F4D-1 Skyray FM Beta Tester

[+baffmeister 1,205]

Attached is a beta test FM for Julhelms' "Totally Excellent" SF2 F4D-1 Skyray, available here: http://combatace.com/files/file/11687-f4d-1-skyray-ultimate-pack-for-sf2/

 

I've been working off and on with this one for quite some time but it's just based on internet information so should be considered a "best guess".  I have been having quite a bit of fun flying it and that's about the only requirement I have to do an informal release like this.

 

NOTES:

 

The landing gear speed is set to 180kts. I think I got that number from a navy training video on YouTube but I'm not sure if that's the actual limit speed or just the standard operating procedure for an approach.

 

The tail trimmer is set up like an automatic flap and deploys and retracts around 200kts. If you want to switch back to the original manual trimmer just scroll down to the controls section and disable the current setup and enable the previous. [look for the xxx to see how it's done.]

 

I found this plane quite difficult to land on a carrier due to some issues with over the nose visibility. The best technique I've found so far is to do a quite steep approach at 150-160kts, speed brakes retracted, and aiming at the far end of the carrier. Once in close, chop the power, stuff the nose down a bit while aiming for the wires, then flare and land.

 

The min/max and collision points on this plane were quite wonky and have been re-worked.

 

From the Navy video [i think], take off rotation speed is 125kts [that works with this FM] and approach speed is 130kts. The actual stalling speed was considerably less than the approach speed but the approach speed was governed by over nose visibility, potential tail strike issues, and probably increased yaw instability at higher alpha.

 

Some pilots thought the Skyray was a good dogfighter but it had a lot of handling quirks with various control input restrictions at different speeds and altitudes. At certain speeds the high roll rate could over stress the aircraft. Safe to say this FM is much more docile than the real Skyray.

 

ISSUES:

 

I like to set the carrier birds up so they can do a trap on the autopilot but couldn't get this one to work using TWs' stock Kittyhawk carrier. It would always overfly the wires, even at speeds down around 110kts. Not sure why, but the aim point for the Kittyhawk might be a bit long. I will probably take a closer look at some point.

 

Make sure to back up the original data.ini, here's the new one: F4D-1_DATA_0.92.zip

 

 

 

 

 

 

 

[+Crusader 2,051]

Flight manual  http://www.avialogs.com/index.php/item/56059-an-01-40fba-1-flight-handbook-f4d-1-skyray-aircraft.html

and supplement with performance stuff http://www.avialogs.com/index.php/item/56060-an-01-40fba-1a-supplement-to-flight-handbook-f4d-1-skyray-aircraft.html

[+baffmeister 1,205]

Thanks Crusader. I was just at that site a few days ago looking at a flight manual for a different airplane and didn't think to check for a Skyray manual.   I will be reviewing that info prior to the next release.

[Fubar512 1,350]

Baffmeister,  the Skyray (like all true deltas) did not stall in the conventional sense.  

 

When deltas exceed a certain alpha at speed, they bleed off airspeed rapidly, an effect that pilots refer to as "mushing". If one is already flying at too low an airspeed, the aircraft will pitch up and appear to fly straight and level at a ridiculously low air speed, while it is actually losing altitude. In fact, it's quite possible to fly at full throttle at such an attitude, losing airspeed and altitude with little or no external references.

 

What I would do is eliminate the stall values on that FM, and play with the alpha/drag tables in order to achieve this.

[+baffmeister 1,205]

Interesting, thanks Fubar. From a quick look at the flight manual there was a risk of spinning the Skyray at high alpha but it seems to be due to loss of yaw stability. It did generate some buffet at high alpha so I will try increasing the AlphaStall / AlphaMax significantly and see how it works. I have to double check the flight manual but I think the buffet and yaw instability occurred somewhere in the 20-24deg range.

[Toryu 156]

The yaw-instability thing is an issue with all swept-wings and deltas.

 

The Crusader for example would run out of yaw-stability well before it ran out of lift.

Due to the Crusader's mass-distribution, this would usually lead to a gyroscopic departure (nose-slice, rapid speed bleed-off and development of a spin when speed was below 170kts) and incipient spin.

[+baffmeister 1,205]

The yaw-instability thing is an issue with all swept-wings and deltas.

 

The Crusader for example would run out of yaw-stability well before it ran out of lift.

Due to the Crusader's mass-distribution, this would usually lead to a gyroscopic departure (nose-slice, rapid speed bleed-off and development of a spin when speed was below 170kts) and incipient spin.

 

It's an interesting area to look into. I have tried playing around with some of the TW alpha tables for the V-stab but haven't been able to get a convincing effect yet. For the next update I would like to get some interesting high alpha yaw instability modeled as well as the large drag increase Fubar mentioned. The flight manual mentions the drag increase as well, warning about high sink rates on approach if the airspeed gets too low.

[Toryu 156]

You probably have seen this already, but maybe you haven't:

 

 

 

NOTE: Look for the yaw-damper (upper half of the two rudders) moving all over the place in many footages.

Edited November 2, 2016 by Toryu

[+baffmeister 1,205]

I have seen that before but it was well worth another look.

[+baffmeister 1,205]

Updated Skyray FM attached, Beta 0.93.

 

I took a closer look through the flight manual to try and get a better idea of the wing design and behavior of the Skyray and it might best be described as a bit of a design compromise. It seems to exhibit some behavior similar to a conventional swept wing and other behavior like a delta. The compromise was likely required to make the delta style wing acceptable for a carrier based aircraft. The useful alpha range is quite low for a delta, with max AoA at 22deg. The flight manual describes AoA past 22deg as the stall zone. Similar to a delta wing, it does generate significant drag at the upper end of the alpha range so I increased the induced drag quite a bit past 16deg AoA to try and replicate the behavior that is experienced during approach to stall practice. The flight manual warns of sink rates around 4000-5000 fpm with idle power during that exercise.

 

After a bit of research I think the low alpha range is probably related to wing sweep angle of 52.5deg compared to the more typical 60deg angle used on the Mirage III and F-102. Another reason might be related to using a thick airfoil and maybe a blunt leading edge that may not generate good vortex flow.

 

The flight manual has some charts showing a buffet zone that I think occurs around 18.5deg, based on some extrapolated data. The flight manual says it's OK to fly up to "moderate" buffet but at any sign of yaw instability the AoA should be reduced. I spent quite a bit of time messing about with some TW alpha tables to try and generate a gradual loss of yaw stability but couldn't make it work in a convincing manner.  With the new FM everything basically lets go all at once, with a departure / nose slice happening only at low airspeed combined with high angle of attack and rough use of the controls. In other words, it's actually quite docile. The Skyray was not approved for intentional spins and required unconventional spin recovery techniques but this FM will recover from spins with the usual power to idle, stick forward and rudder opposite to the rotation.

 

Other stuff:

 

Gear speed is 220kts maximum.

 

The automatic tail flipper has been adjusted a bit to get a smoother transition.

 

This new FM did a carrier trap on autopilot! [no guarantees]

 

The corner speed for 6G is quite low at 280kts and I've set that in the data ini but the speed loss is rapid. If the AI is having difficulties consider increasing it.

 

From the flight manual the recommended procedure for a maximum performance afterburner climb is: After take off accelerate to 500kts IAS at low level. Upon reaching 500kts start the climb while maintaining 500kts. Upon reaching mach 0.87 [around 8800ft] continue the climb to desired altitude maintaining mach 0.87.

 

Here's the new FM: F4D-1_DATA0.93.zip