RFguy Posted January 30, 2022 Posted January 30, 2022 yep FYI Geoff the Reynold's number for the 125mm scat at 41m/s is 343000. at these sort of surface roughnesses of corrugated hoses etc, friction ~ prop to roughness.
Geoff_H Posted January 30, 2022 Posted January 30, 2022 After 40 years of designing constructing and commissioning I have learned that any errors in design and the working end product depends upon the accuracy of your assumptions. The best advice is to do your calcs three times. Once where you expect assumptions to be then do them twice with assumptions at their extremes. The results will be the worst possible outcomes. I was the lead engineer in the middle east in the early 90's. It was an American job and back in Dallas we had PhD people check all of our calculation in a multiday seminar. They were good calcs. Got the design running in Syria, it didn't work as expected. After a lengthy investigation we discovered that our assumptions were wrong! We did modify the plant and it eventually worked to spec. Ever since I question assumptions not the calcs (not as much anyway). Murphy was an optimist. My long held saying. Geoff 3 1
RFguy Posted January 30, 2022 Posted January 30, 2022 (edited) well, I think in Skippys case, the sealing around his radiator will be the difficult thing, the leaks will really hurt, but the leaks HAVE to be sealed because the air will just go around the radiator if it can . go as large radiator as possible to reduce velocity through the radiator, which will reduce pressure drop, and then there wont be such a huge difference between the radiator path and a leak path(s) .... and with no leaks, the cowling will be pressurized and will reduce the performance of the oil cooler radiator hung under the prop. the hot air in the engine bay will preheat the air hitting the radiator reducing its performance, also unwanted. SKip I'd be ducting the air from the inlets to that radiator. Edited January 30, 2022 by RFguy
Geoff_H Posted January 30, 2022 Posted January 30, 2022 1 hour ago, RFguy said: yep FYI Geoff the Reynold's number for the 125mm scat at 41m/s is 343000. at these sort of surface roughnesses of corrugated hoses etc, friction ~ prop to roughness. I have never done an airflow through the engine but I think that the Reynolds number varies with fluid density, would these values and assumption be true for both sea level and 10,000ft? No idea just asking
RFguy Posted January 30, 2022 Posted January 30, 2022 these numbers Geoff are all for sea level, and will hold to 10k feet. the reynolds number falls but its still in the same range of values, nothign much is affected except of coure the mass air flow is down and thus cooling capability is down but of course engine output is down (no turbo)
skippydiesel Posted January 30, 2022 Author Posted January 30, 2022 25 minutes ago, RFguy said: well, I think in Skippys case, the sealing around his radiator will be the difficult thing, the leaks will really hurt, but the leaks HAVE to be sealed because the air will just go around the radiator if it can . go as large radiator as possible to reduce velocity through the radiator, which will reduce pressure drop, and then there wont be such a huge difference between the radiator path and a leak path(s) .... and with no leaks, the cowling will be pressurized and will reduce the performance of the oil cooler radiator hung under the prop. the hot air in the engine bay will preheat the air hitting the radiator reducing its performance, also unwanted. SKip I'd be ducting the air from the inlets to that radiator. I dont actually se the sealing around firewall to be a problem. Exhaust exit another story. I have some high temp material that , with care, can be placed/configured to minimise (best I can do) air loss in this area. My oil cooler will be moved, from directly behind a cowling "nostril" , to below engine, between exhaust pipes. This location will allow for smaller frontal area of cowling and the potential for an additional air inlet direct to oil cooler. I hope the combinator will not a only improve aerodynamics but also facilitate optimum cooling. As for ducting - not in the Mark1 set up but always a possibility down the test track. 1
RFguy Posted January 31, 2022 Posted January 31, 2022 Skip, just remember, pressurizing the whole cowling will reduce the ability of the oil cooler to work effectively because of the low pressure difference. I'll be ducting the air from the inlets to my radiators (as not to pressurize the whole cowling) , and a slight inlet volume for around engine ancillaries cooling. If you want to minimise frontal area / drag , you have to make the most of any radiator area you have , which will mean ensuring you get high pressure differentials...
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