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Is there less propwash on the CEII because it's a biplane?


ekg
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So a few people have likely noticed that on the ground roll you need hardly any rudder input to keep the CEII straight down the runway. I was thinking about it some more and I was wondering if that is happening because it's a bi-plane? That is the extra set of wings disturb the prop wash before it hits the stabilizer. I'm no aerospace engineer so this is pure speculation. Thoughts?

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From this article http://www.kitplanes.com/issues/27_12/flight_reports/Flight_Review_Christen_Eagle_9393-1.html . "takeoffs are easy from grass or hard runways. Line up straight, add a bit of into-wind aileron, softly squeeze the right rudder, gently open the throttle"

 

Though it also states that alot of rudder is needed during most flight regimes, which is not implemented yet in the beta. The slip ball stays centered most of the time now.


Edited by Hoffster
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I’d really like to know if this is a WIP issue. There should be way more rudder work while operating this aircraft. As far as I can tell, besides a lite turn on the takeoff roll (which might’ve actually been due to crosswind), torque and prop wash effects don’t seem to be modeled at all.

i7 7700K @5.0, 1080Ti, 32GB DDR4, HMD Odyssey, TM WH, Crosswind Rudder...

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They are, they just arent as pronounced as they should be, which we acknowledged:

https://forums.eagle.ru/showpost.php?p=3763456&postcount=30

 

But regardless of that, our reference pilot disagreed with the above notion of substantial (way more) rudder use, stating that it needs a little just to stay coordinated, but its very small. As he added, resting your foot on the peddle just about take care of it. Eagle really doesnt need much rudder work unless you try hammerhead, snap roll or knife edge.

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They are, they just arent as pronounced as they should be, which we acknowledged:

https://forums.eagle.ru/showpost.php?p=3763456&postcount=30

 

Ok thanks, didn’t see that post.

The thing that stuck out the most to me was the lack of rudder input required during a wings level power on stall at 45 deg nose up. Every real world single engine prop I’ve flown, aerobatic and non, has required close to full deflection when nearing the stall. Also rapid throttle changes in level flight should cause more than pitch up/down effects. I’d expect a slight tail wag and roll, self correcting or not.

I have zero time in a real CE2 but have gone through aerobatics training in a Pitts S2 and an Extra 200 (started in an aerobatic C150 if that counts for anything), ~15 hrs total aerobatics time. I’ll trust your pilot that the CE2 tracks true down the runway and holds a coordinated turn with minimal fuss, but I’d be surprised if she feels such minor effects in all phases of flight. Sir Isaac still has a say. ;)

I’m glad to hear you guys are still working on it, and for what it’s worth, I’m really happy you brought the Christen Eagle in DCS.


Edited by SonofEil

i7 7700K @5.0, 1080Ti, 32GB DDR4, HMD Odyssey, TM WH, Crosswind Rudder...

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By the way, it's not the wash that causes the plane to move to the left, it's the engine torque

 

It's slipstream, torque, P-factor and gyroscopic precession. It does seem weak to me in this release. I'm sure it will get better.

 

The SME pilot is referencing control forces being light, but rudder and opposite aileron are required in some of these maneuvers. It feels a bit "fly by wireish" to me at the moment.

 

Still a blast and very much worth the investment!

Viewpoints are my own.

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CEII Flight Modelling

 

It's slipstream, torque, P-factor and gyroscopic precession...

 

The SME pilot is referencing control forces being light...

 

Still a blast and very much worth the investment!

 

EDIT: I would LOVE to be corrected in any of the areas below (for the love of aviation and learning) if somebody has the expertise and is willing to be generous with their time!

 

First: I love my CEII and thanks to M3 for bringing it to DCS. And to clarify, I've quoted Victory205 not to disagree with him but because it's the essence of the point I want to try and make.

 

There are a number of physical effects that are peculiar to the way the CEII is modelled in DCS. I'm just a student pilot who likes physics so I'm not a credible expert, however, there are physical effects at play in prop airplanes that are not readily apparent in the CEII. I understand and appreciate that we're WIP and the dev's have a real CEII driver to talk to; But, I think the SME's comments need to be taken in context and understood that they are made in relative reference to the SME's own body of experience (ie flying real prop planes, not drawing comparisons to other DCS flight models).

 

I also understand that the dev's have had to carefully balance getting the 'feel' right for aerobatics while staying within the flight limits of the real CEII and their own simulation flight model... I also understand that tiny changes anywhere threaten to throw the rest of their accomplishments out of balance.

 

All that said, let's start with 'Prop Wash':


  • Set yourself up for takeoff (instant action should work fine)
  • Apply full brakes and increase RPM to 1700
  • Apply back and forward pressure on the stick while observing

 

The airplane should show some effect of pressing the tail into the ground or lightening depending on the direction of the stick movement. This is an effect present in any prop airplane, even a stationary one, where the propeller wash flows over the elevator surfaces. My source is that I've physically done this in a real Cessna on a real runway. Again, I'm just a student and a Cessna isn't a CEII, but this effect is occurring because the elevator is directly in the flow of air created by the propeller washing over it. While the CEII sits in a tail-dragger configuration and changes the geometry a bit, I would expect some effect of the control surfaces (maybe reversed but still present). To be fair, I don't see any of this effect in either the DCS Spitfire or Mustang so either I don't know something about tail-draggers or this is more than a M3 problem.

 

 

Next up, 'Torque' (and 'P-Factor' and 'Gyroscopic Precession'.. 'Slipstream' effects may well be peculiar given the bi-plane configuration):

  • Takeoff from above or otherwise enter level power-cruise flight
  • Reach a non-critical altitude (>1000ft) and hold the nose level
  • Reduce throttle to idle (leave prop pitch maxed) and hold nose as speed reduces to ~65 knots
  • Rapidly advance throttle and relieve stick pressure

 

While the CEII becomes roll-unstable nearing the stall, you will notice almost no yawing effect even with rapid throttle advancements and little aerodynamic effect to counter it. I don't have a useful real world example for this yet; However, try the same experiment with the DCS Spitfire or TP-51. At throttle-advance, both planes will enter a sudden left banking turn and potentially roll inverted.

All 3 effects would play together in this scenario and apply some yawing forces to any prop aircraft. The CEII is a high-performance plane (big engine for the weight/size) so I don't think the comparison is completely Apples-to-Bananas. I believe rapid onset of torqueing forces, even if not warbird-magnitude, should be apparent in our little bird with the stubby wings. The p-factor at this high AoA (near stall) should amplify the effect. I can't reliably see any effect in-game.

 

 

'Adverse Yaw':

  • Enter level power-cruise flight
  • Sharply enter a bank and observe yaw
  • Level off and slow to 90 knots
  • Sharply enter a bank and observe yaw

 

While addressed by the devs, I still want to spell out exactly WHAT is suspicious about the CEII's adverse-yaw tendency. Even in my limited real world, this effect only lightly manifests itself in the Cessna depending on speed. The CEII may also incorporate designs to mitigate the effect - However, the main design-method I'm aware of is balancing aileron drag. The ratio of drag and lift changes depending on velocity so the lack of adverse-yaw at all speeds is suspect.

For a DCS example, try a similar profile in the Spitfire or even the L-39. You'll notice a tendency for opposite-yaw from the bank. As the speeds get slower, this effect becomes more and more pronounced.

The adverse-yaw effect should not stay constant throughout the bank... the effect should be most pronounced during the moment while the actual ROLL is applied to the aircraft. This is observable in the 2 examples above but not in the CEII.

 

 

That's all my limited knowledge has so far... I care because I think the CEII is important to DCS. M3's experience is going to color how all GA aircraft are handled in DCS going forward. Getting some of these effects nailed down really helps to bridge the gap between game and simulator. I would also imagine these effects are critical for the extremes experienced while dog-fighting in a prop (looking at you Corsair!).

 

Thank you again so much for bringing the variety and joy of aviation to the forefront in DCS!


Edited by kojdog
Adding a note that I'd love to correct myself and learn more about any of these topics
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FM Changes for 30-1-19

 

I think they made some flight model changes for 30-1-19 :thumbup:

Or I'm just crazy...

 

I haven't had much time to test but there appears to be a tendency to yaw with roll that varies with airspeed.

 

Great job team!

 

For folks who've been enjoying this bird while she's WiP, it might be a good time to hop back in and do some retesting!

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I own and compete (as a gross, hamfisted amateur) with a Pitts S-1S. I have flown most of the 2-hole Pitts models (S-2A, -B, and -C). Of the three, the S-2C is the most docile and probably most closely matches the Christen—except in performance where the -C far exceeds the Eagle. I too believe that the DCS Eagle is much too forgiving on the ground and too “un-Newtonian” in the air. Hard pull looping figures flown at full power require left rudder, approaching full travel as speed slows to below stall. Conversely, hard push figures require right rudder. My Pitts has a LOCKING TAILWHEEL yet I still groundloop it at low speed either because I wasn’t paying her the proper attention she deserved or I misjudged the wind. (Talking walking speeds here so no damage done except to my ego). The S-1 is shorter coupled and a little “squirrellier” than the Christen so the comparison isn’t perfect. The steerable tailwheel is less forgiving than a locking Haigh-type tailwheel. It certainly is no crutch. Yes, it will dampen outside forces like wind and airplane forces like torque and p-factor. But only to the tune of a few pounds of lateral force. After that she will trend towards where those forces are leading her and require correction by the pilot. The CofG is behind the mains. So once that trend is allowed to start, it will accelerate. Unless you are taxiing in a dead calm with the engine off, these changing forces are almost constant.

 

The “easy”/“hard” arguments are not unique to this forum. Pitts owners have been discussing this since the 50’s. It is difficult. The Pitts probably ranks as one of the most difficult planes to land consistently well of any plane produced in quantity. I’ve talked “Pitts” with many pilots with experience in the type plus time in Mustangs, Spits,109s etc. The Pitts gets total respect in that company as a plane that requires solid and attentive (yet nuanced) footwork. The Eagle is not a Pitts but it is close enough to participate in the discussion. They are difficult but they are also easy. “Easy” because they react instantly to any input be it proper or not. There is zero lag and total control harmony. As long as you are attentive, it is a piece of cake. But overcontrol and you’re done for. After years of flying I still get it wrong about 10% of the time and am forced to save the situation with a fistful of throttle and another spin in the pattern.

 

When Magnitue 3 gets it down to near perfection (and I don’t doubt they will) those of you have haven’t flown one in real life will not believe what an almost religious experince flying an aerobatic sequence in a light biplane can be. No airplane is easier in the box. It's not easy because it was designed to be. It wasn’t. It’s easy because it talks to you like no other aerobatic mount. Spins, snaps, hammers are all predictable if you are open enough to hear and feel what she is trying to tell you. Once you learn the proper inputs it is like an on-off switch. Do a pull-push-pull humpty with full forward stick and a bunch of right rudder over the top, pivoting at zero indicated airspeed followed by a 3/4 snap on the downline, level, half roll and push to vertical again for a perfect hammer—the smile will last you the rest of the day. You will never look at a P-51 with envy again.


Edited by Smokin Hole
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  • 1 year later...

This has definitely improved as of 6/24/2020. I played the plane and, while I can't say it's 100% realistic because I don't know, it's 100% more alive than it was when I made these comments. I believe some contradictory comments that the magnitudes and moments may not be correct, I at least believe that some factors that were previously absent are now accounted for. Again, neither an expert or CEII pilot (just a student pilot) this is far more dynamic now than when I made my original post.

 

Thanks for putting in the work, M3!

 

EDIT: I would LOVE to be corrected in any of the areas below (for the love of aviation and learning) if somebody has the expertise and is willing to be generous with their time!

 

First: I love my CEII and thanks to M3 for bringing it to DCS. And to clarify, I've quoted Victory205 not to disagree with him but because it's the essence of the point I want to try and make.

 

There are a number of physical effects that are peculiar to the way the CEII is modelled in DCS. I'm just a student pilot who likes physics so I'm not a credible expert, however, there are physical effects at play in prop airplanes that are not readily apparent in the CEII. I understand and appreciate that we're WIP and the dev's have a real CEII driver to talk to; But, I think the SME's comments need to be taken in context and understood that they are made in relative reference to the SME's own body of experience (ie flying real prop planes, not drawing comparisons to other DCS flight models).

 

I also understand that the dev's have had to carefully balance getting the 'feel' right for aerobatics while staying within the flight limits of the real CEII and their own simulation flight model... I also understand that tiny changes anywhere threaten to throw the rest of their accomplishments out of balance.

 

All that said, let's start with 'Prop Wash':


  • Set yourself up for takeoff (instant action should work fine)
  • Apply full brakes and increase RPM to 1700
  • Apply back and forward pressure on the stick while observing

 

The airplane should show some effect of pressing the tail into the ground or lightening depending on the direction of the stick movement. This is an effect present in any prop airplane, even a stationary one, where the propeller wash flows over the elevator surfaces. My source is that I've physically done this in a real Cessna on a real runway. Again, I'm just a student and a Cessna isn't a CEII, but this effect is occurring because the elevator is directly in the flow of air created by the propeller washing over it. While the CEII sits in a tail-dragger configuration and changes the geometry a bit, I would expect some effect of the control surfaces (maybe reversed but still present). To be fair, I don't see any of this effect in either the DCS Spitfire or Mustang so either I don't know something about tail-draggers or this is more than a M3 problem.

 

 

Next up, 'Torque' (and 'P-Factor' and 'Gyroscopic Precession'.. 'Slipstream' effects may well be peculiar given the bi-plane configuration):

  • Takeoff from above or otherwise enter level power-cruise flight
  • Reach a non-critical altitude (>1000ft) and hold the nose level
  • Reduce throttle to idle (leave prop pitch maxed) and hold nose as speed reduces to ~65 knots
  • Rapidly advance throttle and relieve stick pressure

 

While the CEII becomes roll-unstable nearing the stall, you will notice almost no yawing effect even with rapid throttle advancements and little aerodynamic effect to counter it. I don't have a useful real world example for this yet; However, try the same experiment with the DCS Spitfire or TP-51. At throttle-advance, both planes will enter a sudden left banking turn and potentially roll inverted.

All 3 effects would play together in this scenario and apply some yawing forces to any prop aircraft. The CEII is a high-performance plane (big engine for the weight/size) so I don't think the comparison is completely Apples-to-Bananas. I believe rapid onset of torqueing forces, even if not warbird-magnitude, should be apparent in our little bird with the stubby wings. The p-factor at this high AoA (near stall) should amplify the effect. I can't reliably see any effect in-game.

 

 

'Adverse Yaw':

  • Enter level power-cruise flight
  • Sharply enter a bank and observe yaw
  • Level off and slow to 90 knots
  • Sharply enter a bank and observe yaw

 

While addressed by the devs, I still want to spell out exactly WHAT is suspicious about the CEII's adverse-yaw tendency. Even in my limited real world, this effect only lightly manifests itself in the Cessna depending on speed. The CEII may also incorporate designs to mitigate the effect - However, the main design-method I'm aware of is balancing aileron drag. The ratio of drag and lift changes depending on velocity so the lack of adverse-yaw at all speeds is suspect.

For a DCS example, try a similar profile in the Spitfire or even the L-39. You'll notice a tendency for opposite-yaw from the bank. As the speeds get slower, this effect becomes more and more pronounced.

The adverse-yaw effect should not stay constant throughout the bank... the effect should be most pronounced during the moment while the actual ROLL is applied to the aircraft. This is observable in the 2 examples above but not in the CEII.

 

 

That's all my limited knowledge has so far... I care because I think the CEII is important to DCS. M3's experience is going to color how all GA aircraft are handled in DCS going forward. Getting some of these effects nailed down really helps to bridge the gap between game and simulator. I would also imagine these effects are critical for the extremes experienced while dog-fighting in a prop (looking at you Corsair!).

 

Thank you again so much for bringing the variety and joy of aviation to the forefront in DCS!

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