unsubscribe On Tue, 21 Jul 2020 at 00:52, Ian Williams <[email protected]> wrote:
> Hi Rob > > > > Im not as technical as you, but if any help, when we were test flying the > Grob 109 with the 2400 Stemme engine, we had to carry out a pre STC > approval series of flight tests. One was relating to engine and oil > cooling. > > So we used a standard ASI with the pressure in the engine and the static > behind the baffles. We were comparing the indicated airspeed with the > “baffle one” > > The results we got were as follows > > 1. Using the original baffles the ASI at slow speed was around 5Kts > faster at higher speeds (100kts) the two came together > 2. When we had finished the new baffles, we were getting a 15 Kt > difference at slow speed and again they came together at high speed. > > In practice it didn’t have a lot of effect on the CHT’s with the Grob. > However a similar effort to make the baffles “as tight as a fish’s bum” on > our Dimona had a really big effect on the CHT’s. We didn’t use the ASI > test as were very happy with the results. > > I have recently installed a MGL 4 ch CHT (nice colours) which confirms our > work. > > > > I hope that is some help Rob. > > Best regards > > > > Ian W > > > > *From:* [email protected] *On Behalf Of *Rob Thompson > *Sent:* Monday, 20 July 2020 12:17 p.m. > *To:* [email protected] > *Subject:* [DOG mailing list] Cooling airflow and Mixture relationship > > > > G'day Everyone, > > As many of you will know I am OCD about sealing every tiny air leak in the > Limbach engine bay compartment with silicone, aluminium tape and rubber > cowl seals. > > > > I have previously rigged up a water manometer in the cockpit with the > tubes running to the top and bottom of the engine. It told me I was getting > very good pressure difference but I didn't take much notice of the actual > measurements. I think it was somewhere around 30cm. > > > > As well as the ram air going into the front of the engine the lower cowl > is designed to "suck". We fitted a big scoop type bottom cowl which seems > to suck pretty well.... particularly with the baffles tightly sealed with > silicon. > > > > What I am wondering now is..... What is the effect of this extra suction > at the back of the engine on the carbs and mixture? > > > > Maybe it is not much different to flying at altitude and the SU carbs > altitude compensating ability can deal with it. > > > > Any fluid dynamics physics experts in this Dog group who can enlighten me? > > > regards > > Rob > > > > Rob Thompson > > 0429 493 828 > > > -- Best regards, Tim Kroeger +49 (0) 178 654 8793 http://au.linkedin.com/in/timkroeger
