What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Unfiltered Ram Air?

13brv3

Well Known Member
Greetings,

Does anyone fly with unfiltered intake air? I've owned a few experimental planes and have never considered such a thing before now. The RV-3B I purchased recently has horz FI with a selection for unfiltered RAM Air, or filtered air. I understand the idea is to open the RAM air on climb out, and then close it again on landing approach. Assuming you're not flying through visible dust clouds, just how bad is that for the engine? The whole idea rubs me the wrong way, but maybe it's not really a problem?

I'd be tempted to use the filtered air all the time, but it's not really made for that. The filter is located inside the cowl where it's not cool or pressurized as much as it could be, so there's a distinct loss of power.

I guess I'm trying to decide whether I should leave well enough alone, or change the system for a better, full time filtered air setup.

Thanks,
Rusty
 
yes,

not an RV, but I currently fly a Laser 200 - no air filter. Also, ever look at the front of an Extra 300, Walter doesn't put a filter.

I did put fuel injection on a 3B several years ago and the fuel servo was slightly taller than the carb pushing the air box down into the cowl. I spent alot of time finding a different ht air filter and cutting down the air box.

Im not saying I dont like air filters, I do. Im just saying it does not bother me not to have one.

Mutter
 
Thanks for the comments. This picture shows the current filter arrangement, which is certainly not ideal for full time use.

https://www.amazon.com/photos/share/...rijSjtI52clht9

I may have to fly it as the builder originally intended for now, but once I get a hangar closer to home, I'm going to probably rework this to a better full time filter configuration.

Cheers,
Rusty
 
My RV-3 did not have a filter. I put about 500hrs on it and it had 700 SMOH when I sold it. Although I think air filtration _on the ground_ is a very good idea, my results were excellent over a 7 year period. Compressions and oil burn were still quite good after 700 hrs on a pumped up O-320. Mine was w/o an oil filter so oil changes were every 25hrs. Maybe that helped.

Anecdotally, I once flew it wide open at sea level on a standard day and the MP gage showed almost 2" of ram air "boost". Mine had an Ellison TB on it.

The plane I'm building now will be set up the same way or may have "filtered air" as an alternate source.
 
My RV-3 did not have a filter...Anecdotally, I once flew it wide open at sea level on a standard day and the MP gage showed almost 2" of ram air "boost".

I flew mine upside down across the Atlantic.

(Note: Both statements are nonsense)
 
I'm currently building a -4 with horizontal induction using the Air Flow Performance Y for filtered or ram air. Its going to work but adds weight and complexity. If I could go back I would just use ram unfiltered air 24/7. I live in the AZ desert and have rebuild a handful of off road engines that have seen pounds and pounds of dirt go through them. All of them showed little problems dirt related. Our planes will see little to no dirt, I say run it the way you got it (ram air) and don't think twice about it.
 
My RV-3 did not have a filter. I put about 500hrs on it and it had 700 SMOH when I sold it. Although I think air filtration _on the ground_ is a very good idea, my results were excellent over a 7 year period. Compressions and oil burn were still quite good after 700 hrs on a pumped up O-320. Mine was w/o an oil filter so oil changes were every 25hrs. Maybe that helped.

Anecdotally, I once flew it wide open at sea level on a standard day and the MP gage showed almost 2" of ram air "boost". Mine had an Ellison TB on it.

The plane I'm building now will be set up the same way or may have "filtered air" as an alternate source.

All the charts I have seen say a 2" rise in MP would required something like 400kts. I think 1" rise is MP on an RV is about all you can hope for, but 1" is 10hp so I will gladly take it.
 
All the charts I have seen say a 2" rise in MP would required something like 400kts. I think 1" rise is MP on an RV is about all you can hope for, but 1" is 10hp so I will gladly take it.

Maximum available dynamic pressure, standard day, is approximately 1.55" Hg at 180 KTAS at sea level. 200 KTAS at 1000 feet is 1.86". Even if your RV will run 200 KTAS in level flight, it is not possible to convert all the 1.86" available dynamic pressure to increased manifold pressure; an engine intake is not a closed end system like an airspeed pitot.

Given an IO-360 at 2700, 3" intake diameter, 1000 feet standard day, and 200 KTAS, MP rise would be about 0.9559" Hg, for a total MP of 29.812".

Returning to the OP's question, there isn't any good reason to run filterless on an everyday airplane, if the system can be built with enough filter media area. By measurement, the pressure drop for my entire airbox, including filter, is 0.19" Hg, as compared to an FM-200 with a standard test bellmouth. For perspective, Rod Bower reported a bit more than that for the open butterfly in his ram air system. With no butterfly, the drop might be half as much, but not zero. We're talking about giving up filtration in return for less than 0.1" Hg, max. Doesn't make sense.

Reno racers? Sure, take no prisoners.
 
I have a Rod Bower RAM air mod for my RV-10

http://www.ramairforhomebuilts.com/

I typically don't open it until I get about 5,000 ft. Although, I usually don't close it on the descent. It yields about a 1" MP increase.

Glad you posted this. I was getting close to sending a message about it! I remember when I came out to look at your airplane and we talked about it, but I was drinking from a firehose and forgot so many things you told me, including who made the ram air for your bird.

Are you still satisfied with it? I remember looking at your build log and not seeing too much in the way of plan modifications to install it. Is that really the case, or did it require a lot of fiddling with the cowl and such?
 
Most of the Harmon Rockets have the Y for Ram or Filtered air. I only use the filter when in dirty environment like taxiing on grass or dirt and also when shutdown. Nothing unusual in oil analysis. Unfiltered for start in case of fire belch in intake!

Russ
HRII
 
Russ McCutcheon's RV4, horizontal induction, no filter. He has flown it that way for many years. I do not know how many hours but a bunch. Perhaps he will chime in.
My '42 Aeronca L3 didn't even have provisions for a filter. It had 1000 hours on it when I got it and I put 600 more in the ten years I owned it. It ate a lot of bugs and never seemed to mind.

So, plenty of examples running without filters but I don't think you will find any real data on engine life comparisons filter vs not.

I agree with DH. There is no reason not too given the small, perhaps insignificant, gain going naked.
 
I have a Rod Bower RAM air mod for my RV-10

I typically don't open it until I get about 5,000 ft. Although, I usually don't close it on the descent. It yields about a 1" MP increase.

As compared to pulling air from inside the lower cowl, through the plastic flap valves. The rise is large because it's so badly choked with the butterfly closed. It is definitely not an optimized filter system.
 
I put one of these 4" O.D. K&N filters (with that rubber fitting on the left end cut off) in my ram air intake. It keeps the bugs out of the carb.

pYh0Ez.jpg
 
Thanks for the excellent comments. Sounds like I'm probably worrying too much about the unfiltered air, but I'm pretty sure I'll change the system at some point to include a low loss filter full time. The engine didn't have an oil filter either, and they were routinely going well past 25 hours on the changes, so that probably did more harm than the unfiltered air. I've already added a filter.

As the 4th owner of this plane, there have been some changes through the years, and plenty of things I need to make right. Dan was right on the money about the RAM air though, the second owner did race it at Reno. I kinda figured he was responsible for the RAM air.

Anyway, thanks again, at least the unfiltered air is not an immediate concern.

Cheers,
Rusty
 
I use a Bower airbox on my rocket for winter use only. With the snow potential where I live I do not like the possibility of plugging the filter with snow. With the ram air closed you lose about 2" of manifold pressure. It is sort of like using carb heat as you are now drawing air from the hot lower pressure area of the plenum. Good for snow conditions though. The system does work well in the summer with the ram air open but I do not like unfiltered air. My engine has a fresh rebuild, ECI cylinder problems, but after that big expense I will use filtered air as much as possible.
I built a custom filter that fits in the same spot as the Bower box. It has a much larger filter and MP are very similar to the Bower set up with the ram air open. It is a clean simple filter box with no moving parts.
 
I had another question about the Rod Bower system. They don't seem to show a lot of details on their web page, but in looking for info online, I could swear I've seen his system with a filter, and then later it looks like the filter was eliminated. Does his current system have a filter or not?

Thanks,
Rusty
 
Hey gusy don't forget Air Flow Preformance makes a alternate air "Y" with nice filter. It's honestly a pice of art work it's so nicely made. Much cheaper than than Rods system and much simpler. I agree ram air is probubly more work than it's worth and filtered air is best but if your like me and have to have ram air check out the Y from Don at Air Flow Preformance.
 
I put one of these 4" O.D. K&N filters (with that rubber fitting on the left end cut off) in my ram air intake.

John, the cone filters are relatively restrictive, as compared to the flat panel K&Ns. The pleats on the flat filters tend to be 7/8" to 1" deep, while the pleats on cone filters are quite shallow. Imagine cutting the media from the filter body and stretching it out flat. BIG difference.
 
As compared to pulling air from inside the lower cowl, through the plastic flap valves. The rise is large because it's so badly choked with the butterfly closed. It is definitely not an optimized filter system.

rod has a new case that resolved that issue. With the butterfly closed, I now get the same MP as the factory air filter. There definitely were issues with the earlier cases.
 
The enticing feature of the K&N filter is that it has screen on both sides of the pleats so there's no possibility of any paper coming loose and lodging in the carburetor. The rubber cap at the small end seems to be really well secured.

OTOH, I have had high silicon readings on my oil analysis since day one. Some say the K&N filters aren't as efficient as paper filtersl. That could well be true, but I doubt my high silicon readings are from dirt passing through that filter. I recently re-plumbed my oil separator to drain to a small cannister rather than back into the crankcase. My crankcase vent hoses are all silicon rubber so that could be the source. I'll know in a few months.
 
Glad you posted this. I was getting close to sending a message about it! I remember when I came out to look at your airplane and we talked about it, but I was drinking from a firehose and forgot so many things you told me, including who made the ram air for your bird.

Are you still satisfied with it? I remember looking at your build log and not seeing too much in the way of plan modifications to install it. Is that really the case, or did it require a lot of fiddling with the cowl and such?

I probably wouldn't do it again. It does what it advertises, it it hasn't been without its issues. You have to install it correctly. Just ask Vic Syracuse about the ones he found installed improperly.

I went through three or four upgrades. I feel like I was doing beta testing for a rod. I had to upgrade the reed materials until I found a thickness that work well with a io-540.

But it does work. It allows me to reduce MP and save a little fuel when doing a cross country.
 
Russ McCutcheon's RV4, horizontal induction, no filter. He has flown it that way for many years. I do not know how many hours but a bunch. Perhaps he will chime in.
My '42 Aeronca L3 didn't even have provisions for a filter. It had 1000 hours on it when I got it and I put 600 more in the ten years I owned it. It ate a lot of bugs and never seemed to mind.

So, plenty of examples running without filters but I don't think you will find any real data on engine life comparisons filter vs not.

I agree with DH. There is no reason not too given the small, perhaps insignificant, gain going naked.
Hi Jon, 1600+ hours on the current engine since 2006 with no filter, the old engine had 900 hours with the same setup and had no problems related to being unfiltered. I don't really have any preference, I'm just not going to do a bunch of work to add a filter when it has proven not necessary.
 
Hey gusy don't forget Air Flow Preformance makes a alternate air "Y" with nice filter. It's honestly a pice of art work it's so nicely made. Much cheaper than than Rods system and much simpler. I agree ram air is probubly more work than it's worth and filtered air is best but if your like me and have to have ram air check out the Y from Don at Air Flow Preformance.

I checked the Air Flow Performance site, and it appears what I have is their FM-100 "Y" and the filter they suggest. I didn't see any pics of the FM-100 Y with filter attached, but on the FM-200 they show a tapered filter attached directly to the Y. I'm assuming there wasn't room to do that will the supplied filter for the FM-100, so it got remotely located with scat tubing, which I'd be willing to bet is horrible for intake airflow. Next time I have the cowl off, I'll do some measuring and browsing of the K&N site to see if there's a direct fit option available that will fit without the scat tubing. that would at least make me feel a little better.

Cheers,
Rusty
 
I probably wouldn't do it again. It does what it advertises, it it hasn't been without its issues. You have to install it correctly. Just ask Vic Syracuse about the ones he found installed improperly.

I bought one, it's sitting in my garage right now. Waiting on my engine to do anything with it. My question is how do you install it wrong? To me it looks like only one way to install it.
 
Conical K&N

Not all the conical filters have shallow pleats.

https://www.knfilters.com/images/l/E-0995.jpg

https://www.knfilters.com/search/pr...201824352406&mp_kw=+k&n +e-0995&mp_mt=b&pdv=c

This is the one I used. I has about 7/8" deep pleats for a bunch of surface area. I don't have the calcs at hand, but I remember the area being substantially larger than the flat filter Van's uses for the snorkel setup. The pleats on that one are pretty shallow, maybe 3/8", if I remember correctly. I built a glass box for it and can tap alternate air off the back of that if needed. I made a custom scoop on the front of my cowl to accommodate it. Superior sump. At 11,500' and 74 degrees OAT, I was making 20.5" MAP. Density altitude had to be about 15K. That same day at 8500' and 83 degrees, 22.9" MAP.

a>


Ed Holyoke

John, the cone filters are relatively restrictive, as compared to the flat panel K&Ns. The pleats on the flat filters tend to be 7/8" to 1" deep, while the pleats on cone filters are quite shallow. Imagine cutting the media from the filter body and stretching it out flat. BIG difference.
 
Last edited:
Unfiltered RV-4 O-360

I finished my RV-4 with an O-360 A1A and carbureted in 2009 and designed the intake on the Sam James cowl to be unfiltered. I have flown my -4 now 8+ years and over 500 hours with no problems and enjoy the 'ram effect' of additional MP for faster TAS! I carry an intake plug when I park my airplane and use the carb heat if worried about ground taxi in dusty conditions. There was a time when most RVs were unfiltered, as was my original purchased RV-4 with a carbureted O-320. That airplane currently has over 2,200 hours on the original engine. YMMV but there will be no air filter on my RV.
 
I bought one, it's sitting in my garage right now. Waiting on my engine to do anything with it. My question is how do you install it wrong? To me it looks like only one way to install it.

The problem/advantage of the Bower Ram Air is that Rod is a tinkerer. He's always improving the product. There were many early variations of the sump elbow and at least two variations of the canister that I'm aware of at the moment.. The new aluminum one is pretty nice. Some of the predecessors lacked some of the elegance of the new one on how they were fasten.

If my memory is correct, I believe that Vic Syracuse found a couple installs in which things weren't fastened in an acceptable manner while doing conditional inspections. I would defer to Vic if he wants to share the specifics. My suspicion is that the installer was a bit na?ve and didn't understand proper techniques.

If you have the aluminum elbow, it's hard to screw up the installation. For the IO-540, Rod upgraded the canister from four holes to six. This helped increase airflow when the butterfly is closed. In comparison to the standard airbox on a RV-10, I'm now generating comparable power with the ram air closed and still getting about a 1" MP above the plans airbox when open.
 
Not all the conical filters have shallow pleats.

https://www.knfilters.com/images/l/E-0995.jpg

I built a glass box for it and can tap alternate air off the back of that if needed. I made a custom scoop on the front of my cowl to accommodate it.

Ed, have any photos of your airbox and inlet?

Straight ram air obviously has no protection against airborne dirt. Ignore it if you wish, but it's there; filters get dirty, don't they? However, dirt isn't the only issue. A good filter system eliminates small rocks, flying insects, snow, ice, plastic bags, balloons, toilet paper, bird feathers, and all the other **** that we, sooner or later, hit with an airplane.

Balloons and bags and ice are pretty obvious. But a bug? Allow an example. A Bendix-style dual diaphragm fuel control balances dynamic (ram) and venturi pressure against a fuel pressure delta:



Plug the ram opening with a fat bug, or snow, or ice, and theory says mixture is going lean. (Nope, I do not know exactly how much.) A Bendix RSA (left) has four ram tubes. A single bug might not get them all, but snow or ice remain as possibilities. An AFP control has one ram opening.



A good intake system takes its alternate air from behind the filter, so the filter can stop the trash, and the engine can still get air. And the alternate air needs to work with 20+ inches of suction pulling on it (i.e. with the filter blocked); quite a few sliding or rotating alternate air doors are not going to move under those conditions.
 
Last edited:
But a bug? Allow an example. A Bendix-style dual diaphragm fuel control balances dynamic (ram) and venturi pressure against a fuel pressure delta:



Plug the ram opening with a fat bug, or snow, or ice, and theory says mixture is going lean.

Wouldn't it stay the same as long as you're at a fixed/steady altitude and power combination? If it was completely blocked (i.e., one port), wouldn't that mimic what a pitot system does if it gets blocked (unchanged until a change in altitude)?
 
I see I've been mentioned a couple of times, so I guess I should chime in. :)

Yes, the early models did not have filters. My RV-4 was that way, and while I didn't like it, it didn't seem to be a problem. I did run safety wire back and forth across the air duct to catch the big stuff, kind of like chicken wire. I was in Cleveland, Ohio at the time, and 99.9% of the time flying off of paved strips. I don't think I would like that today when flying off of grass strips, which I have been doing since 1997. I am amazed at how dirty the K&N filter gets, with all kinds of bugs, grass, and other stuff. And even for the customers who do the majority of their flying off of pavement, the filters do capture a lot of junk.

It was a carburator version of the O0320 on the RV-4, but as Dan pointed out, with an injected system there is no way I would run unfiltered air. It seems silly to me to risk an expensive airplane and engine for an almost imperceptable amount of MP increase. It's not like the RV's are underpowered. :)

For racing, it's a whole different story, and usually there is a nice runway right underneath you.

With regards the Rod Bower systems, yes they may be improved now, but on the two I removed (which were done according to plans) the engines were really choked at full throttle. As a demonstration, on the takeoff rollI would engage the bypass and the engine would immediately surge, dramatically improving the takeoff roll and climb performance. Once the owners saw this, we went ahead and installed the stock FAB and air filter. I assure you that it's not because I like building and installing the FAB's. :)

Vic
 
Filtered ram air

I had the Superior cold air sump and an updraft cowl, so I took a deep breath and cut all the protrusions off the cowl and started over.

20170411_144518.jpg
[/url][/IMG]

This how it wound up.

20160922_193431.jpg
[/url][/IMG]

This is the back side of my airbox. The alternate air door is cable actuated with a pushbutton lock cable.

20160920_193503.jpg
[/url][/IMG]

20160920_193403.jpg
[/url][/IMG]

The alt air door open. I used silicone rubber sheet as both gasket and hinge. The spring steel strap is to insure a good seal. I can pop it open past that with a good hard pull on the control. Should be enough air to get me to an airport.

Ed Holyoke
 
Wouldn't it stay the same as long as you're at a fixed/steady altitude and power combination? If it was completely blocked (i.e., one port), wouldn't that mimic what a pitot system does if it gets blocked (unchanged until a change in altitude)?

Joe, that's a good catch, thanks. Did some checking last night; neither AFP or Bendix air diaphragms have bleed hole (I assumed they did), thus you're correct. Assuming a good solid plug in the ram opening, trapped ram pressure would not bleed away, thus the ball valve would not move if nothing else changed. (Bonus trivia; the AFP fuel diaphragm does have a bleeder, Bendix does not.)

Given a plugged ram opening, ball valve position would go awry with changes in density or throttle. Open throttle, lean, closed throttle, rich, etc. Again, I have no idea exactly how much, but my vote remains with keeping the trash out.
 
This is the back side of my airbox. The alternate air door is cable actuated with a pushbutton lock cable.....I can pop it open past that with a good hard pull on the control.

Ed, you probably have, but be sure to test or calc how much knob force would be required to pull it open against perhaps 20" Hg (a partial filter blockage). An alternate plan might be a trigger release on a door that pulls inward (no significant pilot force required), or a spring loaded door requiring no pilot action at all.

Airbox with a spring-loaded automatic door. A microswitch flashes a cockpit LED in the event the door opens. http://www.vansairforce.com/community/showthread.php?t=44856&page=2

There are some certified airplanes with similar alt air schemes. This one makes the FM-200 go slightly rich, and it would reduce airflow somewhat, so I expect some power loss if I suck up a plastic bag, block the filter, and the door opens. On the other hand, I have a 390, and expect to have enough power remaining to make it a non-event. In return it is truly automatic, no pilot action required, no diagnosis while playing deer-in-the-headlights as the runway end goes by.

Note to readers...Ed and I spoke at OSH. He may have interesting data to share later, after more flight test.
 
Last edited:
I have the Rod Bower and read the same MP with another RV at the same speed and altitude WOT.

SO IT DOES NOT WORTH Use the Snorkel and the filter and get the same results.

BDW I Have the Hartzell Prop, may be with other works beter because the root of the prop does not push air to the scoop in my installation.
 
Howdy Dan,

Thanks for pointing that out. Something perhaps I didn't think hard enough about. I'll probably replace my pushbutton locking cable with a locking Tee handle so I can get more oomph on it if I ever need to. With a good grip and adrenaline, I'll get it open if I have to, I hope.

I have limited space available on the airbox to make it inward opening. I think that I might have trouble making room for the air to get past that in quantity, as well. It would be hard to make the inner face of my very rough homemade airbox as flat as it needs to be to seal, too. As it is, the opening is smaller than the normal intake. I haven't tried to calculate how much that might limit power, but it's got to be better than none at all.

Ed Holyoke

Ed, you probably have, but be sure to test or calc how much knob force would be required to pull it open against perhaps 20" Hg (a partial filter blockage). An alternate plan might be a trigger release on a door that pulls inward (no significant pilot force required), or a spring loaded door requiring no pilot action at all.

Airbox with a spring-loaded automatic door. A microswitch flashes a cockpit LED in the event the door opens. http://www.vansairforce.com/community/showthread.php?t=44856&page=2

There are some certified airplanes with similar alt air schemes. This one makes the FM-200 go slightly rich, and it would reduce airflow somewhat, so I expect some power loss if I suck up a plastic bag, block the filter, and the door opens. On the other hand, I have a 390, and expect to have enough power remaining to make it a non-event. In return it is truly automatic, no pilot action required, no diagnosis while playing deer-in-the-headlights as the runway end goes by.

Note to readers...Ed and I spoke at OSH. He may have interesting data to share later, after more flight test.
 
MAP at WOT - ram air effect?

Using online density altitude calculators, it appears that I am seeing something like an inch or two more MAP than the expected absolute pressure. I have a homemade filtered ram air induction as seen in an earlier post. I need to do more testing to validate that claim, and I'm curious what other people's numbers are at various altitudes and temperatures.

The density alt calculators want: Altitude, OAT, altimeter setting, and dew point. The one I used returns: Density altitude and absolute pressure, among other things. I didn't record dew point for that day, but various numbers make little difference in the output.

https://wahiduddin.net/calc/calc_da.htm

So, for my flight at 13500', 74degree, 30.07 alt setting , I see a calculated absolute pressure of just over 18" and my MAP gauge was reading 20.5 at wide open throttle.

Anybody have numbers to share?

Ed Holyoke

20170703_123857.jpg
[/url][/IMG]
 
Some numbers from my stock -10 with FAB per plans:

Just flew home from KDDC yesterday, at 13,500' OAT 41F alt 30.09 WOT MAP was reading 17.4"
 
You can check your digital MP gauge on the ground for accuracy by moving the BARO setting on your altimeter until the Altitude reads Zero. Your MP indication at that point (with the engine off of course) should be within a couple of tenths of the new BARO setting.

Another way to check your actual RAM air increase is to note your MP prior to starting your engine and then fly donw the runway at 50' or so with wide open throttle and full RPM and check the MP pressure indication. It's better to do this with someone else on board looking at the gauge. :). The difference in indications will show that you have a gain or a loss.

Vic
 
Using online density altitude calculators, it appears that I am seeing something like an inch or two more MAP than the expected absolute pressure.

Remember, the calculated available MP would be equivalent to measuring at a point before the filter, fuel control venturi and butterfly, intake manifold plenum, (if it has one), and the intake tubes, all of which offer some restriction. Since we actually measure at one of intake ports in a cylinder head, there will be a significant difference between what is available and what is seen on the EFIS. There is no good way to guesstimate the total intake tract loss since everybody's system is different, but there are examples; my notes say an RSA-5 fuel control alone is responsible for a pressure loss of about 12.75" H20 at 1560 pph, or 0.94" Hg. An FM-200 is about 4" H2O, or 0.3" hg, same conditions.

So, if you're seeing more on the EFIS than any reasonable calculation, well, it would have to be magic.

So, for my flight at 13500', 74degree, 30.07 alt setting , I see a calculated absolute pressure of just over 18" and my MAP gauge was reading 20.5 at wide open throttle.

Yep, that would magical. If I use your inputs with an assumed a 3.5"D intake and IO-360, pressure before the filter would be about 18.1" Hg. Mr. Short's report of 17.4 displayed on the panel is probably pretty accurate.

BTW, 74F at 13,500 feet? Is it really that hot over California?
 
Last edited:
Hot!

Well, I can't prove any of it, so far and I don't want to be bragging about inaccurate numbers. I'm just going by what my instruments show. That's why I want to hear other people's numbers.

Yup, it was hot. It was 98 when I took off from Chino and there is almost always an inversion. It was 104 at 3500' where I was trying to get some fuel nozzle data. Bumpy too. It was a relief to climb to the cool cool air of 74 degrees. ;-) It was hot the whole time I was flying off my 40 hours - 2, 3, even 4+ hrs a day. I was also commuting 65 miles one way and had to stop down and annual our 6A about halfway through. Wrung me out pretty good. I was trying really hard to make Osh.

I'll have to measure my inlet. It is bigger than standard - maybe about 4.5" tapering to where I could get a short length of 4" scat onto it. I ran out of room behind the prop and had to make it larger to not constrict at the dome of the filter. I'm running an FM-150.

One factor I just thought of - the inlet is right, and I mean right, behind the prop. The 74RV has a pronounced twist and some extra chord at the root. The folks at Whirlwind told me that they had reports that this prop cooled very well on the ground. That might account for some extra MAP. Didn't Kent Pacer note some of that? Where's my copy of Speed with economy?

Next time I go out to the airport I'll check the MAP against field elevation. If it is off, I think I can put an offset into the EFIS. Gotta put a big window in for the missus this weekend. Sigh.

Ed Holyoke


Quote Yep, that would magical. If I use your inputs with an assumed a 3.5"D intake and IO-360, pressure before the filter would be about 18.1" Hg. Mr. Short's report of 17.4 is probably pretty accurate.

BTW, 74F at 13,500 feet? Is it really that hot over California?[/QUOTE]
 
Back
Top