Paul, could you please render a new version of the CH-640
 mount(based on the ch-801, but with a lower rear attach
 from oil pan rear over the nose gear strut), utilizing the
 Doddridge plate, Tracey Cook RD1-C, rear lower oil pan
 vibration stabilizer, etc. (basically all the features of
 the final version you sent) but move the plate and engine
 out 6" further from the fire wall to accommodate for the
 use of the RB light weight center and end plates? I spoke
 with Mathieu Heinz when I picked up the wings in Canada,
 discussed the implications of the lighter weight
 installation, and his recommendation was to move everything
 out 6".

 Also could you make notes for me as to the basic
 raw construction materials used, like different tubing
 sizes, IE diameter and wall thickness. I have both Q-Cad
 and Alibre now, so I should be able to read the cad dwgs
 directly.

 Craig Smith

 snips...

 Preliminary motor mount design.

 One of the unanticipated (by me) side benefits of a light weight 200 pound
 (with PSRU & acc.) 250 HP p-port all aluminum engine moved six inches
 forward in the cowl is more room for the cooling system.

 I would also take advantage of the increased net payload by enlarging
 the fuel tanks for more range. Lots of range is a safety factor as
 you could get somewhere and need to go back because of weather.

 You will also need a 3 blade prop to absorb all this HP.

 This airplane is going to blow a lot of peoples minds.
 Excellent short field performance will be all too obvious.

 Paul Lamar

 snips....


 ------------------------------------------------------
 Craig,

 What do you think about bracing the cowl area with a couple
 of 1/2 inch 4130 tubes to feed rear motor mount loads
 back into the longerons under the gull wing doors?

 Just think of it as an extension to the motor mount.

 Then I can use this top rear mount scheme.

 ----------------------------------

 Update 640 specs etc.

 Paul Lamar


 I will be sending you 7 pages from the prints, including FW
 and Fuselage diagrams. I'm not a qualified engineer, therefore
 unable to determine if your alternate solution is safe. Once
 you have a look at the prints, and can determine if the
 structures are up to the task, I would have no objections
 to another approach.
 Soon as I get home, I'll get them out to you.
 C. Smith


 Could you forward these 3D's to your friend at Zenair and
 ask them if they have any objections. Perhaps send me his
 email address and I will do it.

 Paul Lamar


 I am currently considering options for a Mazda 13b lightweight
 engine installation. these drawings represent one of 2 ways
 to skin the cat. the significant modification I seek
 comment on is the addition of the struts at the top
 of the FW to transmit loads back down to the main spar.
 Please review the included discussion. I look forward to
 your comments, as to wheather this is a good idea, and or if you feel
 any changes to improve it.
 Craig Smith
 CH-640 SN 00078


 Craig,
 This installation looks very messy at best and needs to be
 redesigned in my opinion. However, with the drawings you emailed,
 I can not offer a simple solution for you. The top tube going through
 the firewall will damage the firewall as you will have a large
 up/downward load in that area.
 Mathieu Heintz
 Zenair


 What specifically is "messy" about it Mathieu?

 At 100 FPS second take off/climb speed assume the net thrust from the prop
 is 1000 pounds. To put that in HP perspective that would be 100,000
 foot pounds second. Since one HP is 550 foot pound seconds that is
 181 HP net out of the prop. Since the prop eff. is about 80%
 that translates to 226 engine HP. Since max HP is a constant As speed
 increases the net thrust from the prop decreases until the net thrust
 equals the drag at top speed.

 Given 1000 pounds of net thrust out of the prop the top MM strut takes
half
 or 500 pounds. The two lower rubber bushings take the other half.

 error snips.............

 --------------------------------------------------------------------
 I forgot the down load introduced by the diagonal brace tubes.
 I am so used to thinking of firewalls as being rock solid SS devices
 braced by sheet metal cowling's over the instrument panel area.
 This one appears to be free standing from the longerons up.

 There is a moment around point A of 5000 inch pounds so the download
 on the firewall due to the brace tubes is 5000 / 12.25 or about 400
pounds.

 I don't have a dwg on the fuselage so this is just a guess. I do know
 the 801 had a sheet metal channel section riveted to the front of
 the firewall part number 8F7-3 but I have no dimensions on that either.
 My guess it was 2 inches wide with a one inch flange so the total
 width was 4 inches. I am also guessing on the fire wall thickness as being
 .032" thick. If the channel was also .032" thick that would provide a
 column
 roughly 4 inches wide .064 thick or .256 square inches. Compressive
 stress would therefore be about 400/.256 or 1600 psi. Well below
 the buckling stress of a column only 10 inches high. If it were
 a 5/8 diameter 2024T3 tube with .035" inch wall it would
 take 2500 pounds to buckle it.

 The buckling formula is shown in the jpg for anybody that would
 like to calculate the load the column will take.
 E is ten million as I recall for aluminum and L is ten inches.
 http://en.wikipedia.org/wiki/Column

 I is a bit complicated to calculate but not impossible.

 I would be helpful if we had some dimensions on this stuff.

 Paul Lamar

 So, what your saying is with the addition of the 801 specific parts to the
 firewall, it might very well be a viable design. I guess we would need the
 help of one of our 801 builders to identify the differences in the parts
 and
 reinforcements.
 Paul, are the advantages of the top mount strut brace significant enough
 over the lower brace to the nose gear bracket to warrent the effort?
Sounds
 like a bigger mod than we first thought.
 Why not try bouncing the original method off Mathieu?
 C. Smith

 I would not bother. I have seen his of attitude before. Rather

 than suggest improvements he just bad mouths the entire project.
 He obviously knows nothing about rotary engines. I think it is an
 ideal rear mount as it is the simplest and lightest and half the thrust
 is removed from the lower rubber mounts which are not all that
 good in the radial direction anyway. I got the idea from Steve Beckham
 and Everett Hatch as they used to mount their rotaries that way 15

 years ago. They had to beef up the RV firewalls as well. Since the
 engine is six inches further forward the old 801 bottom mount will not
 work well.

 I have a shear and a brake so when you get the firewall send
 me a picture and I will bend up a reinforcing hat section and send
 it to you.

 Paul Lamar

 Very well, I will take some photographs as soon as I can and forward them
 to you. the firewall pan itself is in my hangar. I can't say I fully
 understand all this, but the point about the longer distance changeing the
 effectiveness of the other system makes some sense. Do you need any more
 structural detail from the prints, or has what I have sent enough for your
 needs?
 I'm sorry about the conflict, too bad there couldn't have been more
 constructive comment. I'm sure that when this aircraft shows up in OSH and
 Sun-N-Fun, we will hear a different song.
 C. Smith

 One high performance take off and they will come with hat in hand :)

 This dwg is good. I think I have enough.

 Is the firewall pan galvanized steel? If so that helps as E is 3 times
 aluminum.


 Paul Lamar


 Let me know what dimensions you need, I'll measure them. I've got a
handful
 of suggestions to help the 801 mount fit a little better too.

 I've been installing the connecting arm to the top-center mount point, and
 had to fabricate a different mount attach to the center section to provide
 clearance between the arm and the top of the renesis front section, among
 other things. I'll send photos.

 --Kenny A.
 http://websites.expercraft.com/kennya/

 I think we have it covered by now Kenny.
 Thanks anyway.

 Paul Lamar

Side topic:

Does anyone know if the nose gear is damaged before the firewall in a
bouncy nose-gear landing on one of these CH's? The nose gear should
fail before the firewall. I know that Heinz is a proponent of
tricycle over conventional, so hopefully he got this right...

Matt-


NTSB has 7 reported 801 accidents, 3 of which the pilot managed some kind of
controlled landing. Of those, 2 suffered collapsed nose gears / firewall
damage. One was a 13B.

*N54RX- "Examination of the airplane by the FAA inspector, who responded to
the accident site, revealed that the firewall was buckled, the nose landing
gear was folded under the airplane, and one propeller blade was bent aft."
*
*
*
*N10627 (13B!) - "**The impact displaced the left wing aft, collapsed the
nose landing gear assembly, and buckled the firewall."**
*

--Kenny A.
http://websites.expercraft.com/kennya/

What year and month  was the 13B incident?

Paul Lamar