Prop Pitch to Slow Plane for Landing
08-20-2013, 02:02 PM
#28
True. Set your rpm to the lowest reliable idle on the ground. Richen just enough to make it idle at the most, 1700-1900rpm but less is better. I have a magnum .91 and a thunder tiger .91 that idle at 1500rpm all day long.
But don't richen so much that it will not transition to full relyably. When flying, especially with a prop pitch any higher than 6, it will speed up with te air blowing over the prop so it can still pull the plane along a little. If its too high on the ground it will be way to high when nose down for final. Even just gliding level at idle it could pick up 300-400rpm which can be enough to really prolong a glide.
You'll want a wider blades prop. Try a master airscrew. No higher than an 8 pitch. The diameter will depend on what top end you want. I'd say use a 14-8 or 15-7. This will still pull the plane under power well but won't spool up too much at idle and you should still get your 8-9.5k rpm on top once tuned.
The aileron reflex is a good idea on any plane with tip ailerons. It acts as wash out which will keep it ffrom tip stalling. 1/16th is all you need BUT you could put it on a flap mix switch so on final you can pop them up even more. (How much will depend on your plane). I had a sig rascal that held speed too long and would never slow down even in a slip, so I added aileron reflex on the flap switch and it took 1/2" up throw to slow the plane and dump a little lift enough so I could land where I wanted every time.
This isn't a band aid. It will help reguardless of having speed issiues or not.
But don't richen so much that it will not transition to full relyably. When flying, especially with a prop pitch any higher than 6, it will speed up with te air blowing over the prop so it can still pull the plane along a little. If its too high on the ground it will be way to high when nose down for final. Even just gliding level at idle it could pick up 300-400rpm which can be enough to really prolong a glide.
You'll want a wider blades prop. Try a master airscrew. No higher than an 8 pitch. The diameter will depend on what top end you want. I'd say use a 14-8 or 15-7. This will still pull the plane under power well but won't spool up too much at idle and you should still get your 8-9.5k rpm on top once tuned.
The aileron reflex is a good idea on any plane with tip ailerons. It acts as wash out which will keep it ffrom tip stalling. 1/16th is all you need BUT you could put it on a flap mix switch so on final you can pop them up even more. (How much will depend on your plane). I had a sig rascal that held speed too long and would never slow down even in a slip, so I added aileron reflex on the flap switch and it took 1/2" up throw to slow the plane and dump a little lift enough so I could land where I wanted every time.
This isn't a band aid. It will help reguardless of having speed issiues or not.
08-20-2013, 03:22 PM
#29
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I'd be real impressed to see any small RC engine that will idle at 1500 rpm. 2000 I'd believe, but 2300-2500 is more normal. My Saito .72 will idle at 2100 for a while, but not 100% reliable. I set it at 2400 and it won't even pull the plane on level concrete. For that plane, the engine has to get up to about 3000 rpm to move at all, and closer to 4000 to get to taxiing speed.
There's a misconception in thatairplaneguy's post that should be cleared up. Your prop, no matter what the diameter and pitch and no matter what the idle rpm, will provide some engine braking at idle. If the speed of the prop is below the speed of the plane, then the prop is adding drag. So a 6 pitch prop at 2400 rpm is 13 mph at 100% efficiency. So for the prop to be contributing anything to the forward movement of the plane, the plane would have to be going less than 13 mph. And since we know from watching our engines idle while the plane just sits there, we know that prop efficiency at those low rpms is extremely low. So it's not possible that your engine at idle is actually extending your glide slope. It is providing some braking, it's just a matter of how much. A high idle or coarse pitch prop will provide LESS braking, but never none.
So once again, if you plane lands well with some headwind, it's likely that you're just not used to landing in the calm and managing the airspeed. Most pilots I know who fly in windy places say they have trouble with that, and I've definitely had my share of go arounds because of it too.
There's a misconception in thatairplaneguy's post that should be cleared up. Your prop, no matter what the diameter and pitch and no matter what the idle rpm, will provide some engine braking at idle. If the speed of the prop is below the speed of the plane, then the prop is adding drag. So a 6 pitch prop at 2400 rpm is 13 mph at 100% efficiency. So for the prop to be contributing anything to the forward movement of the plane, the plane would have to be going less than 13 mph. And since we know from watching our engines idle while the plane just sits there, we know that prop efficiency at those low rpms is extremely low. So it's not possible that your engine at idle is actually extending your glide slope. It is providing some braking, it's just a matter of how much. A high idle or coarse pitch prop will provide LESS braking, but never none.
So once again, if you plane lands well with some headwind, it's likely that you're just not used to landing in the calm and managing the airspeed. Most pilots I know who fly in windy places say they have trouble with that, and I've definitely had my share of go arounds because of it too.
08-20-2013, 05:07 PM
#30
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If you have two aileron servos and a computer TX you could try CROW braking [ both ailerons move UP together ].
To be clear on prop pitch, a low number means slower, and high means faster speed.
Although a low pitch will slow your plane, I fully agree that it's not the 'headwind', it's your left thumb that needs to reduce the speed. As stated earlier, learn to fly level at the slowest speed possible. This speed is one which, if you reduce power even a tiny bit, the airplane will descend or even stall. Then just increase power slightly (for a margin of safety) and practice slow flight and approaches to landings.
08-20-2013, 06:04 PM
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You say that your approach is fine but are looking to props to slow it down - that sounds like your approach is still too fast. Your flight path may be OK but it sounds like you are still carrying too much energy on final. Changing props may affect how fast a plane can slow down, but unless you are backed into an aerodynamic corner between stalling and level airspeed in ground effect at idle due to your prop pitch, you can still slow your approach.
If your plane won't settle before you run out of runway your problem is that your approach is too fast!
An approach that is too slow results in a stall. An approach that is too fast means that the aircraft needs to burn off energy before you can safely touchdown.
I don't know you or your skill as a pilot so please know that I absolutely don't want to offend you. But, as people are writing about there are things you can do to help it fly slower but they won't make any difference if the pilot doesn't make some changes too.
At the risk of being repetitious, you say you "can't seem to slow down enough for landing unless there is a decent wind."
That is the very definition of flying too fast on approach!
Unless your plane will maintain level flight at idle (changing your propeller may help the plane slow down) it is the pilot rather than the prop that is not allowing the plane to slow down. Aerodynamically slick airplanes do not slow down real fast. You need to start early.
Too many people cut the throttle on final and swoop into a landing. Many models will let you get away with this. With some models, like higher performance real aircraft, your head needs to be ahead of the airplane because things like bleeding off airspeed and losing altitude take time. In real aircraft, like your warbird, you will overshoot the airport if you are not ahead of the plane.
As people mentioned earlier, take your plane a couple mistakes high, pull your throttle back to idle and keep pulling back on your elevator to hold your altitude until it begins to wallow just before a stall - remembering that it can happen quickly with some warbirds. As you approach stall speed slowly add throttle until you can maintain altitude with an airspeed just above stall. Practice flying the pattern at altitude at this slow speed maintaining altitude with your throttle and airspeed with your elevator - This is how you fly slow!
Practice this. Don't just read this.
Once you are confident that you can fly level with a small but safe margin above stall speed, set up your approach starting with the downwind leg in this configuration:
As you pass mid-field on your downwind leg maintain the same airspeed using your elevator but slowly bring back the throttle a little until the plane begins to descend.
Continue this as you turn onto your base-leg and onto final, adjusting the throttle so that the rate of descent sets you up for your desired glidepath. (Make sure you practice enough so that you don't stall on your turns)
As you cross the threshold you should still at the same airspeed you were mid-field on your downwind leg.
If you take the time to do this you will not have all that extra airspeed/energy to bleed off as the runway disappears behind your plane.
Your approach is the time to bleed off the extra energy - not the runway.
Please know that I invested the time to write this in an effort to help you. I hope that I did not come across badly trying to write so much in such a short period of time.
Paul
If your plane won't settle before you run out of runway your problem is that your approach is too fast!
An approach that is too slow results in a stall. An approach that is too fast means that the aircraft needs to burn off energy before you can safely touchdown.
I don't know you or your skill as a pilot so please know that I absolutely don't want to offend you. But, as people are writing about there are things you can do to help it fly slower but they won't make any difference if the pilot doesn't make some changes too.
At the risk of being repetitious, you say you "can't seem to slow down enough for landing unless there is a decent wind."
That is the very definition of flying too fast on approach!
Unless your plane will maintain level flight at idle (changing your propeller may help the plane slow down) it is the pilot rather than the prop that is not allowing the plane to slow down. Aerodynamically slick airplanes do not slow down real fast. You need to start early.
Too many people cut the throttle on final and swoop into a landing. Many models will let you get away with this. With some models, like higher performance real aircraft, your head needs to be ahead of the airplane because things like bleeding off airspeed and losing altitude take time. In real aircraft, like your warbird, you will overshoot the airport if you are not ahead of the plane.
As people mentioned earlier, take your plane a couple mistakes high, pull your throttle back to idle and keep pulling back on your elevator to hold your altitude until it begins to wallow just before a stall - remembering that it can happen quickly with some warbirds. As you approach stall speed slowly add throttle until you can maintain altitude with an airspeed just above stall. Practice flying the pattern at altitude at this slow speed maintaining altitude with your throttle and airspeed with your elevator - This is how you fly slow!
Practice this. Don't just read this.
Once you are confident that you can fly level with a small but safe margin above stall speed, set up your approach starting with the downwind leg in this configuration:
- Airspeed a small but safe margin above stall (be careful with the turns!)
- Maintaining airspeed with your elevator
- Maintaining altitude with your throttle
(Too many pilots can't slow their planes down when they get this backwards!)
As you pass mid-field on your downwind leg maintain the same airspeed using your elevator but slowly bring back the throttle a little until the plane begins to descend.
Continue this as you turn onto your base-leg and onto final, adjusting the throttle so that the rate of descent sets you up for your desired glidepath. (Make sure you practice enough so that you don't stall on your turns)
As you cross the threshold you should still at the same airspeed you were mid-field on your downwind leg.
If you take the time to do this you will not have all that extra airspeed/energy to bleed off as the runway disappears behind your plane.
Your approach is the time to bleed off the extra energy - not the runway.
Please know that I invested the time to write this in an effort to help you. I hope that I did not come across badly trying to write so much in such a short period of time.
Paul
08-20-2013, 07:31 PM
#33
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Agreed! Very well said Paul. Even though they are linked, It's amazing how many people get how to control speed and altitude backwards on an approach. Once you understand and get experience flying this way you'll blow people away with your approaches and landings. Plus you'll be much more confident, thus more comfortable flying any model. If your approach isn't any good (unstabilized, plane not going where you want it to go, etc.), the landing isn't very likely to be any better. It will probably take a bunch of go-arounds before you get it nailed down, but just remind yourself that it's better to do that and try again (further refining your skills) than risk trying to force it down when it's not ready to and damaging your beautiful airplane
.
Just remember-
Pitch controls speed.
Power controls vertical position (altitude).
The physics doesn't change just because it's small. It's no different than full-scale aircraft, so why would we fly our models any different?
Well, I guess that's not 100% true; our model's power-to-weight ratios tend to be a "tad" higher than our full-scale counterparts
.
dasintex-I hope the suggestions give you something to work with. Have fun experimenting! BTW-You have my dream plane. I absolutely love the P-47. I bet it just looks, and sounds, great in the air
.
.Just remember-
Pitch controls speed.
Power controls vertical position (altitude).
The physics doesn't change just because it's small. It's no different than full-scale aircraft, so why would we fly our models any different?
Well, I guess that's not 100% true; our model's power-to-weight ratios tend to be a "tad" higher than our full-scale counterparts
.dasintex-I hope the suggestions give you something to work with. Have fun experimenting! BTW-You have my dream plane. I absolutely love the P-47. I bet it just looks, and sounds, great in the air
.
08-20-2013, 08:47 PM
#34
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So does the plane fly too fast while maintaining level flight at idle? i.e. can you fly around all day at idle? i.e. can you maintain airspeed and altitude at idle? How slow can you get it at idle, while maintaining altitude? Do you have a feel for when it is too slow? If you can't answer these, then I wouldn't blame the prop just yet.
Kurt
Kurt
08-21-2013, 03:12 AM
#35
Ok, here is what I got and what changes I made to help slow the Plane down for landing, the Plane is a Hanger 9 60 Size P-47, the Engine is a RCV 91CD; in my opinion and experience not as strong of an Engine as a OS 90; the Prop is a 13 X 8 APC Sport; the Balance was a little Nose Heavy so I changed the CG to Slightly Tail Heavy, put a Slight Aileron Reflex in; I will try this first, I'm reluctant to change the Prop because this Prop pulls the Plane around with some authority, I have a 13 X 6 Master Airscrew K Series Prop I can try at the field as well.
I have had this Plane for some time, and landing has never been an issue until I changed Props to one that pulled the plane a little better, with the 3 Bladed Prop I used before it would slow right down to a crawl to land, but had absolutely no authority to pull the plane, if I had to power out of a problem, it struggled; however, I had made a change in the Air Valve and placement which I believe changed the CG from the initial CG.
If these changes don't help slow it down I can try the 13 X 6 Prop, my approach is good, and the throttle is as low as it can go without killing the engine, so hopefulluy the changes will work.
I have had this Plane for some time, and landing has never been an issue until I changed Props to one that pulled the plane a little better, with the 3 Bladed Prop I used before it would slow right down to a crawl to land, but had absolutely no authority to pull the plane, if I had to power out of a problem, it struggled; however, I had made a change in the Air Valve and placement which I believe changed the CG from the initial CG.
If these changes don't help slow it down I can try the 13 X 6 Prop, my approach is good, and the throttle is as low as it can go without killing the engine, so hopefulluy the changes will work.
If you are using a 13 x 8, I would have thought that would have been perfect. It will give you a good climb rate when you need it. Just a lot of 'p' factor, but a somewhat heavy warbird, like a P47 can handle it.
If you go to a 13 x 6 prop, you will lose performance and speed, but you just may prefer that to slow the plane down. Be careful, the plane will slow down faster than you may expect, and then it could stall.
A 14 x 6 prop will do the same, and create more drag.
However, there is a big difference between sport props, wide props (MasterAirscrew K series), wood props, and APC props.
APC props are very efficient. Whereas a wood prop, or a Master Airscrew glass-filled prop are not as efficient. So the latter may be the better choice for your P-47. Use the same pitch also (13x8). You will see a big difference, and have to re-adjust your high end needle for the different prop.
I have a P-47, and use a Master Airscrew 13x8 K series prop. It gives excellent climb performance and does slow the plane down when I reduce the idle. I can even hear the drag it creates as the plane comes across the numbers for touchdown.
Hope this helps!
Last edited by Airplanes400; 08-21-2013 at 03:15 AM.
