Race 92 update...The quest for 400 mph

[RAD2LTR]

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

[Race5]

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.

[RAD2LTR]

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

[knot4u]

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.

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.

[AAFO_WSagar]

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

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...

[RAD2LTR]

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

[RAD2LTR]

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

The start of the Friday Silver race 2016.



Will

[CubersWrist]

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.

[knot4u]

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.

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.

[CubersWrist]

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....

[Desertdawg]

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....

Heres one from 2012

[knot4u]

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

Heres one from 2012

[ATTACH=CONFIG]24066[/ATTACH]

Oof, that's even uglier than I remember. Trying to get all of those tubes to align, and not be pretensioned, after who knows how many heat cycles could be an exercise in frustration. In the picture you can see where it's off a little bit on the lower exit pipe, it shouldn't be pointed at that fairing, but I bet whoever installed it spent many hours trying to get it perfect and finally had to be satisfied with what was possible.

[knot4u]

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....

Baffling stinks, and Greg Shaw was adamant that we'd get it completely sealed. It was either the first or second Phoenix race and we were still working on the baffles in the pits. I was up on a ladder with a caulking gun full of sealant filling the gaps, one of my best friends to this day was working below me on the lower cylinders. I came across a gap I could not fill regardless of the amount of silicone I pumped into it, then I looked down and saw a saucer sized pool of goop on top of my friends head. He was not pleased, but we managed to endeavor to persevere. Years later he had lost a lot of his hair and suggested to me it might be my fault, I once again profusely apologized. But then I reminded him that every time he would come to the house and sit on the couch my Jack Russel would jump onto the back of the couch and lick the top of his head so it might have been her fault. I have tact, I'm tactful.

[RAD2LTR]

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

With everything sealed up, and with so little space around the cylinders, how did the air get out of the cowling area? Both Rare Bear and 232 have some of the tightest fitting cowlings out there, but I don't see an obvious way for the hot air to escape aside from the exhaust stack exits. I'd imagine that even with a cylinder spraybar setup, Id guess you are still going to run into stagnant non moving air which neither assists cooling, or drag. I know Pete Law has looked at both 77 and 232 and offered ideas to make them both cool better.

Will

[knot4u]

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

With everything sealed up, and with so little space around the cylinders, how did the air get out of the cowling area? Both Rare Bear and 232 have some of the tightest fitting cowlings out there, but I don't see an obvious way for the hot air to escape aside from the exhaust stack exits. I'd imagine that even with a cylinder spraybar setup, Id guess you are still going to run into stagnant non moving air which neither assists cooling, or drag. I know Pete Law has looked at both 77 and 232 and offered ideas to make them both cool better.

Will

It did exit through the same opening as the exhaust, that's why the fact that it acted as an augmenter for the pressure cowl was so important. The small gap between the cowl and spinner would only allow a certain amount of air in, everything else just blew away (tee hee). That's what made the baffles so important, the air that was sucked out needed to be used properly to keep CHTs in a reasonable range. The cowl came off of a DC-7, as did the majority of the baffling, but no airline ever tried to push their 3350s as hard as the bearcat did, and it required special attention. I'm still pretty sure it has the capacity to be the fastest piston powered contraption that's been conceived yet, but it's going to take a lot of work to simply climb back up to the lofty heights it used to frequent.