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What's the theory on F1 Rocket Air Inlet Shape and Placement

Sure....ride along for an NTPS triangle in the early AM.

We talked about this before. No VNE plus in midday rough air for me.....sorta like "Never fly through a thunderstorm in peacetime".

I certainly respect that choice Dan...though I might go over or around a thunderstorm, even in combat (or make the bad guy fly through it! ;))

FWIW, most of the SARL races are in the morning glass, or at least attempt to be. WOT and VNE+ not required...good nav and turn technique exercise as well, followed by a good BBQ, etc. Just wanted to present the other face of SARL...not a bunch of VNE+ cowboys. And all respect that choice, for sure!

Maybe a $100 burger somewhere, sometime, eh! :)

OK, back to the inlet shape and placement topic...;)

For those that know, or have used one or both types of inlets: Do you see any reason the same airbox and connection to the throttle body could not be used for my experiment of swapping out round and smily inlets?

My concept it to have the hole in the cowl with a flange on its perimeter with nutplates. Shape each inlet to drop into place on the flange, and screw into place. I figure the airbox would be connected to the back of each inlet, and the assembly gets slid into the flanged opening, with the fiberglass tube from the back of the airbox being pressed to fit into the silicone hose or sceet tube that is mounted to the throttle body. From discussions with Mark, the picture in my mind is that the silicone or sceet tube is held in place on the throttle body with a hose clamp, but the airbox side is an interference or press fit. Now the Q's:

1. Is that an airtight enough fit (the side that is the press to fit)?
2. Would that press to fit on one side concept work with the silicone hose?
3. Any issues with the same airbox being interchangeable with two inlets?

An alternative would be to have a second access panel that could be off for installation, so the front connection of the silicone or sceet tube could also be clamped (like Lee has with his fixed inlet, though this would be added to each removable inlet, or right behind the forward hole in the cowl). Not sure, but seems like a lot of nutplates and panels...still trying to get a good conceptual picture of this. Getting arts in hand and a little sitting on the ground below the cowl cyphering away will help, I'm sure! :rolleyes:

Thoughts?

Cheers,
Bob
 
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WOT and VNE+ not required...

Ahhh, good buddy, I think your pants just caught fire ;)

OK, back to the inlet shape and placement topic..

Maybe there is no need to modify a cowl just to determine which inlet system yields best total pressure. Kick this idea around.

Attach both of them to a crossbar high above a pickup truck, or out front on a brush guard, or whatever gets them into clean air. Mount entire inlet and airbox assemblies, then add an outlet tube about 6" long (scat, silicone, cardboard, whatever). Tape an identical orifice to the end of each outlet tube (an aluminum disk with a hole in it). Poke a hole in the side of each tube at the 3" point for a pressure tap. Now connect the pressure taps to the opposing legs of a water manometer (vinyl tube and a yardstick).

Find a safe place to go fast (hmmm...14/32?). The best inlet will be the one with the lowest water level. You can run a few different orifice sizes if you want a plot for variable CFM, or calculate the orifice size which results in CFM (or lbs per hour) correct for your 540 at 2700.
 
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WOT and VNE+ not required...

Ahhh, good buddy, I think your pants just caught fire ;)

Well now, I didn't say it wasn't required for me! ;) Then again, if was really bumpy, I wouldn't be pushin' it that hard either. I've been there (fast and bumpy), didn't like it, and backed off. This is for fun, and it does not pay enough to press it that hard (not sure there is such thing as enough $$).


Maybe there is no need to modify a cowl just to determine which inlet system yields best total pressure. Kick this idea around.

Attach both of them to a crossbar high above a pickup truck, or out front on a brush guard, or whatever gets them into clean air. Mount entire inlet and airbox assemblies, then add an outlet tube about 6" long (scat, silicone, cardboard, whatever). Tape an identical orifice to the end of each outlet tube (an aluminum disk with a hole in it). Poke a hole in the side of each tube at the 3" point for a pressure tap. Now connect the pressure taps to the opposing legs of a water manometer (vinyl tube and a yardstick).

Find a safe place to go fast (hmmm...14/32?). The best inlet will be the one with the lowest water level. You can run a few different orifice sizes if you want a plot for variable CFM, or calculate the orifice size which results in CFM (or lbs per hour) correct for your 540 at 2700.

My first thought upon reading this was "I need a 250 mph pickup!" :D Then I saw your last sentence and am wondering if you can elaborate on that aspect (correcting for the 540 at 2700).

If the advantage of one over the other is apparent at one (truck) speed, and the delta between the two increases with speed, then you might extrapolate that it would continue that way to full (Rocket) speed (or could you? :rolleyes:). If the delta was decreasing however, you might expect an equalizing of recovery, or even a crossover, at some point (or would you? :rolleyes:) I also wonder if the shape of each inlet and the actual curve shape at the inlet lip would show large variations of recovery impact at various speeds (one might work well at low speed, yet at high speed, not so well)...just thinkin' (always dangerous!)

The other side of that is the systemic approach. A truck-borne test might not take into consideration the effect of the propeller, spinner and the remainder of the cowl structure.

Purposefully overthinking it for fun, as I think its a neat idea. At the very least, it'd make a great You-tube video. :p Access to a wind tunnel would be kinda cool too!

Cheers,
Bob
 
rvmills;584481 Access to a wind tunnel would be kinda cool too! Cheers said:
Do you have a leaf blower???

Many of them make over a hundred MPH wind.

As Hackett says, "obtainium";)
 
I've seen a pair of gas powered leaf blowers used as a makeshift twin turbo for a big block car engine. Not practical at all, but it actually did "work" and the engine made more HP. Not exactly a clean "wind tunnel" air stream though. I think the truck idea would yield more realistic results. But, I am not an aeronautical engineer.

On second thought, wouldn't you need to add a prop to the equation?

I like the look of the smiley air inlet and am curious of the results here.
 
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Do you have a leaf blower???

Many of them make over a hundred MPH wind.

As Hackett says, "obtainium";)

And now I'm seeing a cool episode of Mythbusters shaping up! :D

Jamie and Adam, saying, "don't try this at home, we're what you call...professionals!"

"Smily Inlet test in 3...2...1..."

Now if I can talk Mark outuva couple of spare Rockets cowls...:p

Joking aside, there's some great ideas here. Mike, will you come up and hold the leaf blowers...or drive the pickup? :)

Cheers,
Bob
 
Just my thinkin'

Dan's test method is interesting but I like your proposed direct application experimental testing approach best. If you could develop a friendship across the hills to the west at Moffett Field, I'll bet there are some Ames employees that are RV builders that could tell you if a personal wind tunnel is a possibility. That would allow you to run multiple tests with small refinements to get the best induction intake. Here's another thought, the properties of air flow in confined systems are no doubt well known. If you could identify the variables and constraints you could possibly create a simulation of the system on an analog computer and work with the infinite variables to find the best combination or you could look for digital application software or write your own code that would allow you to make small incremental changes and check the results. Anyway you look at it the surest and simplest way to get the information you want is to do what you planned to do. I would only vary the intakes for the initial testing and not change the airbox. Use the interface that will allow you to run the comparison test and refine it when and if a better way becomes apparent. Once you select the forward intake configuration you could work back into the system to evolve the best overall intake system experimentally.

I must admit that I think the payoff for all the work on the intake system is not worth the trouble for me yet but since I saw your last race speed of 254+ mph you may be there (I still don't like flat wing tips though). I will keep my eyes on your progress while I work on drag reduction of the wing and the wheel fairings.

Bob Axsom
 
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If the advantage of one over the other is apparent at one (truck) speed, and the delta between the two increases with speed, then you might extrapolate that it would continue that way to full (Rocket) speed..

Correct. Better at 50 will be more better at 100 or 200. At low speeds the resolution of a manometer may be small. However, simply lay the manometer over at an angle to increase resolution.

A truck-borne test might not take into consideration the effect of the propeller, spinner and the remainder of the cowl structure.

Yes, but you don't care. It only matters if you expect to locate the different inlets in different locations on the airframe.

Purposefully overthinking it for fun, as I think its a neat idea.

It was good enough for Rutan. Still is actually:

http://www.scaled.com/images/uploads/gallery/spaceshipone/ground_general/wind_tunnel_800.jpg
 
If we're talking about the shape of the inlet, I think we only have to look at what has gone before. If we can get the inlet out of the boundary layer and in front of any bow wake into clean air, then I'd think round is the way to go. After all, pod mounted jet engines are done this way. On the other hand, the "smiley" is much like a fuselage mounted jet intake which often has to deal with lots of interference from the parts of the airplane out front of the inlet. The common half round inlet has many challenges hiding in those sharp corners, often overcome by vortex generators and other tricks to make the air behave.

I think it comes down to aesthetics... A smiley looks better in profile than a typical low hanging Formula One style scoop, but I bet a well designed bell curve divergent duct is hard to beat for ease of construction and pressure recovery. I'm about ready to start building the plug for my duct, so we'll see.
 
I also continue to

look at what the F1 guys do. They are in wind tunnels spending big bucks to go fast (at speeds similar to us). They seem to like big square inlets (yea I know, their available space tends to be rectangular) with generous radii from the openings. From data in references posted in previous threads, this general configuration is very spill tolerant, and looks a lot like a Van's stock inlet.

I suspect that if one particular shape had significant advantage, these F1 guys would be all over it.

Slightly different application (no prop effects) but pretty close.

I suspect that if you have a good pressure recovery design with good sealing and well directed airflow, that we are splitting hairs here with the rest.

Fun to work with though.
 
Did some pairing of posts to add to the dicussion:

Yes, but you don't care. It only matters if you expect to locate the different inlets in different locations on the airframe.

Perhaps, but I'm not fully sure of that. My thoughts were that the different shapes may interact with the same external influences (structure and flow) differently. Michael touches on it below.

If we're talking about the shape of the inlet, I think we only have to look at what has gone before. If we can get the inlet out of the boundary layer and in front of any bow wake into clean air, then I'd think round is the way to go. After all, pod mounted jet engines are done this way. On the other hand, the "smiley" is much like a fuselage mounted jet intake which often has to deal with lots of interference from the parts of the airplane out front of the inlet. The common half round inlet has many challenges hiding in those sharp corners, often overcome by vortex generators and other tricks to make the air behave.

I think it comes down to aesthetics... A smiley looks better in profile than a typical low hanging Formula One style scoop, but I bet a well designed bell curve divergent duct is hard to beat for ease of construction and pressure recovery. I'm about ready to start building the plug for my duct, so we'll see.

I'd like to see what you come up with Michael!

There is certainly benefit to both testing methodologies (and loved the Rutan photo!). I'll need to see if time available meets time required for ground and flight tests. I'm cuttin' a hole in the cowl anyway, so if I can make them both fit one hole, I'd lean towards what Bob said about on-aircraft tests as the final arbiter. And who knows, perhaps I can finagle some sort of artificial wind testing set up.

Cheers,
Bob
 
Split it

Bob
Mark's idea of making the inlet removable is a great idea but it comes with it's own weaknesses. The first being the need to use scat or sceet for the connection with the filterbox. When the unit is installed there is no way to confirm that the sceet/scat is seated properly. I hate hoping that I got it on right. This is very simply taken care of by slitting the assembly just aft of the filter box, creating a flange and installin 2 nutplates. Now you can confirm the sceet/scat is installed correctly or even better use a smooth walled medium for the connection.
If you are constructing two different systems then why not test them at 250 mph on the flying Rocket test bed/wind tunnel thingy.
This winter I will also be building a new inlet to test but I am taking a different route than you. I am sure at best we are talking nano knots but then I have to be able to keep up to you.
I am looking forward to seeing you in Taylor.
Smoke on!
 
Wayne,

Trying to visualize the split-with-two-nutplate access method. Are you talking about two hinged doors on the lower cowl behind the filter box? I was thinking about an access panel somewhat like Lee's picture, but on the removable section of the inlet. Not sure there is enough real-estate to do that. However, on the part that Tom is sending me, I think it has just such an access panel. Would be interested in seeing what you are describing. Any pics or drawings? (I'm a picture-book kinda guy, but I do well with stick figures too! :rolleyes:)

I need to crawl around the Rockets in Taylor next month and get eyeballs on this stuff!

So what type of inlet are you experimenting with...should we join forces across the border to test all of them, or is is a secret Kitchener Skunkworks project!? ;)

Oh, and who is trying to catch who, my friend? Last I saw you were still out in front (dagnabit!)

"Flying Rocket test bed/wind tunnel thingy"...now that's funny! :D

See ya in Taylor!

Cheers,
Bob
 
Split it

Bob
I think mine is done the same as the one you will be getting from Tom. I will send pics this week of my instalation and the mods that I have done to the filter box. Are you running Bredix/Prescision or Airflow Performance? I will have to email as I have not solved how to post pics here.
Bob J is sending me his unused Mk1 and I want to modify it to move the smile up against the spinner. I think I will come forward as far as possible but we will see once I get eyeballing it. Visualise the P51 or Harmon Rocket or the top inlet of Mark's EVO. I am not after increased MP but frontal area reduction. I do not care for the round hole look and I want to keep the more traditional F1 look. I think if I can get rid of the frontal area above the smile that I will pulverize less bugs. I will be able to swap out each system for test comparisions. I have some concerns that I will end up with an unsightly bump in the lower cowl. It should be a fun project.
Wayne
 
Wayne,

I have a Bendix, and your test sounds like a good one. From earlier discussions and posts, I wonder if you are right under the spinner, if it would be better to come forward with the scoop, or actually imbed it in the cowl and make it flush. I think one of the posts discussed this, saying flush might get accelerated air off the spinner, but I'm not sure if I interpreted that correctly.

Will look for those pics, and I can post them here if you'd like me to.

Good stuff...fun discussion!

Cheers,
Bob
 
I think I have a pretty good method of keeping the airbox sealed and flexible, but it is limited in its ability to handle extreme fore/aft movement. If anyone could characterize this movement with an actual dimension that would be a great help.

With the dynafocal engine mounts, the engine will wobble about its geometric center (and CG) as defined by the dynafocal angle. This will cause components furthest from the geometric center to displace the most distance from the at rest position. The propeller flange, for example will walk around in the cowl opening quite a bit. That said, does anyone know how much the front mounted servo will move in the fore and aft plane (due to engine rotation in pitch)? I?m not worried about side to side and up/down of the front face of the servo ? just the fore/aft translation.
 
Engine movement

Michael
When I was doing experiments to create a prop seal I was not able to get movement of more the 1/4 inch in any direction at the prop hub. It was less than I was expecting. There are not extreme movements for and aft. On my RV10 I have less than 1/8 inch between spinner hub and cowl and no touching has occurred. The F1 and RV 10 uses IO 540s I do not know if the same is true for other engines.
Wayne
 
Thanks for that info Wayne. With some of the close fitting cowls I have seen, that certainly seems reasonable. However, the fore/aft movement in plane with the crankshaft is but one variable. If the engine itself changes pitch in relation to the aircraft (seen as a wobble at the spinner), then the accessories hanging some distance from the "center of wobble" will have a primarily fore and aft component of movement. The further from the center, the more dramatic the movement.

As I'm typing this, I think I just figured it out. If the engine is allowed to shake about it's center of gravity, then one simply has to decide how out of plane the spinner backplate gets in the worst case of the wobbles (the spinner backplate being an easy to measure datum). then it is simply a mathematical ratio to decide how much fore/aft movement an oil pan mounted accessory will see. For example, if the backplate is 12 inches in front of the engine CG and it moves up and down 1/2 inch, then a component hanging 12 inches below the CG (like a servo) will move fore/aft 1/2 inch.
 
There's very little shake along the crankshaft axis...if there was any sort of shake there you would be calling your prop balancer guy. If you watch a Lycoming shake it only shakes on startup and shutdown. The cylinders move up and down +-3/4" if you could measure it at the valve covers.
 
Depends on the airplane... The B1E in my airplane has a distinct and very noticable wobble at certain taxi speeds and RPM. I suspect a resonance between engine, prop and landing gear legs. Also, during hard acro, the spinner backplate moves enough to dig into the cowl a little.

I might be able to use some rubstrips of clay or foam on the -8 to see how much the spinner moves in relation to the cowl in flight.
 
I might be able to use some rubstrips of clay or foam on the -8 to see how much the spinner moves in relation to the cowl in flight.

In the machine building industry we would clamp a pencil or marker to the moving member so it would record the full range of movement on the stationary member. Over the years we spent a lot of money on test equipment that basically provided the same information as the low cost pencil method.:confused:
 
That's a great idea... I might be able to rig up a marking device to record how much the front face of the servo moves in a flight.
 
I just received the RC-9640 filter and yesterday evening was comparing it to the RU-5111 filter. It appears that the oil requirements are a good indicator of pleated filter area. The depth of the pleats on the 5111 are 5/16" and on the 9640 are 1/2", and the base diameter is also 1/2" larger. So going from 0.6oz of oil to 0.9oz correllates to the increase in filter area. Jim will be doing some testing soon to see if there's a difference in MP between the two.
 
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I just received the RC-9640 filter and yesterday evening was comparing it to the RU-5111 filter. It appears that the oil requirements are a good indicator of pleated filter area.

Let's look at the actual media area of the 9640. Could you please supply the missing dimensions (media without rubber):

i76iza.jpg
 
Length measurements were made on the centerline of the pleats with a dial caliper.

RC-9640: 5.260"x0.5"x43 pleats x 2 flats per pleat= 226.18 sq. in.
RC-5111: 5.020"x0.3125"x44 pleats x 2 flats per pleat = 138.05 sq.in.

63.8% more filter area, and fits in our air box perfectly.

I measured the 33-2104 flat filter that is the stock F1 smiley filter:
5.990" width x .71875 depth (23/32, no I'm not measuring to hundred thousandths) x 26.5 pleats x 2 flats per pleat = 228.18 sq in.
 
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They're cone filters. The pleats are of constant depth along their length.

The interesting thing to note now is that the RU-5111 filter Jim is using did improve the pressure recovery even with a filter with far less area as it turns out. So it will be interesting to see what difference it makes to swap filters again. Actually he can test all three (flat stock smiley, and the two cones) pretty easily.
 
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well, maybe

Hey Dan:

I'll wager the filter media is a cylinder squashed into a cone...so the simpler equation will work.

Now I gotta go see if I can cram the larger one into my filter box...

Carry on!
Mark
 
No because each pleat is rectangular, and they're tighter at the narrow end than the bottom end.

Ahhhh, ok. Squeezing the pleats together makes a particular cylindrical filter compromise even worse, but hey, let the measurements being!

14v2ww5.jpg
 
I figured you figured that the way to figure the area of the filter was based on your autocad figure...go figure. So thats why I figured the area.
 
Meanwhile, back at the inlet...

I was pondering the F-1 inlet and it occurred to me that the arc of the smiley inlet might capture a longer duration of the prop pulse. That would be a good thing, yes? :) Perhaps Bob will prove this when he tests on his aircraft.
 
I resemble one of those

Mr. Cone, would that be a de-pleated cone, a re-pleated cone, of a com-pleted cone? :p

And now back to our regularly scheduled broadcast ;)...

With respect to filter media area, can the area be measured by sacrificing one of each, laying them out, and measuring LxW? I'll chip in for the sacraficial filters. Then we could test for comparative performance and see how it correlates.

Speaking of testing, have we discussed the metrics of performance?

My thought (based on discussions with gents much smarter'n'me) is to measure maximum MP at a specific set of conditions...say 6000' DA, WOT, 2600 RPM. Highest MP wins that round (correct?).

Then I'd like to measure the lossy-ness of the filter by reducing RPM to 2300 and see how much MP goes up. Smallest rise when reducing RPM indicates the least lossy filter, would you guys agree with that?

This assumes that only the filter is changed. If the airbox or ducting changes when swapping filters, then the entire systems are being compared.

One would think that the filter (or system) that wins the first test would also win the second test, but it will be interesting to see.

I'm interested in how others have or will test the recovery/performance of each system or filter.

I was pondering the F-1 inlet and it occurred to me that the arc of the smiley inlet might capture a longer duration of the prop pulse. That would be a good thing, yes? :) Perhaps Bob will prove this when he tests on his aircraft.

That is possibly a factor in the performance of the smiley. It may very well be more tolerant (than a round inlet) of the various angles imparted to the flow by the propeller without creating spillage drag (if it has a nice rounded lip). The duration factor is an interesting idea as well...the wider curved inlet perhaps providing a longer time exposed to the angular inflow from the prop. All theoretical, but I do remember "Boss" Mark saying they just seemed to hit on a good design with the smiley...and Greg Nelson's MP sure showed it at Reno with his MkI smiley.

Hopefully I can keep everything consistent between the two inlet/airbox systems, and only swap the filters...we'll see when I get the stuff and start getting dusty again (sand-fill, sand-fill :rolleyes:).

Will be very interested in your testing Bob J, to see how your various filter set-ups perform.

Cheers,
Bob
 
Do you guys know if there are any official Lycoming SCFM numbers for their engines? I know we can approximate with BSFC, but am curious if we can get a hold of these numbers.
 
Paul prototyped a fiberglass cuff to fit over the root of the prop blade to do what that flap does on the Lopresti prop. and then some. I've talked to him at length about this...man I miss that guy.
 
Well I have a MKII smiley inlet in hand, and one of Tom Martin's earlier round inlet experiments as well, and I've been sitting in the hangar the past couple days mulling over my options on an inlet experiment. The more I've looked, the more I've come to realize (frustratingly) that making an interchangeable inlet to test the relative MP recovery of the MKII smiley, the round inlet, and my current inlet is probably not do-able with my cowling.

I feel like I'm lettin' the boys down, but a few things lead to this decision:

First, at the Rocket 100, Tom, Mark, Wayne and I compared notes on MP during the race and we were all quite close...within a couple tenths. Now a couple tenths is not trivial in race circles (Mark and I discussed today that it appears each .25" is worth about a knot...unscientifically, but seems to be a trend we've seen). Now if I'm 10 knots slower than their EVO-winged beasts, would that add some ram to their MP, so my recovery is pretty close to theirs at equal speeds...dunno. But when Tom looked at me and asked if I wanted to tear into the cowl to get a tenth or two, it was cause for pause.

Still, I brung their inlets home and started matching them up to my cowl, and found that the geometry of each is quite different from my cowl, and from each other, so doing a single cutout that I could flange and nutplate, and swap inlets looks like a non-starter....bummer. I know you can do almost anything with glass, but it becomes a time/cost/benefit thing, even if the experimenter inside is willing!

Additionally, the adapter that I have to make my Bendix FI forward facing is at a different angle than what would be required to make the angle to the Rocket filter airbox work, and my cowl is wrapped fairly tight to that adapter. I looked at changing the adapter, but then the fuel line and control cables need to be replaced. Cost and complexity is rising!

The filter airbox for the Rocket-appropriate K&N won't fit between my current cowl and my starter and alternator, so it means adding surface area to the cowl by lowering it a bit. That is exacerbated by the width differential between my cowl center channel and those of the other two inlets, as shown in these pics:

Rocket Smiley II:
Smiley%252520Inlet%2525202sm.JPG


Tom's Round (the width differential is notable through the access opening):
Tom%252520Inlet%2525202%252520sm.JPG


Smiley nose on:
Smiley%252520Inlet%252520sm.JPG


Round nose on:
Tom%252520Inlet%252520sm.JPG


So for a potentially small gain in MP, I'm concerned that I'm adding too much area to the cowl exterior, and it'll be a zero sum game, or worse. Perhaps a chicken's perspective (buck, buck ;)), but I've been evaluating it before getting out the saws-all, and I keep coming back to the same decision.

If I stay with my lower cowl, I can work the radius of my inlet a bit, since it seems to converge a bit on the sides, and perhaps make it a bit more efficient. I also have to remake the tube to the servo, as the original started breaking during the Reno races, and has been working under a field repair status until this winter mod season, now upon us. Since I'm replacing my baffles and plenum (both showing age at 13 years and having just cracked 1000 hours), I figure a good look at improving how I get filtered induction air and ram air, while working my inlet's shape slightly and doing the baffles/plenum is a good dose of winter work.

Then I hit the exit, and Gary, thanks for the templates for your exit extensions...I've been looking at, playing with and mulling over them for a bit now too!

Hope this doesn't sound like all too much whinin' or excuses, and my apologies for not coming through on a modular, switchable inlet fellas. But I will let ya know how this mod work comes out (and I'm open to thoughts and ideas on the ram air inlet!), and it'll be interesting to compare MP with the boys when we meet up again in Taylor this spring!

Oh, one other cost factor for me is a pair of really bad prop dings apparently picked up on my last flight this year (found on post-flight). Wanna see something that'll make ya cry (well, if ya just bought a BA prop 3 months earlier it will):

prop%252520ding%2525201%252520sm.JPG


prop%252520ding%2525202%252520sm.JPG


Each about 1/16" or so deep, and in line chord-wise on the back face of the blade, about 13" out from the hub. Queries in to 4 prop shops and Hartzell as to the repairable or fatal (to the blade...it aint flyin') nature of the dings...worst I've ever seen, and no clue how it happened. Ouch! So some other stuff had to be scaled back due to this too. But stuff happens...pressin' on!

Cheers,
Bob
 
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Bob,

I have some comments about the pictures of your current inlet. However, in the interest of full disclosure you need to know two things: First, this is simply a TLAR assessment based on my own prejudices, research and experiment. Second, I'm friends with Coach... one of your competitors. :D Fortunately, what I'm going to suggest can be easily tested without a lot of work or modification to your current cowl.

OK, I see 4 discrepant areas in your current inlet.

1. The inlet lip radius appears to be so large that the duct itself is convergent for a few inches. The smallest area of the opening is several inches inside the lip, right? The problem with this is that you likely have a bunch of spillage out the mouth which is going to create airframe drag. You only want just enough air to feed the engine without any spillage.

2.. The inlet is opening is flush with the OML of the cowl, and is therefore ingesting some of the slow(er) moving boundary layer. You need a true pitot inlet that is operating in clean air - it should stand proud of the surface by at least the thickness of the boundary layer (which isn't real thick that far forward, but still...)

3. The inlet opening is too far back. I have done testing on this and the closer it is to the prop TE, the better.

4. The inlet opening is too big. For a high speed, efficient inlet, I don't think you have to go any bigger than the smallest choke point on the servo - so I'd pick the throttle butterfly as your target size.

OK, so to verify my assumptions, you simply have to fabricate an "inlet correction adapter" which indexes into your existing inlet. Fabricate it right, and you can plug this thing in, secure it with speed tape and go test. I'd say your first step is to fabricate an extension duct which interfaces exactly with the narrowest portion of your current inlet and places a round opening (matching the throttle blade size) as close to the prop TE as you dare. If the scale of the pictures is right, this duct will be slightly divergent as it moves aft, which is exactly what you are looking for. Once you have this slightly cone shaped extension sticking out of your inlet, I'd look to angle it perfectly with the direction of flight (figuring the ships AOA at race speed), and pour some of Dan's magic expanding foam around the cowl's existing "mouth" to lock it in place. You will want to wax your cowl so this thing will release cleanly. In this position, the new inlet opening should be well clear of the existing boundary layer and breathing unobstructed air. The next step is to simply fair in the OML of your new extension duct so it interfaces with the existing cowl. I would not go too large on the inlet lip radius however - I'd start with maybe an 1/8th inch to start... You can always build it up and test to find the optimum radius.

So when you're done with this mess, you glass it up and should be able to pop it on and off in a matter of seconds between flights. This will be about as close to real time testing as you can get.

Sorry about your prop, BTW... Ouch!
 
Bob,

Interesting data point from your discussion with Mark and Tom. I did these calculations last fall when this thread first appeared, but didn't bother posting them since for racing purposes, it's all about making a multiple sequence of small improvements that end up with your ship in the winner's circle.

You can get pretty close to the results you posted with a set of simple calculations.

First, take a look at the power charts for any of the 260HP Lyc. If you plot HP vs MP for a given RPM (say 2700) and altitude (say sea level), you will get a nice linear response. In this case, you will find that the slope is about 11.7 HP per inch MP. The slope will differ if you are running more HP, of course, and different RPM.

Second, calculate the HP ratio per inch of MP. In this case, you will get about
7% more HP per inch of MP (i.e., HP2/HP1=1.07 for each inch of MP).

Third, use the speed-HP relationship--(v2/v1)=(HP2/HP1)^(1/3). In this case,
V2/V1=1.07^(1/3)=1.023. If you are indicating 200 KIAS, and can get 1 more inch of MP, you will go 200*1.023=204.4 KIAS. In other words,
1 inch will yield 4.4 KIAS.

Or .25" will yield 4.4 KIAS/4 = 1 KIAS

Pretty close for a ball park calculation on where to spend your time and money.

Now, the next time you corner Tom and Mark, don't ask them what manifold pressure they are running. Ask them how much power they are running, and we can get some more interesting data on Cd!
 
Bob,

Interesting data point from your discussion with Mark and Tom. I did these calculations last fall when this thread first appeared, but didn't bother posting them since for racing purposes, it's all about making a multiple sequence of small improvements that end up with your ship in the winner's circle.

You can get pretty close to the results you posted with a set of simple calculations.

First, take a look at the power charts for any of the 260HP Lyc. If you plot HP vs MP for a given RPM (say 2700) and altitude (say sea level), you will get a nice linear response. In this case, you will find that the slope is about 11.7 HP per inch MP. The slope will differ if you are running more HP, of course, and different RPM.

Second, calculate the HP ratio per inch of MP. In this case, you will get about
7% more HP per inch of MP (i.e., HP2/HP1=1.07 for each inch of MP).

Third, use the speed-HP relationship--(v2/v1)=(HP2/HP1)^(1/3). In this case,
V2/V1=1.07^(1/3)=1.023. If you are indicating 200 KIAS, and can get 1 more inch of MP, you will go 200*1.023=204.4 KIAS. In other words,
1 inch will yield 4.4 KIAS.

Or .25" will yield 4.4 KIAS/4 = 1 KIAS

Pretty close for a ball park calculation on where to spend your time and money.

Now, the next time you corner Tom and Mark, don't ask them what manifold pressure they are running. Ask them how much power they are running, and we can get some more interesting data on Cd!
 
Michael,

Thanks for the reply...does Coach know you're giving up secrets? :p

You've hit on items I'm concerned with, and might have asked, had the previous post not already been longer than War and Peace :rolleyes::
-Boundary layer impact with a flush lip (how bad is it?)
-Inlet proximity to the prop (closer = better?)
-Inlet shape (round = really better?)
-Inlet size?

Your comments about size match my neighbor and mentor's. He pointed to many fast Lancair's at Reno that have very small induction inlets. Then again, we've seen Dan's work on larger inlets (I think his induction inlet is larger than stock, as are his cooling inlets), and Tom went from the gray inlet you see in the pics above to a Bower inlet, and picked up MP. So correct size still stymies me a bit. I was considering procuring a Bower butterfly valve to build my ram air duct around, but it is larger than my throttle body opening, as far as I can tell. I've heard that a little extra size can compensate for a little inefficiency in inlet lip radius...true story? So what do others say about right-sizing the induction inlet.

I like your ideas though Michael...I might even be able to start with the opening of Tom's gray outlet and build something around it as a test piece. Hmmmm....

Thanks!

Paul,

Interesting that our experience matches your calcs. As another data point, say a guy launches on a SARL race, and forgets to open his Ram Air door after takeoff (not that I know anyone that would ever do that! :eek:). When that guy had the "V-8 moment" and opened his Ram Air door, he saw a 0.7-0.8" increase at 212-215 knots, and then picked up 3 knots...each time it happened...ahem!. So your 4 knots per inch hits the mark we've seen.

To show you how non-trivial it is, at Reno, I was seeing 26.5" MP or so at speed. I believe Greg "Coach" Nelson was seeing 27.7". Greg (F1 Rocket), Rick (Glassair), and Jeff (Radial Rocket) ran 249, 248 and 247 respectively on Thursday. while I ran 244. 1" of MP would have put me in the fight, rather than watching it happen from 1/2 to 1 pylon back!

So it's truly a case of gimme an inch, I'll take a mile! I'm hunting!! :)

Cheers,
Bob
 
Someone please correct me if I am wrong, but the sharp inlet lip profile is not best in "real world use". From what I have read that would be best, only if you know the exact AOA of the oncoming air and the exact amount of mass flow the engine will be taking and calculate the opening area accordingly.

In any other case you will either have less air going in than you can convert and use or more air which will spill. If the lip shape is contoured correctly the spill will have little not effect on drag. The same theory and execution as the cooling inlets.
 
Bob, not a IO-540 or speeds you are seeing....but I'm running the Bower Ramair behind the James cowl with the round inlet on my 360(~190hp). After the Wenatchee race, Bob B and I were comparing notes. He is running a IO-375(205hp) with the Vans smooth cowl (intake air in the cowl inlet). At 200mph, I was showing almost +1"MP more than he had. The Vans system is supposed to very good at pressure recovery, so I suspect my ramair and cowl was a horsepower equalizer.
 
Michael,

Thanks for the reply...does Coach know you're giving up secrets? :p

You've hit on items I'm concerned with, and might have asked, had the previous post not already been longer than War and Peace :rolleyes::
-Boundary layer impact with a flush lip (how bad is it?)
-Inlet proximity to the prop (closer = better?)
-Inlet shape (round = really better?)
-Inlet size?


Coach does not ... yet:D

I'm thinking that a scoop running in the boundary layer is far more critical further aft (where the boundary layer is thicker), but you still have that spinner, prop hub, and waste air spillling out of the cowl/spinner gap to deal with now. I'm guessing that's a lot of dirty air. I'd get as far away from or in front of that mess as possible.

I have verified that close proximity to the prop is beneficial. Closer is measurably better in tests that I've conducted. That said, you also want to be outboard, in the wake of the "good" part of the blade as much as practical.

As far as shape goes, I think that as long as you don't pinch any corners and cause flow separation, it doesn't really matter. Round is just the easiest way to keep it pure.

Inlet size should be kept small to eliminate spillage, but large enough to feed the engine. To me, that means no bigger than the smallest choke point in the servo. Spillage hurts you both with the added drag of all that waste air going overboard, and also hurts pressure recovery in the inlet system. The hard core acro guys run those big "bug catcher" funnels because they are looking to feed an engine at low to zero airspeed; you have high speed working for you - take advantage of it. I think that I told you in another post that I went from a straight 3 in dia tube as my inlet, to which I added a machined lip which reduced the ID to 2.5 and I picked up MP.
 
Someone please correct me if I am wrong, but the sharp inlet lip profile is not best in "real world use"...

"Sharp" is relative... A 1/8 inch radius is far from sharp for a true pitot inlet - most fiberglass work has a much more generous raduis because it's just easier to fabricate. You really do want to split the air, but not cause any off axis relative airflow to stall the inlet. Most of what we see today is far bigger than required IMHO.
 
"Sharp" is relative... A 1/8 inch radius is far from sharp for a true pitot inlet - most fiberglass work has a much more generous raduis because it's just easier to fabricate. You really do want to split the air, but not cause any off axis relative airflow to stall the inlet. Most of what we see today is far bigger than required IMHO.

I agree with not wanting to upset the axis of the airflow, but still feel that trying to hit the moving target of perfect variables is not practical. I talked some with Paul Lipp's about my induction and cowl exit ideas. On the inlet he encouraged me to have the inlet radius be 1/4". If I remember correctly he referenced the Phantom biplane as an example.

It's all probably splitting hairs at our speeds, but hey it makes for great discussions. :)
 
It's all probably splitting hairs at our speeds, but hey it makes for great discussions. :)

In many ways we are absolutely splitting hairs...its one of the things that makes this fun! And it does make for "lively" discussion (sorry Wade, couldn't help it!) ;) I've studied some, and learn more every day, so I asked those questions to generate more discussion, and listen to the experience out there.

Michael has me thinking about the plug idea to try a round inlet versus mine. Probably do-able with minimal scarring. I'm cypherin' on the ram air duct right now, and may be able to open up my inlet enough to accommodate a 2.5" round duct that might work with both my inlet and a plug made with Tom's. Still thinkin' on it.

Brian, thanks for the note...your inlet has a 3" radius, right?

With respect to inlet radius, another RV guy here has a rotary-powered 8 that has had mucho cooling problems. He's just made large round inlets with generously radiused lips for his induction and cooling inlets, that were designed after a bunch of research on his part. I'm pouring through his folder of papers now to dig deeper. His engineering problems are different, due to the different engine and cooling system, but his research on inlet shape crosses over.

Beyond the inlet, since I don't have room to accommodate a flat K&N filter behind the inlet, I need to have a filtered path and a ram path (self imposed limitation of not wanting to increase the girth of the lower cowl). Discussed this with Tom and Mark, and one option is a round ram air duct with a throttle body like in a Bower, then a side-mounted flange to take filtered air from a filter mounted under the left inlet (in the lower cowl). That filter could be fed directly by ambient air (like with some IO-550's) or via a sceet tube from the left inlet. Another option is making the duct more like the shape of an RV FAB inlet (flat-sided horseshoe, if you will) and making a door that will close off ram air in one position, and close off the flange to the filtered air inlet in the other position (thus the door is fully out of the way in the ram position). I'm concerned about losing efficiency in an odd-shaped duct, and the engineering of the actuator is still evading me a bit.

But this is all theorizing and thinking out loud. It's great to see and hear the discussion along the way...just gotta order some parts after the XMAS spending binge is over and git er dun!

Cheers,
Bob
 
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...Michael has me thinking about the plug idea to try a round inlet versus mine. Probably do-able with minimal scarring. I'm cypherin' on the ram air duct right now, and may be able to open up my inlet enough to accommodate a 2.5" round duct that might work with both my inlet and a plug made with Tom's. Still thinkin' on it...

Bob, I don't think you have to modify your existing cowl to try the "correction adapter"... Just make a splash of your inlet (so you can capture the exact shape) and transition the new round inlet to your existing oval smoothly along the length. I suspect that despite the shape change, you will still be increasing in volume as you move aft, and the new duct should be about 6 inches long which should provide enough fineness ratio to keep the air happy. I suspect that your gains are going to come from pinching the inlet down a bit (less spillage), increasing the length of the divergent duct (better pressure recovery), and getting it out into clean air.

Come to think of it, you could almost make the thing out of a single chunk of tooling foam, tape it in place and fly. If the new shape provides positive results, then look at scratching the paint. In any case, make it so that it is easily modified. Try different lip radius, opening size, length, etc to see what works best for you.
 
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