Gross Design Modifications

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Well-Known Member
Aug 23, 2004
Ottawa, ON, Canada
As a new comer to this forum, I spent a little time browsing the previous posts and came across a few “scary” threads. One in particular, that was an eye opener for me, was about making some major mods to an afordaplane (in the light stuff category) and asking the question “is it strong enough?”

Here is my reply to the posting:
I would just like to make a general comment/advisory about making gross structural mods as described by adam in the initial post.

I do not advise anyone to undertake such huge changes to kit designs without consulting the original designer or someone who is capable of doing a propper analysis (i.e. engineer).

The question "will it be strong enough?", especially when it comes to the suggested design mods, cannot be resonsibly[/I] answered without a lot of detailed work. You need to know what the loads are before you can even begin to answer questions about strength.

For your own safety, and for the protection of the homebuilt community image, please exercise due diligence with all of your projects and be responsible.

I didn’t write that to criticize or offend anyone. I simply want to help promote safety within the aviation community. If we practice the hobby (career for some) safely and responsibly, then we will obviously make more headway in the promotion of our case when it comes to the governing bodies (and therefore not get hammered with increasing legislations!).

Perhaps some of the more senior/experienced members of this forum can comment on this topic and maybe make some suggestions.



Well-Known Member
Mar 2, 2003
Western Washington
You are right and in providing support to this area I try to get that across to those who ask. It is certainly beyond the capability of this and other forums to answer questions such as "Is it strong enough?". At times this is about the same as trying to answer "How high is up?".

The most I (and others) can do is answer the general questions as best as I can and at the same time try to steer the prospective builders in the right direction. Yes, I do this for a living and so I do tend to "hint" to have myself do the analysis and the design of the modification, but the overall goal of my support is not so much to promote my services but more so to explain that many aspects of airplane design are much more invlolved than what the first glance reveals.

However, although your point of trying to contact the original designer is well intentioned, most folks have found that this is not the most practical approach since the answer you are likely to get most of the time is a rather bursque "NO!". Many plan and/or kit providers reach a stage in their company's growth that pretty much prevents them from expending any more energy in re-evaluating every modification that assuredly many customers might want. All the designer can realistically do is gather the information and questions, and possibly incorporate them into the next product.

As such, if one wants to modify his or her airplane, it is best to find knowlegable and experienced help that is able to do the work to the detail necessary. Only that person will be able to make the judgment call as to how much modification is reasonable and how much work will need to be done to assure the owner/builder that the new configuration will be as good, if not better, than the original.

As such, I'm sure your reply was not taken as a criticism (or at least it shouldn't have been). If your read through some of my responses, there are a few where I tend to be rather blunt, especially where I think the questions are somewhat naive or even flippant. But I think sometimes it is necessary to dump a bucket of cold water over someone's head in order to make sure that their approach is safe and reasonable.