Q400 to the stars! (FL600+)

[Nick M 106]

Hi All,

 

Let me start by saying how much I love the Majestic Dash 8. The combination of fidelity, performance and the challenging short-haul sectors flown by the real thing makes it the best airliner sim for FSX in my book. My thanks go to all those involved in its development. 

 

There's one area of the flight dynamics which does trouble me though, as I posted in the thread: 'Help with Q400'. However, I think this subject is a bit off-topic for that thread, hence the new one.

 

I've now had the opportunity to do some more testing: this time with a fully-loaded Q400. I've posted a series of screenshots below showing what I experienced. I'd like to emphasize now that I'm in no way a real-world pilot (let alone a Q400 driver) so I'd appreciate the input of other Q400 users on this issue.

 

Here's the weight and balance sheet for the test flight. Close to max take-off mass with a 29000kg aircraft (including 4000kg of fuel).

 

Here's confirmation of the aircraft weight and fuel quantity in the sim prior to engine start. Following take-off from EGTE I set the condition levers to 900rpm (MCL) and climbed at 200 kts using the IAS AFCS mode. Needless-to-say vertical speed and deck angles were pretty extreme during the first part of the climb. Lucky this was a test flight!

 

 

Here we are just over 15 mins after take-off passing FL250. By this point V/S has decayed to +600fpm so you could be forgiven for thinking she hasn't got much climb left in her. However, after this shot was taken, I reduced the commanded IAS to 180kts which allowed the rate of climb to increase to +800fpm.

 

12 minutes later we're climbing through FL300: still at 180kts and +800fpm.

 

A further 10 minutes into the flight sees us still climbing at +800fpm at 180kts: now we're passing through FL460! However, a few minutes later V/S does start to drop rather suddenly.

 

An hour into the flight, we're passing through FL522, and V/S has dropped to 'only' +300fpm but we're still climbing steadily. I've also reduced the IAS to 158kts (Vclmb for out T/O weight) where it'll stay for the rest of the climb. You may notice the engine rpm starting to creep away from the FADEC commanded setting of 900rpm at this point.

 

After another hour in the air*, we've finally reached what seem to be the absolute ceiling for the aircraft at this weight: FL636! (We've also burned about half of the fuel on board by now.) I could have traded a bit of airspeed for more altitude as I did in the previous test when I flew right up to stick-shaker activation. RPM is clearly over-speeding at this point. Wonder what would happen in the forthcoming pro version which I think has failures? (*I'll own up to using time compression for this bit, although I hadn't previously in the flight.)

 

Here's the final portion of the flight see through the FSX 'flight analysis tool'.

 

In posting this, I just wanted to provoke a bit of discussion about what's causing this odd ability to reach excessive altitudes in a flight model which otherwise seems so accurate. Any input from the developers would be very welcome, although I realise the Majestic forum is probably the best place to get this... (I know - I should register there!) 

 

All the best,

Nick

[MarkW 1,490]

Pretty interesting result.  If you could get that up to Mach 2.0 it would make a great replacement for Concorde !!!

[Nick M 106]

Pretty interesting result.  If you could get that up to Mach 2.0 it would make a great replacement for Concorde !!!

 

It's certainly a bit odd Mark. There was a topic started on the Majestic forums on the subject about 18 months ago, but it didn't seem to be noticed by the Majestic developers. (I'd post a link, but can't work out how to link to a specific topic on the Vanilla forum they use.)

 

Anyway, the topic poster also compared the Q400 to the 'new fuel efficient Concorde'!

 

In spite of this, I really do enjoy flying it. (Although I've been distracted by a certain little Cherokee recently!)

 

Cheers,

Nick

[MarkW 1,490]

Majestic have used a completely different flight dynamics engine outside of FSX to make the Q400 so this may be a side effect of that technology.  FSX does very strange stuff sometimes....as an example on Concorde you can fly at FL550 - FL600 and Mach 2.0 but have the fuel balance all wrong and the CG in the wrong place....it will still fly just fine.

[Nick M 106]

Yes - that sounds like a likely explanation. I  know very little about JSBsim which I believe is behind the Majestic FDE (except that it's 'successor of the LARCSIM built by NASA'), but I'm sure it involves all sort of complex integration into FSX.

 

I suppose the obvious answer to this issue is "don't try and fly the aircraft above the service ceiling of the real Q400" (which I believe is 25,000-27,000 feet depending on equipment).

 

However, I'd still be interested to know if many other Q400 flyers can replicate this behaviour, as some people describe struggling to reach FL250.

[martin-w 3,234]

Might be worth posting this over at the Majestic forum Nick, then we'll get a direct answer from the developer.

 

 

http://majesticsoftware.com/forums/

 

Would be interesting to see what they say.

 

I know one of the beta testers very well, I'll give him a shout.

[Nick M 106]

I know one of the beta testers very well, I'll give him a shout.

 

Thanks Martin.

 

I'll be dropping Majestic an email a bit later to apply for forum membership.

 

Cheers,

Nick

[martin-w 3,234]

Well worth joining the forum, nice people the developers and no nonsense over there.

[KingGhidorah 209]

This kind of bums me out, if it's true. 

[ckyliu 1,749]

How do we know this behaviour is unrealistic? Perhaps a Q400 could reach those altitudes if the engines continued to function well in the thinner air and the cabin was de-pressurised!

 

Whilst this is a bug, I consider it a very minor one and I'd rather the Majestic team invest their time and resources elsewhere; I can't see anyone bothering to fly the Q400 significantly above the service ceiling other than curiosity. Providing it flies realistic up to the service ceiling, that should be enough for 99% of users.

[Nick M 106]

How do we know this behaviour is unrealistic? Perhaps a Q400 could reach those altitudes if the engines continued to function well in the thinner air and the cabin was de-pressurised!

 

That's a good question and one which I posed in this post. However, even with such powerful engines on the Q400, altitudes approaching 70,000 feet where the curvature of the earth and daytime stars are both visible seem a bit extreme.

 

This is another image from a test flight with a 22,000kg take of mass. For this one I flew up to stick-shaker activation at FL688.

 

Your point about "providing it flies realistic up to the service ceiling" is well taken. I'm just interested to see if this issue is one which affects all users, as some posters have said they struggle to reach FL250 (maybe these are P3D users?).

 

Cheers,

Nick

 

P.S. I admit it - I'm a frustrated test pilot!

[ckyliu 1,749]

I'm just interested to see if this issue is one which affects all users, as some posters have said they struggle to reach FL250 (maybe these are P3D users?).

It shouldn't make any difference as JSBSim does all the flight dynamics and performance simulation, FSX/P3D just acts as graphics engine and provides some environmental variables (e.g. weather, terrain).

 

Users struggling to attain FL250 are likely trying to climb at an IAS or V/S that is too fast for their gross weight and SAT.

[Nick M 106]

No - I guess you're right. Perhaps iffy climb profiles would be responsible for simmers posting that they're 'struggling' to reach the service ceiling. As I've said, none of this detracts from my enjoyment of the Majestic Q400. I do think it's an interesting little quirk of the FDE, but I suppose I'd be happier if I felt it was truly reflecting the real aircraft's behaviour at the edge of the flight envelope. However, I know this is one area where desktop PC sims do often struggle. 

[KingGhidorah 209]

ckyliu, I respectfully disagree that, if true, it's an issue of little importance because it's outside of a realistic flight envelope.  While no realistically conducted flight would ever take us higher than FL270, If the plane can continue climbing to 60,000 feet, then it  likely possibly means that it's performance climbing up into the FL270-ish altitudes is off, an altitude at which it does affect us during realistic use.   Maybe next time I fly the Majestic, I'll try this out myself; tbh I'm not on a Majestic kick right now, so I don't feel like loading it up for a flight.  But when I do get back to flying it, like what NickM is getting at, I would also be happier to know that the FDE isn't hopelessly incorrect up at a realistic cruise altitude.  He's climbing at 800 fpm through FL270, near max weight, so I'm sure somebody ought to be able to scrounge up some real numbers from a manual or somewhere

[GHarrall 494]

ckyliu, I respectfully disagree that, if true, it's an issue of little importance because it's outside of a realistic flight envelope.  While no realistically conducted flight would ever take us higher than FL270, If the plane can continue climbing to 60,000 feet, then it likely means that it's performance climbing up into the FL270-ish altitudes is off, an altitude at which it does affect us during realistic use.   Maybe next time I fly the Majestic, I'll try this out myself; tbh I'm not on a Majestic kick right now, so I don't feel like loading it up for a flight.  But when I do get back to flying it, like what NickM is getting at, I would also be happier to know that the FDE isn't hopelessly incorrect up at a realistic cruise altitude. 

 

 

According to Brendan Hatch (United Q400) and the FlyBe Q400 FO (Josh?) from the Airline2Sim videos, the Majestic is on the money for the most part.

 

It certainly climbs as expected up to normal cruise levels. Not really a concern here IMHO.