Produced by Beech Aircraft since 1937, the model 18 was also used by USAF and US Navy in training and utility roles as C-45 Expeditor and AT-7 Navigator during many years.
Air America have used many D 18 and C-45 during Vietnam war and Volpar converted D 18, fitted with turboprops.
There is only one Beech D 18, FSX compatible:
the Beech D 18 from Milton Shupe, Scott Thomas and Andre Folkers model
Freeware, available at Flightsim.com Air America texture by Dominique Klein available at Flightsim.com
North-American OV-10 Bronco
Produced by North-American and immediately introduced in Vietnam in light attack and forward air control roles
Bronco was a light attack airplane, powered by 2 turboprops, intended to replace in Vietnam operations Cessna L-19 Bird Dog and O-2 Skymaster
Produced by Cessa from 1949 until 1959. 3200 L-19 are ordered by Defense Departement. Mainly used in Vietnam by USAF in a forward air control role, flying 100 ft above ground and guiding air strikes by jet fighters. Also used by many air forces as a utility and liaison airplane.
There is few FSX Bird Dog:
An old model created by Massimo Taccoli, FSX version.
Freeware, available at Flightsim.com
Also , a new model is available as payware ( 25 €) , at SibWings.com
North-American T-28 Trojan
Produced by North-American as a basic training aircraft, Trojan was compact and solid. Used by many air forces as trainer and light attack airplane mainly by USAF, South-Vietnamese air force, French air force (refurbished and modified, renamed as Fennec operate during conflict in Algeria), Laotian air force in counter insurgency role.
There is few FSX T -28D Trojan:
FSX Version by Tim Conrad, updated by Nor-Cal Prop Club.
Freeware, available at Flightsim.com