Right Angle, Down Thrust?
11-22-2010 | 11:01 AM
#1
Thread Starter
Banned
Joined: Jan 2010
Posts: 1,840
Likes: 0
Received 0 Likes
on
0 Posts
From: Lacona, NY
Right Angle, Down Thrust?
It might be a crazy question, why does some planes require more right angle down thrust than others when attatching a engine and engine mount to the fire wall. Is it that some designers have it this way making it easier to handle a aircraft for those who don't use a rudder? In my time I have built a couple of aircraft and I notice that some don't have it so noticable, and others have it where you can see it angled.
Is it that some aircraft that has a lot of drag and have short fuses has more torque, and they design it that way for handling reasons?
My Hanger 9 Fokker has a little down thrust and no right angle, and my Great Planes Fokker DR1 has it way more and it is noticable.
Can someone educate me about this?
Thanks,
Pete
Is it that some aircraft that has a lot of drag and have short fuses has more torque, and they design it that way for handling reasons?
My Hanger 9 Fokker has a little down thrust and no right angle, and my Great Planes Fokker DR1 has it way more and it is noticable.
Can someone educate me about this?
Thanks,
Pete
11-22-2010 | 11:33 AM
#2
Senior Member
RE: Right Angle, Down Thrust?
Often has to do with how the center of drag of the airframe lines up with the center of thrust for the up/down.
The right is often a way to deal with the p-effect and "torque".
The right is often a way to deal with the p-effect and "torque".
11-22-2010 | 12:19 PM
#3
Thread Starter
Banned
Joined: Jan 2010
Posts: 1,840
Likes: 0
Received 0 Likes
on
0 Posts
From: Lacona, NY
RE: Right Angle, Down Thrust?
ORIGINAL: da Rock
Often has to do with how the center of drag of the airframe lines up with the center of thrust for the up/down.
The right is often a way to deal with the p-effect and ''torque''.
Often has to do with how the center of drag of the airframe lines up with the center of thrust for the up/down.
The right is often a way to deal with the p-effect and ''torque''.
Pete
11-22-2010 | 01:18 PM
#4
RE: Right Angle, Down Thrust?
Probably not, if both planes have the same engine and propeller.
However, as stated above, not all designs react the same to the same P and torque.
More draggy models, in the air and on the ground, seem to be more sensitive to those non-symmetrical forces.
I would say that, for each specific design, those angles are found by experimentation and flight-tests more than over the drafting table.
Once the prototype flies OK, the designer specifies those angles, incidences and CG location on the final drawings before the kit or ARF goes on into massive production.
The down-thrust angle tries to keep the pitch balance the same regardless the thrust force is high (full throttle) or low (idle).
The side-thrust angle is more of a compromise, because it tries to keep the yaw balance the same, while the thrust force on the right side of the propeller disk changes with AOA (P-factor), and the rolling-torque changes with rpm’s and speed of the airplane.
However, as stated above, not all designs react the same to the same P and torque.
More draggy models, in the air and on the ground, seem to be more sensitive to those non-symmetrical forces.
I would say that, for each specific design, those angles are found by experimentation and flight-tests more than over the drafting table.
Once the prototype flies OK, the designer specifies those angles, incidences and CG location on the final drawings before the kit or ARF goes on into massive production.
The down-thrust angle tries to keep the pitch balance the same regardless the thrust force is high (full throttle) or low (idle).
The side-thrust angle is more of a compromise, because it tries to keep the yaw balance the same, while the thrust force on the right side of the propeller disk changes with AOA (P-factor), and the rolling-torque changes with rpm’s and speed of the airplane.
11-22-2010 | 05:20 PM
#5
Thread Starter
Banned
Joined: Jan 2010
Posts: 1,840
Likes: 0
Received 0 Likes
on
0 Posts
From: Lacona, NY
RE: Right Angle, Down Thrust?
I see.
Here are a few pictures of what I'm talking about. The cowl was measured evenly around the fuse and the engine was even on the mount. I got it where the crankshaft of the motor exits the crankshaft hole perfectly, and I get that funky down and right angle.
I'm using a O.S.-91FX on this bird and will be swinging a 17x6 prop on the DR1 I'm rebuilding. No one has chimed in my Thread about the funky angles.
The Hanger 9 Fokker DVII uses a 13x6 or 14x6 prop and has a O.S.-60FX. The Fokker DVII has about the same down angle- or close to it as the DR1, but has little right angle.
When I fly the Fokker DVII, I use little right rudder on take off, and it flys straight enough. I trim it depending on the wind conditions.
I'm wondering if anyone who has built the Discontinued Great Planes .60 Fokker DR1 if they remembered if they had that obvious right-down angle. The inverted firewall box does have that angle.
Thanks guys, it's the first time I run across such a thing as this and I knew this is a good place to ask.
Pete
Here are a few pictures of what I'm talking about. The cowl was measured evenly around the fuse and the engine was even on the mount. I got it where the crankshaft of the motor exits the crankshaft hole perfectly, and I get that funky down and right angle.
I'm using a O.S.-91FX on this bird and will be swinging a 17x6 prop on the DR1 I'm rebuilding. No one has chimed in my Thread about the funky angles.
The Hanger 9 Fokker DVII uses a 13x6 or 14x6 prop and has a O.S.-60FX. The Fokker DVII has about the same down angle- or close to it as the DR1, but has little right angle.
When I fly the Fokker DVII, I use little right rudder on take off, and it flys straight enough. I trim it depending on the wind conditions.
I'm wondering if anyone who has built the Discontinued Great Planes .60 Fokker DR1 if they remembered if they had that obvious right-down angle. The inverted firewall box does have that angle.
Thanks guys, it's the first time I run across such a thing as this and I knew this is a good place to ask.
Pete
11-22-2010 | 05:49 PM
#6
Senior Member
RE: Right Angle, Down Thrust?
If the kit mfg has been in business awhile, you can make book on the angles they build into the firewalls of their planes. If it's a plane that was a really great price, it might or might not be appropriate.
The amount of down thrust really seems to be fairly constant. The amount of right thrust is usually constant for an average airplane, for example one that doesn't have something like really short wingspan (like triplanes
).
With established mfg's like Great Planes and Hangar9, they seem to take care to either develop the model with some care, or insure the stuff they get from China is tested and fixed before sale. You are sensible to wonder about earlier versions. On the other hand, the earlier version would have had a problem with a different thrust if this later version shows it being there. Make sense?
If the provided motor mount screwed to predrilled holes for it puts the prop shaft where the provided cowling has a hole for it, there is a good bet the right thrust is going to be a good idea for your plane.
Also, you're not usually going to see really bad things from too much or too little side thrust until you really start pushing the envelope.
The amount of down thrust really seems to be fairly constant. The amount of right thrust is usually constant for an average airplane, for example one that doesn't have something like really short wingspan (like triplanes
). With established mfg's like Great Planes and Hangar9, they seem to take care to either develop the model with some care, or insure the stuff they get from China is tested and fixed before sale. You are sensible to wonder about earlier versions. On the other hand, the earlier version would have had a problem with a different thrust if this later version shows it being there. Make sense?
If the provided motor mount screwed to predrilled holes for it puts the prop shaft where the provided cowling has a hole for it, there is a good bet the right thrust is going to be a good idea for your plane.
Also, you're not usually going to see really bad things from too much or too little side thrust until you really start pushing the envelope.
11-22-2010 | 06:08 PM
#8
Thread Starter
Banned
Joined: Jan 2010
Posts: 1,840
Likes: 0
Received 0 Likes
on
0 Posts
From: Lacona, NY
RE: Right Angle, Down Thrust?
ORIGINAL: da Rock
BTW, models didn't originate down and side thrust. Full scale planes often have some.
BTW, models didn't originate down and side thrust. Full scale planes often have some.
No kidding, I didn't know that... I thought it was the other way around.
ORIGINAL: da Rock
If the kit mfg has been in business awhile, you can make book on the angles they build into the firewalls of their planes. If it's a plane that was a really great price, it might or might not be appropriate.
The amount of down thrust really seems to be fairly constant. The amount of right thrust is usually constant for an average airplane, for example one that doesn't have something like really short wingspan (like triplanes ).
With established mfg's like Great Planes and Hangar9, they seem to take care to either develop the model with some care, or insure the stuff they get from China is tested and fixed before sale. You are sensible to wonder about earlier versions. On the other hand, the earlier version would have had a problem with a different thrust if this later version shows it being there. Make sense?
If the provided motor mount screwed to predrilled holes for it puts the prop shaft where the provided cowling has a hole for it, there is a good bet the right thrust is going to be a good idea for your plane.
Also, you're not usually going to see really bad things from too much or too little side thrust until you really start pushing the envelope.
If the kit mfg has been in business awhile, you can make book on the angles they build into the firewalls of their planes. If it's a plane that was a really great price, it might or might not be appropriate.
The amount of down thrust really seems to be fairly constant. The amount of right thrust is usually constant for an average airplane, for example one that doesn't have something like really short wingspan (like triplanes ).
With established mfg's like Great Planes and Hangar9, they seem to take care to either develop the model with some care, or insure the stuff they get from China is tested and fixed before sale. You are sensible to wonder about earlier versions. On the other hand, the earlier version would have had a problem with a different thrust if this later version shows it being there. Make sense?
If the provided motor mount screwed to predrilled holes for it puts the prop shaft where the provided cowling has a hole for it, there is a good bet the right thrust is going to be a good idea for your plane.
Also, you're not usually going to see really bad things from too much or too little side thrust until you really start pushing the envelope.
I'm guessing my plane is a little over 10 years old. Not sure when Great Planes discontinued the model. It had the updated landing gear do to the first few batches had issues, so I'm guessing it's a later release.
Anyway, I really liked how you explained it to me da Rock, and I also thank Lnewqban explaining the theory on engine angles. The Fokker DR1 also has a short fuse as well short wings. I guess with anything with a long fuse like my Hanger 9 Fokker DVII doesn't need as much right angle.
This stuff is good to know because after I'm done with the Fokker DR1 I plan on doing some kit building eventually.
Again I thank you all,
Pete
11-23-2010 | 11:24 AM
#9
My Feedback: (11)
RE: Right Angle, Down Thrust?
Basically, downthrust or sidethrust is used to reduce trim changes when the throttle is moved. If the airplane tends to go nose-up when the throttle is increased, then downthrust is added. The same if the airplane yaws when the throttle is applied. Ideally, you want the model to have a little pitch or yaw change as possible when the throttle moved.
Two full-size aircraft that had downthrust and side thrust are the Aircoupe (or Ercoupe, depending upon the maker), and the Beechcraft Bonanza. Stand 'way back, and you can see it!
Two full-size aircraft that had downthrust and side thrust are the Aircoupe (or Ercoupe, depending upon the maker), and the Beechcraft Bonanza. Stand 'way back, and you can see it!
11-23-2010 | 04:39 PM
#10
Thread Starter
Banned
Joined: Jan 2010
Posts: 1,840
Likes: 0
Received 0 Likes
on
0 Posts
From: Lacona, NY
RE: Right Angle, Down Thrust?
ORIGINAL: Bax
Basically, downthrust or sidethrust is used to reduce trim changes when the throttle is moved. If the airplane tends to go nose-up when the throttle is increased, then downthrust is added. The same if the airplane yaws when the throttle is applied. Ideally, you want the model to have a little pitch or yaw change as possible when the throttle moved.
Two full-size aircraft that had downthrust and side thrust are the Aircoupe (or Ercoupedepending upon the maker), and the Beechcraft Bonanza. Stand 'way back, and you can see it!
Basically, downthrust or sidethrust is used to reduce trim changes when the throttle is moved. If the airplane tends to go nose-up when the throttle is increased, then downthrust is added. The same if the airplane yaws when the throttle is applied. Ideally, you want the model to have a little pitch or yaw change as possible when the throttle moved.
Two full-size aircraft that had downthrust and side thrust are the Aircoupe (or Ercoupedepending upon the maker), and the Beechcraft Bonanza. Stand 'way back, and you can see it!
I'm a pilot and I've never noticed it on the Beechcraft Bonanza, of course I wasn't looking for it at the times I was around that aircraft.
Thanks Bax!
Oh by the way, can you tell your bosses that I want to see the O.S. 91FX Ringed come back? It was a fine engine.
Pete
11-23-2010 | 07:46 PM
#11
My Feedback: (10)
RE: Right Angle, Down Thrust?
hi
my citabra usa balsa calls for 1% down and 1% right if i use washer to get this do i put one washer under each top and one on these on the left bottom or should i put two on the left side top ? this plane calls for a 120 4 stroke at the high end so we are using a dle -20 gas engine should i use more then 1 % on both thanks rye
my citabra usa balsa calls for 1% down and 1% right if i use washer to get this do i put one washer under each top and one on these on the left bottom or should i put two on the left side top ? this plane calls for a 120 4 stroke at the high end so we are using a dle -20 gas engine should i use more then 1 % on both thanks rye
