Made some changes to the T-45 .air file

[average_joe]

By the way caging the HUD solved my earlier problem ...

I made some changes to the T-45 .AIR file to modify the flying qualities when the speed brake is deployed. Normally the real T-45 has a bit of a pitch up when the speed brake is opened. Current T-45 reaction is a loss of lift (flight path vector dips below the horizon; nose doesn't pitch up). I did a couple of test flights to convince myself ... used a reference point on the HUD frame. Deployed speed brake ... reference point stayed put. Flight path vector went well below the horizon.

I think the speed brake was modelled as a spoiler. AIR file shows a negative CL contribution due to spoiler (-0.09). Because NATOPS the nose pitches up, I made the delta CL due to spoiler zero and made delta CM (pitch moment coefficient) due to spoiler (speed brake) a -0.02 (after a couple of tests). So now there a enough pitch up with speed brake deployment that the pilot has to control it (per Stretch's comment. By the way Stretch is our new T-45 test pilot!).

I also reduce delta parasite drag (CDo) due to spoiler (speed brake) to .055. Current deceleration is just too much.

I also tried to increase on speed to 120 knots by reducing delta Cl due to flaps ... best I could do was 112 knots with flaps Cl almost zero. Need to work on the entire lift curve to fix approach speed. That's another project.

I sent a copy of the AIR file to Sludge and will send a copy to Stretch if I can can do the personal e-mail from the forum correctly. You folks can test fly it for me.

[Stretch32]

Joe,

Test pilot!? You don't pay me enough, do I get hazard pay now  Anyway, I like the new airfile. I think the pitch up is pretty good just playing with it for a little while. There's a fair amount of forward stick to hold it level like there should be. The speed brake retraction has some nose dip as it should but maybe just a bit more force might be good if possible. It takes a little back stick to stay level when you retract the S/B's. Also, I did notice the on-speed issue (guess I never really payed much attention before). I was on speed with 2500 lbs of gas at 110 kts according to the fuel gauge and AoA Indexer. At that weight/fuel load it should be about 124 kts. As I posted before, on speed in the T-45C is calculated as half your fuel load added to the base numbers of 111 kts for full flaps, 131 kts for half flaps and 151 kts for no flaps. In this case 2500 lbs would be 12.5 kts (13 for good measure) added to 111 kts for full flaps so 124 kts. I think it's a great fix and good work overall.

Stretch

[average_joe]

Stretch,

1. What did you think of the change in parasite drag due to speed brake extension - deceleration too much, too little?

2. New Cm due to Speed brake deployment: -0.023 (that a 15% change).

3. What is a good stall speed in the clean configuration - 95 KIAS?

[SpazSinbad]

Would the performance data from a Goshawk T-45A NATOPS be more or less equivalent to the performance data of the T-45C? Or is there too much airframe/engine difference for the T-45A data to be transposed to the T-45C? My guess would be that it is not equivalent - but I have no idea really. A Zipped 4 page PDF file (0.35Mb) is attached now:

T-45A Stall Speed graphs for:
Max. Rated Thrust
Approach Power
Power Off
&
AoA conversion

[average_joe]

T-45A stuff is close enough. I was trying to get a few known performance points and work some calculations to reverse engineer the CL vs AoA curves. The AoA conversion chart might be the key. Might take me a couple of days. Stand by.

As I understand the diff between T45A and C is mostly analog vs glass cockpit. Our new Chief Test Pilot - Stretch - is the designated expert.

[Stretch32]

The only difference between the Alpha and Charlie that I'm aware of is the glass displays vs. steam gauges. As far as I know all numbers for performance are the same. I've not flown A's since Meridian only has C's but talking to K-ville guys thats the only difference (no airframe or engine mods, same aircraft basically). So the data for both aircraft should be the same. I still haven't found a scanner to upload graphs but what SpazSinbad has available should be just fine. As far as Joe's questions:

1. I think it needs a bit more decel with the boards extending but I need to fly it a little more and get my friend to fly it as well to see what he thinks. 2 opinions are probably better.

3. I'm not really sure about stall speed numbers since nobody actually uses a speed. We considered the a/c stalled at 30 units AoA and that's the only number I really look at. I remember hearing that 85-95 kts depending on power setting was where the aircraft actually stalled but I'm not sure. I'll do some looking tomorrow and try to get some better figures.

Stretch

[SpazSinbad]

AvJoe, thanks. I guess the reason why the performance charts in T-45A are not included in T-45C. My knowledge of this aircraft (and variations) is very vague at best.

[average_joe]

Think I did it ... reverse engineered the CL vs AoA curve ... plus one anal extraction.

Aircraft flys very close to correct airspeed for on speed AoA. I was at 124-126 KIAS. Might still be a knot ot two slow as I was close to a full fuel load. Took off from Pensacola at 5 min later dirtied up for an on speed check.

Also bumped up the speed brake parasite drag contribution per Stretch's comment. Will send the AIR file to Stretch, Sludge, and Spazsinbad.

Spaz ... need a good e-mail address. My e-mail didn't like the address that's on your profile.

Not sue the reverse engineering is totally accurate given the size of some of the scaling values in the .cfg file but it seems to work across the flight regime.

By the way any input on engine performance will be appreciated ... I think its overpowered in the 70-85% regime. I was at 3000' 430 KCAS at 75% power ...

[SpazSinbad]

AvJoe, e-mail corrected (dropped old one of two). There are performance graphs for the Goshawk A model in that NATOPS AFAIK without checking at moment. Do you have NATOPS for Goshawk?