Very interesting but….

There have been some interesting developments since MYRO’s Permit Inspection and weighing. For some reason MYRO’s CG position has come out a long way aft, so far so that although it’s OK with just the single standard tank, as soon as you do the calculations for adding the second tank, you find that it’s impossible to do so and still remain within the TADS aft limit.

But when I contacted the BMAA Tech Office, I found that there’s a Serial Mod for a twin tank set up using the AX2000 tanks, which are bigger than what I’m proposing and would therefore exacerbate the situation even more! So what’s happening 😯

Now I just happened to decide to do my own weighing on Sunday using a good set of digital bathroom scales, not to ‘check up’ on Tim’s results, which I didn’t have at the time, but just to see out of interest what I got MYRO’s empty weight out to. The reason was because when we did it on Saturday, I wasn’t very happy about the flimsy hardboard sheets that we had placed the scales on. I know from my own experiences of weighing myself on different surfaces that the results can vary hugely depending on the type of surface the scales are on and ideally you need something that’s firm and rigid.

I used a rigid sheet of thick plywood as a platform for the scales and placed a concrete paving slab under each of the wheels that were not being weighed. The outcome was that I got a weight that was slightly more than Tim’s figure but with a weight distribution between the wheels that was very different indeed. I got much more weight coming out on the nose wheel, to the extent that my numbers worked for both the official BMAA Serial Mod and, of course, for the tank mod that I want to do. Tech Office also found that there is some confusion with the official Serial Mod calculations and they are now very interested to see what happens because, of course, I will now have to pursue it to find out the true situation. Rob in the Tech Office said that they have done some important work recently which shows the great variations in weight distribution that can result from not having the aircraft totally level and he said that in fact they are now strongly suggesting that a spirit level is placed on the tail boom, or in MYRO’s case, the main tube, to ensure that it is dead level when the weighing is done.

I think that this is the source of the problem. Earlier in the day I spoke to Joan Walsh of Saxon Microlights about their AX3, G-MYHM, which has the same Arplast prop as MYRO and differs only in not having an electric fuel pump. That comes out slightly heavier than MYRO but the weight on the nose wheel is far greater and there would be no problem whatsoever with fitting an extra fuel tank because its empty CG position is far further forward than MYRO’s. I phoned Tim this evening to tell him about my conversations and to ask if he will be available for a re-weighing at the week-end under stricter conditions. Hopefully he will be and we’ll be able to get to the bottom of the mystery. This is a further complication that I could have well done without but I might as well try to get everything sorted out in one go now so I can have a more quiet life in the future. There can be no reason for MYRO to be so different from other AX3s and I can’t let this rest if I am to have my twin tanks – and I would like them if it’s at all possible 😉