I have built an inverted VTail for aerial surveys which is a bit of a mix of all the bits I had lying around. The wings come from a EPP FPV and the rest I made myself.
I have maidened it, and it flies well enough although in slow flight, the tail tends to drop a bit too much for my liking. I would say about 4-5 degrees below level. At around 80% throttle, the tail levels out.
I did a fair bit of research on how long the tail has to be and believe to have that correct, also based on the previous dimensions of the EPP FPV but I may be wrong.
In its first version, the boom was even 10cm longer and then the first flights had the same issue, 4-5 degrees below level.
So before I shorten the boom again, what other reasons could there be for the dragging or what can I do to fix it?
I'm no expert but im pretty sure the problem will be your wing incidence.
All aircraft fly a different angles of attack according to their speed and lift requirements. The faster you go the flatter they will fly.
So it's not so much that your plane has a problem, its more that you need to design it as such that it fly's at the angle you want at the speed you want and I believe that comes down to wing incidence.
Of course once you get it right for slow speed you will have to use downtrim to keep it level at high speed so its a balancing act between the two.
Hopefully someone with more expertise will chime in.
Thanks, that makes sense and was what I thought about giving a go. Since my wings are attached via rubber bands its easy to change the angle teporarily by putting something under the wing edge.
Looks to me like the thrust line of the motor is your problem, try putting a couple of washers bethind the top two motor mount holes, that should give it some more downthrust when opening throttle, it'll be trial & error as to how much you need but the idea is to get it flying on the same plane with high & low throttle, once you've got that have a look at elevator if it's central then wing incidence is ok if you need up elevator to keep level flight then a bit of packing under the rear of the wing & visa vesa. hope that helps,
looks good BTW.
Excellent info - thanks! Will do afew test flights with a few washers to see if that helps first.
this is one I had a couple of years ago and that flew with the tail down
http://www.fpvhub.com/index.php/topic,1177.0.html (http://www.fpvhub.com/index.php/topic,1177.0.html)