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  1. #1
    dasintex's Avatar
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    Prop Pitch to Slow Plane for Landing

    I have a 60 size Warbird, no Flaps, with a 90 4S that I can't seem to slow down enough for Landing unless there is a decent wind; would changing Props with a different Pitch help slow a Plane down if so, which direction do you go Higher Pitch or Lower Pitch?

    Thanks.
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  2. #2

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    Prop pitch can help but instead could the issue be your approach? Too high on the base leg or final leads to too much airspeed.
    if it were me I'd go up in pitch.

  3. #3
    dasintex's Avatar
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    Approach is good, just can't slow it down enough, never a problem if there is a decent wind, slows down and lands great, no wind, it won't slow down for a decent landing, so a Higher Pitch may help, that's kinda what I thought always great to get feedback to be sure.
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    You actually need lower pitch to slow the speed down. If you are running something like a 14x8, go lower pitch to maybe a 14x6. Each rotation of the lower pitch prop bites less air, given the same rpm of the engine. Are you sure your CG is correct? Nose heavy birds can often lead to higher landing speeds. If you are nose heavy, try slowly shifting your balance point back without getting the elevator too sensitive for your liking. This helps to slow the birds down too. It might be your particular plane just is not going to slow down more due to design and higher wing loading. It may just have to be landed faster than your other planes. Good luck! Let us know how it goes. Jon
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  5. #5
    dasintex's Avatar
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    I'm glad I asked, for some reason I thought Higher Pitch would help slow a Plane down; I will try a Lower Pitch; to answer all the questions, the CG is good, I was running a 3 Blade Prop on this plane and it slowed down without any problems but I switched to a 2 Blade prop to get more speed and throttle response, the Plane just labored to get up to speed, and if I got into trouble I couldn't throttle out of it quick enough, but now I can't slow the thing down to land when I don't have the wind to help.
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  6. #6
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    Lower pitch and a lower idle speed will help.

    If you have two aileron servos and a computer TX you could try CROW braking [ both ailerons move UP together ]. TRY OUT AT ALTITUDE .

    I used to fly real slippery slopers and CROW helped a lot even without flaps.
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  7. #7
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    Have been rather involved in warbird pylon racing for a lot of years now and setup and flown many racers for the fellows and myself. Heck I thought I had retired but recently got dragged back kicking and screaming by the fellows and even involved with a local race next weekend.

    The point of this is those airplanes which are typically grossly overpowered ARF's will use rather short propellors and very high pitch, They also will use a CG that is a tad forward than even what one would use sport flying the same airplane. These are things that do make it a bit harder to slow down for landing it is obvious if one ever watchs that type of event.

    So what to do? The answer is really simple and very quick to accomplish and costs nothing, it is also counter intuitive: You need only to reflex both ailerons up in neutral, perhaps only about 1/16th inch above the intrail position at neutral. This can simply be done with clevis if you like or electronically. Counter intuitive because most think of flaps but this is actually the opposite and has the effect of reducing lift ever so slightly. What doing that does is allow you to carry just a tad more power on the approach and control the approach even better than what you doing now. Give it a try only takes just a moment and it works.

    Oh by the way it will actually make the airplane a tad faster at speed but the naysayers will suggest it messes up you arrowbatic flight, just not so and you notice nothing in that way but then agine a warbird is not exactly an IMAC competitor anyway.

    John
    Last edited by JohnBuckner; 08-19-2013 at 09:36 AM.
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    John is right, but a lower pitch prop- especially one with wide blades- will help.

    I had a problem with an aerobatic model that was too fast on the downline, even at idle. I put a lower pitch APC "wide" prop on it (these have very wide/fat blades), and dropping to idle was like throwing out a drag chute. It provided better acceleration on uplines, as well.

    As noted, try out any changes at altitude; you don't want any surprises when you're flaring for touch down.

    .

  9. #9
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    Usually, when an RC airplane "lands too fast", it's because you're landing it too fast. You need to take the airplane up to altitude and work with it to see how slowly it will fly. You then need to do some traffic patterns at altitude so that you can get used to flying the airplane more slowly. A lower-pitch propeller will not actually slow the airplane, but will make it descend faster on a steeper approach path. Again, you need to find out what the speed range of your airplane actually happens to be. You'll may be quite surprised at how slowly the model can fly.

    If the model will not allow you to fly it slowly at altitude, then your model is either too heavy for its wing area, is balanced badly, or has a bad wing/tail/control surface setup/arrangement. As Mr. Buckner has stated, a slight reflex of the ailerons will help with the approach path, and others have stated that a balance point that's too far forward can also contribute.

    Typically, though, RC flyers tend to land their airplanes too fast. Work with it in the air at an altitude that allows for mistakes, and you'll be able to nail down a good approach speed. I'd bet it's slower than you think.
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  10. #10
    dasintex's Avatar
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    Appreciate all the info, as far as the CG I will recheck that, I generally put the CG on all my planes to what the manuals suggest usually right smack in the center of the suggested range, however, I did make a change in the plane which may be the source of the problem because the CG may not be where it had been originally, and if that checks out I will try Aileron Reflex and possible drop the Prop Pitch; again I appreciate all the great Info.
    Last edited by dasintex; 08-19-2013 at 10:30 AM.
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  11. #11

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    What type of plane is it? The 14x8 that you are using is a decent prop for a 91FS. A little on the fast side, but manageable depending on the idle speed as well. Try a 14x7 or even a 14x6 as suggested earlier.

  12. #12
    Moderator j.duncker's Avatar
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    APC 15 x 4 wide would be my choice.

    That should slow the sucker down.
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    Bax in post #9 hit the nail on the head. Don't miss it.

  14. #14
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    Made Some Changes

    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.
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  15. #15
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    Quote Originally Posted by dasintex View Post
    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.
    A 13x8 apc sport? Really? that's the prop I've used on my YS63. The CRV engine may be trully this anemic, I don't know....let me suggest a couple things to get a lower reliable idle....higher nitro, 20-25% heli blend. A hotter plug such as an OS F. The hotter fuel will produce a better top end too. It sounds to me like your CG may be fine...be careful moving it aft, especially if the model is heavy for its wing area. A 60 size warbird with maybe 650 squares shouldn't weigh more than about 8 1/2 pounds for decent flight envelope, and 6 1/2 pounds is far better. If it's heavier and the CG is moved aft, it's a recipe for a crash on the landing. Come to think of it, if the CG is moved too far foreward, the same crashed landing may result. In both cases the wing stalls.
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    Ok. I am very familiar with that plane. A H-9 P-47 of a friend that I assembled, flew almost 200 times before the batt switch caused its demise. All I can say is that of all the H-9 .60 size warbird that was released that time, the P-47 was the most forgiving of them all in terms of stall speed and ground handling (as compared to the P-51-Marie, Corsair and Spitfire- with flaps). If you were using the 13x8 APC before, then the 13x6 would be too small for that engine. I suggest you try the 14x6 APC so it will have a similar load as the 13x8, but slightly slower. Also, check your idle speed. Most guys have a very high idle that makes their planes uncomfortably fast during landings.

  17. #17
    dasintex's Avatar
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    Quote Originally Posted by MTK View Post
    A 13x8 apc sport? Really? that's the prop I've used on my YS63. The CRV engine may be trully this anemic, I don't know....let me suggest a couple things to get a lower reliable idle....higher nitro, 20-25% heli blend. A hotter plug such as an OS F. The hotter fuel will produce a better top end too. It sounds to me like your CG may be fine...be careful moving it aft, especially if the model is heavy for its wing area. A 60 size warbird with maybe 650 squares shouldn't weigh more than about 8 1/2 pounds for decent flight envelope, and 6 1/2 pounds is far better. If it's heavier and the CG is moved aft, it's a recipe for a crash on the landing. Come to think of it, if the CG is moved too far foreward, the same crashed landing may result. In both cases the wing stalls.
    MattK;

    Appreciate the reply, that RCV91 is a good reliable engine, but trust me, it's just not nearly as strong as a YS or OS, never was really; I chose this engine because it is heavier than other 90 size 4-Strokers and I needed nose weight to balance; your right, I also used a 13 x 8 on a YS63 that I had; the fuel would be a good idea, but the Manufacturer of RCV Engines doesn't recommend anything higher that 10 to 15% and I have been running exactly that without any problems, the Low idle I can get is smooth and reliable, and like I had said previously, never had a problem landing with a 3 Bladed Prop but the prop would not pull the plane with any balls, the 13 X 8 does the job, I just can't seem to get it slow enough for a decent landing unless there is at least a 5 mph wind in the plane's face, Also, like I mentioned I believe the CG changed from when I originally built rthe plane because I changed the Air Valve and Placement and the CG was off, more Nose Heavy then when I originally balanced it.

    Anyways, I will try the plane with the changes I made, the shift of CG slightly more AFT will be manageable, I can move it forward if need be, but the change was slight, it may not even be enough to affect anything, we shall see.
    Last edited by dasintex; 08-19-2013 at 08:49 PM.
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  18. #18
    dasintex's Avatar
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    Quote Originally Posted by ton2di View Post
    Ok. I am very familiar with that plane. A H-9 P-47 of a friend that I assembled, flew almost 200 times before the batt switch caused its demise. All I can say is that of all the H-9 .60 size warbird that was released that time, the P-47 was the most forgiving of them all in terms of stall speed and ground handling (as compared to the P-51-Marie, Corsair and Spitfire- with flaps). If you were using the 13x8 APC before, then the 13x6 would be too small for that engine. I suggest you try the 14x6 APC so it will have a similar load as the 13x8, but slightly slower. Also, check your idle speed. Most guys have a very high idle that makes their planes uncomfortably fast during landings.
    Ton2di;

    Thanks for the reply, I have plenty of Props and several 14 X 6 in several styles including APC, I will give them a try if my changes don't help, I flew the plane for a long time with nothing but 3 Bladed Props but never liked the performance, just got lazy to change it until last fall I almost crashed because I didn't have enough power to get out of a problem, so I bolted on that 13 X 8 2 Blade and loved it, but if there is no wind in the Plane's face, it doesn't want to slow down enough. I will tweek the engine some more to see if it's as low as I can get it, worth a try.
    Last edited by dasintex; 08-19-2013 at 08:10 PM.
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  19. #19
    Leroy Gardner's Avatar
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    Thanks for posting this thread, I have just learned a few things about props, landing speed effects and power to pull it around all with the right prop.
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  20. #20

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    This doesn't make sense to me. With a 5 mph headwind, the plane will slow properly for a good flare and soft touchdown. So you know that the CG is good for landing, it's not overloaded, and the engine will idle low enough to let the wing quit flying. My first question is where in Texas are you that not having a head wind to fly in is a common situation for you? (I'm DFW and the wind is always blowing) Second, if you know the plane will land, have you not tried just doing a longer and shallower landing approach? I know when I've been used to the 10 mph winds that I normally fly in and then get a calm day, it makes me feel that the planes are landing hot. But if they will land smoothly in 10 mph wind, they'll land smoothly in dead calm conditions with 10 mph more ground speed.
    No kid, I said break ground and fly into the wind!

  21. #21
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    How about learning to use your rudder and do a slip. No flaps needed. No prop change needed. Full rudder against the wind (no with the wind so that the max fuse area is presented to the wind) pitch for glide speed. Keep wings level with ailerons.

    Try it with a trainer or sport plane first because too much rudder can cause it to pitch down and snap roll. But with a trainer or sport plane it would be much easier to correct.

    Start adding rudder untill the plane starts to pitch too much or you run out of rudder.

  22. #22

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    First, From everything I've read, and discussed with others, when changing from a 3 to a 2-blade prop, add 2 inches to the length of the 2 blade prop. Second, you didn't state the size, or pitch of the 3-bladed prop you had been using.
    Third, If it were me, I'd use a senario like this: Changing from an 11x 8x3, I'd use a 14x8 2-bladed prop. If I then found my landing speed too fast, I'drop to a 14x7. I have found that length affects thrust, and braking, Pitch affects speed and acceleration.
    Fourth, If you changed the prop, and the airplane is not flying or landing well, work with the prop, before trying any airframe/control surface "bandages".
    Fifth. Make only one change at a time. Too many changes may make the airplane act in a way that is very difficult to control.

  23. #23
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    Got All The Info I Need, Thanks.

    Thanks for all the replys and suggestions, gives me some ideas to work with, fortunately, it's not too often we don't have wind in Texas, it happened the other day and I had a Hard time landing, it's that simple, probably just me, couldn't possible be the plane.
    Last edited by dasintex; 08-20-2013 at 05:04 AM.
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  24. #24

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    I find it helpful to make a few landing passes 20-30 feet up in unfamiliar wind just so I know what the plane needs. Your plane probably lands with a 15 mph airspeed, so going from 10 mph wind to calm increases your ground speed by triple.
    No kid, I said break ground and fly into the wind!

  25. #25
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    Ain't no way a .60 size warbird lands at 15mph. 30-35 at the VERY least. We had a cop in our club and he would radar us. The slowest nitro plane we had was my old CG eagle trainer. Its slowest speed for sustained flight was 27mph.


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