P-38 J

[FLS]

I suspect something was missed in the calc.  Your 'no flap' minimum turn radius/max turn rate turn seems way low for 108mph stall speed. 

That manuever would be close to 3g, pretty good banked turn and it should be stalling ~ 165-170mph not 108.

I think you're misreading it. The 108 straight and level stall speed is a calculation based on cactuskooler's measured turn rate of 17.83 at 198 MPH. If you look at Badboy's EM diagram his no flaps best sustained turn is at 3.2 G at 190 MPH and you would be stalled at 185 at 3 Gs. At 165 you could only pull 2.4 Gs.

[drgondog]

I think you're misreading it. The 108 straight and level stall speed is a calculation based on cactuskooler's measured turn rate of 17.83 at 198 MPH. If you look at Badboy's EM diagram his no flaps best sustained turn is at 3.2 G at 190 MPH and you would be stalled at 185 at 3 Gs. At 165 you could only pull 2.4 Gs.

I did misread it, seeing only the reference to 108mph in your tables.  Having said this, IIRC the 3g stallspeed for the P-38J/L @17500 GW is approximately 165-170 per Dean's tables - but I have not fooled with P-38 calcs.  I have not yet been able to see the actual notes from the October 1944 Patuxent River Fighter Pilot Convention to see what references Dean used for his tables.

I don't question the EM plot or Badboy's derivations but curious regarding the boundary conditions.

They are easy enough to derive (for my understanding) with another couple of questions

What are you using for Limit Load for a P-38J/L at 15,483 pounds and what CLmax are you using for clean config and at what Bhp?  Did you derive 'eta' for efficiency at high Hp/low speed or use something like .85? Did you derive CD0 from a flight test result for 15,483 pounds @Bhp for this model at SL?

[FLS]

We fly the Aces High aircraft and time the turns. I don't know what Badboy used for his Bootstrap Calculator. I don't know why we'd be concerned with limit loads. There is a 6 G limit for the pilot. We are mostly concerned with shooting each other down. Have you tried Aces High?

[drgondog]

We fly the Aces High aircraft and time the turns. I don't know what Badboy used for his Bootstrap Calculator. I don't know why we'd be concerned with limit loads. There is a 6 G limit for the pilot. We are mostly concerned with shooting each other down. Have you tried Aces High?

No, but Brooke's calcs on the internet brought me to the site because I was curious to ask how he treated the aerodynamics of high AoA and lower speed range to stall - in context of the use of Oswald efficiency, Power efficiency and the unchartered drag rise at near stall high G manuevers.  IMO, Oswald efficiencies as used in the game models understates the significant increases to viscous drag which are related to angle of attack (instead of the Oswald factor associated with the smaller parasite drag of lower angles of attack).

The V-n diagrams are all about limit loads.  And stated Limit loads are deceptive. For example the orginal P-51 was designed to 8G Limit/12 G Ultimate... but at 8,000 pounds for P-51A... so as the airplane grew, say to ~10K for a P-51D. As a result the Limit load reduced to (8,000*8G)/10,000=6.4g

Ergo - if 8g Nmax is used, the resulting Vc=~ 11.8% too high... =  f(sqrt(8/6.4))

[FLS]

In this discussion on the use of flaps we're just looking at how different flap settings change the turn rate and radius.  The 6 G limit in the diagram is the pilot limit modeled in AH not the airframe limit.

It would be interesting to know the practical effect of "significant increases to viscous drag"  and if the effect is the same for all aircraft or if it would change the relative performance under your conditions.

[drgondog]

In this discussion on the use of flaps we're just looking at how different flap settings change the turn rate and radius.  The 6 G limit in the diagram is the pilot limit modeled in AH not the airframe limit.

It would be interesting to know the practical effect of "significant increases to viscous drag"  and if the effect is the same for all aircraft or if it would change the relative performance under your conditions.

Short answer, should raise the minimum stall speed/turn radius as well as relative energy losses - and no, I don't believethat the behavior between a draggy 109 and a very clean 51 would continue in a linear fashion.. but no proof points as yet

I started a thread on discussions regarding Oswald efficiency factor.  Candidly, I am a graduate aero and practising aero (and airframe structures), looong out of the biz after a stint at lockheed and Bell, but know for a fact that we did nothing related to changes in CDo due to changes (moderate to high)  in angle of attack related viscous drag. Everything was focused in preliminary design on range, take off and landing performance, climb, max speed, cruise speed, and ceiling - but symmetrical flight...

I have looked at a lot of spreadsheets out there and have problems with detail assumptions - and particularly in the behavior of high throttle/fine pitch prop behavior in low relative speeds (near stall), as well as assuming Oswald efficiency estimates behave as a constant as the AoA increases to CLmax.

Summary - My thesis is that the effects are significant - and vary in the significance between a draggy beast like a 109 and a clean 51  at the bottom of the drag bucket where the high G turns are played out in the games.

[FLS]

Once you figure out what the model should be doing you can try Aces High and see how it compares. The Aces High flight model hasn't been published so I assume Brooke published something general and not specific to the Aces High flight model.

[drgondog]

Once you figure out what the model should be doing you can try Aces High and see how it compares. The Aces High flight model hasn't been published so I assume Brooke published something general and not specific to the Aces High flight model.

I have no quarrel with Brooke's model or his internet publication.  I came to this forum to exchange ideas.

Having said this, it is just a game but seems to have a lot of thought built into the model.

[FLS]

I didn't think you were quarreling. I don't know what's in the Aces High flight model but I'm interested in how it could be improved.