# Test beds for Magnus effect, does it provide useful upward lift?

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#### BABAR

##### Builds Rockets for NASA
TRF Supporter
Okay, @Dotini has has some outstanding results with his Magnus series

and is moving on to more exciting projects.

I am still not buying that Magnus effect provides useful upward lift for a falling rocket.

i propose a test bed, hoping for input from the Magnus Master, @Dotini himself, @Rktman , @mooffle , @boatgeek , and anyone else that want to chime in.

build two fin cans.

both 6 tube fins, one with clockwise cutouts and one normal.

one 34 inch long rocket body with a side port just behind the nose cone.

add weight to the fin can of the cutout fin can to match the intact fin can.

both models should Back Slide, but only the cutout one should spin.

time and observe the flights.

the only unaccounted for variable will be drag, I think it may be different although I am not sure which will be draggy-er, I am guessing the cutout fin can.

I may add an altimeter bay up front, to see if they are reading different altitudes, but that may turn them from BackSliders into LawnDarters, so I may try it with a dummy weight before I risk my new AltimeterTwo.

any thoughts?

#### mooffle

##### Well-Known Member
TRF Supporter
Okay, @Dotini has has some outstanding results with his Magnus series

and is moving on to more exciting projects.

I am still not buying that Magnus effect provides useful upward lift for a falling rocket.

i propose a test bed, hoping for input from the Magnus Master, @Dotini himself, @Rktman , @mooffle , @boatgeek , and anyone else that want to chime in.

build two fin cans.

both 6 tube fins, one with clockwise cutouts and one normal.

one 34 inch long rocket body with a side port just behind the nose cone.

add weight to the fin can of the cutout fin can to match the intact fin can.

both models should Back Slide, but only the cutout one should spin.

time and observe the flights.

the only unaccounted for variable will be drag, I think it may be different although I am not sure which will be draggy-er, I am guessing the cutout fin can.

I may add an altimeter bay up front, to see if they are reading different altitudes, but that may turn them from BackSliders into LawnDarters, so I may try it with a dummy weight before I risk my new AltimeterTwo.

any thoughts?
First thought, get a stopwatch ready. Probably time from pop to ground hit.

Second, are your 'spin tubes' sliced or have windows in them? If sliced, instead of tube fins do two pairs of flat set (rectangles) fins. The first with the same frontal area as your spin half tubes, the second with the same lateral area. You could try whole tubes if windows are in play as the frontal area is the same.

#### boatgeek

##### Well-Known Member
This sounds pretty reasonable. The fully intact tubes are going to be a bit draggier, so you need to account for that somehow. I like the idea of a stopwatch from apogee/noseblow to the ground, with some means of getting a representative altitude.

#### neil_w

##### Doldrum dweller
TRF Supporter
I like better the idea of using an altimeter that measures descent rate... if you can get your hands on one.

#### BABAR

##### Builds Rockets for NASA
TRF Supporter
I like better the idea of using an altimeter that measures descent rate... if you can get your hands on one.
Does jl a2 do that?

#### Dotini

##### Well-Known Member
TRF Supporter
I commend any and all further research into horizontal spin with possible Magnus Effect. I endorse the careful measurement and recording of descent rates. I have been able to achieve a descent rate of 18 fps, which I believe compares favorably to most streamers, and is not too terribly far off an acceptable descent rate for a parachute. I will assist in any way I can. But unfortunately my friend and field research associate (Blair) is off on a multi-state vacation until sometime in June, so my little operation will not see much field work until then.

#### boatgeek

##### Well-Known Member
I commend any and all further research into horizontal spin with possible Magnus Effect. I endorse the careful measurement and recording of descent rates. I have been able to achieve a descent rate of 18 fps, which I believe compares favorably to most streamers, and is not too terribly far off an acceptable descent rate for a parachute. I will assist in any way I can. But unfortunately my friend and field research associate (Blair) is off on a multi-state vacation until sometime in June, so my little operation will not see much field work until then.
18 FPS is a very respectable descent rate. I normally shoot for 20-25 under parachute.

#### mooffle

##### Well-Known Member
TRF Supporter
I always thought the target was 12-15 fps.

#### Dotini

##### Well-Known Member
TRF Supporter
I always thought the target was 12-15 fps.
On page 167 of Model Rocket Design and Construction, Van Milligan gives 3.5 to 4.5 meters per second (11.5 to 14.8 fps) as a general rule of parachute design. On page 172, he discusses performance and design efficiency, which he bases on descent rate vs. weight of the parachute.

He recommends streamers for models under 30 grams (1.05 oz), and, crucially, for larger models which would drift out of sight if a parachute were used.

I vividly recall last week, when I launched a rocket over 400 feet into the air, and it drifted over 300' on a meager 4 mph wind. This was using horizontal recovery with spin. My horizontal recovery rocket without spin fell to Earth much, much faster and closer to the pad. My simpleminded assumption is spin accounted for the difference in performance. This assumption needs to be verified, or otherwise explained.

If it can be verified that spin is responsible for the difference in descent rate, then it seems plausible that the Magnus force, which is created by spin, contributed "lift" or "drag" or "something" to reduce the descent rate.

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#### BABAR

##### Builds Rockets for NASA
TRF Supporter
I like better the idea of using an altimeter that measures descent rate... if you can get your hands on one.
Neil as usual wins the prize. Descent rate is exactly what I am wanting to figure. Fortunately my new Jolly Logic AltimeterTwo says it measures descent rate, so it should be a good tool for this.

I am guessing that rapid rotation should NOT affect the readings, but I am not sure, guess we will find out. I am wondering if I should put the vent hole at the tip of the nose cone (basically cut the tip off), as since the Magnus effect is generated BY the spinning of the lateral surface of the rocket, there may be some weird pressure changes. On the other hand, ANY rocket must have some pretty impressive wind shears across the vent hold on ascent, so maybe doesn’t matter.

I dunno, this is first altimeter I have used.

#### Dotini

##### Well-Known Member
TRF Supporter
Neil as usual wins the prize. Descent rate is exactly what I am wanting to figure. Fortunately my new Jolly Logic AltimeterTwo says it measures descent rate, so it should be a good tool for this.

I am guessing that rapid rotation should NOT affect the readings, but I am not sure, guess we will find out. I am wondering if I should put the vent hole at the tip of the nose cone (basically cut the tip off), as since the Magnus effect is generated BY the spinning of the lateral surface of the rocket, there may be some weird pressure changes. On the other hand, ANY rocket must have some pretty impressive wind shears across the vent hold on ascent, so maybe doesn’t matter.

I dunno, this is first altimeter I have used.
Doing proper science requires proper instruments, which sometimes aren't cheap. At Boeing, we were not allowed to use any tools which were not calibrated and certified. I expect there may be a range of altimeters available to the model rocketeer. Is there an available list of altimeters on the market with objective reviews of their relative price, performance and capabilities? How much do they weigh? How do they work? Do they require access to the atmosphere outside the rocket, or can they be sealed inside? I would like to acquire an altimeter.

#### BABAR

##### Builds Rockets for NASA
TRF Supporter
Doing proper science requires proper instruments, which sometimes aren't cheap. At Boeing, we were not allowed to use any tools which were not calibrated and certified. I expect there may be a range of altimeters available to the model rocketeer. Is there an available list of altimeters on the market with objective reviews of their relative price, performance and capabilities? How much do they weigh? How do they work? Do they require access to the atmosphere outside the rocket, or can they be sealed inside? I would like to acquire an altimeter.

#### neil_w

##### Doldrum dweller
TRF Supporter
Responding to @Dotini :

Virtually all common rocket altimeters are barometric-based, and depend on vent holes to operate properly.

Jolly Logic altimeters are about as good as you can get, but there are plenty of brands that are considered good and accurate (many are certified for competition). Not all report descent speed though.

@BABAR ‘s observation about proper venting of something coming down spinning sideways is an interesting one. I tend to think it’ll be ok.

#### BABAR

##### Builds Rockets for NASA
TRF Supporter
Responding to @Dotini :

Virtually all common rocket altimeters are barometric-based, and depend on vent holes to operate properly.

Jolly Logic altimeters are about as good as you can get, but there are plenty of brands that are considered good and accurate (many are certified for competition). Not all report descent speed though.

@BABAR ‘s observation about proper venting of something coming down spinning sideways is an interesting one. I tend to think it’ll be ok.
Thanks, Neil, glad to know it’s a good one. I wanted something with an LCD readout, I didn’t want to count lights or beeps.

#### neil_w

##### Doldrum dweller
TRF Supporter
Thanks, Neil, glad to know it’s a good one. I wanted something with an LCD readout, I didn’t want to count lights or beeps.
Main downside is that it's on the heavy side for small LPR stuff. I have an Alt3 because I wanted the ability to grab more detailed data onto my phone. If buying right now I'd likely grab a couple of FS Minis, at least until JL releases the long awaited Alt4.

#### DrewW

##### Rocket Surgeon
TRF Supporter
Going to sit and watch science happen on this one. Let me know if we need to enlist the help of NIST for calibration standards.

#### Dotini

##### Well-Known Member
TRF Supporter
Responding to @Dotini :

Virtually all common rocket altimeters are barometric-based, and depend on vent holes to operate properly.

Jolly Logic altimeters are about as good as you can get, but there are plenty of brands that are considered good and accurate (many are certified for competition). Not all report descent speed though.

@BABAR ‘s observation about proper venting of something coming down spinning sideways is an interesting one. I tend to think it’ll be ok.
Main downside is that it's on the heavy side for small LPR stuff. I have an Alt3 because I wanted the ability to grab more detailed data onto my phone. If buying right now I'd likely grab a couple of FS Minis, at least until JL releases the long awaited Alt4.
Thanks for this information, I'm closer to finding the right altimeter for me, but not quite there yet. I agree that a certified-for-competition altimeter is a good idea for this sort of research, and I agree it should be resolved that such an altimeter, while rapidly spinning, still produces certifiable data.

Since the known history/publication of horizontal spin recovery, backslider and super roc research seems to have been done with low power rockets of mainly the BT20 size (my X-2 is BT50), it seems reasonable to keep it that way, at least as the entry point. A suitable altimeter for that size/weight needs to be identified.

I have seen rockets with altimeters attached to the exterior surface. Would this be considered a drawback in any way, or could it be the standard way for this research?

I'm too new to the current state of rocketry to know many of the terms such as Alt3, FS, JL etc. I would appreciate being brought up to speed on these vocabulary contractions and abbreviations. In formal academia or science, it might be preferable to use the full words.

#### Dotini

##### Well-Known Member
TRF Supporter
Where have you seen this? I haven't. I wouldn't recommend it in any case because it's going to add asymmetric mass and drag, especially bad for a rocket that is going to be spinning horizontally.
My mistake. In checking with the rocketeer - a forum member - it turns out to have been a camera.

TRF Supporter