Mailing List Message #66052
From: Charlie England <>
Subject: Re: [FlyRotary] FW: [FlyRotary] Re: Aviation Specific 13B/20B Mazda Front Side Housing-pics
Date: Thu, 9 Jul 2020 13:07:55 -0500
To: Rotary motors in aircraft <>
That's actually a dynafocal mount. 'Conical' is the nonsensical term for all four mount surfaces being parallel to each other. Think small Continental 4cyls, and early Lycs (and their helicopter engines).
Dynafocal on left; conical on right. Perhaps the 'conical' term originates with the rubber components. the rubber parts of a dynafocal are basically flattened donuts, while the rubber parts of a conical mount really are cone shaped. the 'focal' in dynafocal refers to the extended lines of the four mount bolts converging to a single focal point inside the engine mass. When configured properly (rare occurrence these days), the focal point is at the CG of the engine/prop package. Hence 'type 1' & 'type 2' mounts; type 2 has a shallower angle and was used in some twins that used extended hub c/s props, which shifted the CG of the engine forward.

The pics that came through do look like Mistral stuff, but Kelly is a lot more familiar than I am.

I think that the total message size is limited to around 200KB, so image size somewhere under 130K usually makes it through. Depends on how much other stuff is in the body of the email.


On 7/9/2020 12:38 PM, Marc Wiese wrote:


Great stuff. I saw and read that Kitplanes article with great interest back when.

Here’s some conical mounting back plate pictures I found on my hard drive, I believe they are all Mistral, but don’t know where they came from originally (perhaps Paul Lamar’s group) One is a 13B named ‘Steve’. Hopefully these pics get thru-there is a picture limit on this list that makes it difficult to send larger files, so I didn’t send all of them I have just of the backplate, what is the MB/KB limit here?



From: Rotary motors in aircraft
Sent: Thursday, July 09, 2020 1:28 AM
To: Rotary motors in aircraft <>
Subject: [FlyRotary] Re: Aviation Specific 13B/20B Mazda Front Side Housing


Le Roux,

    Thanks for digging this up as it will answer a lot of questions from the group..........This was the final iteration of "Mistrals" alloy side housing / accessory drive

that was headed for US & European certification.........It incorporated the "30 Degree/#1 Dyna Mount Ears" for the Lycoming O/IO 540 engine mount..........This is

what this thread is all about..........My friend is attempting to come up with a less expensive version of this plate but without all the accessory drives and using the

stock RX 8 front cover with stock water pump and ignition pickup (electric airplanes)............Photos are worth a thousand words..........

Thanks Again,

Kelly troyer  


On Thu, Jul 9, 2020 at 12:24 AM Le Roux Breytenbach <> wrote:

Kelly : Just saw this on the archive on our group thread you post in April 2011  




Dating back to April 2011 that you have post regarding the Mistral mounting here you post some photos of the Mistral dynafocal set up and mounting

Here is the article of Paul Janssens Glasair 111



Le Roux


On Thu, Jul 9, 2020 at 6:35 AM Kelly Troyer <> wrote:

  Dave & Charlie,


    Only the early "Mistral" 13B/20B based engines used the bolt on front cover/accessory drive alloy cover that had mount points that used the Lycoming O/IO 320-360 "Dynafocal Type 1" mount ring.........I know this

as fact as I am the proud owner of one of these alloy housings.........I have all the housings and parts to build a bastardized part alloy "P port" 13BREW engine.........I retained the cast iron front (Rear in tractor A/C) 

side housing because I was not comfortable having my engine hang on its mounts from a housing attached only by several 6 mm bolts threaded into a cast alloy "Racing Beat" front side housing.........All the other

housings (Center & Rear) are alloy "Racing Beat"..........The earliest "Mistral" 20B engines also used this alloy front cover but also had mount points at the redrive end of the engine (Essentially a Bed type Mount) and

only used the bottom two mount points on the accessory end of the engine.........At that point in "Mistral's" engine development the engines they sold to experimenters were basically "Mazda" engines and all their parts

were directly adaptable to a stock "Mazda" engine (such as my engine)............The last iteration of their engines were designed to be certifiable so they had to have a verifiable manufacturing trail..........So they made

engineering changes in their parts to eliminate things about the stock "Mazda" parts that were not needed or were improvements for aircraft use..........Most of the last versions of their engines had parts that were not

adaptable to the stock "Mazda" engines...........Long winded but perhaps will enlighten some about the "Mistral" series of engines..........



Kelly Troyer    


On Wed, Jul 8, 2020 at 10:45 PM Kelly Troyer <> wrote:

Charlie and Mark,

     Yes Charlie the accessory "iron" side housing is what would be replaced with an aluminum housing with built in mount points that replicate the Lycoming O/IO 540 mount ears and locate the Mazda eccentric 

shaft centerline in the same place as the Lycoming crankshaft centerline and make the Mazda a bolt in to any aircraft using the O/IO 540 30 degree "Dyna1" mount system.............


     Mark I am well aware of the different opinions on using the rear dyna focal mount on the Mazda.........Bill is correct about the need for .500 in/12.5mm studs and a stiffening plate and/or rigid oil sump to

further resistance to torsional twisting..........But remember that the O/IO 540 family of engines with firewall forward weights of 400+ to over 500 lbs for some turbo models are all using this mount system and

that an all alloy 13B or 20B (even with reduction drive) will be much lighter..........I do not believe that the "Mistral" 13B or 20B used alloy housings for other than the front accessory housing and I have never 

heard if they used the oversize .550 inch/12.5 mm studs in any of their engines..........This is probably a question that will have to be proven one way or another in actual use..........IMHO


Kelly Troyer


On Wed, Jul 8, 2020 at 5:49 PM Marcus Wiese <> wrote:

Wonder why Mistral used dynafocal type mounting on their 13b and 20b designs?


Sent from my iPad


On Jul 8, 2020, at 12:11 PM, William Jepson <> wrote:


The "dynafocal" type mount has been tried on the rotary but has not worked out well..One of the obvious rotary traits is that it has a hot and cold side. Various methods have been used to limit this but there is no way to eliminate it completely. Because of this the engine tends to "work" and move around on the studs. Using the engine as a stressed member is not recommended with the rotary. If  you were to do this anyway I wouldn't do it without a stud kit. You will have better results using a bed mount. YMMV

Bill Jepson


On Wed, Jul 8, 2020 at 1:18 AM Kelly Troyer <> wrote:

I am in contact with a person with the design and manufacturing capability to produce an Aviation Specific 13B/20B Mazda Front Side Housing machined from 7075-T6 with mount points that would allow these engines

to be a bolt in to the engine mount ring (30 degree number 1 Dyna) as used by the "Vans" RV-10 and other aircraft that use the Lycoming O/IO 540 engine..........This side plate is in the preliminary design stage and at this

point I am a go between to see if there would be any interest in this product if and when it is produced...........I personally am interested this side plate........As we on this forum know both the 13B / 20B are capable of truly

amazing power levels both naturally aspirated and turbo boosted.........The 20B would make the Van's RV-10 , Glasair 3 or Lancair's that use the Lycoming O/IO 540 an easy 300+ hp almost bolt in engine...........

The "Reno" Sport Class "Glasairs" and Lancairs" are producing almost 400 mph speeds using dual turbo Lycoming IO-550 engines that are virtual hand grenades pulling over 700 hp...........There are turbo 20B's pulling

1200 hp out in the auto racing world with good reliability..........A 20B boosted to 700+ hp is not even breathing hard.........IMHO

Would like to hear what interest there may be in this product if and when it may be produced............Or any comments pro or con..............



Kelly Troyer





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