Integrating alternative engines

[thomaswimmer]

Hi,

Question to you guys who integrated a non-standard (ie. non-Lycoming/Continental) engine into their RV:

• How do you manufacture the engine mount? Use the supplied one from Vans and modify it or start from scratch?
• How did you set the offset angle of the thrust line in the horizontal plane (the english expression escapes me)?
• What did you not end up using from the finish kit?
• Did you do any reinforcement on the fuselage for a heavier engine?

Thanks,

Thomas

 

[WAM120RV]

Engine mount.

Hi Thomas

1. Generally start fro scratch but I guess if the there
were only minor differences in the engine a mount could be modified.

2. You have the firewall a a starting point, the dimensions of the engine are known. The thrust angle is a known.You therefore just have to factor in the weight of the engine to get the C of G right, for what might be a lighter or heavier engine. All these combined give you a point in space from the firewall for where you want the centreline of the prop hub to be.

Another important consideration is that the new mount puts similar loads onto the airframe, in the same places as the original mount. The firewall is designed to carry these loads if you put the loads anywhere else or overload a mounting point, you could have to re-design the airframe itself. We ran into this problem when the mount for the Wilksch was originally designed.

3 Virtually everything firewall forward.

4. Refer to the answer above. Simple really, if you put more load there there is a question mark over whether the airframe can take it.

A thorough stress analysis is vital especially if you are going to do aeros. We supplied all of the stress calcs to Vans for the Wilksch mount which showed very similar load paths and loads to the standard lycoming mount. Vans were happy to give us a letter of no technical objection which helped the mount gain approval in the UK.

 

[rv6ejguy]

If your engine installation will be much more than about 10% heavier than the original, you should certainly look at possible reinforcement of the pickup points in the fuselage and absolutely so if you intend to do aerobatics.

As a general point, it is probably not a good idea to install an engine package which is a lot heavier than the standard Lycoming, it just creates many more issues for you. You certainly need an accurate weight and C of G for the engine/ gearbox/ prop you intend to use plus dimensions and I'd say you should not start at all until you have everything in the flesh, rather than just drawings.

It does not hurt to use the longest available cowling in most cases unless your engine is a very different shape and you need to custom build that too.

Since the gear mounts are integrated into the engine mounts on RVs, it is often easier to use these portions of the stock mounts, cut off what you don't need and progress from there. If you go this route, try to ask for a non- powder coated one as this will save you many hours of stripping. The gear mount spigots are very precise and hard to duplicate without distortion during the welding process.

As far as getting all the angles right, this takes a lot of time to set up. For my RV10, I built a special stand to hold the entire engine and gearbox from the prop hub while measuring and mating to the fuselage, others have done it vertically on a firewall mockup. Neither is really easy or fast.

Here is a link from my old RV6A project page which shows some details of the process: http://sdsefi.com/rv4.htm

You may find this page on isolators useful too: http://www.barrycontrols.com/products/product.cfm?cid=1&fid=47

I'd be interested to know what engine you are contemplating?