Marty d's CH-701 build log

[IBob]

You're welcome to ask whatever you wish, Marty. I'm not particularly knowledgeable, and in this case I'm just putting together the bits in the box.

 

1. Yes, those are rubber bushes, with a steel sleeve up the centre. The ring (white) and other bit (black) arrive already assembled, and packed where they are bolted together with washers, to give appropriate alignment: this is done in a jig at the factory, presumably they vary some after welding. There's not much give in those rubbers, so I assume the black frame needs to be strong, and also rigidly mounted to the aircraft.

 

2. The curved lower member is to allow room on that side for the oil tank, which mounts to the flat plate.

 

Cheers, Bob

 

 

 

 

 

 

[Marty_d]

Thanks Bob... this stuff is gold. It's great to see how that bit is constructed.

 

So where the rubber mounts go through, that would be a segment of tube welded in. Just had a look at Aircraft Spruce and there's a variety of rubber mounts around. I'm going to have to research this a bit more for sizes etc.

 

 

[IBob]

You're welcome.

 

1. Where the bolt goes through the ring mount (white) there's a small diameter tube welded through the ring mount, so that tightening the bolt does not distort the ring mount tubing.

 

2. Where the bolt goes through the black frame, yes, there's a segment of bigger welded tube, which takes the rubber shock mount. The shock mount itself look very much to me like what you get in car auto suspension on the end of the shocks. And they're a tight fit in there: having counted the washers etc, I disassembled the white from the black for painting and had to mask round the rubbers as I was unable to withdraw them with moderate force.

 

The segment of black tube is 38mm OD and 25mm long, with a wall thickness of approx. 2mm (I cannot get at that to measure it). The bolts are AN5.

 

3. The bolts attaching the black frame to the fuselage are AN4 at top and bottom, and AN5 at the sides.

 

4. The manual says the packing washers between black and white frame are adjusted to give 0 to 2deg downwards with reference to the rear upper fuselage, and 2deg to the right plus/minus 1 deg.

 

My setup has 2off AN5 washers in each of the LH mounts, and none in the RH mounts.

 

 

[Head in the clouds]

Thanks Bob... this stuff is gold. It's great to see how that bit is constructed.So where the rubber mounts go through, that would be a segment of tube welded in. Just had a look at Aircraft Spruce and there's a variety of rubber mounts around. I'm going to have to research this a bit more for sizes etc.

Yes, gold it is ... gather all the information you can before you get to the engine mounting process Marty. In fact if you can buy a mount, at any price and even if you have to modify it, I'd recommend that, I found the build of the engine mount to be the most difficult and most frustrating part of my entire DooMaw project, so far. There's just so very little space to play with, even fitting the ring mount itself to the engine is quite a tricky job and requires a fair bit of disassembly at the back of the engine, I also had to buy and fit new water inlet/outlets to the waterpump, available from Floods.

 

Also - it would seem logical enough to just prop the engine where you want it and tack the mount together, but by the time you have the ring-mount on the engine it's so buried behind 'stuff' that it's hard to get anywhere near it to weld anything, not that you'd want to in case you harm parts of the engine ... not saying it's impossible but it's tricky.

 

In the end I was able to get a 3D CAD model of the 912 from a fella in Russia (I can get his permission to share it with you if you can make use of it) and that provided me with the positions of the mounting holes on the engine (they're also provided in the 912 installation manual in x,y,z format) then I built a crude adjustable threadbar jig to hold the ring-mount in place. I'd made up aly facsimiles of the rubber mounts to bolt the receivers to the ring-mount (so I could weld without melting rubber), and had modelled the whole mount in CAD and pre-cut and coped the tubes - it's on Page 12 of the DooMaw thread if it helps.

 

Here is a link to the Vibration mounts, this is where I bought mine, they're generally known as Universal Mounts. I bought three sets in different durometer rubbers so I can try harder or softer ones and see which produce the best damping at cruise revs. Note that these ones have a 9.9mm hole in the inner sleeve, to suit 3/8 bolts, whereas IBob said his are 5/16, so you need to check your ringmount to see what size the holes are, my ring-mount has holes about 10.5mm so I could use 10mm or 3/8 bolts.

 

Regarding the receiver for the rubber mounts, it's like a piece of tube with a washer welded inside it, although it's not welded, they're machined from a piece of solid. You can see them in the last three photos in this post. If you need a better resolution picture send me your email address by PM.

 

Hope it helps.

 

EDIT - if you order anything from Vibration Mounts they tend to send by USPS expedited which costs about US$70 so talk with them about cheaper ways if you're not in a hurry and/or let us know you're ordering and others may want to buy stuff too and share the cost. If you want any kind of rubber mounts for your exhaust, instrument panel, ute toolboxes etc, they have everything you can dream of.

 

 

[IBob]

I can certainly imagine the process you describe, HITC.

 

And at this point, it may be worth asking what is so wrong with the old style bed(?) mount, for which there presumably are dimensioned drawings available?

 

A friend here has a VG Savannah with the old mount, and while the engine moves a bit, it's a very good aircraft, and that arrangement seems to work fine...

 

 

[Head in the clouds]

I can certainly imagine the process you describe, HITC.And at this point, it may be worth asking what is so wrong with the old style bed(?) mount, for which there presumably are dimensioned drawings available?

 

A friend here has a VG Savannah with the old mount, and while the engine moves a bit, it's a very good aircraft, and that arrangement seems to work fine...

I think the bed mount is superior in many ways. Though they're rather more susceptible to transmitting vibration to the airframe through the rubbers because the rubbers are often oriented so that the attach bolt is vertical i.e. the engine is sitting on the rubber instead of suspended off the side of it, and if you orient the rubbers with the bolt horizontal coming in from each side, then one side's rubbers tend to fight the other side's. That's where the dynafocal mount concept comes into its own, but they're even more difficult to fabricate because they're only geometrically 'right' when the bolts are tightened so they tend to be mechanically 'locked' when you're trying to assemble or disassemble them - or to fabricate them unless you have a jig.

 

An even better mount than the bed mount is on the Foxbat where it's effectively a three point attachment and to get at the difficult bits at the back of the engine (flywheel, magnetos, water pump etc), all you do is disconnect the top mount from the gearbox and the engine hinges down. I wished I'd seen that one early in the design process of DooMaw, I would have adopted it.

 

 

[IBob]

"........but they're even more difficult to fabricate because they're only geometrically 'right' when the bolts are tightened so they tend to be mechanically 'locked' when you're trying to assemble or disassemble them - or to fabricate them unless you have a jig."

 

I'm wanting to more clearly understand what you are saying there, HITC.

 

What do you mean by "mechanically locked when you're trying to assemble or disassemble them"?

 

Thanks.

 

 

[Head in the clouds]

Google Dynafocal mount ... the mounting bolts all point in towards a focused point so you can't move the engine back or forth until you remove the bolts and rubbers individually because the bolts' longitudinal axes are not in line of draw.

 

 

[IBob]

Ah thanks...I had thought you were referring to the ring-mount.

 

 

[Marty_d]

Got the noseleg on today. (For tailwheel pilots - that's the bit that holds the full-size third wheel....)

 

 

 

 

[Marty_d]

Wheels on!!

 

After a marathon shed-cleaning exercise (5 days worth, it hasn't been cleaned out properly for 10 years...) I hoisted the plane from the roof beams and this morning got the gear mounted.

 

Is there a specified celebration for when a plane gets its undercarriage on for the first time? Scantily clad maidens dancing around waving rosemary or something?

 

Credit must be given to my son Harry (8) who came down to the shed before he'd even had breakfast, held one side of the main gear up, and put on the nuts and got them started.

 

 

 

 

 

 

 

 

 

 

[IBob]

Magic moment! And congratulations. I think, once the maidens have departed, you're supposed to put the seats in and sit there, flexing your imagination???

 

This is a little way off for me yet: when it comes to spray-guns, I need all the help I can get, so I've left the U/C off so that I can rotisserie the fuselage.

 

But.

 

I saw nifty timelapse Sav build the other day...in Iceland, i think...and to put the main U/C on they turned the fuse over and sat it on the cockpit steelwork. Which was definitely different...)

 

 

[Kyle Communications]

Flexing your imagination means sitting in it making vroom vroom noises

 

 

[Old Koreelah]

A great achievement, Marty. Not the wheels- that’s easy. Cleaning out the shed is harder than divorce.

 

 

[Marty_d]

The maidens haven't even turned up and the seat bottoms aren't in yet...

 

 

[Marty_d]

A great achievement, Marty. Not the wheels- that’s easy. Cleaning out the shed is harder than divorce.

Yes, but now that SWMBO has seen it all clean, she's making plans to convert it into a bedroom. Divorce may be on the cards after all...

 

 

[M61A1]

You can use that to your advantage.......It can't be a bedroom until the plane is completed. You might have to spend more time, money and effort to get it done sooner.

 

After that you may need a bigger shed down the back somewhere, don't forget to negotiate that.

 

 

[eightyknots]

Great stuff Marty!

 

Crack open a champagne.

 

 

[nomadpete]

I don't believe it. That can't really be your shed. You must have Photoshopped it.

 

 

[Marty_d]

I don't believe it. That can't really be your shed. You must have Photoshopped it.

I know, it's hard to believe. Drop in next time you're going past Peter - see for yourself!

 

Picked up my rivets from the post office today - courtesy of Aircraft Spruce. So this evening was spent happily riveting most of the front end, it's gone from looking like an echidna, to an echidna with a crew cut.

 

Now that all the underneath rivets are pulled, I decided to lower her down from her eyrie and she's sitting on her wheels. Judicial placement of an almost-full 10L tin of ceiling white is providing enough weight in the front end to keep the rear end off the floor.

 

She looks pretty level, not sure at this stage whether to leave those tyres on or get larger ones - having read some of the horror stories when it comes to Savannah wheels I'm not real keen to muck around with them!

 

 

[IBob]

I know, it's hard to believe. Drop in next time you're going past Peter - see for yourself!Picked up my rivets from the post office today - courtesy of Aircraft Spruce. So this evening was spent happily riveting most of the front end, it's gone from looking like an echidna, to an echidna with a crew cut.

 

Now that all the underneath rivets are pulled, I decided to lower her down from her eyrie and she's sitting on her wheels. Judicial placement of an almost-full 10L tin of ceiling white is providing enough weight in the front end to keep the rear end off the floor.

 

She looks pretty level, not sure at this stage whether to leave those tyres on or get larger ones - having read some of the horror stories when it comes to Savannah wheels I'm not real keen to muck around with them!

Savannah Wheels Horror Stories.........is this something I need to know???

 

 

[eightyknots]

Savannah Wheels Horror Stories.........is this something I need to know???

...and me? I haven't heard of any major issues with Savannah wheels!

 

 

[Kyle Communications]

Only a problem trying to fit the std tyres onto the rims on the sav kit. My 600-6 tyres fitted a breeze

 

 

[IBob]

...and the problem of moving the valve hole like the manual says...then moving it back if fitting the 600-6 Condors, as the bead is very heavy and fouls the moved hole.

 

I don't know if this is the case with other 600-6 tyres???

 

 

[IBob]

Don't the tyre folk have some miraculously slimy compound for fitting tight tyres???