Tools

Aircraft designs for flight in icing are improved and proven effective by several tools, including analysis, icing wind tunnel test, and flight test in icing conditions.

Design handbooks

Design handbooks have charts and tables that can be used to perform analyses for aircraft icing and ice protection.

Figure 2-47. Airfoil profiles for impingement parameter plots in Figures 2-48 through 2-59.
from "Aircraft Icing Handbook", DOT/FAA/CT-88/8 apps.dtic.mil

Analysis

There are computerized icing analysis tools available from NASA, and from commercial vendors. There is also "bespoke" software created for special purposes.

LEWICE3D. LEWICE3D prediction of collection efficiency (color contours) and the resulting ice shape (at discrete cuts) along a wing.
from "Glenn Research Center Software" www1.grc.nasa.gov

Laboratory tests

A wind tunnel is a large tube with a fan to produce air flow at a calibrated airspeed. Wind tunnels are used to study many effects on aircraft, including icing. Artificially produced ice shapes (often 3D printed) may be adhered to airplane models, and the effects studied.

To simulate in-flight icing conditions, "Icing Wind Tunnels" often use refrigeration to reach air temperatures below the melting point of ice, and water spray to produce drop sizes similar to those in nature (some do not have refrigeration, and wait for a day with cold enough weather for testing).

Common Research Model, CRM, in the Icing Research Tunnel.
Two researchers observe glaze "lobster tail" ice on the leading edge of a test airfoil.
from "Glenn Research Center Icing Research Tunnel Facility Overview" www1.grc.nasa.gov

Flight tests

Flight tests are used to determine that ice protection systems operate as intended.

NACA 1947 conference Neel Figure 1. C-46 test airplane showing the manner in which the test airfoils were mounted (protruding from the upper fuselage).
A research test flight from "NACA Conference on Aircraft Ice Prevention - A Compilation of the Paper Presented by NACA Staff Members on 26-27 June 1947" apps.dtic.mil

Flight tests may be conducted using artificial ice shapes.
The above picture is of artificial ice shapes (shown in red) on the unprotected areas of the wing
leading edges and also simulated runback ice behind the protected leading edges.
from "Introduction to Icing Certification" faa.gov

Flight test is one way of determining the effects of ice on the performance of the aircraft.

Figure_14 of NACA-TN-1598. Airspeed loss caused by ice accumulation on
various components of airplane. Total airspeed loss, 41 miles per hour,
from 204 to 163 miles per hour.
from "Effects of Ice Formations on Airplane Performance in Level Cruising Flight." NACA-TN-1598, 1948. ntrs.nasa.gov

As a final proof that everything works as intended, flight tests in natural icing conditions are conducted.

Glaze Ice formed in flight on an airplane:
Figure 13. Formation of ice on horizontal stabilizer.
Average icing rate, 4 inches per hour; liquid-water content,
0.4 grams per cubic meter; drop size, 17 microns. (Painted stripes are
1 in. wide)
from "Effects of Ice Formations on Airplane Performance in Level Cruising Flight." NACA-TN-1598, 1948. ntrs.nasa.gov