FM question - wrong effect of Flaps?

[Kwiatek]

I recently had some time with BoB2 (2.05 ver.) and made some take off and landing practise. After these i wonder if effect of using flaps is correct in game? I wonder if turn on flaps shoudln't increase lift and effected that nose of plane going up? In game when you press flaps (above stall speed) nose of plane going down. It shouldn't be rather opposite? I think that should.

Other question is if Hurricane should have only when pressing 1 position of flaps like Spitfire - landings? In game Hurricane have 3 position of flaps like Bf109.

[Bader]

I haven't flown one of these planes in real life, but I can answer the second bit: the Spitfire had two positions, up and down. The Hurricane had an adjustable system with an indicator on the right of the cockpit. It is modelled as three stage here.

[Manta]

I recently had some time with BoB2 (2.05 ver.) and made some take off and landing practise. After these i wonder if effect of using flaps is correct in game? I wonder if turn on flaps shoudln't increase lift and effected that nose of plane going up? In game when you press flaps (above stall speed) nose of plane going down. It shouldn't be rather opposite? I think that should.

Other question is if Hurricane should have only when pressing 1 position of flaps like Spitfire - landings? In game Hurricane have 3 position of flaps like Bf109.

I have raised the same question some time ago. It seems like that with flaps open up you are able to lift at very low speed, but you need to compensate with trimming your Emil nose up, otherwise you'll end crashing into the ground. This behave makes me wonder...

[Kwiatek]

I haven't flown one of these planes in real life, but I can answer the second bit: the Spitfire had two positions, up and down. The Hurricane had an adjustable system with an indicator on the right of the cockpit. It is modelled as three stage here.

I checked manual for Hurricane II and it have more flaps possiton. Probably Hurrciane I have the same system.

Still is the question about effect of using flaps in planes. In my opinion if plane fly with speed greater then stall using flaps should incrase lift and effecting also in rasing nose of plane not droping.

[Scott - A2A]

There is lift, but also leverage on the wing. When the Spitfire flaps are full down, the forces twist the aircraft forward, and speed bleeds fast. I can only speak from my direct experience in other props, and when I drop full flaps on final, the aircraft lifts up but the nose points down. As speed bleeds, it settles out better.

One spitfire pilot said, "the Spitfire pitches nose down, which improves your view, and making speed control on finals relatively easy."

It's a neat feeling dropping those flaps at 130 mph. It's a genuine flying experience.

Scott.

[Osram]

Yes, this is one thing not every sim gets right as it is somewhat counter intuitive. Actually there are (IMO even the majority of) planes that pitch up when flaps extend. However the 109 is not one of them.

Like Scott says, do not mix up more lift and a pitch up moment. Flight models have six degrees of freedom, so they have three linear forces (lift/weight, drag/thrust and sideways force) and three angular momentums (pitch yaw and roll momentum).

[blue six]

Hi Kwiatek, Scott is correct, have a look at the notes under "change of trim" on page 18 of the Spitfire Pilot's Notes, here:

http://zenoswarbirdvideos.com/Images/sp ... Manual.pdf

blue six

[blue six]

Hi Kwiatek, what the notes are saying is that when the landing gear or the flaps are lowered, the nose of the aircraft will try to drop. You need to apply back pressure on the stick, or nose up trim, to maintain the same angle of attack.

Here's another link, go to page 11 and look at the section called "Trim change due to power and flaps." The last three lines in the table show what happens when landing gear, or flaps, or gear and flaps are dropped at 120 mph. A one pound pull was needed to "maintain trim" (keep the same angle of attack) when the gear was dropped, a two pound pull for the flaps and a three pound pull for gear and flaps together.

http://ntrs.nasa.gov/archive/nasa/casi. ... 092582.pdf

blue six

[SeaVee]

Blue Six - you are the man!!! Where do you find this stuff?

For those that don't know, Blue Six has done ALOT of work on the FMs for the Spit, Hurricane and Bf109 in recent months and we are currently testing some more of his work that will likely be in 2.06.

Blue Six REALLLLY knows his stuff on aeronautics and Scott is a RL pilot. I think some of the other Devs may have direct pilot experience too. Buddye is a retired software development program manager at NASA who did work on the US space shuttle program.

[Bader]

I had not read that second (US NACA Sept 1942) report, Blue Six, it's absolutely fascinating.
The slight forward pressure in normal flight and increasing backwards pressure in landing configurations (trim aside) is very well done in BoBII now, great stuff.
What was also fascinating was to see that it takes 3/4 inch of backwards movement of the stick (in powered flight rather than glide) to induce buffet. Now that is a sensitive elevator.

I was aware that the Spitfire had been rejected by the US(AF?) for lack of stability but had not read the report before now. The second item in the conclusions sections stating that "longitudal stability was either neutral or unstable, and therefore failed to meet the accepted standards" is quoteworthy in its own right. Plainly US and British requirements were wholly different.

Conclusion 4 echoes the point about stick travel "Stick motion required to stall in manoeuvres [I'm not going to type the American version of this ] is 3/4 inch. This value is much less than the 4 inch stick travel recommended for satisfactory flying qualities."

[Kwiatek]

Thx for good info and replays. Man is teaching all the time. But still i have some doubts. There should be differnce between engine on idle and with power. As we see in Naca report if Spitfire is flying at 120 mph with engine power (44 in. hg.) with flaps drop there is no needed stick force. With engine on idle after drop flaps plane nose down and required stick force to trim. I tested in game and these is quite acurate.
I tried similary test with Bf109 with diffrenet positions flaps at speed 300 km/h and engine power and always its nose is drop. I wonder if at such speed and engine wiht power after drop flaps (at least first stages) nose should be drop? I rather think that should be raise. I didnt test Hurrciane yet which has also different position of flaps.

[Osram]

I don't have numbers for the 109 but I do know that the 109 was extreme in this regard, that is why I mentioned it specifically in my post above. When you hear "extreme" don't think something that is hard to handle by a pilot. Of course pilots were taught to expect this behaviour and actually in the 109 you have the flaps and trim directly side by side. You were able to grab only one of them if you wanted but the normal procedure, at least for landing was to grab both and turn both.

With "extreme" I simply mean it had not only a pitch down moment but a stronger one than some other planes.

[Kwiatek]

Ok i tried Hurrciane with flaps at different stages speed and engine power and it behavies the same like Bf109 - nose drop with flaps drop no metter of power settings and speed and flaps stage.

BTW landing in Bf109 is hard lesson. I wonder about work of slots. These is the most dangerous moment when aproching and slots open casuing nose moving hard up. During counter action slots usually closing and these is the most dangerous moment - i wonder if slots should be closing completly or rather stay open?

[flybywire]

Hello,

There are 4 types of flaps on aircraft, plain, split, fowler and slotted.
The brits have split flaps on these aircraft which mainly produce a huge amount of drag...like barn doors really, hanging in the slipstream.

If the aircraft is trimmed say for 120 mph with this type of flap...whatever you do...chop power, slip or whatever, the aircraft will maintain it's trimmed airspeed. So now when you extend those barn doors...adding huge drag...the aircraft will nose over due to the added drag and the fact that the aircraft is still trimmed for 120 mph. It's kind of like in modern jets when we extend speed brakes (spoilers) and don't change the trim the aircraft will have the increased drag and have a sharper decsent until you change the aircraft trim...that is why you have the natural nose over effect.

So the FM is correct here in BOB 2 in my opinion. You are flying the approach...trimmed at 120 say, extend the flaps the nose will naturally go down so you need to trim nose "up" which will give you a slower trimmed speed, next you will add power to maintain your correct flight path. Cross the fence around 90 mph or so with full flaps and lots of power.

I am a real pilot, flying all kind of aircraft from the C150 up to the B744 with around 25,000 total hours.

[Smokin256]

Here is the NACA report on the Hurricane;
http://ntrs.nasa.gov/archive/nasa/casi. ... 092603.pdf
Fascinating reading these are. Unfortunately there is no specific info regarding trim changes with gear or flaps down as in the Spitfire report. There is also a report in there about the stalling characteristics of the Spitfire but I didn't copy the url for it. It says there are a number of US aircraft that were tested also but I haven't been able to find those. I found a couple of other types of reports on the P-40 so hopefully there is one for that aircraft in there somewhere.

Cheers.................Smokin256