing back pressure on the yoke. The  steeper the turn, the more back pressure you need. The nose will not rise by itself in the turn - you, as the pilot, have to provide the necessary up elevator input

The lift does decrease, and the nose drops. However, the airspeed then increases, and the nose should start to rise again. At least, that is what happens with the PMDG airliners (and most of the other aircraft that I have). What are your thoughts regarding the refusal to change pitch with variable airspeed?

[Milviz 919]

It's not about the amount of power you add...  It's about pulling back on the stick and getting lift in return.  Force doesn't equal lift.  

 

[ShawnG 1,823]

Again.  Slats are different than flaps.  You will need to approach more nose up than you are used to.  

[ahsmatt7 1,199]

It sounds almost everyone of you are misinterpreting the problem this man describes.

The airplane flies funny. You are right. Unless the airplane has a CWS mode such as the 737, if you are in a turn and let the nose drop, airspeed will increase. You should eventually see the nose start to come up due to the increase in airspeed. Now thst may take a huge increase in airspeed to do that, but it will happen. T-tail aerodynamics are not that much different in terms of handling outside of what happens when thrust changes occur....its still an airplane.

Also, this has nothing to do with slats or flaps...

It's like the stability algorithm is messed up.