Engine Baffle

Discussion in 'Flight Following' started by Adam Weiss, Jun 13, 2018.

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  1. Adam Weiss

    Adam Weiss Pre-takeoff checklist

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  2. NordicDave

    NordicDave Line Up and Wait

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    OMG, that's odd. I'd think it would trap heat after landing and shutdown.
     
  3. Adam Weiss

    Adam Weiss Pre-takeoff checklist

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    It's odd that this is a fresh overhaul...some shop just did this. That made me wonder if it's a "new thing"?
     
  4. nauga

    nauga Pattern Altitude

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    When I followed the link I just got the ad. Are you referring to the engine "cover"? It's a cooling plenum, it forces more air over the cylinders for more effective cooling. As a result the cooling duct size can be reduced and cooling drag goes down with it. They've been around for years...the RV world seems particularly fond of them.

    Nauga,
    who ain't got the time to go that fast
     
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  5. GRG55

    GRG55 Final Approach

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    Airplanes on eBay not that uncommon?

    Low ball bids also not that uncommon.
    Quite a few of the piston racers at Reno have used these types of plenums too.
     
  6. Adam Weiss

    Adam Weiss Pre-takeoff checklist

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    Thanks @nauga. First I've ever seen one. I learned something today.
    So now my dumb question (maybe my second one)...if it really cools better, why don't we see more of them?
     
  7. GRG55

    GRG55 Final Approach

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    Any tightly cowled airplane engine traps heat after shutdown. Wheres it going to go by convection, regardless whether the plenum top is as shown, or the top cowl?
     
  8. GRG55

    GRG55 Final Approach

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    PITA to work on the engine. Normally the top cowl forms the upper surface of the plenum. Pull it off and there's comparatively unfettered access to the top of the engine.

    The most common problem I notice with cooling is inlet or outlet cross-section. Too much, or too little. My Aztec is a good example. It is a lousy design from an outlet area standpoint (not enough with the cowl flaps closed) as it came stock from Piper.
     
    Last edited: Jun 13, 2018
  9. Adam Weiss

    Adam Weiss Pre-takeoff checklist

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    My thoughts exactly...so some folks must think the improvement in airflow (vs. the rubber baffling) is worth it?
     
  10. GRG55

    GRG55 Final Approach

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    It's a trade off that's for sure. But you would be surprised how much improvement one can get on many airplanes just paying attention to how well the stock baffling is sealed. Even small leaks around the rear part of the baffling make a huge difference in reduced cooling efficiency and increased drag.
     
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  11. zaitcev

    zaitcev En-Route

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    I would like to turn this question around. My engine has no baffling whatsoever and the cooling is inadequate. Would adding some baffling do anything, or do I need to create a real tight plenum before anything changes?
     
  12. Lndwarrior

    Lndwarrior Pre-takeoff checklist

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    So I'm sure some people more knowledgeable than I will comment on your question but I can provide a little insight. I recently finished building my own aircraft and had to design the baffling for the O-235 engine. Some things I learned are that many Cessna's and Pipers have engine baffling that uses the top of the cowl as the top of the "intake plenum".

    So air comes in thru the cowl openings and is then forced down thru the cylinder fins by the pressure between the "intake plenum" and the "relief air plenum" (the bottom of the cowl and the air exit opening). Yes, I understand you probably know this but I want to make an important point in regards to your question. The point is - the relief air opening size and configuration can have as much effect on the engine cooling as the baffles/intake plenum. So it's just not the baffles on top that need to be considered, it's also the size, configuration and location of the air exit opening that is critical to maximize engine cooling.

    This issue is discussed over and over on the Vans RV web site. Some people there have done some scientific testing on this and there is a lot of discussion on the subject as the higher performance engines they use create difficult cooling challenges.

    While the baffle system intake plenum is adequate for most production aircraft, many in the homebuilt world are using solid/sealed plenums fabricated from metal, fiberglass or carbon fiber. The design and complete seal of the solid plenum can do a better job of cooling - and directing the air over the worst case cylinders.

    If you look closely at many RV's you will notice the air outlets are quite small and tightly cowled. You will also notice they have a compound curve lip to them (around the exhaust pipes). The design of the exit lip has been proven to have a dramatic effect on the cooling airflow. They have it figured out to exact degree of angle for maximum airflow.

    Engine cooling is kind of an interesting subject when you get into it. And a lot more complicated than many would guess.

    This is the extent of my knowledge on the subject.
     
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  13. GRG55

    GRG55 Final Approach

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    If it is powered by a conventional air-cooled aircraft engine there should be downdraft airflow to cool the cylinders. If you have "no baffling whatsoever", how is the engine being cooled?

    What engine do you have, and what type of airplane is it?
     
  14. Salty

    Salty Pattern Altitude

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    That looks exactly like my factory original baffling on my m20c, only new and properly sealed. Mine is bent and dented and has all sorts of gaps in it. It’s commonly called a “doghouse”.

    This is a good thing. It keeps the airflow over the engine in flight as designed to keep it cool. Someone spent a lot of money getting that just right.

    I bet the seller paid 18 grand for the engine overhaul. There’s either something else very wrong with that plane, or it’s a hell of a good deal.
     
    Last edited: Jun 14, 2018
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  15. steingar

    steingar Taxi to Parking

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    I bet his reserve is high. I'd love to have a doghouse like that, mine's bent, drilled, cracked, dented and riveted all over the place. The one on that aircraft cost big bucks. And yeah, it does make it a PITA to work on the engine. Thankfully I don't do that.
     
  16. Capt. Geoffrey Thorpe

    Capt. Geoffrey Thorpe Touchdown! Greaser!

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    The object is to get as much air as possible to flow around the cylinders and do some useful cooling - air that just blows over the top and out the back is pretty much wasted as far as cooling is concerned, but still adds to the cooling drag. I would think that the more you redirect the air to where it does some good, the better it gets.
     
  17. Bill Jennings

    Bill Jennings Final Approach

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    Yeah, the design of the air intakes and cooling on the pre-J Mooneys left some things to be desired. The new cowling and air intake designed by LoPresti for the J and beyond greatly reduced drag and increased engine cooling..
     
  18. Adam Weiss

    Adam Weiss Pre-takeoff checklist

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    Same plane, different question.
    In the pictures in the Ebay listing, it shows the overhaul from Corona on December 2, 2003.
    The very next picture shows a logbook entry indicating the engine was installed on April 25, 2016, still with 0 SMOH.
    Any ideas why this engine would (hopefully) have been pickled for 13 years?
     
  19. Zeldman

    Zeldman Final Approach

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    Yep, that sure is baffling.....
     
  20. Adam Weiss

    Adam Weiss Pre-takeoff checklist

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    bu dum, tissss
     
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  21. Dan Thomas

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    Leakage doesn't just waste air. It helps destroy the low-pressure zone under the engine that is created by a properly-designed exit. If the pressure differential between the top and bottom diminishes. cooling is also diminished.

    That doghouse was used by some Cessna 170s and other older models. I used it on my Jodel. The typical lightplane has stiffeners on the underside of the top cowl that interfere with good sealing of the rubber baffle seals. I have seen some of those seals cut to fit closely around the stiffeners to try to close the gaps, but as the engine moves around on its shockmounts the seals are damaged as they're forced sideways against the stiffeners. Doesn't do the cowl any good, either.

    With the doghouse the only seal is around the front. None needed along the sides and rear as with most installations. Points of leakage and wear and vibration agains the cowl are reduced. Sure, it adds to maintenance times, but getting the cowl off most airplanes is a big pain already. That's where some savings could be made if anyone was serious about maintenance times.
     
  22. donjohnston

    donjohnston Line Up and Wait

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  23. donjohnston

    donjohnston Line Up and Wait

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    Because it's a massive PITA to work on the engine (at least compared to traditional setups). First you remove the cowling. Then you got to disassemble the plenum. Lots more work for a little improvement in cooling.
     
  24. Eric Gleason

    Eric Gleason Pre-takeoff checklist

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    Depends on the engine and installation, but a good plenum design can even out the cooling airflow across all the cylinders as well as improving cooling for all of them a little bit. It can also make for huge decreases in drag because you can use smaller inlets to direct the air where it's needed.

    The designs we're used to looking at on the legacy planes (Cessnas, Beeches, Mooneys, etc.) were really lousy cooling designs. They didn't know any better, so they made huge gaping holes out front and hardly left any place for all that high pressure air to go out. A lot of it just spills out of the front of the cowling. Take a look at LoPresti-designed cowlings, like on the Archer III. They're little tiny holes barely as big as your fist, but they allow the right amount of air in and give it a good escape route.
     
  25. Dan Thomas

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    The Super Cub has cooling issues. Lots of mods have been tried, and someone finally did some tuft testing and air-to-air photos to see what the air was dolng around the inlet. They found that lots of air went into the inlets but much of it spilled back out around the prop hub. The flows were all messed up. It didn't help that there were huge gaps around the starter and alternator as well, upsetting the pressure differential. Some other lightplanes have the same problems.

    The thing with little inlets has a secret purpose. It not only allows just enough air for cooling so that spilling back out is eliminated, but it uses the principle of decreasing velocity/increasing pressure to raise the pressure differential. (Jet and turboprop engines use the same idea to get an initial pressure rise even before the air gets into the first stage of compression.) Those little LoPresti inlets lead into a large plenum to do the trick.
     
  26. nrpetersen

    nrpetersen Pre-takeoff checklist

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    Early small Pipers use wool felt to seal the pressure plenum to the cowl. Breathe through it some time & then tell me what they were thinking.:oops: