I consider my project to be more “owner assembled” than Experimental. I don’t write plans, I follow them. But is it OK for me to go off-plans? Can I add modifications? The simple answer is, yes. No matter what I call my project, it is still Experimental, which gives me some leeway in the way my final project will look and feel. Even the new guy can make modifications, but I never do that by myself. Here are 10 tips about mods and going off-plans:
1. Going off-plans adds significant time to your project. Even small changes will add to your build time. My avionics tray cost me three weeks, but I love my avionics tray.
2. Does the modification affect safety of flight? I never go off-plan on these mods. My plane has magnetos and a carburetor. I’m really overly cautious here. Keep safety issues at the top of your list.
3. Some mods are wishful thinking. More speed? Better economy? Lower operating costs? These can cost time and money and not give you the results you expected. Do your research and listen to advice from flying projects.
4. Remember, weight is the enemy of flight. Consider the weight penalty of your mod. These build up over time, so one modification might not make a difference, but many can.
5. Is saving money a good reason to go off-plan? Think about the long-term impact of saving a few bucks. Using cheap electrical connectors is not a good idea. Using an automotive alternator? That’s OK with me. Lots of flying planes do that, and there are lots of examples where the automotive industry has advanced and the aeronautical world has not. But never save money if it affects safety of flight.
6. Is this a well-documented modification? Are there many examples of this mod flying? This is not really going off-plans, it is just a plans addendum.
7. Is the mod a kit I can buy that many others have already done? My nav lights fall into this category. LED lights for wings and tail that many others have used will be a great update to my plane. It will save a few bucks and a few pounds as well!
8. Be sure you understand the maintenance implications of an off-plans modification. Does it need extra work at condition inspection time? Does this mod have a limited service life?
9. Is the modification legal? Just because it’s an Experimental aircraft doesn’t mean you have carte blanche freedom. Using bolts from the local hardware store or building your own transponder may not get you past inspection. For some mods, getting in touch with a DAR early may be a good idea.
10. If going off-plan involves a new vendor, do your homework. Make sure they are going to be around for support. If not, can you support this mod yourself?
The parking brake valve is pretty important to me, and I’ll add it to the annual condition inspection checklist.
Building an Experimental aircraft is possible even if you are not an aviation engineer. Thousands have done it! Modifications are a natural part of the process and even expected in certain areas such as avionics. When considering modifications, keep safety as the top factor, then add cost, time to build, performance, and cool-factor after that.