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Ruderdyne
08-03-2005, 02:15 AM
Technical nitpick. Props that strike the ground with the engine throttled back will bend backwards, as simulated. But props that strike the ground with engines throttled up will actually bend forward. They got a lot of technical details right with this oustanding sim. Wonder why this detail was overlooked?

Ruderdyne
08-03-2005, 02:15 AM
Technical nitpick. Props that strike the ground with the engine throttled back will bend backwards, as simulated. But props that strike the ground with engines throttled up will actually bend forward. They got a lot of technical details right with this oustanding sim. Wonder why this detail was overlooked?

Utchoud
08-03-2005, 02:25 AM
You may be right, it's logical what you say. I have (fortunately) no real experience with this issue.

The game contains many simplifications, and this is one of them. When the prop hits the ground, its model is simply replaced by an universal "bent prop" model.

Interesting observation!

FritzGryphon
08-03-2005, 03:32 AM
I've never seen or heard of blades bending foward, unless maybe the plane was flying backward when the prop hit the ground... This is a joke for your 1st post, Ruderdyne?

Maybe you could tell us why that happens. My first impression is that the motion of the plane relative to the ground dictates which way the blades will bend. Throttled up, down, windmilling, siezed, whatever.

Or perhaps a plane with little or no airspeed struck the ground with a nose high attitude, that might bend them forward.

http://members.shaw.ca/evilgryphon/bent.jpg

Utchoud
08-03-2005, 03:49 AM
I think I see the reason: When the engine is throttled up, the driving force for the deformation of the propeller is its rotational motion. The propeller has a certain angle of attack under which it strikes the air, as well as the ground, and the resulting force causes the prop to be bent forward.

With throttle down, however, the driving force of the deformation is the relative movement of the aircraft to the ground. Thus, the prop is bent backward.

VVS-Manuc
08-03-2005, 04:28 AM
any photos to proof this 'forward bend' theory?
I know only pictures with the blades bend backwards.

BBB_Hyperion
08-03-2005, 04:59 AM
I read that one Problem is when props are set for idle pitch the plane tends to nose over so you need to increase pitch to lowest possible climb on crash landing.

I think i know what he is talking about consider a rotating prop with medium or high pitch setting that rotates when it strikes the ground . The forces rotation vs ground makes it bending forward. Not so when you approach in a slight dive.

Stigler_9_JG52
08-03-2005, 09:45 AM
*sigh*

Why we even waste time nitpicking eye candy for bent props in crashes (which come seconds before you hit the refly)??? I mean, really, what difference does this make to gameplay? Absolutely none. Whether a prop is bent forwards, backwards, sideways or in a nice, cute bow, the plane is down and ain't going anywhere until a truck comes to tow it off.

Perhaps ask *important* graphics-related questions like...

1) Why can aircraft disappear at less than 1km against terrain?
2) Why can't you make out MORE of a "dot" when you zoom in, rather than LESS?
3) Why can't we see airstrips (against the surrounding terrain) in the desert?
4) Why can't we have a ground only external view, even if in-flight externals are turned off (to simulate that we might actually know something about the layout of the taxiways and even where the h#ll we are on it).


All these actually affect gameplay.

Utchoud
08-03-2005, 10:15 AM
I agree with you, Stigler, that this is only a minor issue. However, Ruderdyne has the right to post it. If he is right (I'd like to see the photos like Manuc said, too), this technical nitpick can find its way to BOB and make it a bit closer to perfection.

All the photos I have seen show blades bent backward. One reason can be that pilots usually don't give much power when crash-landing.

Utchoud

Brotrob
08-04-2005, 03:40 AM
Of course he's right.

A plane with high speed and a fast rotating propeller hitting the ground, will bend its blades backwards, as modelled in the game. It happenes on nearly every crashlanding.

Now imagine a plane starting, on a unprepared airfield, with grass instead of concrete. The propeller is rotating with very high speed, but the plane is still very slow. Now perhaps becouse of high tourge or to much brakes, the plane flips slightly over the nose, and the propeller hits the ground. It will screw into the earth and thus bend forward. Yust remember the shape of the propeller, and you will see that this is quite logic.

There are even cases, where the speed of the plane and of the propeller are balanced in this way, that the prop neither bends forward or backwards, for example I know a story of an flight-instructor who slightly ditched into the atlantic with the prop, and the only effect was that the blades ware sanded of and the black colour was gone, so they shined silver.

So to summarise:

crash-landing: blades bend backwars
starting-accident: blades bend forwad

Best regards,

Brotrob

Ruderdyne
08-05-2005, 04:02 AM
Well I did qualify my post with "nitpick". No, it's not very important, but as a picky sim fan, I've been facinated by the realism details in this game. I've never seen this level of realism in a sim before. In that light, I was surprised that they missed the props bending forward while under a load.

The propellor damage issue is pretty academic. Just ask any accident investigator. Props bent back: engine idle or already failed at time of impact. Forward, and the engine was producing power. Yes, there are many photos of this. This is a well known fact.

It is likely this happens because the prop is essentially a screw. In the air, this screw can "slip" and cavitate, because the air is compressible and can move out of the way. The ground is not compressible, and will not move out of the way. When the prop tips start slicing into the ground, it's sill trying to act like a screw, and it grabs violently, trying to pull the airplane foward faster than it's already moving. The prop blades ultimately fail under such a load, curling forward in the direction of thrust. That's just my theory. Whatever the reason, it's a fact that it happens.

GH_Klingstroem
08-05-2005, 02:22 PM
never heard of it and dont belive it till I see a picture! The forward motion of the aircraft will bend the props backwards no matter what pitch u have got! thats my opinion!

VFS-214_Hawk
08-05-2005, 04:16 PM
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by VVS-Manuc:
any photos to proof this 'forward bend' theory?
I know only pictures with the blades bend backwards. </div></BLOCKQUOTE>

Thats because most prop strikes are caused from planes landing or at a point where there is "no-power" such as in a landing.

VFS-214_Hawk
08-05-2005, 04:19 PM
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by GH_Klingstroem:
never heard of it and dont belive it till I see a picture! The forward motion of the aircraft will bend the props backwards no matter what pitch u have got! thats my opinion! </div></BLOCKQUOTE>

If the planes foward motion is greater than that at which the prop/blade angle are hitting the ground, it will bent backwords. If the plane is sitting still with "power" and the plane drops striaght down, the blades will bend foward due to the blade pitch angle as it hits the ground.


I will get some pics posted as soon as I can, may be a few days

VFS-214_Hawk
08-05-2005, 04:44 PM
http://www.geocities.com/vmf_214_blacksheep/prop1.jpg

However, in Olegs defence...if he needs it, this is a rarity and is not worth modeling.

Shrimp2
08-05-2005, 05:52 PM
It's true. Propellers bend forward when hitting the ground with high power settings.

Nevertheless, one will see far more crash landings at idle, windmilling or with a seized engine.

The request is perfect and is a question of real physics modelling and not just a "I want this because... because" request.

And the detail the simulation has attained so far makes it deserve this type of advanced details.

Best regards!

LEXX_Luthor
08-05-2005, 06:46 PM
Makes a fascinating discussion. http://forums.ubi.com/images/smilies/25.gif Its a waste of programming time to include this in a combat flight sim.

Ruderdyne
08-05-2005, 07:41 PM
Well, I'll put this duscussion to rest. The reactions were interesting, although not surprising. On the surface, it's counterintuitive. The prop is a screw. Under power, it is trying to screw itself through the air faster than the airplane can fly. Even in a full power cruise, there is a certain amount of slip. In other words, it doesn't travel it's theoretical distance forward through space in one revoluation (like a screw does through wood), because the air compresses and moves out of the way (rearward toward the tail). However, when it encounters a medium such as the earth, there is now no slippage. The tips try to drag themselves forward at 100% efficiency, as long as the prop is still turning--which it is for a second or two before the blades and engine fail. Just like a screw through wood. The tips will try to move forward faster than the airplane, and will bend FORWARD. As the airplane settles, they will continue to deform in the direction that they started to curl.

As I said, this phenomenom is academic in the (actual) aviation world. It's not that rare. Investigators use this clue to tell them if an engine was producing power in a crash. And yes, there are many instances where an airplane hits the ground in an accident with the engine howling. Believe me.

I can't believe this started a debate about whether this is an actual phenomenom. What I wanted to discuss was why it wasn't simulated and whether it was worthwhile to do so. However, if so many people won't believe it to begin with, it's most certainly a waste of time to simulate it! http://forums.ubi.com/groupee_common/emoticons/icon_smile.gif~ I do a lot of roaring around low level in the sim, and occassionaly catch a prop on the ground and keep flying (such as in the P-38). Just thought it'd be an interesting effect to simulate.

I'll shut up now, and we can end this discussion.

Cheers

VFS-214_Hawk
08-05-2005, 09:04 PM
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Ruderdyne:
Well, I'll put this duscussion to rest. The reactions were interesting, although not surprising. On the surface, it's counterintuitive. The prop is a screw. Under power, it is trying to screw itself through the air faster than the airplane can fly. Even in a full power cruise, there is a certain amount of slip. In other words, it doesn't travel it's theoretical distance forward through space in one revoluation (like a screw does through wood), because the air compresses and moves out of the way (rearward toward the tail). However, when it encounters a medium such as the earth, there is now no slippage. The tips try to drag themselves forward at 100% efficiency, as long as the prop is still turning--which it is for a second or two before the blades and engine fail. Just like a screw through wood. The tips will try to move forward faster than the airplane, and will bend FORWARD. As the airplane settles, they will continue to deform in the direction that they started to curl.

As I said, this phenomenom is academic in the (actual) aviation world. It's not that rare. Investigators use this clue to tell them if an engine was producing power in a crash. And yes, there are many instances where an airplane hits the ground in an accident with the engine howling. Believe me.

I can't believe this started a debate about whether this is an actual phenomenom. What I wanted to discuss was why it wasn't simulated and whether it was worthwhile to do so. However, if so many people won't believe it to begin with, it's most certainly a waste of time to simulate it! http://forums.ubi.com/groupee_common/emoticons/icon_smile.gif~ I do a lot of roaring around low level in the sim, and occassionaly catch a prop on the ground and keep flying (such as in the P-38). Just thought it'd be an interesting effect to simulate.

I'll shut up now, and we can end this discussion.

Cheers </div></BLOCKQUOTE> http://forums.ubi.com/images/smilies/11.gif

Tully__
08-06-2005, 11:38 PM
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by VFS-214_Hawk:
http://www.geocities.com/vmf_214_blacksheep/prop1.jpg

However, in Olegs defence...if he needs it, this is a rarity and is not worth modeling. </div></BLOCKQUOTE>

It's considerably more common in ditches at sea, but the wrecks are generally a lot harder to get a look at http://forums.ubi.com/groupee_common/emoticons/icon_wink.gif

VFS-214_Hawk
08-07-2005, 10:01 AM
Just in case, the prop pictured was not from a dicth in the water. http://forums.ubi.com/images/smilies/16x16_smiley-wink.gif

TAGERT.
08-07-2005, 10:58 AM
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Ruderdyne:
Technical nitpick. Props that strike the ground with the engine throttled back will bend backwards, as simulated. But props that strike the ground with engines throttled up will actually bend forward. They got a lot of technical details right with this oustanding sim. Wonder why this detail was overlooked? </div></BLOCKQUOTE>WOW and they call me nit picky for talking about climb rates.. Out of all the things not modeled in a simulation.. this is at the top of your list? I have to agree with Stigler on this one.. There are far more important things that NEED to be done in flight simulaitions. At the same time I realise that not all can be done, but given a choice props bending forward would be very Very VERY low on my list of things to do.

VVS-Manuc
08-07-2005, 04:27 PM
and don't forget that some planes had wooden propeller blades which broke and didn't bend when touching the ground. That is not modelled, too

but leave it as it is and fix more important things, please!

TAGERT.
08-07-2005, 04:37 PM
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by VVS-Manuc:
and don't forget that some planes had wooden propeller blades which broke and didn't bend when touching the ground. That is not modelled, too

but leave it as it is and fix more important things, please! </div></BLOCKQUOTE>actully the wooden props on the TB3 do break off and not bend. I think some of the DORA's do that too.. ie break off.

MEGILE
08-07-2005, 05:27 PM
Seafire also.

FOKite
08-08-2005, 12:28 PM
Heres my contribution to this fun topic; I have also noticed that if you pancake with a stopped engine you still manage to bend all three blades even tough the "Top" one never hit anything. http://forums.ubi.com/images/smilies/16x16_smiley-surprised.gif

LEBillfish
08-08-2005, 02:41 PM
Oh, I don't know that it is pointless, perhaps though would be difficult to model as now yo'd have to ask that the sim determine forward speed vs. prop rpm and torque and then calculate that to give you the forward strike....However, I have currently seen Props bent back, props "shattered", and up pointing prop left alone.....That shows a lot of effort to monitor what is going on simply to select the correct prop damage...The tools might already be there.

GH_Klingstroem
08-09-2005, 05:50 PM
Tully that prop looks bent backwards to me.
Anyway even if the prop bends forward when ittouches the ground, surely as the aircraft skids forwards it will bend the prop back again even if it was bent forwards first...
I still cant see how this can happen!

Burnzoire1
08-09-2005, 06:20 PM
I've read on several occassions about the prop bend thing when reading reports on aircraft going down. Things like "it's apparent the pilot had powered down due to the props being bent backwards". I've yet to read a detailed explanation of this though - I'm interested but not phased about it's implementation in PF/BoB.

VFS-214_Hawk
08-09-2005, 08:01 PM
lol, just checked the prop pile at work and discovered two that have blades bent foward and one three bladed prop with two blades back ond one forawd....want pics?

GH_Klingstroem
08-10-2005, 05:25 AM
yes pls Hawk post a picture so I can finally admit defeat! http://forums.ubi.com/groupee_common/emoticons/icon_wink.gif

VFS-214_Hawk
08-10-2005, 03:30 PM
http://www.geocities.com/vmf_214_blacksheep/props.jpg

Here ya go.

Tully__
08-10-2005, 08:57 PM
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by GH_Klingstroem:

I still cant see how this can happen! </div></BLOCKQUOTE>
Klingstroem, think about a helicoptor rotor. With power on the blades curve up, with power off they sag. Same for an aircraft propellor, except that up is forward and down is backward.

It doesn't matter what the prop is turning through, if the pitch & rpm combo is high enough it wants to turn forward.

As ground & water are much less elastic and more dense than air, the prop works much better, generating enough "pull" on the medium to bend itself forward if it strikes at high power settings. On high performance aircraft, the bend is often sever enough that the prop is bent out of contact with the ground as the aircraft tail settles and it will consequently not bend backwards during the subseqent slide.

I imagine that in many cases the engine would stall or the crankshaft/gearbox break as a result of the original strike and with the engine stopped only one blade (or maybe two on a prop with 3 or more blades) would be at risk of being bent backwards in the subsequent slide anyway.

GH_Klingstroem
08-11-2005, 04:41 AM
Ok Tully that explains it well enough for me! Thx!
But in this case, shouldnt only one blade bend forward, the one that strikes the ground. The other two(a 3 bladed prop) should be unharmed or go backwards?
thx again for the explanation!

Tully__
08-11-2005, 05:38 AM
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by GH_Klingstroem:
But in this case, shouldnt only one blade bend forward, the one that strikes the ground. </div></BLOCKQUOTE>
While a prop strike will often stop an engine quickly, it rarely stops it dead. The prop will still get in several revolutions before stopping allowing all blades to be bent. The pic above shows one with two blades bent one way and one bent the other, an example of a prop that stopped with one blade up and the other two down and still straight enough to be bent backwards by striking the landing surface.

berg417448
08-12-2005, 01:16 PM
One side forward and one side back...

http://www.warbirdsresourcegroup.org/LRG/images/lrg1795.jpg

marcocomparato
08-16-2005, 07:37 PM
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by LEXX_Luthor:
Makes a fascinating discussion. http://forums.ubi.com/images/smilies/25.gif Its a waste of programming time to include this in a combat flight sim. </div></BLOCKQUOTE>

its not about programming time. this whole discussion suffers from the same problem. this about CPU time. what you guys like about Oleg's sim isnt its realism. if it was, you would play X-Plane which is an actual world-simulator. (ie: there is no model. the engine actually reacts based on structural bearing and load factors and aeronautics.

we play IL2 because of its optimization.

because we can play online with a tight netcode integration, in a balanced plane-set, with hi-framerates on a wide range of low-end compatibility specs.

Good ideas are needed, but physics-simulation isnt what were here for. its the dogfight.

LEXX_Luthor
08-19-2005, 12:42 AM
Great Post marco.

I was thinking they could program a routine that would use forward bending prop grafix under certain conditions...no physics calculations...just read in the current engine speed and landing speed data and use the forward/backward bent prop grafix as needed. Even that is not needed for either dogfight game or air warfare simulation. Its still a nice theoretical discussion though, for General Discussion forum.


<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Good ideas are needed, but physics-simulation isnt what were here for. its the dogfight. </div></BLOCKQUOTE> http://forums.ubi.com/images/smilies/16x16_smiley-happy.gif

Philipscdrw
08-22-2005, 08:59 AM
I was under the impression that aircraft that crashed on the metal deck of a British carrier would end up with the propellor bent forwards. Maybe that was if they tip forwards on takeoff.