Bf109 K-4 pre-stall buffeting...

All three.

Trust me, I never thought there were actually so many sources of Thrust being modeled in DCS World!!! Wow!

I know that slats reduce the Vs. Maybebenefit of a wing with slats but then if you reach the new Vs that wing is going to stall from the wingtip to the root near at the same time thus entering in a more "violent" stall"

At almost the same wing loading you have:

Messerschmitt Bf 109K uses this airfoils: NACA 2R1 14.2 NACA 2R1 11.35

The 109 airfoil is better suited for turning compared to the laminar flow wing p51.

Better horsepower/ ton ratio.

And you are trying to tell me it's because of the 109's slats that the 109 stalls harder ? When every pilot that's flown both planes tells the exact opposite.

Well designed exhaust is a pretty important part of any high performance engine, it can hurt or help for sure.

No doubt, hence the careful attention to this by German designers with ejector exhausts.

Oh and exhaust thrust is pretty important to jets too isn't it? ;)

Difference is that here we actually have detailed energy charts available for each aircraft that have to be mirrored, i.e. less guesswork - and I actually think ED has done a great job with the jets.

Sadly I have at this point lost faith in how ED is modeling the WW2 propjobs, esp. after how what I see as properly backed constructive criticism has basically been brushed aside without any real explanation other than short phrases forcing us to guess what info might have been used. In other words no actual answers have been given, and whilst one might say that we are in no position to demand answers I can only say that to expect not having to defend your FM for what is described as a simulation is utopia. No sources need be shared, but figures used most certainly do IMHO, as this leads to higher credibility plus the chance that the community might provide information that was previously missing. Sadly this is not the case however, thus henceforth I will be looking elsewhere for a simulation of the WW2 birds. I will however keep enjoying the jets.

I am not disagreeing, and I am not an expert on it, but wouldn't the stall be harder/violent with slats as the slats can take you further than a wing without slats? if that makes any sense :)

Well nothing is impossible.Just had to say what was on my mind.

I think we can't have it all at the same time.

For sure DCS's prop modeling isn't probably the PERFECTION, nor it's flight dynamics, because that is practically impossible to achieve in a flightsim...

Sometimes on pure table-based approaches one can probably get some figures closer to what we think are the correct true values, based on data from RW documents, etc... I still use ELITE as my preferred IFR training tool for GA aviation. I use Aerowinx PSX for the 744 simulation, and I use Condorsoaring for when I can't fly for real...

Then I can't but use DCS when I want to feel the closest to reality in terms of flight and systems modeling of ww2 and rotary ( and I use Il2 Battle of Stalingrad too because, probably not being up to the level of detail of DCS it still gives me, together with DCS, the closest to real sensation of being there )

None of these sims I use is perfect, and I have raised here, a few times in the past, doubts based on my assumptions. Yo-Yo has refuted some, accepted one, and with further investigation, and talking to many RW pilots, like Klaus Plasa very recently, and others, I found that some "weirdness" was actually "realism" to a level not modeled in any other simulator I had used or use ( il2 BoS included, because as plausible as it can be, there are many aspects modeled in DCS that it doesn't model at all !!! ).

Why am I writing this ? Because I think there are moments in life where debating, pointing out, refuting is more armful than beneficial.

Yo-Yo has gained my highest respect, and I can only thank him, and ED for providing me with what DCS is, so, now even if something doesn't look plausible to me, I try to figure it out using all of the possible explanations I get, and the information he can provide - certainly not all because that's ED business, and should probably not be a good idea to reveal in full detail...

Hummingbird, point a flight simulator where we can get better ww2 aircraft like those modeled in DSC World right now ? Is there one ?

All three.

Thx for the answer Yoyo!

Regarding oil/water cooler thrust - is it constant thrust amount from these or is also effected by varying inlet/exit flap area, i.e. internal thermodynamics of the radiator assemblies...?

Yes, real methodics for cooler design was used that calculate cooling effectiveness and drag/thrust using radiator constructive parameters and flight parameters.

DCS is the Aerowinx PSX of flghter and rotary wing aircraft :-)

I am not disagreeing, and I am not an expert on it, but wouldn't the stall be harder/violent with slats as the slats can take you further than a wing without slats? if that makes any sense :)

[ame]https://www.youtube.com/watch?v=q_eMQvDoDWk[/ame]

Slats demonstration starts at 8:30.

What happens to a 109 when it stalls with the slats extended?

Yes, real methodics for cooler design was used that calculate cooling effectiveness and drag/thrust using radiator constructive parameters and flight parameters.

Amazing.

Seriously, IMO the best way to advertise your products would be simply to describe publicly how many aspects are modelled of a single plane...

:thumbup:

What happens to a 109 when it stalls with the slats extended?

The slats work like an air scoop, diverting air over the wing. Even if the wing stalls, as long as the aircraft is moving some air will get diverted over the wing, making the stall less pronounced.

Pilot records show that the 109 was very hard to stall and easy to recover.

Until the slats themselves stall you should have air rerouted above the wing, airflow attached and therefore some amount of lift induced. This holds true for both normal and accelerated stall. Furthermore there should be aileron authority until airflow has completely seperated from the control surfaces and some aileron authority on the downward pointing aileron right up until complete stall, correct?

So in a power off situation the wing root stalls before the outwars wing section, inducing drag and diminishing lift but aileron authority remains good since the slats increase critical AOA.

Now in a power on situation the wing root is energized by the prop wash increasing critical angle of attack. The slats keep the airflow attached to the aileron section. That is favorable and even necessary since AFAIK the 109 wing did indeed not have any wing washout. Since the prop is turning clockwise in a 109, the prop wash is directed downwards on the right wing side. This means right wing root will stall after the left wing root. This in turn would lead to asymmetrical wing stall and therefore wing drop to the left side. (torque coming into play as well)

Now if slats were indeed effective enough to keep the ailerons from stalling up until power on root stall the wing drop effect would be very benign and easily controllable.

I dont know if there are any reliable documents around about critical angle of attack on wing root (power on) and for the slats, but the stall behavior at the moment seems indeed a bit vicious if I think about it. In an power on stall the wing drop is aprupt and not very controllable atm. The pre stall buffeting on the other hand is well done Id say. If I may pass a question directly to YoYo here, is the stall behavior hard coded or aerodynamically calculated?

The few pilot notes available mention a very benign stall which is easily rocoverable with no spin preference observable. In the sim i cant see a spin preference, so that is also well modeled.

Edit: Just want to add this statement. The relevancy is questionable since its about the E model, but tendency should be similar.

Me 109 E:

"The airplane was equipped with a 60 foot trailing static head and a swiveling pitot head. Although, as may be imagined, operation of a trailing static from a single-seater with a rather cramped cockpit is a difficult job, the pilot brought back the following results:

Lowering the ailerons and flaps thus increases CL max of 0.5. This is roughly the value which would be expected from the installation. Behaviour at the stall. The airplane was put through the full official tests. The results may be summarized by saying that the stalling behaviour, flaps up and down, is excellent. Both rudder and ailerons are effective right down to the stall, which is very gentle, the wing only falling about 10 degrees and the nose falling with it. There is no tendency to spin. With flaps up the ailerons snatch while the slats are opening, and there is a buffeting on the ailerons as the stall is approached.. Withs flaps down there is no aileron snatch as the slats open, and no pre-stall aileron buffeting. There is no warning of the stall, flaps down. From the safety viewpoint this is the sold adverse stalling feature; it is largely off-set by the innocuous behaviour at the stall and by the very high degree of fore and aft stability on the approach glide.

It is important to bear in mind that minimum radii of turn are obtained by going as near to the stall as possible. In this respect the Bf.109E scores by its excellent control near the stall and innocuous behaviour at the stall, giving the pilot confidence to get the last ounce out of his airplanes turning performance."

- RAF Royal Aircraft Establishment (RAE) Farnborough handling trials,Bf.109E Wn: 1304. M.B. Morgan and R. Smelt of the RAE, 1944.

https://www.youtube.com/watch?v=q_eMQvDoDWk

 

Slats demonstration starts at 8:30.

I only question the slat modeling on the K4 because the slats don't seem to have any varying degrees of extension. They seem to always be fully open or fully closed and not independent from each other. Both wings seem to pop out at the same time no matter what and sometimes the slats do more harm than good because the transition from closed to opens doesn't seem to be there. At what AoA and air speed/pressure should they start opening/closing?

Klaus Plasa kindly answered me about that a few days ago, regarding the G10 :

"The slats do deploy either during combat maneuvers or prior to an unaccelerated stall. They are very smooth and unless the pilot watches them he wouldn't be able to tell when they pop out. A very nice feature on this airplane.

As in most of this class of aircraft there is virtually no pre stall buffeting. The wing drops usually right or left to about 30-40* bank and about 30* nose down pitch attitude.

It is very good controllable and recovers easily ."

Klaus was very kind in answering my questions regarding his extensive experience on the 109s he flies from the "Messerschmitt Museum", and, as I was reading most of his messages ( which I passed to Yo-Yo ), my

appraise of the K-4 in DCS made me think we really have here another of Yo-Yo's / ED's Masterpiece...

You do hear from people like Gunther Raal that they worried about asymmetrical deployment of the slats.

It'd be good if that sort of phenomenon was modelled. I'm sure it'd ruin your whole day if it happened mid-dogfight.

You do hear from people like Gunther Raal that they worried about asymmetrical deployment of the slats.

 

It'd be good if that sort of phenomenon was modelled. I'm sure it'd ruin your whole day if it happened mid-dogfight.

You have it already in DCS's K-4.

Try a skidding tight turn :-)

You do hear from people like Gunther Raal that they worried about asymmetrical deployment of the slats.

 

It'd be good if that sort of phenomenon was modelled. I'm sure it'd ruin your whole day if it happened mid-dogfight.

If slats are installed correctly and you keep the ball centered, slat deployment should be symmetrical. Some pilots encountered unsymmetrical/ early/ late slat deployment which caused trouble, so a guideline for correct installation was made. There is a document on kurfurst.org and/or wwiiaircraftperformance.org concerning the resolvement of this issue I believe.

Also slats either deploy fully or not at all, aerodynamic forces being strong enough for split second deployment once preset AOA is reached.

Jcomm thanks for posting Klaus Plasas insight.

That is quite interesting, since wartime pilots talk about a wide margin of pre stall buffeting/ lots of warning before stall and a loud bang when slats deploy. Infact even loud enough to scare inexperienced pilots. Does this means he doesnt experience aileron snatch as well? Very interesting. The loud bang may be attributed to the swivel arm design of the E/F models, since G/K models used a roller track mechanism.

Nice read right here.

http://109lair.hobbyvista.com/techref/systems/control/slats/slats.htm

You have it already in DCS's K-4.

 

Try a skidding tight turn :-)

It happened only in the Emil, not the others. On the Emil if the mechanism wasn't kept completely clean the slats would either stick (causing the slats to bang out violently) or sometimes altogether jam which would cause a premature stall and sometimes result in a spin. This happened to Rall.

Dave Southwood who flies Bf-109G Black Six

"In a turn at 280kphwith display power set, stall warning is given by light buffet at 3g, and the stall occurs at 3.5g with the inside wing dropping. Again, recovery is instant on easing the stick forward. One interesting feature is the leading edge slats. When these deploy at low speeds or in a turn, a 'clunk' can be heard and felt, but there is no disturbance to the aircraft about any axis. I understand that the Bf109E rolled violently as the slats deployed, and I am curious to know the difference to the Gustav that caused this."

Btw the slats are supposed to deploy slightly assymmatrically in certain situations, as the inside wing goes slower than the outside one. However the slats already start to deploy well before the critical AoA, so in a tight turn they will both be fully out, regardless of a little slip.

No disturbance around any axis should be felt, and the stall should be mild.

Atm we have excessive flutter and wing rock during tight turns, which wasn't/isn't present on the real aircraft.

I only question the slat modeling on the K4 because the slats don't seem to have any varying degrees of extension. They seem to always be fully open or fully closed and not independent from each other. Both wings seem to pop out at the same time no matter what and sometimes the slats do more harm than good because the transition from closed to opens doesn't seem to be there. At what AoA and air speed/pressure should they start opening/closing?

That may be part of the problem with the ingame aircraft and why it experiences wing rock, on the real aircraft slats start to deploy already at ~7 deg AoA, gradually extending until fully open around 11-12 deg AoA. Really the pilot should hardly notice or feel them deploy.