F-86 shows a strange attitude: it doen’t descend and slow down after power cut

[wernst]

When flying F-86 at 160 - 170 kts IAS on downwind, gear down, flaps deployed and turning to (long) final

the speed would not slow down even with power cut (throttle to idle).

Lowering the angle of attack to approach config makes this phenomenon even worse, speed increases.

Even with speed brakes deployed I can’t reduce speed to healthy landing at 120 kts,

 

All real planes I have flown, e.g. C206 with 2.000 kg take-off weight, would start descending like a stone and bleeding off airspeed

as soon as I pull throttle back to idle with nose up config.

The original F-86 flight manual advices throttle to idle AFTER touchdown with 110 kts.

 

This strange behavior can be observed with other DCS aircraft too, but less pronounced.

[Holbeach]

I've no doubt you'll get plenty of advice on this, so here's my go.

 

 

To get back in to DCS after a break, I bought the beautiful Belsimtec F-86 in a sale and found it surprisingly difficult to get the hang of (which is why it's so good), so this is as far as I've got with the landing. Attention to correct airspeed and trim is essential.

 

 

 

 

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[wernst]

I've no doubt you'll get plenty of advice on this, so here's my go.

 

 

To get back in to DCS after a break, I bought the beautiful Belsimtec F-86 in a sale and found it surprisingly difficult to get the hang of (which is why it's so good), so this is as far as I've got with the landing. Attention to correct airspeed and trim is essential.

 

..

 

 

Yes, of course, attention to correct airspeed is essential. That's basics.

All I'm saying is that getting to correct landing airspeed seems difficult.

Trimming the Sabre is another "speciality". It's the only (real) airplane of which I know which gets tail heavy when being trimmed.

 

For me the only safe way to land the Sabre is to make a flat approach keeping speed at max. 130 kts

and carefully watch speed when flaring above ground avoiding stall below 110 kts.

 

I'd like to see your video but it's blocked: "private".

[Holbeach]

Yes, of course, attention to correct airspeed is essential. That's basics.

All I'm saying is that getting to correct landing airspeed seems difficult.

Trimming the Sabre is another "speciality". It's the only (real) airplane of which I know which gets tail heavy when being trimmed.

 

For me the only safe way to land the Sabre is to make a flat approach keeping speed at max. 130 kts

and carefully watch speed when flaring above ground avoiding stall below 110 kts.

 

I'd like to see your video but it's blocked: "private".

 

I've unlocked it, don't know how that happened.

 

The main point in question is that you should need about 70% power just to keep the approach speed up rather than have difficulty in slowing down.

 

A standard cross runway join is used, or a runway heading join would be an alternative.

 

 

GL.

[1.JaVA_Platypus]

Yeah, I always found it a bit suspicious. I've got the super-sleek aerodynamic MiG-21. It really needs 90% power in the approach if you come in a bit heavy and you want to maintain a reasonable airspeed. And in the F-86 and the MiG-15, you really need to work to slow down the airplane. I think there must be some kind of simple flight model that Belsimtek implemented in those aircraft.

[wernst]

I think there must be some kind of simple flight model that Belsimtek implemented in those aircraft.

 

Yes, there seems to be something odd with the flight model of the Sabre, e.g. when flaps are deployed.

Flaps should give a nose down pitching moment and slow down the plane.

But with the Sabre it’s the opposite. Flaps give a strong nose up pitching moment when deployed.

You’ll have to down trim quite a lot to compensate for level flight. And, even more surprising,

the plane does NOT slow down significantly when flaps are lowered fully and power set back to idle.

 

All real SEP planes which I have flown, e.g. C206 (2.000 kg take-off weight)

are getting nose heavy and reduce speed after flaps are deployed.

The C206, which is much less heavy than the Sabre, would bleeding off airspeed and

immediately start sinking like a stone as soon as I pull throttle back to idle.

There is no way to safely land this real SEP plane with idle power.

 

Not the Sabre (flight model).

Neither power back nor flaps down have any noticeable effect on speed and sink rate.

Sometimes the Sabre flares endlessly over the runway, it feels as being in a glider.

Only the speed brakes help to finally come down, hopefully before the end of the runway.

 

My way for landing the Sabre (flight model) is an unsafe flat approach with

carefully keeping the speed in the (unhealthy) range of 110 - 120 kts IAS on final.

A tail wind gust could finish this kind of unnatural approach immediately.

 

.

[Holbeach]

Speedbrakes open from airfield approach and left open.

Lower flaps in 1 second increments to alleviate the trim up tendency ( my way).

Downwind 170 kts.

Final 145 kts.

Touchdown 120 kts. Idle engine only when landing assured.

 

Follow the manual procedure, as above and you should have no problem.

 

 

..

[Art-J]

Yeah, I always found it a bit suspicious. I've got the super-sleek aerodynamic MiG-21. It really needs 90% power in the approach if you come in a bit heavy and you want to maintain a reasonable airspeed. And in the F-86 and the MiG-15, you really need to work to slow down the airplane. I think there must be some kind of simple flight model that Belsimtek implemented in those aircraft.

 

Be careful with making such comparisons, because with such different wing planforms and airfoils, these two are just not comparable.

 

Max lift-to-drag ratio for delta wing plane like the -21 was probably lower than 9 (more like 7-8 I'd say), while the same ratio for subsonic planes with swept wings would easily exceed 13-14 (for example, look at modern airliners - even with those bulky engines under the wings, they have L/D ratios of no lower than 20!). At approach speeds the difference would be much higher.

 

The slowing down rate is suspicious, but after one of first F-86 patches it's still much better than just after release, when it was a damn glider :D. Now, as soon as I get it to 180 IAS, drop gear and flaps (airbrakes deployed much earlier), it slows down to ~150 quickly and I have to keep the throttle up quite a bit again not to pancake onto the ground.

[wernst]

 

. . . as soon as I get it to 180 IAS, drop gear and flaps (airbrakes deployed much earlier) . . . .

 

just to make sure: You don't keep the airbrakes ON (extended) until touch down, do you?

 

. .

[Holbeach]

just to make sure: You don't keep the airbrakes ON (extended) until touch down, do you?

 

. .

 

Speedbrakes should be open when overhead the field and before landing gear and flaps are deployed, then left open till after landing, as stated previously.

 

 

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[Holbeach]

just to make sure: You don't keep the airbrakes ON (extended) until touch down, do you?

 

. .

 

Airbrakes should be open when overhead the field and before landing gear and flaps are deployed, then left open till after landing, as stated previously.

 

 

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[wernst]

Airbrakes should be open when overhead the field and before landing gear and flaps are deployed, then left open till after landing, as stated previously.

 

..

 

o.k., I learned that it is standard landing procedure keeping speed brakes extended until landing completed.

I was always using the speed brakes to control the speed to 170 kts IAS before I lower gear and flaps.

Afterwards I closed the speed brakes controlling speed by power only.

With less success. Obviously wrong . . . with Sabre flight model!

 

But I still wonder how a Sabre could fly like a glider with gear and flaps down, speed brakes in (closed) and power set to idle.

It’s not a glider which performs a glide ratio up to 1:70. Gliders do need to have speed (air) brakes, it’s essential.

Without air brakes a glider would never safely come down to the beginning of the field.

 

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[AG-51_Razor]

I have been practicing Holbeach's technique and have been able to faithfully reproduce his results pretty much every time. About 70% RPM is a good power setting at the break, boards out and then trim to level off during the turn and be patient. The speed will bleed off, just as it does in his track. Once below 180 kts, flaps a little at a time and gear and use altitude (descent) to control speed to the threshold then flare gently (I use trim for this) and kiss it on, power off. Works every time......except for those couple of times I misjudged my altitude and speed and wound up wrapped around some approach lights! ;)

[Art-J]

just to make sure: You don't keep the airbrakes ON (extended) until touch down, do you?

 

. .

 

Sure I do, as per manual instructions. Retracting them only for a go-around. Also note that throttling to idle in flight doesn't really give "stationary" idle RPM and the engine still produces quite a bit of thrust. I agree however, that L/D ratio with brakes off seems optimistic.

 

Edit - Ooops, I didn't notice this thread has a second page. You've read about the brakes already. Disregard :D.

Edited May 23, 2015 by Art-J

[Holbeach]

I have been practicing Holbeach's technique and have been able to faithfully reproduce his results pretty much every time. About 70% RPM is a good power setting at the break, boards out and then trim to level off during the turn and be patient. The speed will bleed off, just as it does in his track. Once below 180 kts, flaps a little at a time and gear and use altitude (descent) to control speed to the threshold then flare gently (I use trim for this) and kiss it on, power off. Works every time......except for those couple of times I misjudged my altitude and speed and wound up wrapped around some approach lights! ;)

 

 

I also use the trim to flair, partly because of a sticky stick and also keep a little power on to flatten the roundout.

 

This is for anybody who would prefer a faster rejoin speed.

 

 

 

 

 

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Edited May 28, 2015 by Holbeach
replaced with a video