Aerodynamics Discuss the physics of flight revolving around the aerodynamics and design of aircraft.

Don Lein FW190

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Old 03-26-2017, 05:04 PM
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voodoodb
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Default Don Lein FW190

Am building an old Don Lein FW 190. Am getting ready to mount the engine and have noticed that the firewall has no right or down thrust built in. Am I right in thinking that it will need some built in? Have never seen a model that didn't have it. Also looked at the vert fin and there is no incidence built in there either. Can someone please help? Did the 190 have no thrust built in?
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Old 03-26-2017, 05:48 PM
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You can live without the thrust. I set up all my planes at 0-0-0 with no flight problems. I'll post a couple of my planes to show you that I know what I'm talking about. They are 50cc powered and weigh 20 pounds. By the way we a building small slow flying aircraft. What the full size had at 300mph has no relationship to what the models need. Dan.


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Old 03-27-2017, 04:57 AM
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Thanks Dan
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Old 03-28-2017, 08:41 PM
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Probably pay to build in some washout though...the originals had 3 deg washout so it wouldn't be 'scale' without it...
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Old 03-29-2017, 09:44 PM
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Chad Veich
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Engine thrust is measured against the incidence of the horizontal stab which may or may not be parallel to the fuselage datum line. Just because the engine is not angled down as compared to the datum line does not necessarily mean it does not have down thrust. In fact I would hazard to say that most WW2 fighter types have the engine set to zero as compared to the datum but have the horizontal stab set with positive incidence. The end result is down thrust. As for side thrust my experience has been that most full size WW2 fighters do not have any. Instead they use an offset vertical fin or some other method of countering engine torque. A degree or two of right thrust cannot hurt but is not absolutely necessary if you have a well trained left thumb. We are generally not dealing with the massive propellers that featured on the real airplanes and the torque is manageable with good piloting. My .02 cents only of course.
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Old 03-30-2017, 06:34 AM
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You might want to consider the concept of "positive error". The statistical probability of getting an exact 0-0-0 setup is pretty small. If you incorporate a bit of right-thrust and downthrust, you can be certain that you do not have left-thrust or upthrust. With the long landing gear, nose-high posture of the FW190 at rest, left-thrust and upthrust might(?) cause issues during takeoff.
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Old 03-30-2017, 09:47 AM
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The need for downthrust plays hand in hand with the CG position and final elevator trim. Dan up above is getting away with the 0-0-0 setup because he's comfortable with his models flying like precision aerobatic models. Nothing wrong with that at all if you're an attentive pilot and don't mind making your own minor corrections. But most folks will set up sport and scale models with a whiff of positive decalage (wing to tail angle) and a slightly forward CG to get SOME degree of trimmed in pitch stability. And when you do that you may find you want a touch of down thrust.

Side thrust is another puppy. It does pay to use a degree to degree and a half of right thrust to aid in counteracting torque on takeoff and during climbing.

Full size aircraft often use some slight fin offset on the old big engine prop planes. But our models do not have the same issues with prop to wingspan ratio as the heavily powered old fighters and some trainers had. So we are fine with the fin and rudder being centered.
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Old 04-03-2017, 06:58 PM
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Dan,

Speed is a squared root function whereas volume/sized is qubed root. Doing the calcalutions likely you'll discover your models are exceeding their scale speed. An example is a 1/4 scale Cub 1/4 x 1/4 = 1/16 so a full sized cub @ 80 mph x 1/16 = 80/16 or 5 mph. Obviously to take off the model as already exceed the Cubs Vne limit. Even your models are grossly exceeding Vne for the actual aircraft. Of course most flyers don't care but, when an engineering scale model is evaluated this does. Ed
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