From: "Finn Lassen finn.lassen@verizon.net" <flyrotary@lancaironline.net>
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Subject: Re: [FlyRotary] Re: Intake progress
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
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Date: Thu, 12 Sep 2019 21:33:26 -0400
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I think I'll go with the plywood box: :)
Tracy also told me that it's better to go with too big an inlet opening 
and external diffusion will take care of the rest (given no leaks in the 
ducting, of course). So he also seems to be a believer in external 
diffusion.

I think I'll take your route and extend throttle body opening all the 
way out to the prop.

Something I don't know: You see those nicely rounded edges on inlet 
scoops. Is that just for looks or does a stove pipe directly into the 
wind cause some turbulence around the pipe edges? (Here I'm thinking of 
the 6" inlet to radiator under the engine sticking out the way out to 
the prop, but should also apply to oil cooler inlet and engine air intake.)

(OK, I should probably spend a week or four studying Hoerner, etc., but 
I'm lazy and it's so much easier to just ask here :)

Finn

On 9/12/2019 8:59 PM, Charlie England ceengland7@gmail.com wrote:
> My '1st draft' (before the box) was a 6 " aluminum tube (irrigation 
> tubing) that I re-contoured into a wavy contraption a little closer to 
> flat where the bellmouths faced. 1/4" aluminum plate for the ends. 
> That looked questionable, so I went worse. :-(?? I would expect a 
> round tube with 1/4" end plates to handle the loads, but I haven't 
> proven it.
>
> On intake size, most of the stuff I've read addressing both induction 
> air and cooling talks about taking in every bit of the air needed and 
> no more, because trying to take in more than needed either adds drag 
> as the extra air flows through the plane's systems, or adds drag due 
> to spillage & turbulence around the lips of the intake. Achieving that 
> goal is a pretty high bar, though, given the wide speed variations of 
> fast a/c. Bernie Kerr (Hi Bernie, are you still watching?) used to 
> talk about 'external diffusion' (as opposed to internal diffusion, 
> where the air enters the duct at system airspeed and slows within the 
> duct), which apparently works well by slowing the air in front of the 
> duct and minimizes spillage losses by optimizing the lip of the 
> entrance. Apparently has the additional advantage of making duct shape 
> less critical.
>
> You can calculate the volume of air the engine ingests per second, 
> then calculate the intake size required to take in that volume of air 
> per second, all at expected operational speed. I suspect that's what 
> Tracy did. I chose the easy (lazy) way out & sized the inlet the same 
> as? the throttle body/total intake tube area, and am willing to accept 
> 'external diffusion' spillage at speed.
>
> Or, like Lynn often says, I could be wrong. :-)
>
> Charlie
>
> On 9/12/2019 5:47 PM, Finn Lassen finn.lassen@verizon.net wrote:
>> Thanks Charlie,
>>
>> I was planning on using 1/4" plywood wrapped in fiberglass. (Tracy 
>> had warned me.) I do have a length of 6" OD 0.035 SS pipe, but what 
>> about the ends (or end opposite throttle body)?
>> I can weld SS with my Henrob, but no success with aluminum. Also the 
>> curve of the pipe would make me shorten the intake runners a bit to 
>> make room around the bell mouths.
>>
>> I started reading the grapeape-inductionsystems.pdf paper and 
>> realized that's going to take quite a bit of study and research. Like 
>> what is the VE (Volumetric Efficiency) of a Renesis?
>>
>> Seems I start with the best intentions to design the optimal 
>> installation and end up copping out and doing "looks about right" or 
>> "what he did".
>>
>> Like, I have no clue how big my air intake opening should be. Just 
>> the size of the throttle body? Tracy mentioned something about the 
>> air intake should gradually open up to the size of the throttle body. 
>> I should now have plenty of room in the left cheek for a straight run 
>> from near the prop to the throttle body mounted on the plenum (shoe 
>> box).
>>
>> Finn
>>
>> On 9/12/2019 5:26 PM, Charlie England ceengland7@gmail.com wrote:
>>> Like most people's dad used to say, "Don't do as I do (did); do as I 
>>> say." :-)
>>>
>>> Tracy looked at my box after it was built & pointed out what I 
>>> should have considered: those big flat (thin) aluminum panels won't 
>>> survive intake pressure waves. I knew better, but that part of my 
>>> mind had gone on break during the entire construction of the box. 
>>> Car makers don't waste aluminum making cast 1/4" thick plenums just 
>>> to get rid of surplus aluminum. :-)
>>>
>>> That box is now lined with 1/4" plywood and fiberglass, and weighs 
>>> far too much. I'm doubtful that it will be a flight item.
>>>
>>> I'd suggest doing what Tracy did, & start with plywood/fiberglass, 
>>> or use a 4"-6" round aluminum tube for the plenum. I can probably 
>>> dig up some 6" if you want to try it, or check local farm-market 
>>> publications down there for surplus irrigation pipe.
>>>
>>> I never did find any tube length/plenum sizing advice for the rotary 
>>> that I trusted. Very few Renesis car guys ever touch the stock 
>>> manifold, since it would be very difficult to improve on Mazda's 
>>> design for a car.
>>>
>>> Charlie
>>>
>>> On 9/12/2019 12:02 PM, Finn Lassen finn.lassen@verizon.net wrote:
>>>> 6 1/2 years later I'm about to do the same and would like to ask 
>>>> the same question before I make my "shoe box":
>>>>
>>>> "I'm curious about how others have adapted the common Helmholtz 
>>>> intake tuning formulas to the rotary. Would anyone care to 'show 
>>>> their (math) work'?"
>>>>
>>>> Rather than building it as big as possible, I'd like to know if 
>>>> there is an optimal size.
>>>>
>>>> Finn
>>>>
>>>> Charlie's photo:
>>>>
>>>>
>>>>
>>>> On 2/17/2013 3:41 PM, Charlie England wrote:
>>>>>
>>>>> Now that everyone's awake again, I thought I'd send a pic of my 
>>>>> intake progress (RV-7 Renesis with James Lyc cowl). I played with 
>>>>> a couple of different materials for the bell mouths. I tried 
>>>>> gluing up some 1/4" plexi from an old windshield, but used super 
>>>>> glue instead of proper plexi cement (which I wasn't able to find 
>>>>> locally in a hurry). The 1st try popped apart on the lathe; the 
>>>>> 2nd turned out ok. Next effort was with 3/4" MDF (medium density 
>>>>> fiberboard). That went well, until I put a little too much side 
>>>>> pressure on the ring (homemade cutting tool) after undercutting 
>>>>> the center section. Overall tube lengths will be ~11 3/4" block 
>>>>> surface to bell ends. The plenum is *much* bigger than most tuning 
>>>>> sites recommend. I figure that I can experiment with plenum size 
>>>>> by just stuffing it with rigid foam to take up some volume, if 
>>>>> needed. Going the other way wouldn't be so easy. :-)
>>>>>
>>>>> Since I don't have Mark's TIG skills, I thought I'd ask what 
>>>>> others have used in joining thin wall tubing to 1/4" aluminum 
>>>>> plate. Aluminum brazing rod? High temp epoxy? JB weld? I do intend 
>>>>> to add bracing from the plate to the plenum assembly to take some 
>>>>> of the cantilever & vibration stress off the tubes.
>>>>>
>>>>> I'm using this length and concept because Tracy has had great luck 
>>>>> with both HP & BSFC on his Renesis with a similar configuration. 
>>>>> However, I'm curious about how others have adapted the common 
>>>>> Helmholtz intake tuning formulas to the rotary. Would anyone care 
>>>>> to 'show their (math) work'? Renesis users would be better for me, 
>>>>> but any calcs would do. When I tried to adapt the common formulas 
>>>>> to a rotary, I was getting 'interesting' results, so I'd like to 
>>>>> know if I got lost somewhere while trying to plug rotary 'valve' 
>>>>> timing into the formulas.
>>>>>
>>>>> Charlie
>>>>> (Sorry for the sideways iphone pic; I guess you can pretend that 
>>>>> you're looking down on it...) 
>>>>
>
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