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Spacer for motor mount?

bret

bret

Well Known Member
I thought I read somewhere, someone placed 5/8" steel spacers in between the firewall and motor mount to move CG forward. I think he was using a Catto prop? Anyone have the engine ARM #s to calculate a formula for engine location? I know folks have used a heavy prop spacer or crush washer-weight but that would add close to 15-20 Lbs compared to 24oz for 3/4" steel spacers.........
 
Be really careful! Moving the mount forward could impact a whole host of other areas - such as cowling fit. How about a Prestolite starter or a steel prop spacer?

Pete
 
bret said:
I thought I read somewhere, someone placed 5/8" steel spacers in between the firewall and motor mount to move CG forward. I think he was using a Catto prop? Anyone have the engine ARM #s to calculate a formula for engine location? I know folks have used a heavy prop spacer or crush washer-weight but that would add close to 15-20 Lbs compared to 24oz for 3/4" steel spacers.........
Click to expand...

Not really necessary Bret. Install the battery on firewall and you will be ok.
 
It's another angle on the problem of light prop and CG in the 7A.Keep in mind your moving the nose strut socket away from the firewall also.The 12" mount gains 2" over the 10" mount wile keeping the firewall attachments in there original location.Sam James will be happy to make you a cowl for this combination.I take it you've given up on the Twin Turbocharged IO-720 driving counter rotating props:D?
 
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Well, I am looking at the ACE IO 379 218+HP :) it only weighs in 250 LBS or so.....that's what 40-60 LBS lighter than the norm. and If I go Catto prop, I will be severely aft CG.....ya? no?.....
 
Spacer

I planned on using a Catto prop , decided on a Hartzell . After flying behind a constant speed prop I'm spoiled . Ditch the Catto and look for a used Hartzell .
The F76666 (-2) blades are very common they are used on Mooneys and Arrows , was the blade Vans used in the past .
 
When I told Vans what I wanted to do,I got shot down I needed the 0-360 cowl but wanted the 0-320 mount 10" vs 12" for the same reason I have a Catto 3B this creates a rear bias CG and less baggage weight.Others have done this mount on the 7 and 7a it doesn't cure the W&B issue but it helps,sorry I don't have any concrete numbers,Chad Jensen gave me the idea when he built his 7 and used the long mount and a Sam James cowl.My engine and prop are here 0-360A1A and Catto sans leading edge guards. Without a finish kit your options are open.
 
Well, I do have the finish kit done except for the long SJ Cawl, I know I read about a 5/8 spacer on here in the past, I made a 3/4" one, 4 oz. I don't think the cowl will be an issue or the spaced mount, heck, they move props out what, three inches, and it's spinning?
 
Engine mount spacer

True enough.If I may ask which mount do you have the 10" or 12"?How much extra space did you have on the back side of your cowl?
 
bret said:
Well, I do have the finish kit done except for the long SJ Cawl, I know I read about a 5/8 spacer on here in the past, I made a 3/4" one, 4 oz. I don't think the cowl will be an issue or the spaced mount, heck, they move props out what, three inches, and it's spinning?
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Isn't there an issue that you'll be putting the bolts in a bending application rather than a pure shear application?
 
bret said:
Well, I am looking at the ACE IO 379 218+HP :) it only weighs in 250 LBS or so.....that's what 40-60 LBS lighter than the norm. and If I go Catto prop, I will be severely aft CG.....ya? no?.....
Click to expand...

That's a dry weight, very dry, no accessories.

If you go the route you plan, your airplane will be a significant departure from Vans plan. Nothing wrong with trying something different, I did it for 5-6 years with Subby engines. It was interesting but stupid from a financial point of view. The money is invested and there is no return except the adventure of doing something different. It is very challenging to make a change that comes out better than what Vans has done - considering cost. The standard build Vans airplane is a compromise cost wise but the end result is a darned good flying machine that people like.

When it comes time to sell and move on a plan build airplane always brings more return of investment than anything else. But of course that is not important if trying something different is more important. Just stuff to ponder....for sure the RV-7 does not need much more lHP than it has for good flying qualities.
 
David-aviator said:
That's a dry weight, very dry, no accessories.

If you go the route you plan, your airplane will be a significant departure from Vans plan. Nothing wrong with trying something different, I did it for 5-6 years with Subby engines. It was interesting but stupid from a financial point of view. The money is invested and there is no return except the adventure of doing something different. It is very challenging to make a change that comes out better than what Vans has done - considering cost. The standard build Vans airplane is a compromise cost wise but the end result is a darned good flying machine that people like.

When it comes time to sell and move on a plan build airplane always brings more return of investment than anything else. But of course that is not important if trying something different is more important. Just stuff to ponder....for sure the RV-7 does not need much more lHP than it has for good flying qualities.
Click to expand...

Thanks for your insight, so why did you remove the subi? The ACE engine is not an auto engine, it is in the same class as other Lyclones out there, except that these will run on non 100LL. Sure the cylinders are only a couple years old but seam to be doing well. The counterbalanced crankshaft is stronger than Lycoming and the EFII system is proving to be a winner also. If the cylinders end up not working, we can bolt on another brand right? So as far as a total waste of money, the only risk is the cylinders. I have wasted WAY more in other hobbies, well, maybe not a total waste........(Brake Out Another Thousand)
 
Mogas the answer...

bret said:
Thanks for your insight, so why did you remove the subi? The ACE engine is not an auto engine, it is in the same class as other Lyclones out there, except that these will run on non 100LL. Sure the cylinders are only a couple years old but seam to be doing well. The counterbalanced crankshaft is stronger than Lycoming and the EFII system is proving to be a winner also. If the cylinders end up not working, we can bolt on another brand right? So as far as a total waste of money, the only risk is the cylinders. I have wasted WAY more in other hobbies, well, maybe not a total waste........(Brake Out Another Thousand)
Click to expand...

Use 8.5/1 cylinders and you can use all the non-ethanol 92 oct. mogas you want, currently 3.80/gal around here. I used it for years, never a problem, equal performance to 100LL in an IO-360 Superior who recommended same.
 
Kyle Boatright said:
Isn't there an issue that you'll be putting the bolts in a bending application rather than a pure shear application?
Click to expand...

Yes.

At the very least the bushings should be as large in diam. as possible and the center hole should fit the bolt as closely as possible.

Even then I would never do it and I am not sure it is necessary. I am very doubtful that the weight difference is as much as posted here. Even if the 250 lb is correct (which I wonder how it is possible with a counter weighted crank), that is only about 30-40 lbs lighter than a typical (I)O-360.
 
The one test spacer I made is 1.25 dia, to match the engine mount pad, and with a 3/8 center hole. it would still be in shear, double shear like the washer that is SPACING the two lower center mounting pads. still looking for that RV 7 that has the 5/8" spaced motor mount. he is here somewhere, does anyone here remember his post? I've only been here five years so....
 
Even at 2" you gain some movement but still not enough compensation to load 100 pounds behind the spar with low fuel. I just found this clip of the last time Bret filled up with ethyl! https://youtu.be/CPnwlNvwBLI It caused some commotion south of Fresno.:)
RHill
 
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Give Vince a call and see what he says,N540VF is a modified 8 and doesn't have the nose gear to contend with,neither did Chads 7. Two and a half years later I'm still looking for a new unwanted 12" mount,my concern is the added force if any on the nose gear.It is tight,changing oil filters with the 10" mount and adding all that extra weight to the crank defeats the advantage of a lightweight prop.IMHO
 
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