Motor Upgrade help needed

Sorry if i sound daft but i probably am.
This weekend gone i repositioned the bulk head on my century mx2 1inch further forward as there was damage to the area around the original.
At the same time i cut down the motor mount by the same 1 inch the plane flew really badly for a short while before becoming a bag of rubbish.
So would it be moving the motor forward caused a problem or is it more likely i didn't get the thrust angle right?

Which brings me nicely on to my dilemma i now want to put this big power train into my riot but i am not sure if i should set the thrust angle to where the Riot has it on its original motor or where the MX2 had it.
Is thrust angle to do with airframe design or motor power and size?
Thanks in anticipation

Andy

Regarding the MX2...
After making the modification you should have checked that the CofG was still in the right place. Even if you didn't, it won't have been too far out. Assuming the CofG was near enough, it should have flown OK even if the thrust line was out a little bit. A bit of trimming should have got it flying, so it's not clear why you went home with a bag of rubbish.

Re. the Riot...by all means add the more powerful motor but make sure you check the CofG before flight. Keep the thrust angle exactly the same as the old Riot motor. After a trimming flight you can decide if you need to adjust the thrust angle. Jon Tappin can give better advice here, so I'll sign off and leave it to him...

Mike

Andy, moving the firewall forward I would suggest was not the problem as the motor was still in it's original postition after making mods to the motor bracket. If I remember rightly you did put in some right and downthrust angle as per the original which is very noticeable. I am thinking along the lines as Mike suggested - Cof G! The MX should still have flown of sorts anyway. After all it did fly reasonably even when the motor was slopping about.

As I mentioned previously there is no issue in making a turbo charged Riot except the motor will stick out a bit from the Riot's cowl. As it is quite a torquey motor put some down thrust and right thrust angle in as discussed. Becaus the motor is a lot heavier your going to haveto either get the battery pack back further to balance and/or add some ballast in the tail. If you go ahead let me watch the maiden first..... :lol:

Thanks for the replies
i checked the cog before flight and seemed ok and yes phill your right it did have some down and right angle possibly not as much as the original, but before i did this it flew great after it was hyper responsive to control in that the slightest touch of up elevator caused a tight loop a roll that used to be smooth and on its axis became a cork screw of maybe 3m Diameter and off power it was really hard to control wings dropping left and right
very odd anyway it will be fun to see a riot on steroids
andy a new MX is on the cards
Andy

Andy

Thrustline is affected by prop, power and airframe design, so initially is a bit of a guess, I would suggest starting at 2-3 deg right side thrust and zero downthrust, this shouldn't be too far out but will probably need adjusting as necessary after test flights.

Your description of the flight after mods sounds like you may have been tail heavy, but I guess we will never know now

Jon

thanks Jon
really i know it must have been something stupid, shame because it was my favourite plane to fly but i will replace it soon.last week it was flying fine with loose wings and a motor that wiggled up down and left and right along with the firewall it was mounted on, then after hours of addressing the problems it was UN flyable (for me at least)
but in the mean time I'm kind of happy to do crazy power upgrade to my riot, just dont want it to be un flyable during set up flights but as they say no pain no gain
Andy