seb7701

I've been reading like crazy about plenums and especially cowling intakes and exhausts and boy oh boy, isn't there some material out there!!!! It was coincidence that the latest Kit Planes has an article about reducing drag, including intake drag. Turns out there is a bloke out there who is often referred to by the name of David Anders, who appears to be one of the authorities on drag reduction and is the owner of a 220kt RV-4, which I would say is no mean feat. Whilst I best not copyright Kitplanes, these articles include some shots of his plane (and another). Of particular interest are the curvy bits inside the lower cowl to 'arrange' the air prior to it's exit and more relevant still is the cowl exit, which he claims is much better running parallel to the airflow. The icing on the cake?? His outlet is about 75% the size of his INLETS!! His intake is 34 square inches whilst outlet is 26 sq in!!! Happy reading if you're keen, along with a picture of Anders' cowl outlet. Twisted: Cowling design - Part 2

Anyone have thoughts or knowledge of a big one-piece plenum like the green one above?

Hi Derek - hi went to the silicone hose myself, so good to see this one. I have wondered about the pod filter quite a bit, particularly when I've seen then so often on Rotax 912's. Did you find any great changes when you strayed from the airbox? Was leafing through a recent Kit Planes mag and was unsurprisingly intrigued by a plenum setup on a Titan air cooled engine fitted to a Kitfox. Bit like yours I reckon Ken, complete with some big outlets on the rear which I wondered could have been part of a balance hose setup too. Here's the shots.

They're great temps for 30 degrees Bruce, no doubt there. I have done my best to change only one thing at a time, yet sealing the gaps and adding the oil cooler duct were the worst things yet??? Adding the bit in the photo below on the rear of no 4 was similarly pointless and possibly negative in fact! Interestingly my plane only had a CHT ring on no.4 which, knowing what I do now, explains why they appear to have had a heat related incident on no.2 which would be why I just ended up replacing that cylinder the other day. The ultimate quandary is why enclosing my left duct made it hotter and not cooler. Anyhow, I have a replacement 'old style' duct on the table here and will soon dig out the die grinder and open the intake RIGHT up, as 1.5cm off the bottom edge of it dropped around 10 deg off the CHT from memory, so perhaps there will be some more gains left in that realm. Would love to know if balancing the ducts like Ken's really is the go... Also been eyeing off the sonex baffle kit - complete sealing...hmmm.... Sonex Web Store - CAMit/Jabiru Universal Cooling Baffle Kit CAMit/Jabiru Universal Cooling Baffle Kit

Definitely alright Bruce - very nice. What was the OAT on that occasion? I too generally level out from a climb when my no.2 problem child reaches 165deg. On a 30deg day no.1 only sees 116 degrees, so really is some variation among our engines!! Am interesting in the joining of the two ducts by the SCAT hose as per Ken's, but the rest is just odd. My right duct is stock and untouched and doing well. The left side as been recently enclosed as I touched on and made things worse!!! Bruce - what's been your greatest mod? Old or new ducts, opened up intakes?? Spill the beans!!! I am starting to wish there was a Jab get together some time where I could check out some of your aircraft before mine does my head in!!!

No dramas at all Ken, will just take what I can get as you really seem to have the best figures I have ever seen!!!

Oh heck yes Ken, if you do happen to dig up the vid...I have often wished I had a wind tunnel so I could actually see what is going on. Here's a stock intake, so not quite sure but looks a little smaller... Fascinating overall and someone has put in a LOT of work - great to know what can be achieved at least! One last thing - do you have the standard deflector inside the duct coming down over the rear cylinder? What's inside?? Thanks again, Seb

A kit produced from a well respected manufacturer is a good start, such as Vans, Rans, Kitfox etc. who have been in the biz for a long time with a proven track record. That way some of the variables have at least been eliminated, as opposed to a plans build where much more of the aircraft has been put together from parts gathered up by the builder saw them as fit to do the job. As Happy Flyer mentioned, many kits have been lovingly and meticulously completed in a far better manner than any factory aircraft, whilst others...not so much. Just read a copy of 'Kitplane' to see. As an example, I was happy with a kit Jab, as the majority of structural aspects have been completed by the factory, with much less critical aspects left to the builder. (Yes, I know that still leaves lots of other important points, but you get the idea..) Meanwhile, 90% of items such as controls, fittings etc. can be visually checked for manner of assembly, whereas the timber structure inside a fabric covered Fisher Koala's wing might be a bit harder to verify in terms of proper construction technique. At the end of the day, the manner of completion tells the story to a large degree, so a kit aircraft is just fine....depending!! A good LAME or L2 who IS FAMILIAR with the type of aircraft should soon be able to guide as to the manner of completion of a kit plane which could quite possibly meet your budget requirements a little cheaper than some other factory versions. Lastly, as one-track mentioned, a flight with the owner to see how they handle it is also very telling sometimes, as treatment is also everything and a good indicator with a potential purchase. My two cents..

VERY interesting cowl work! Sorry, but there were always going to be some questions!!! 1. Sorry to be painful, but any chance of some rough dimensions of your intakes at some stage (even just the yellow sections)? I took a chunk out of mine, as per the red section in the attached photo, but looking at them both, mine still has a LOT to open up! Interestingly yours still seem to have more material on the bottom of the openings, so I guess the top of your cowls have flared upwards a fair bit? 2. Are there any thoughts on what the insert in the intake is doing (just focussing some flow through the head?) and is there anything similar on the left hand side at all, given the upwards prop blasting on the 'driver' side? 3. Which oil cooler and is it ducted exclusively out the bottom or is all exhaust air mixed in together? The scat joining the two ducts, well that's got me beat, but fascinated... Thanks again!

Thanks Ken!!! Just got back from hols, so hadn't noticed the post but just about to pour over the photos for some solutions!!!!

Thanks Ken - although those temps are almost depressing!! Just goes to show what is possible. All I can say is next time you have the cowl off, I would very much appreciate a few snaps if you have the time, as you obviously have the golden goose of setups with temps like that!!! I would be particularly interested in the lower cowl opening and lips also. Those temps are just a marvel, particularly in terms of how even they are!

Thanks to all of you guys - appreciated. Previously, a lot of the comparison temps were at much lower OAT's. I must say that the first flight today was at 25 and the last at 30deg, by which point the EGT's are now longer as even. I do wonder what effect air density has on the EGT's... My readings got more bizarre as the day went on after 4 test laps with same temps regardless of various mods. Annoyingly, no.4 is now within 2 degrees of no. 2. If it weren't a breach of forum rules, I'd be using profanities by now!!!!!n Just ridiculous when my pax side duct was whacked on stock standard and shows a temps of 116/140 wile the driver's side is was a pair of 160's by the end. New duct in the mail and hopefully will regarding some normality...I am sooooo over this!!!!

Out of curiosity, what CHT's are you guys seeing at 30deg OAT??? I need some comparisons if possible....

You know what the spirit of the legislation is, so why look for loopholes when you know the original intent of the reg,..

--------------------------------------------- Monday - with butterfly added between cylinders and that rear deflector looking thingy OAT 28deg Oil - 92ish #1 110deg #2 160deg #3 141deg #4 151 Today - with oil cooler duct added OAT 29deg #1 116 #2 162 #3 142 #4 160 Oil temp was weird - 92ish, but later saw 100, but it may have not cooled down after a quick climb, so hard to say, but was expecting great things in the oil temp especially. ------------------------------------------------- As a comparison - before getting a new barrel on no2 and modification of the left hand duct to enclose the plug leads, this was a typical set of numbers- OAT 27deg Oil 95 #1 112 #2 154 #3 139 #4 146 Overall - if I can get back to this, I think I'll live with it and concentrate on some more lower cowl mods, which I have played with and shaved a few more degrees off. Oh, and I haven't even bothered to put a fence in front of no.1, but I know it knocked 18 degrees off!!!

Yeah well...don't rush into the duct thing.... Tested briefly this afternoon, with very odd results. No.1 up by 6deg?? (still only 116 on a 30 deg day...it's my golden haired cylinder!) No.4 up around 9 degrees. (which is just bizarre, as it is now within 2 degrees of no.2. They are usually 20 degrees difference.) I am wondering whether the outlet size has something to do with it, given the relatively slim outlet. Might possibly need to tape a big lip just in front of it to see if that get the flow happening or perhaps just chuck it in the bin... It's been an odd week. First I chopped the side out of the duct and enclosed the plug leads (ala picture) which simply jacked up the temp on the back cylinder, rather than helping with some increased volume and reduced leakage with no plug lead holes. I also added a read deflector, which seems to have made bugger all difference also. At this stage it looks like I'll have to re-order and 'old' style duct again, as thing were pretty bearable at least with that configuration. I am at a loss. Here's the outlet area and the modified duct for interest sake.

Well, after some very enticing claims regarding ducting of oil coolers, I spent some time over the past two days knocking up something similar. To say that I am curious as to the effect is an understatement!!! Here's the before and afters...

Not sure about you guys, but I'll be a while racking up 1000hrs, so for the more affordable initial outlay, I fine with the Jab, particularly when it comes to parts costs!!!

Well there you go eh? Only had the pleasure of flogging (and I mean FLOGGING) 1 x '85 350 and 3 x 600's from the 90's and gosh darn, the can't be killed. As such, very popular with contract musterers out here and further, who would probably pass out if they saw their own oil temps some days I would reckon!

Ah-ha, I KNEW you old fellas were talking pre-80's Hondas!!! Lol!!! Love to see a photo of the oil thingy....although even I can't figure out how to post pics at present??? My oil temps is OK, but I have often thought of cheating and whacking in a 6cyl cooler...

Not sure which XR's they were, (have to be one of the very first perhaps?) as they are about THE most bullet proof air cooled bike around since the mid 80's at least, but that's for a different forum I guess!!!

Yep, I know a few blokes still running one CHT monitor on their engines, in which case I guess ignorance is bliss, although that ignorance is what caused others to overheat my no.2 pot once upon a time, as there used to be a CHT ring on no.4 only!! I'm sure VW's and Honda XR bikes are immune to the effects of normal thermodynamics!!!

Agreed, I'm off to ffind some ally sheet to make up an oil cooler duct for sure...just hope I can get similar results!!

HF - so glad you posted the photo as I am looking at ducting my oil cooler at present. Considering you scored what I would call a terrific reduction is CHT's, do you reckon it's a case of directing oil cooler exhaust somewhere a little better, (probably downwards?) rather than randomly in the lower cowl where it can bugger up the downwards flow from the heads etc?

Also on a solid lifter, now with 54hrs on the clock.. The running in oil will definitely affect the oil cooling, so you will get some improvement once you go to W100, but depends on how everything else is set up too as to how good you can get it. I have given myself 'virtual' ambient temp goal of 30 degree ambient temp, which so far I won't be able to fly in, due to my wretched no.2 CHT which on a 30 degree day would have been 156, but now with a fresh no.2 barrel and piston would be more like 161deg, which is close to the limit I use on climb! To add insult to injury, have just modified one of my ram air ducts to now ENCLOSE the plug leads, like the newer ones, only to find a 3 deg increase in the front cylinder and, wait for it...btwn 8-11 deg diff on the rear cylinder!!! Go figure....