Riff Raff carb induction changes?

[cragdweller]

I was watching an interview with Hoot Gibson and at around the 30 minute mark he begins discussing the racing development of Riff Raff. The first image shown of the airplane shows a carb air inlet on top of the fuselage behind the cowl. Subsequent images do not have this inlet and I assume they were in the stock location at the wing roots. I've never seen pictures of the airplane with the dorsal scoop. Does anyone know the development of this and why changes were made?

Investigating Accidents | Hoot Gibson Episode 12 | P-51 Mustang Galloping Ghost And Space Shuttle (youtube.com)

[wingman]

This is Reno 1999 , with the Skyraider style induction. September Fury tried a similar setup some years later. IIRC there were issues maintaining boost at racing angles of attack. Both were removed pretty quickly.

[wingman]

Reno 2000

[RAD2LTR]

Neither setup is ideal. The wing root setup requires the air to make several 90 degree or 180 degree bends. Neither of those are conducive to good fluid dynamics. The Skyraider setup sits too far back to make good boost as its now dealing with very dirty air coming over the cowling. This is why we see the scoop moved to the front of the cowling on both Sept Fury and Rare Bear. This however causes other issues in that you can't see over it, and it causes the top cylinders to get too hot. (Note which cylinders always grenaded on 232). It does give a boost in manifold pressure however.

Perhaps John Slack will chime in here, but I'd bet this is why Lyle never moved the intake to the top of the cowling on RB. The wing root induction wasn't the best, but it was better than cooked upper cylinders. If you look at Sawbones reliability over the years and then look at 232s, you will find that yes, 232 was faster, until it melted down. Yep they ran vastly different power settings as well, but you can't place if you don't finish.

If I'm wrong, please correct me. I'm going off a conversation I remember from several years ago.

Will

[RiffRaffRay]

This was an early attempt to gain speed with drag reduction. The idea was to use a stock sky raider inlet to eliminate all the twists and turns the air made and close up the huge holes in wing inlet. Quite the learning experience on that one. Hoot flew the plane from Kankakee, Il. to Reno and loved the performance he got cross country. When qualifying started we lost speed but thought it was because of air leaking out from where the scoop went into the panel. We had left 1.5 inches open to compensate for engine torque. We then attached rubber to the under side of the panel to keep it from leaking out. First race we ran we were still slow and found the rubber had squeezed through the gap. Here's where the thought process went wrong. We doubled the rubber and figured that would fix the problem. Next race Hoot was 3 laps in and the engine sneezed. We had our first and only mayday. The rubber had sealed that gap but also prevented the scoop from rolling with the engine torque. The stock sky raider scoop had bird shavers just inside and when the engine torqued over the inlet got squeezed in an oval and 4 the shavers went down the scoop. The engine never quit but it was toast
Riffraffray

.

[Big_Jim]

This was an early attempt to gain speed with drag reduction. The idea was to use a stock sky raider inlet to eliminate all the twists and turns the air made and close up the huge holes in wing inlet. Quite the learning experience on that one. Hoot flew the plane from Kankakee, Il. to Reno and loved the performance he got cross country. When qualifying started we lost speed but thought it was because of air leaking out from where the scoop went into the panel. We had left 1.5 inches open to compensate for engine torque. We then attached rubber to the under side of the panel to keep it from leaking out. First race we ran we were still slow and found the rubber had squeezed through the gap. Here's where the thought process went wrong. We doubled the rubber and figured that would fix the problem. Next race Hoot was 3 laps in and the engine sneezed. We had our first and only mayday. The rubber had sealed that gap but also prevented the scoop from rolling with the engine torque. The stock sky raider scoop had bird shavers just inside and when the engine torqued over the inlet got squeezed in an oval and 4 the shavers went down the scoop. The engine never quit but it was toast
Riffraffray

.

I remember talking to Mike K at ICAS 1999 (about the time he was putting the F-86 out on the circuit) and asked him about the rumor I'd heard about putting the inlet on. "Well...works great on the Skyraider", he said with a smile.

Not being critical, but in hindsight, racing a Sea Fury at big boost isn't like cruising a SPAD on a COIN mission.

Looked cool, though.

[wingman]

For some reason I kind of overlooked Riff Raff during much of her career. I didn't know these guys much at all, and I didn't much like Mike's choice of paint schemes. But as Hoot points out in the video they went from a 385 airplane to a 437 mph airplane over the years. And with only one mayday?

[wingman]

And Hoot spent time in proximity to Stew Dawson, with his fancy hood scoop.

[wingman]

They were racers.

[RAD2LTR]

Riff Raff worked, and worked well. I was sad when it left the country. I think many of the go fast parts went to Sawbones, and Sawbones went pretty well in their own right.

Perhaps Stu's blown engine can be tallied to the cowling scoop. It would be interesting to look at all the Sea Furies that have raced, and compare how many had Cowling scoops, and how many didn't, then look at the records for finishing the week.

Will

[cragdweller]

Wow, great information, thanks all! And great photos Wingman! And fascinating stuff RiffRaffRay with the attempt to seal the Skyraider style inlet.

RAD2LTR, with the long dorsal inlet (as seen on 232 during it's fastest runs) did the tops cylinders run hotter simply because cooling air wasn't making its way out of the top of the cowling as efficiently?

Anyone have pics of the ducting setup (with cowlings off) with the dorsal inlet?

Really hitting me this time of year that I'm not preparing to head to Reno. Major bummer...

[RAD2LTR]

Wow, great information, thanks all! And great photos Wingman! And fascinating stuff RiffRaffRay with the attempt to seal the Skyraider style inlet.

RAD2LTR, with the long dorsal inlet (as seen on 232 during it's fastest runs) did the tops cylinders run hotter simply because cooling air wasn't making its way out of the top of the cowling as efficiently?

Anyone have pics of the ducting setup (with cowlings off) with the dorsal inlet?

Really hitting me this time of year that I'm not preparing to head to Reno. Major bummer...

That is my understanding, but as I said, I might be wrong. I think we will find a correlation with grenaded 3350s and cowling scoops vs those aircraft that didn't run them. Yes, super modified Sea Furies like 232 and Blind Mans Bluff/Critical Mass were running far higher power settings than say, Sawbones or Riff Raff, but ones like Stu's bird vs RR or Sawbones might be a better comparison. I think we will find that those with the cowling scoops had a higher likelihood of engine failure than the ones running the wing root intakes. I can extend this to include Rare Bear (no, not a Sea Fury, but running a 3350, and did get a cowling induction when they went to the full boil off system. That said, I don't think RB ran with an equivalent hot 3350 with the cowling induction as it had when Lyle raced it still running the wing root intakes. I have to guess the RB guys would have done it years ago if they thought the change would yield more power with reliability (You can't win, if you don't finish.) I have to guess someone in their braintrust knew the potential issues with such a setup so they never went there.

More ram air effect in the manifold pressure with the cowl induction, but higher cylinder temps on the top of the engine, and likely, higher induction temps from those hot cylinders as well, vs lower manifold pressure, but a cooler running engine. Pick your poison. Hopefully someone with more inside info on this will chime in.

Will

[wingman]

I'd certainly like to hear more on this also. I've never heard of the top cylinders running hotter with the hood scoop, and it's hard to see why they would. It's interesting that some of this stuff is only emerging into public knowledge now (another example being the use of magnesium in the Stiletto build). There were also huge differences between the Dawson/Ezell version versus the Sanders ideas used on 232 and Dreadnought.

Both of these airplanes were built up by Nelson Ezell in Breckenridge, Texas....

[RAD2LTR]

I have to say, the Sanders cowl induction is more elegant than the Dawson/Ezell setup. The D/E variation reminds me of the early F2G setups from the Cleveland era. They might be functional, but not a clean setup. (Harold G Martin photo.)


Hmmm, that might be an interesting topic, how the cowl induction scoop has evolved over the years. As we have seen, there have been some pretty ugly ideas, and some that are elegant and work really well.

Will

[wingman]

Well here is the second Sanders scoop -- more elegant is a good description. I'm not sure any more how they dealt with cowling movement. Unlike the Dawson type this one apparently did involve considerable violation of the Sea Fury cowling -- made up of unobtainium these days. There were threads on this many years back in the aafo archives.