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Cut the ruddder!

tramsgar

Senior Member
#1
I'm putting together an EDF kit (HK Phazer) and thought it would be nice to at the same time add a rudder to the vertical stabilizer. The problem is that I lack a proper education in aerodynamics (I might have that in common with the one designing the kit, btw) and I need your help to make the incision, experienced and knowledgeable as you are.

I've marked three likely (?) candidates in the picture; A, B and C. Take a look and vote. Please give some reason for your opinion, and by all means suggest a totally different way to cut it if needed. (Or if you think this is all a horrible idea please say to too, and why.)

Thanks a lot!

cut the rudder.jpg
 

pgerts

Old age member
Mentor
#2
I would have made the rudder parallell to the B-line but more aft to get the b-point where you have the C.
Are you aiming for knife egde flying?
Fast planes does not need a lot of rudder area or movement.
I do not think this is a plane for hovering.
 

quorneng

Active member
#4
I would go further and say unless you want to do some rather specialised aerobatics like a knife edge for which you probably wont have the thrust to maintain I favour doing without the rudder and saving the weight of the servo.
On an EDF every gram/fraction of an ounce costs performance.
 

tramsgar

Senior Member
#5
Thank you all for your input! I agree that B and C would give a too large control surface now that you mention it. pgerts, wouldn't an angled rudder give a deflection that's not parallel to the direction of flight? I.e. also act a bit like an elevator? So would D below be more appropriate:

cut the rudder 2.jpg

quorneng: the purpose of the rudder is not to do advanced aerobatics, this EDF doesn't have the thrust for such, I agree. Rather, I'd like more control besides bank&yank and open up for some less advanced maneuvers than knife edge. I think I can spare the weight of the rudder servo, especially as it doesn't have to be so large if the surface area is small, as pgerts and earthsciteach suggested (I will also be skipping the gears).
 

quorneng

Active member
#6
tramsgar
I am slightly puzzled by your desire for more control on an EDF jet. Have you flown one?

I can only say mine require just a touch of bank to execute a turn.
Most EDF jets have little or no natural roll stability so be prepared for a rudder input to produce some 'interesting' results.

Do post how you get on.
 

tramsgar

Senior Member
#8
tramsgar
I am slightly puzzled by your desire for more control on an EDF jet. Have you flown one?

I can only say mine require just a touch of bank to execute a turn.
Most EDF jets have little or no natural roll stability so be prepared for a rudder input to produce some 'interesting' results.
Do post how you get on.
Sure, I own and fly EDFs with rudders =). As mentioned above I'm not trying to make a 3D EDF here (although that would be fun for another project!), just get more maneuverability. And it's the "interesting" results I want to avoid (sorry pgerts) by making a good cut here! As I figure, a cut along the D line would also press the tail down somewhat? One of my EDFs has a rudder cut like that and I'm not entirely happy with the rudder response on it.