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Dave and contributors, Spent yesterday finally getting specific answers that I should have had 12 months ago. The guru that I sent the stock turbo to in the end had no idea as to an upgrade for temp in the hot section. The up grade that Dave suggested is approx. $900 USD. Real problem at the moment is the exchange rate with all the bank charges, the great Ozzie dollar is approx. half. Then freight---- I see freight on a turbo from the US at up to $800 Oz dollars!! Then internal freight in OZ, plus labour costs --- I will have to sell 2 kidneys! Then considering I do not have a stock RX7 manifold to bolt the turbo to – I am manufacturing an adaption of the stock Renesis manifold, so whatever turbo I get it means work to make it fit and I am ¾ down that path. So having already having a “dummy spit” due to 12 months lost, I lauch out to find a new turbo in OZ. I find that Garret and others have a hot section wheel that will stand 1050 degrees C!! Wow that fixes anything that the rotary puts out with no phone calls involved trying to explain. Once again I make the usual; mistake telling the company with all these shiny new turbos that I want it for a drone!! Thought that would by pass the usual arguments---- silly boy, NO they do not supply for aeronautical applications!! So I am back to “dune buggy” even though the nearest beach is 300 miles away. Seems the turbo I require is the smallest they make. Price is yet to enter the discussion. Will update as I get abused. I am asked continually for Make, Model, Vin Number, year of manufacturer! All I want is a turbo! Thanks to all, Neil. From: Rotary motors in aircraft <flyrotary@lancaironline.net>
Sent: Friday, May 8, 2020 11:17 PM
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Subject: [FlyRotary] Re: Turbos Hi Neil, It all depends on how you size and operate your turbo. In general, the pressure relief, or pop-off valve is not needed in aircraft. Those come more into play during the fast throttle closures that occur in highly boosted race cars during shifting. They spend almost all of their time closed. These valves are not intended to be the primary pressure regulation and would not function well in such a capacity. They only limit peak pressure but do not do so with a high level of accuracy or control ability. They would also be highly inefficient if used in this manner, as the turbo would be producing continuously higher back pressure than needed. The turbo would be short lived and your fuel consumption would suffer greatly. The wastegate issue is a much bigger question but the short answer is that yes, you probably want/need one. The only exception might be a large turbine turbo that is sized so big that the max boost was only achieved at WOT operating conditions. Even then, you would be limiting the usefulness of your turbo at altitude because if it were sized for WOT at sea level, it would not be very useful at altitude. If sized for WOT at altitude you could use throttle to control boost down low, but you always run the risk of overboost. Similarly, a fixed exhaust bypass would allow a smaller turbo to be used in the same manner but with less efficiency and shorter life. I have experimented with my turbo in this configuration. By removing the flapper valve from my wastegate and creating a fixed bypass I was able to run at WOT and have approximately the boost I wanted, but only at a very specific altitude. Any higher and boost drops off precepitously. Any lower and throttle is needed to control boost. There is not much of a sweet spot as the natural variations in conditions created a oscillating situation that is simply not tolerable. But for maximum benefit from your turbo, longest life and efficiency there is no substitute for a wastegate of some sort. Can anyone help me with the following? With a turbo, can I just use a pressure relief valve and negate the wastegate totally?? Looking for simplicity and weight saving. Neil.
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