From: "Charlie England ceengland7@gmail.com" <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 21:09:55 -0500
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See Lynn's post from a few minutes ago. :-)

NACA/NASA expended a lot of effort into research on inlet lips; if I can 
find the pertinent paper I'll email it to you, but Tracy used it to 
re-contour his cooling inlet lips & saw, I think he said, 'surprising' 
improvement in cooling. The paper describes one optimum lip shape for an 
internal diffusion duct, and another (more rounded) lip shape for an 
external diffusion duct. My understanding is that this is because there 
is constant 'spillage' with external diffusion, and the sharper the 
transition (lip), the more turbulence you get as the air leaves the edge.

(An extreme corollary to the above is the 'plume' of, for example, and 
exhaust pointed at any angle other than parallel to the free stream. The 
air flowing past the plane sees that plume of exhaust, etc as if it's a 
stick hanging off the airframe. As the freestream hits it, it's forced 
to move around it as if it's a solid object, and there's a big wedge of 
turbulent air aft of that plume.)

Charlie

On 9/12/2019 8:33 PM, Finn Lassen finn.lassen@verizon.net wrote:
> 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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