Message 6497

From:     "sheffield_ma"
To:         x-plane-tech
Date:     Sun Jul 25, 2004 7:58 pm
Subject: Prop Wash onto the Wings

I have been experimenting with a model in X-Plane version 7.41, and do not know if I am interpreting the result correctly. The result indicates to me that prop wash onto the wings does not significantly affect the maximum weight of an Osprey-like plane for a vertical takeoff. Alternatively, I may have made an mistake or there may be a limitation in X-Plane.

I used the V-22 Osprey that comes with the software and changed the engines from turboprop to injected recip. using Plane-Maker. I also set the thrust vertical cant to 90% and turned off thrust vectoring, so that the thrust would be vertical. The standard V-22 starts up in X-Plane 7.41 with the engines in a not fully vertical orientation, but instead tilted slightly forward. I opted for vertical because I thought this would accentuate any affect from prop wash onto the wings. I then experimented with substantially larger sizes for the length and chord of the wings, while keeping the position of the engines and propellers the same relative to the reference point. With longer wings, the engines were no longer at the lateral ends of the wings. The wings “grew around” the engines and propellers, exposing more wing surface to the prop wash during VTOL.

In spite of the wing changes, the maximum gross vertical takeoff weight from San Diego International remained approximately 34955 lbs.

I would like to mention an additional point. While increasing the wing size, I kept constant the long arm, lat arm, and vert arm parameters in the Foil Specs section of the Wings screen. These arm parameters are based on the 25% wing chord in Plane-Maker. (Deflections and pivots are now at the 50% chord.) So, for example, as I increased the chord size, the 25% chord remained in the same long arm position while the 50% chord moved toward the rear of the fuselage. I made a previous query to a forum in which I asked if the 25% chord is the center of wing lift. The feedback I received was that it was so.

I would appreciate feedback on these comments.