It Broke!

Homebuilt Aircraft & Kit Plane Forum

Help Support Homebuilt Aircraft & Kit Plane Forum:


Well-Known Member
HBA Supporter
Jul 15, 2020
Quite true....depending on the design of the cowling, of course. Part of building a liquid cooled installation is to do anything BUT have random airflow for cooling and induction. The worst example of any such thing I can think of is the STC that put the Thielert engine into 172s using the complete stock cowling. Made a mediocre performing airplane into a total dog.
Wow, not sure where you got these 'facts' from. The CD155 172 conversion uses the existing 172 nostrils for both intercooler (stbd side) and radiator (port side). From the photo you can see the actual scat duct size is less than the nostril on the intercooler and therefore required airflow is LESS than a than a 172. Drag is therefore LESS.


And RV6EJGUY assertions that TDI needs disproportionate draggy intercooler air in addition to more radiator air are visibly false when you can see that ALL the radiator cooling is achieved with only one 172 nostril, and ALL the intercooler air with a only portion of the second one.

The simple fact is less CD155 required total cooling air than a stock 172 means less drag. This is what happens when better TDI BSFC equals less waste heat to remove from the engine for a given horsepower.

As for 'doggy' performance, the CD155 172 takeoff distance at 2500# to 50ft is 1582 feet and a standard 172R is 1685 feet. CD155 is BETTER.

CD155 172 cruise speed at 12,000 is 131KTAS (7.8GPH) and the standard 172R is only 117KTAS (7.9GPH). CD155 is BETTER

CD155 Max cruise speed (any altitude) is 134KTAS (7.8GPH) at 14,000 and the standard 172R is only 121KTAS (9.2GPH) at 8000. CD155 is much BETTER.

CD155 172R time to climb to 12,000 is 16.9 minutes and the standard 172R is 31 minutes. CD155 is wayyyy BETTER.

I can go on and on, however the facts simply dont agree that either the weight, nor the drag, nor anything about the CD155 conversion is doggy or more draggy than the stock 172R. In every measure the TDI is better.
Last edited: