yes this is very true regarding down thrust on the engine, this engine down thrust is only there for initial air lift but when it comes to a 3D type models with monster wing areas ect this down thrust can be set neutral. also the right prop should be used for maximum vertical lift, something like the master airscrew 14 x 6 with the 80 size 4 stroke. don,t forget to make this model abit on the rear c.o.g.