Thatcher CX4 – Any Takers?


Our piece in the February Issue of Light Aviation has certainly generated a flurry of interest, (and some speculation in the new CX4 section of the LAA forum).


We would like to clarify the current approval status of the CX4 to assist anyone in deciding whether they want to become involved in building the aircraft at this point in time.


The first thing to say is that the design is not fully approved yet. The original permit applicant for the aircraft has pulled out of the approval process. We feel that this is a very promising aircraft and would be a useful and popular addition to the LAA fleet, hence our interest in finding someone else to take on the approval task and build the UK prototype.


We have reviewed the plans, build manual and reports on a number of structural tests carried out on the aircraft. We are happy with the overall structure of the aircraft and don't anticipate any major snags in the remainder of the approval process, but there are some items which will require re-design before approval can be granted.


These modifications will need to be supported by engineering drawings and stress calculations or test reports. (See LAA Technical Leaflet TL 1.07 Section 2.3 c, d & e, elsewhere on this website). Responsibility for providing this information will lie with the first permit applicant,

i.e. the builder of the UK prototype, although a group of applicants could pool their resources to spread the cost around.


The main components currently identified as requiring re-design are in the flying control system within the fuselage.


If the aircrafts original designer cannot be persuaded to make the required changes, or if the applicant does not feel competent to carry them out,  LAA engineering has a list of design and stress engineers who are able to do these tasks for a fee. The applicant may alternatively use consultants of their own choice.


Various other aspects of the detail design require further information to be supplied. An example of this is the harness attachment points. We may require stress calculations or tests to be performed to demonstrate that these are adequate.


LAA Engineering will carry out inspections (in addition to those done by the build inspector) on various occasions during the UK prototype build, to determine if there are any further aspects of the detail design which require investigation or attention.


We are currently allowing registration packs for the CX4 to be sent out, on the basis of the positive results of the type investigation so far, but builders should be aware, as always, that they proceed with the construction of a currently un-approved aircraft at their own risk.


Previous information on the Sonex, Speedtwin Mk 2, X’Air Hawk and Vans RV6 and RV7A can be found here.