P3 Retractable Landing Gear

I would suspect very little. Lift doesn't happen because of the air blowing down, that's a side effect. The lift happens right at the prop itself. Once the air leaves the prop blade, its no longer doing any work.
That's an interesting theory you have. So if I were to attach a horizontal plastic plate on top of the P3 body but under the props, blocking all air flow downward, this won't affect flight time?
I doubt if that would even fly. Air flow does affect performance, the less flow the less flight time imo.
 
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The major contributor to [reduced] flight time is the added weight. To what extent, I haven't heard thus far (or don't recall).
 
I didn't know the landing gear was ever visible in the camera's eye? I know it wasn't when I had my P3P.
 
That's an interesting theory you have. So if I were to attach a horizontal plastic plate on top of the P3 body but under the props, blocking all air flow downward, this won't affect flight time?
I doubt if that would even fly. Air flow does affect performance, the less flow the less flight time imo.
Try it and see what happens. I think you'll be surprised by the results.
 
Try it and see what happens. I think you'll be surprised by the results.
Funny, how about you try it, I'll be waiting. Here's what you'll find. You'll have a windstorm from the props putting 100% of the force pushing the P3 body downward, essentially making the craft weigh 10+ pounds, flying nowhere. Any lift is virtually cancelled out, zero aerodynamics.

Folding legs in the up position will do the same thing to a lessor extent, catch the down draft of air from the props, virtually increasing the weight of the craft from poor aerodynamics, shortening the flight time. I just asked how much shorter?

Notice the OP isn't answering, likely because it's a significant impact on flight time. I'm guessing 2 min less. I'm sure someone out there knows.
 
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IMO the landing gear do not represent enough surface area to be of significance in this context.
How much of the prop 'disc' is over/on top of the shell arms? 10-20%???
 
Funny, how about you try it, I'll be waiting. Here's what you'll find. You'll have a windstorm from the props putting 100% of the force pushing the P3 body downward, essentially making the craft weigh 10+ pounds, flying nowhere. Any lift is virtually cancelled out, zero aerodynamics.
Well I suspect if you were block off the area under the props completely, you would have a hard time getting off the ground, but not for the reasons you suspect, i.e. the lack of air pushing down behind the props. The reason is because the props do indeed move air and that air has to go somewhere. So if you block off its path downward, you're much more likely to have it dirty up the flow around the boundary layer of the upper prop surface and thus end up with props in VRS and therefore making very little lift.

Now if you to redirect the air flow below props somewhere other than down and somewhere other than back up into the props, say off to the sides or something like that, it would fly just fine. Why? Because the props are airfoils and airfoils make lift by virtue of air flow around the top and bottom surfaces of the foil. That's where most of your lift comes from. Not from the air pushing down.

Now, would doing something like this lower flight time? Of course it would. But again, not for the reason you likely suspect. It would lower flight time because anything you add to redirect air flow below the prop disks is going to also add weight. And any weight you add is going to eat flight time. There ain't no such thing as a few lunch. And that's why adding retracts will lower flight time. Because adding retracts also adds weight. But the gear itself sticking out in the air flow would have an almost immeasurable effect on lift and/or flight time.
 
Well I suspect if you were block off the area under the props completely, you would have a hard time getting off the ground, but not for the reasons you suspect, i.e. the lack of air pushing down behind the props. The reason is because the props do indeed move air and that air has to go somewhere. So if you block off its path downward, you're much more likely to have it dirty up the flow around the boundary layer of the upper prop surface and thus end up with props in VRS and therefore making very little lift.

Now if you to redirect the air flow below props somewhere other than down and somewhere other than back up into the props, say off to the sides or something like that, it would fly just fine. Why? Because the props are airfoils and airfoils make lift by virtue of air flow around the top and bottom surfaces of the foil. That's where most of your lift comes from. Not from the air pushing down.

Now, would doing something like this lower flight time? Of course it would. But again, not for the reason you likely suspect. It would lower flight time because anything you add to redirect air flow below the prop disks is going to also add weight. And any weight you add is going to eat flight time. There ain't no such thing as a few lunch. And that's why adding retracts will lower flight time. Because adding retracts also adds weight. But the gear itself sticking out in the air flow would have an almost immeasurable effect on lift and/or flight time.
I agree with most of your logic, except no affects on flight time. I'm not so sure there's no effect like you. If you measure the square inches of the landing gear in the air path when retracted up, then put that area under the props, I'm guessing the added weight is a couple pounds, plus the added weight of the mechanism. It's interesting debating this because aerodynamics is key for efficiency imo. Landing gear just doesn't seem aerodynamically efficient, especially for virtually no benefit other than looking cool.

One post mentioned advantages of the ability to store the craft in a thinner case with the gear retracted. You would also have to remove the camera, which is a hassle.... Just for a thinner case? It's not worth the hassle, especially when I don't need a thinner case. My backpack is 9" deep, within tolerance for carry on luggage.
 
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I agree with most of your logic, except no affects on flight time. I'm not so sure there's no effect like you. If you measure the square inches of the landing gear in the air path when retracted up, then put that area under the props, I'm guessing the added weight is a couple pounds...
I think you're grossly overestimating that. Look at the cross section of the landing gear shape. Its kind of a rounded oval yes? And a rounded oval shape is roughly (ok very roughly) what an airfoil cross section looks like.

I've read so many books and articles on aerodynamics and drag/efficiency when it comes to aircraft design factors that I don't recall which one contained this little tidbit, but I recall an aerodynamics engineer talking about the typical Cessna 172 wing strut. I suspect the exact size might vary from model year to model year but most 172 struts are about 2" in diameter and maybe 8' or 10' long. Those struts are just hanging out there in the wind slowing the plane down. But those struts are also a pointed oval shape. And because of that, when you do the math on them, you find that they present a drag profile to the wind which is roughly equal to the amount of drag you'd get if that 2" thick strut were actually a 3/8" braided steel cable.

Now obviously, the phantom landing gear are not a finely tuned airfoil shape honed in wind tunnels by the finest minds on the planet. But it ain't exactly a brick wall either. That rounded profile presented to the downwash is going to mean that the net resistance in drag will be much lower the sum of its surface area. Significantly lower. And we're talking about a net surface area that is not all that big to begin with.

If you took a phantom equipped with these retracts and did 10 flights with the gear down and locked and then 10 flights with the gear up, I'd be very surprised if the difference in flight times were greater than the statistical margin of error.
 
I think you're grossly overestimating that. Look at the cross section of the landing gear shape. Its kind of a rounded oval yes? And a rounded oval shape is roughly (ok very roughly) what an airfoil cross section looks like.

I've read so many books and articles on aerodynamics and drag/efficiency when it comes to aircraft design factors that I don't recall which one contained this little tidbit, but I recall an aerodynamics engineer talking about the typical Cessna 172 wing strut. I suspect the exact size might vary from model year to model year but most 172 struts are about 2" in diameter and maybe 8' or 10' long. Those struts are just hanging out there in the wind slowing the plane down. But those struts are also a pointed oval shape. And because of that, when you do the math on them, you find that they present a drag profile to the wind which is roughly equal to the amount of drag you'd get if that 2" thick strut were actually a 3/8" braided steel cable.

Now obviously, the phantom landing gear are not a finely tuned airfoil shape honed in wind tunnels by the finest minds on the planet. But it ain't exactly a brick wall either. That rounded profile presented to the downwash is going to mean that the net resistance in drag will be much lower the sum of its surface area. Significantly lower. And we're talking about a net surface area that is not all that big to begin with.

If you took a phantom equipped with these retracts and did 10 flights with the gear down and locked and then 10 flights with the gear up, I'd be very surprised if the difference in flight times were greater than the statistical margin of error.
You may be right, however the lack of response from the OP who's promoting them appears to indicate otherwise. If it was less than a minute less, no big deal, however I still don't see much of an advantage to paying the $220 for little in return, other than the cool factor, and it does look cool when gear retracks on other quads. I wish he'd respond with some test data to prove me wrong.
 
Well to be fair like we said, they're adding weight so an impact on flight time is to be expected. As for the utility of it, I can't comment on the P3 as I don't have one. But on my P2 with a gopro, I have the gear and props in the shot if I shoot wide. The props is somewhat manageable if I don't allow the camera to tilt all the way up. But there is nothing I can do about the gear so this type of solution would help. As it is, I just shoot medium or narrow and solve the problem that way. But it's be nice to be able to shoot wide once in a while too.
 
I bought the retracts for my FC40. It's really about the "cool" factor more than anything else. Quite frankly, I have no plans to buy for my P3P.
I will same RCDepot hobbies is a solid company. I live nearby and after a small crash that caused damage to the retract module, they fixed it quickly when I just "walked in".
 
I have experience with physics and aerodynamics and I can honestly tell you that everything has an effect on flight time and aerodynamics is pretty critical for large aircraft. The saving grace with the retracts is that 1. its not completely impeding the airflow, and 2. its symmetrical disturbance is very unlikely to cause an imbalance or instability. What I do see is likely 5% decrease in maneuverability and 5% decrease in battery flight time.

I was planning to buy a set but 200 is about 150 more than I would ever spend for such a luxery. All I see is cool factor and the fact with aggressive maneuvers the landing gear will be out of shot. ALSO increases the probability my gimbal will certainly break the phantoms fall in a crash... I read about a failsafe mod but in reality this stuff is getting so ridiculously expensive I'd be willing to invest in a parachute or insurance...

BUT a real world flight test would have to be done with the P3. Math rarely helps in these complicated situations especially when its a small difference. I have seen retracts on phantoms before and they look cool and I have never heard anyone complain about flight time or lack of maneuvering... Its about 3oz in weight I've read about so that will decrease flight time alone.

TEST:
  • same P3 with and without the retracts
  • same battery
  • same charge time (balanced too)
  • same identical maneuvers in flight (nothing aggressive)
  • flying until the low battery indicator comes up on the HUD.
 
Yep it does, the signal path changes from horizontal axis to vertical axis, so unless you are standing directly under the bird it's going to decrease range.

I would think it would change the orientation of the antennas in the legs. And not for the better .
 

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