MaddogX test flight

[G550flyer 1,011]

Greetings all,

First I would like to say congrats to the MaddogX team for continuing the MD80. The Leonardo MD80 has always been a great aircraft.

Though the DC10 was the first MD jet I flew, the MD80 has always been my favorite aircraft. I do have a lot of love for the DC10 because I flew her for 10 years. I quickly grabbed the MaddogX and decided to do some quick tests.

I loaded the aircraft to 130,000 pounds and took the runway for some stall tests. One of the first of things designers get wrong with MD jets is the takeoff and approach pitch. The MD theory of design is low lift high speed wings. This design brings efficient wings but requires higher takeoff and landing speeds. In this design, lift is largely created by AOA. In these aircraft, we force them to fly. We joked a lot in the DC10 by saying you could go from coast to coast across the USA if you never rotated. You will notice that MD jets have a high deck angle at V2+10 and on approach. You are routinely looking at 17 to 20 degrees pitch during takeoff and 4 to 5 degrees pitch on approach with the first detent of landing flaps. This is how the aircraft generates it's lift and why slats are important. The slats are like glue as they guide the top layer of air over the leading edge and keeps it from separating at high AOA.

During engine start, I noticed that the engine acceleration was fast. The MD80 is started at max motor. It takes about 15 seconds to get to max motor. The MaddogX was spot on. Once fuel is introduced and the engine lights off, it takes about 22 to 25 seconds to accel to idle. The MaddogX does it in 13 seconds. Would be nice and natural if the spool from ignition was slowed to 22 to 25 seconds. The EGT spikes quickly also. I do find the engine response in the MaddogX to be twitchy and a little too responsive. There should be some lag between throttle movement at lower range, but a little more responsive above 1.4 EPR. I am also plagued by the locked brakes problem. 

At 130,000, you are looking at 18 degrees pitch with rated thrust for V2 + 10. The rotation is about 3 degrees per second with the jet lifting off at 8 degrees. The MaddogX was spot on at 18 degrees with V2+10 right on cue with proper rotation rate. The feel of the aircraft was as expected requiring trim adjustments while hand flying. Some FSX aircraft, you never have to trim much, but this 80 makes you trim realistically. At 3000ft I ran through some stall series and here are the results.

130,000 clean, stall should occur at 160kts. Stall warning at 165kts, but was able to maintain altitude till 135kts. Stall warning should occur 10% above stall of 160 and pusher at 160.

130,000 Slats, stall should occur at 125kts.  Stall warning at 140kts, altitude loss near 140kts. Earlier than expected.

130,000 slats/F28 gear down, stall should occur at 110kts. Stall warning at 110kts, altitude loss at 110kts. Stalls on cue, but warning should occur 10% above.

The plane flew like a dream. I did notice that on descent in IAS hold with the throttles at idle, the auto throttles suddenly surged to full power and I had to click them off. I also found that the VREF speeds are a little off from my manual by 3 to 4 kts. For example, at 117,000 pounds I have 129(F28) for thresh and the 5 kt additive puts me at 134. The FMS and speed card had 137, 132 + 5.

The aircraft pitch was perfect on approach. This tells me the stall speed and lift was spot on. I did notice that the ground effect was a little bit strong. I have a standard ground effect adjustment that I use to get aircraft where they should be.

Basically, ground effect is a gradual decrease of 200 to 300 feet per minute in sink rate. Happens at about half of your wing span. The flare is a 2 to 3 degree pitch change that's held until touch down. Between the 5 knot bleed at the threshold and the nose drop tendency in ground effect, there is a positive input in the flare. The technique for the MD80 is starting your flare at the 20ft callout, 2 to 3 degree input and throttles reaching idle by touch down. With a proper threshold crossing of 50ft, you should be down 1000 to 1200 from the threshold with a pitch around 7 degrees(F28). The 80 will tend to float if you flare more than the 2 to 3 degrees or are hot crossing the threshold.

This was my initial look and will continue look as I enjoy this wonderful aircraft. Congrats team!!!!!

Edited February 24, 2018 by G550flyer
error

[Meekg 86]

I’ve personally put a couple of months of full time work to redesign the aerodynamic model and I’m all open to feedback.

When it comes to stall I don’t think we are as close as I would like it to be mainly because “our stall” is internally controlled. We all know the limitations of the FSX/P3D aerodynamic envelope.

If you like to run similar tests, please do fly the aircraft pitch and power tables (you can find in the the unreliable airspeed abnormal procedure) and tell me what you think.

We narrowed down the error to very reasonable figures.

If you appreciate this aspect of simming (as much as I do) also check climb and descet tables, they are very very close.

Fuel consuption and EPR at all levels and weight are also within an impressive margin of error.

I’m not trying to brag (maybe just a bit) but I know only a minority of simmers would pay attention to these details (which literally drove me nuts to adjust).

It’s nice to know someone takes notice.

Regards

[G550flyer 1,011]

Greetings Michele,

Sorry you only got the beginning of my post. I fat fingered a keyboard setting and it posted before I was finished. As you can see from my post, you did a great job with the flight model. I can tell it's solid. I love those pitch and power tables. A lot of people fall for the hidden gotcha in the approach section of the pitch and power tables. Some don't realize that it's based on VREF + 10. You got it right on. I didn't try flaps 40 and will give it a shot. I also noticed it had the appropriate pitch when at min maneuver speeds at different configurations.

Great job. The things I pointed out above are just icing on the cake. If you would like to try out my ground effect adjustment, I'll send you the file to give it a test for your landings.

Rick   

[Meekg 86]

Rick, I agree with the engine spool and the timings you gave are pretty valuable information.

I will definitely put it in the do list for SP1, as soon as we stabilize the “main” bugs and everybody is happily flying we’ll get straight into SP1 developement.

The VRef discrepancy is mainly due to the fact that they are computed by a formula, not by a table, so we still face occasional discrepancies also due to the fact they are all coded in kgs.

I’ll look into that particular weight and see if we can fix it.

Keep the feedback coming. Thanks.

[RichieFly 728]

Thanks for the post, Rick.

Very interesting to read some feedback from a pilot who knows the aircraft.

[beep747 93]

Better feedback than from a RW pilot, you can't get. Very interesting reading. Thank you.

Jos

[Iceman2 110]

This product is certainly shaping up to being in the best of the best category when it comes to study level aircraft.

Feed back like this is terrific (thank you Rick) but getting the developers response as posted above puts the Maddog right up there with the best.

Ive flown the 727 through to the 747 but never got close to the MDs. However sitting in the cockpit of the Maddog X using my VR headset gives me the wow factor. There’s really something very special and unique about the MD80. Tonight I had a spare hour for a quick SIM flight but ended up just sitting at the gate in the Maddog X looking around with the VR headset. Such a joy and so many things to switch on & off.

 

Awesome Job team.

 

ICE