‘Jack’ and fuzzy drag
This week I started to implement the new props, these seem to be working as expected in most cases and I’m fining good improvements now with these prop changes.
I decided to tackle one of the tougher planes in the fleet, one which we have just completed new 3D for the turbo version, the J2M ‘Jack’ series. I have never been happy with the flight feel or the performance of this plane, based on reference data I use it was slow and suffered roll/yaw issues. It seems very draggy and I always had trouble even getting the plane up to speed spec. Even with the repaired canopy a number of symptoms still existed. This plane was a toughie and even with the new prop it was not adding up the way I liked.
Anyway, it was not right, but why??
A few days ago whilst testing max speeds at alt I stepped out to get a drink, I returned to hear the unmistakable sound of stress loads on the airframe causing damage. I checked the log to find negative ‘G’ loads on the wing had been stressing the fuz and wing at high speeds (i.e. the fuz was lifting in one direction and the wing the other). As you can imagine the forces here would obviously be causing a ‘large’ amount of associated drag (the smoking gun). This was a direct pointer that helped guide me to lowing fuselage lift area and effectively reducing the high drag.
For a long time now GH has been working at this same thing and his findings proposed lowing the values of fuz lift and profile by a ratio of ~0.25 – 0.16 based on area. I have been using 0.6 as a ratio for awhile now, preferring to take it slowly until I could establish the need for this change myself. With the latest developments re the Jack I started to revisit the issue as a way to trim the Jacks drag issues. It was instantly apparent that the lower lift area also assisted in reducing high speeds at alt, good new indeed. Often in the past we used prop mach as a way of slowing planes that were fast above FTH, the combination of prop and fuz area changes has vastly reduced the need to do this.
I used the calculated prop solidity for the Jack as 0.14 (broad 4 blade prop), lowered lift and profile areas by 0.16 ratio, added some minor aileron tab trim to wing outer panels (0.6deg), fitted a new fin and i’m now having heaps of fun in the rebuild Jacks. 
The process seems to indicate that GH is indeed onto something with the lower lift and profile areas. Together with the prop alphas fixed at 0, and the solidity as a proportion of the disk, the end results are very pleasing. I’ll start to rework the N1Ks next as these also have high speeds issues, I am confident that large improvements to these will be the outcome.
I can’t wait to get these latests changes in game, the feel is much tighter and pointed and I find flying these altered planes much more realistic. There are a number of other issues we discussed (chatted via skype for 4 hours) as we continue to improve the feel and performance of TW planes. These are related to wing stall progression, another topic for another day.
Back to work.
