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Thread: Race 92 update...The quest for 400 mph

  1. #1
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    Default Race 92 update...The quest for 400 mph

    Following the his 2016 Silver Unlimited win, Dusty was thinking there were two Sea Furies he might be able to beat with some further development of his Yak. Upon looking at one of my pics I shot from the hillside, it was very apparent that his exhaust system wasn't doing him any favors, noting the large heat plume being directed straight down from the plane. He started doing some research and found that the NACA did some testing and found there was power/speed to be found by getting rid of the collecter style exhaust in favor of individual stacks for each cylinder. Dusty is thinking the change will be good for 10-15+ mph.

    He's also looking to move the intake from the right wing and move it to the top of the cowling like Steadfast. This will eliminate two 90 degree turns and one 180 degree turn. He thinks this will be good for 3-4 inches of manifold pressure as well.





    Will

  2. #2
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    Default Re: Race 92 update...The quest for 400 mph

    It will be interesting to see what the new scoop position does. Rare Bear lost MP when they went to the over the top induction.

  3. #3
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    Default Re: Race 92 update...The quest for 400 mph

    Yeah it could be interesting. Steadfast moved it to the top, but Czech Mate appears to still use the intake in the wing root. I'm pretty sure Dusty knows about Rare Bears issues after moving it since he is friends with Stu Dawson.

    I saw the intake track on Full Noise, and it is indeed a bit of a flow constriction. The 90s are pretty tight, and the 180 is crazy. I'm no fluid dynamics expert, but its pretty easy to see how there could be gains to be made. That said, apparently Full Noise will pull the same MP as one with the ugly little scoop on the top of the cowling, so who knows.

    Will

  4. #4

    Default Re: Race 92 update...The quest for 400 mph

    Quote Originally Posted by Race5 View Post
    It will be interesting to see what the new scoop position does. Rare Bear lost MP when they went to the over the top induction.
    The wing root intakes on the Bearcat were a bit problematic but offered some advantages. The flexible ducts between the carb and wing acted as a "fuse", in case of a nasty backfire the "snooters" would fail first reducing any further damage. They also provided an ideal place to introduce liquid nitrous oxide cooling the intake charge and helping combustion, win-win. Not to mention the airplane looks way better without a snout. And whoever built the aluminum intake duct that used to sit on top of the carb might have had some questionable political opinions but he was a very talented fabricator, I wonder where that piece is now? Also the old exhaust system had a lot of thought put into its design, it actually provided a small amount of thrust due to pairing cylinders based on firing order to maximize scavenging. It was a nightmare to remove and install and it needed to be replaced because it was just flat worn out, but it should have been copied not reengineered.
    Last edited by knot4u; 12-25-2018 at 05:39 PM.

  5. #5
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    Default Re: Race 92 update...The quest for 400 mph

    Quote Originally Posted by knot4u View Post
    The wing root intakes on the Bearcat were a bit problematic but offered some advantages. The flexible ducts between the carb and wing acted as a "fuse", in case of a nasty backfire the "snooters" would fail first reducing any further damage. They also provided an ideal place to introduce liquid nitrous oxide cooling the intake charge and helping combustion, win-win. Not to mention the airplane looks way better without a snout. And whoever built the aluminum intake duct that used to sit on top of the carb might have had some questionable political opinions but he was a very talented fabricator, I wonder where that piece is now? Also the old exhaust system had a lot of thought put into its design, it actually provided a small amount of thrust due to pairing cylinders based on firing order to maximize scavenging. It was a nightmare to remove and install and it needed to be replaced because it was just flat worn out, but it should have been copied not reengineered.
    I'm not sure but I think Nelson and company trashed the old "made no sense" exhaust system... I've made the joke... the answer to the question "where did the Bear's speed go?" is... it's lying in the scrap pile at Ezell Aviation...
    Wayne Sagar
    "Pusher of Electrons"

  6. #6
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    Default Re: Race 92 update...The quest for 400 mph

    Here is the shot that has led to the new exhaust setup. You can sort of see how well defined the heat plume is in the head on pic.

    I was wondering if something like RBs old exhaust might have been a better way to go or not. Exhaust scavenging is great on cars, so I'd have to guess it would also be useful on a radial. The NACA info Dusty found was specific to the R1830, and was done as part of the testing for the Seversky XP-41. I don't know if they did a scavenging type exhaust on it, or just straight stacks out of each cylinder.

    If I'm not mistaken, this new exhaust system is much like the one on September Fury that sounds awesome (Yes is nearly twice the size of the R1830, but still.) I can't wait to hear what this one sounds like.

    Will
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  7. #7
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    Default Re: Race 92 update...The quest for 400 mph

    The start of the Friday Silver race 2016.

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    Will

  8. #8

    Default Re: Race 92 update...The quest for 400 mph

    The A6m5 changed from a collector exhaust to individual stacks and got some more speed. So there might be some data out there. And they did work on individual stacks for Conquest 1, though that did make the cockpit really hot.

    On Race #30 we added the exhaust augmenters so the flow would be parallel to the fuselage without burning the belly. Not sure if you can say we are getting "thrust" or drag reduction, but either way you are getting faster speeds.
    Last edited by CubersWrist; 12-26-2018 at 07:29 AM.
    "young" Thomas

  9. #9

    Default Re: Race 92 update...The quest for 400 mph

    Quote Originally Posted by CubersWrist View Post
    The A6m5 changed from a collector exhaust to individual stacks and got some more speed. So there might be some data out there. And they did work on individual stacks for Conquest 1, though that did make the cockpit really hot.

    On Race #30 we added the exhaust augmenters so the flow would be parallel to the fuselage without burning the belly. Not sure if you can say we are getting "thrust" or drag reduction, but either way you are getting faster speeds.
    Your post reminded me of another thing the old bearcat exhaust, and probably the new exhaust system, do to reduce drag. The airplane has a pressure cowl, with such a small gap between the cowl and spinner it will only allow a certain amount of air into the cowl. With the exhaust augmenting the exit air from the cowl like a venturi it would help move air out. The problem became controlling that air so that it would pass through the areas on the cylinders that need it most rather than just leaking past the baffles and blowing out the exhaust exit. Just like the exhaust system the baffles that directed that air had to be paid special attention to ensure proper cooling and it was an enormous pain in the ass, but just about everything about working on that airplane is difficult if you want to go real fast. When we had our mystery horsepower loss we actually went faster due to drag reduction, 491mph if I remember correctly. I'd love to know how fast it would've gone if we had a healthy engine.
    Last edited by knot4u; 12-26-2018 at 08:25 PM.

  10. #10

    Default Re: Race 92 update...The quest for 400 mph

    Are there any good pictures of the old Rare Bear exhaust system?
    I've heard about it, but haven't seen an explanation of why it was supposed to be better?

    Baffling is annoying. I wish the cowling/plenum could be clear so we could blow smoke through it and get some flow visualization. Especially when it comes to spray bars. Or I wish that CFD was easier to use and more reliable...

    Not to get too off topic, but reminds me of a story. A couple of years ago we had some cooling issues with the plenum (I think it was cylinder 3) and the new intake tube layout. We figured we could troubleshoot and fix the airflow inside the plenum or add another spray bar nozzle above that cylinder. We decided we would be lazy and add another nozzle. Next test flight we found the messed up airflow caused our new nozzle to cool cylinder 1 instead! So we had to fix the plenum....
    "young" Thomas

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