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Float length - 2/14/2010 8:35 PM   
Gravity Storm


 

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Status: offline 		What size floats do I need for a Kadet Seniorita ? I have read that they need to be 75 to 80 percent of the length of the fuselage. This plane only weighs 4 lbs. Any suggestions would be appreciated.

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RE: Float length - 2/14/2010 9:05 PM   
beau0090_99



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Status: offline 		Well,
The size is going to help with stability, but you don't want to make them too heavy. I would look at some foam core floats in that length. I guess 4 lbs would be a .25 or .32 size plane. You could always make your own.
Good Luck,
Curtis

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RE: Float length - 2/14/2010 9:11 PM   
scale only 4 me



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Float length being 75% is not all about buoyancy, it about stability on the water, Length and spread is about being a stable platform,,

The lightest 36" floats you can find will work well

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RE: Float length - 2/14/2010 9:59 PM   
Gravity Storm


 

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Status: offline 		Thanks for the info. Any manufacturer you prefer ?

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RE: Float length - 2/14/2010 10:16 PM   
Desertlakesflying


 

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Status: offline 		Yes, 75% of the length from the thrust washer on your motor to the end of your rudder. Floats level with the horizontal stabilizer. Step no more than a 1/4" ahead of the CG, BUT NOT BEHIND.

Sea Commander, and you'll never have a problem with them.

http://www.seacommander.com/

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RE: Float length - 2/15/2010 1:39 AM   
scale only 4 me



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Status: offline 		I disagree with Cowboy's answer regarding CG/Step (behind relative to what?)

Jim Casey has a nice web site devoted to float planes, look around,, it has some very good general info
http://www.smilesandwags.com/Floats.html

especially here http://www.smilesandwags.com/Floatsite/FAQ2.html

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RE: Float length - 2/15/2010 11:29 PM   
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Status: offline 		Hey, I just tell people what works instead of what most people think works. Seems there was just a conversation like this in a seaplanes thread. Puzzling

Let me rephrase. DO NOT PUT THE STEP OF THE FLOAT BEHIND THE CENTER OF GRAVITY AT ALL.

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RE: Float length - 2/16/2010 1:10 AM   
scale only 4 me



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quote:

ORIGINAL: CowboyLifesaver

Hey, I just tell people what works instead of what most people think works. Seems there was just a conversation like this in a seaplanes thread. Puzzling

Let me rephrase. DO NOT PUT THE STEP OF THE FLOAT BEHIND THE CENTER OF GRAVITY AT ALL.


If I remember right in that thread you said cublover else helped you set up your plane. Go with what works for you, but, I respectfully disagree, That is like putting the mains on a tricycle gear set up infront of the CG,, the tail will drop. That step location could have the plane leaning on the rear of the floats all the time while taxing and will possibly allow the plane to rotate to quickly, this all depends on float desgn also. Although ith a flat bottom airfoil light wingloading plane you could get away with almost anything.


Gravity Storm,
Some more research docs to view
And so does Great Planes http://manuals.hobbico.com/gpm/gpmq1870-1874-manual.pdf (see page 12)

Seaplane supply http://www.seaplanesupply.com/faq.htm






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RE: Float length - 2/16/2010 3:20 AM   
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Status: offline 		The plane tilted up while taxiing keeps the prop away from the water and reduces spray. When you start to get up to speed you move the elevator stick forward and keep building speed until you are ready to takeoff.

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RE: Float length - 2/16/2010 8:09 PM   
Desertlakesflying


 

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Status: offline 		I guess I just prefer planes that fly off the water and don't have to be forced because the step is in the wrong place, which is the case on 99% of the planes that have to be forced off the water. Having the floats level to the horizontal stab will produce the needed incidence in most of the airplanes out there, unless of course they are kits built with 0 wing incidence which I can't understand why anyone would build a plane which could be put on floats that way. Most prop planes have incidence, maybe not the jets. My plane sits perfectly level on the water, and I'm exactly even with the step and the CG. The cub I recently helped get set up is the same way and reacts the same. No extreme angles, no bigger motors, just the right setup the first time.

Cublover post from other thread to add context:
"Scale, just so you know, those floats are NOT wrong. How do I know? I've been putting on floats for over 18 years, other than being a tad bit to tall, and there is a reason for that, "prop is big" I have flown Cowboys Husky several times and its flawless. People who put floats on planes do everything wrong, and some just "get it right" and think there an expert on it.

I KNOW your gonna tell me I'm wrong, and thats OK. But the fact is, is that this plane fly's perfect EVERY TIME, with no bad habits. The reason you have to tap the elevator is because like all good RC pilots, we fly with just a tad bit of "down" in it.

Every plane I have EVER done, including this one, have flown real well with the float set up that was put on it. and there is a reason for that as well. Just like EDO and all float manufactures will have in there install manuals. it is set up that way


Step,,,,,,,,,,,,,,,,,,,, just ahead of the CG 1/8 to a 1/4 inch

and deck of float,,,,,,,,,,,,,,,,,, level to horizontal stab

If you keep with this formula you WILL have a great fly'n plane, no matter if you put floats on a 330L or a Stearman. hahaha

Have a good day...Rod"

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RE: Float length - 2/16/2010 11:27 PM   
Himat


 

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Status: offline 		As the tread have sidetracked, I will follow.

While at rest, the distrubution of bouyancy do set the attitude of the aeroplane. If it is tail up or down do have practical considerations, like keeping the prop out of the water. If there is wind, distribution of submerged side are relative to side area in air start playing. A plane that weathervane extremely strong into or away from the wind can be anoying. To have the plane sit close to level like an aeroplane with tricycle undercarriage on land is probably a good starting point. Some into wind weathervane is good, but do not overdo it.

At planning speed the angle, size and position of the planing surfaces do set the attitude of the aeroplane together with the aerodynamic forces. Note that it's the planning surfaces that's important. The deck line is a dubious reference as the planning surfaces might be arranged different by different designers. A starting point is to have the aeroplane planning with a few deegrees of positive incidence on the wing at take off speed. A little more speed or some elevator input and the plane is flying. Note that the plane must be able to rotate to make the elevator work.

Step forward or aft of CG? If it's in the fractional inch range it's probably just fine tuning, if not something else is wrong.

Sveinung

(One engineer, one answer.
Two engineers, two answers.
Three engineers, an interesting discussion.)



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RE: Float length - 3/4/2010 1:56 AM   
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Status: offline 		If you go to post #5 and click on Jim Casey's web site, then go to Randy Lindermans site with Chuck Cunningham, you will find all the info on floats and float flying you will need............

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RE: Float length - 6/3/2010 8:25 AM   
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Status: offline 		One difference I see is that Chuck Cunniham places the step 1/2" 'Behind' the CG. Others on this post place the step just 'Ahead' of the CG. I personnaly use the Chuck Cunniham method and have had wonderful results. I guess it all boils down to what works best for you.

Good Luck and happy flying

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RE: Float length - 6/3/2010 9:18 AM   
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Status: online 		I love those who claim everyone who does not do exactly as they say are totally wrong.

Step slightly aft of the CG is indeed an excellent setup and this aids in directional stability while on the step.

John

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RE: Float length - 6/4/2010 3:43 PM   
JimCasey



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Status: offline 		Chuck Cunningham's articles are the holy grail of RC float Flying. The main article is available in several places on the net. Randy Linderman got permission from Chuck himself to post it, so I still refer to that link. http://flyinglindy.homestead.com/skisandfloats.html
Chuck puts the step slightly behind the balance point.

Within a month or 2 of Chucks article which appeared in RCM, Ed Westwood wrote a similar but more techie article in MAN. He says to put the step under 40% of the MAC. For those of us from Tennessee, that means slightly behind the balance point. http://www.smilesandwags.com/Floatsite/westwood.html

Andy Lennon used a line swept back 10 degrees from the CG to locate the step. that still puts the step slightly behind the balance point, but it scales better.

Ken Willard used a step location slightly behind the balance point.

Each of the gentlemen above have researched NACA papers, have built and published many airplane designs, and their designs and articles passed peer review, and were demonstrated thousands of times to work well.

Take a look at the Wipline website and you will see the Full-Size airplanes with the steps even farther back...approx 50% of the wing chord.
http://www.wipaire.com/wipline/index.php

Now CowboyLifeSaver suggests that the only TRUE setup is with the step ahead of the balance point. One thing I have learned about float setup is that the "rules" are merely guidelines and things can still function properly when the "rules" are not strictly adhered to. This setup probably fits his flying style and his particular airplane. However, when I suggest setup tips to a newbie, I'm going to give him the guidelines to set his plane up dead center in the middle of what the tried and true practices are. CowboyLifeSaver's assertions that, with traditionally located step position, you will lose the ability to rotate the plane for takeoff are (as diplomatically as I can muster): incorrect. Still his setup works for him, and you probably won't get into trouble until your floats are far enough forward to adversely affect lateral stability.

I also don't agree with Cowboylifesaver's instruction to set up the float with the deck of the float parallel to the horizontal stab. The incidence of the horizontal stab is "usually" zero, but not always. If it's in the wing wash, the designer may have compensated by correcting the incidence of the horizontal stab to be zero to the local airflow in the wing wash. Roll out a set of plans for a Goldberg Eagle or a Telemaster to see what I'm talking about. Still- it usually works, it's just an inferred measurement. If you know your stab is at zero incidence, it can be an easy place to set a spirit level. The true, meaningful measurement is the wing's incidence should be 2-3 degrees positive to the deck of the float, if the float has a straight deck on top.

My particular bug about putting floats on planes is that newbies buy floats and then ask about setting them up. "I just bought a set of these huge heavy plywood floats from a big mailorder house and I want to know how to make my plane fly with them". I list several suppliers of foam-core floats on my website. Plane Fun Floats, Sea Commander, and Seaplane Supply, in alphabetical order. Foam-core floats are light, strong, efficient, and can't leak. I don't get a penny from the endorsements, I just want to see flyers succeed.

< Message edited by JimCasey -- 6/4/2010 4:10 PM >

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RE: Float length - 6/5/2010 2:31 PM   
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quote:

ORIGINAL: CowboyLifesaver
Step no more than a 1/4'' ahead of the CG, BUT NOT BEHIND.
http://www.seacommander.com/

I don't agree with that at all.
First, to answer the original question, the float need to be long enough to have minimum 10% of their length, up to 15%, ahead of the prop. I usually measure from the prop to the CG and multiply by 2.5 to get the float length.

As for step placement, I did some systematic tests a number of years ago and wrote it up in a magazine article in March 1998. here are my findings.

Aft Step Position
We usually recommend placing the step just aft of the CG on models (floats or flying boat hull). On the full size Catalina the step position is a long way aft of the CG, and one supposes they did it for good reasons. Adrian Rowe-Evans wrote about building a nine foot span model of the Catalina in the British Waterplane Association newsletter, and noted that to get it airborne he had to put a step in the hull just aft of the CG; the scale step 6" aft of the model CG wouldn't do. He could get the model planing, but not airborne. I decided to investigate the effect of an aft step on a model floatplane.
I took my trusty 76" span PeTe floatplane and extended the step with 6" of blue foam to about 7" behind the CG. It will be impossible to take off like this so I took some tools along. The idea was to cut off the added foam, bit by bit, until the model would take off. I would then find out how critical the step position is.
First time, with a gentle breeze rippling the water, I opened the throttle and off it went across the water, and up onto the step. I teased on some up elevator to get the feel, and up it went. It took off. "Don't you read the books, you stupid plane?" Oh, Well! I flew it around for a while and of course it still did all the loops, bunts and rolls it could do before. What about touch and go landings? Yes, them too.
The modification had increased the step depth to 0.83" and the sternpost angle effectively increased from 5 degrees to 8 degrees, which may be significant. I added more blue foam to restore the original step and angle, and took it back on a glassy calm, still day. Initially it seemed to be sitting a little more nose down, and throwing up more water than usual, perhaps because of the extra buoyancy behind the step. It did eventually get up on the step and, accelerating well, the model set off across the smooth water, planing at high speed as I pulled more and more up elevator. I hit full up, then up it went. It STILL flies! Granted it needed full up and full power, but it took off and flew.
However, landing was a little bit fast, and on touching down the model suddenly plunged its nose forward into the water. It has never done THAT before. It appeared that the new surface area just ahead of the step, which is now a long way behind the CG, hit the water first and gave it a nose down pitch which was enough to drive the floats nose first into the water, and the model came to a very abrupt halt. Further landings were flared out a bit more and were more normal, though not quite so easy as with the standard step position.
I then started tearing off the blue foam, a bit at a time, flying the model after each change, and the original delightful handling gradually returned. I proved that step position is not critical, but if the step is too far behind the CG the model may sit more nose down and throw up more spray. It may not be as directionally stable when planing. It may be more reluctant to rotate and leave the water surface. And it may be more difficult to land.


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RE: Float length - 6/5/2010 4:51 PM   
scale only 4 me



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quote:

ORIGINAL: JimCasey

Chuck Cunningham's articles are the holy grail of RC float Flying. The main article is available in several places on the net. Randy Linderman got permission from Chuck himself to post it, so I still refer to that link. http://flyinglindy.homestead.com/skisandfloats.html
Chuck puts the step slightly behind the balance point.

Within a month or 2 of Chucks article which appeared in RCM, Ed Westwood wrote a similar but more techie article in MAN. He says to put the step under 40% of the MAC. For those of us from Tennessee, that means slightly behind the balance point. http://www.smilesandwags.com/Floatsite/westwood.html

Andy Lennon used a line swept back 10 degrees from the CG to locate the step. that still puts the step slightly behind the balance point, but it scales better.


I tried Ed's theories from the "How to" MAN article to test and set up few different models, I sure wish I would have held onto that issue.
I seem to remember Ed used a right angle off the afterbody up to the CG to locate step location relative to CG, not like you mention Andy's 10 degree down method, If you figure 3 degree incidence + 3 degree afterbody angle it ends up more like 6 degrees not 10. 10 would shoot it aft of CG even further, but again depending on many factors, it still could work fine.

Optimum location (and workable range) of step and incidence angle can vary greatly depending on the model, A flat bottom airfoil Cub or Senorita like the OP's plane will be set up quit differently with a much wider workable range that a semi-symmetrical Scale plane like my Kingfisher or fully symmetrical Extra 230 I've built for example. The more rotation angle the plane needs to take off and land the more critical these angles and location become.

There's just not one answer for all air frames. You can't just say "always put it 1/X" infront/behind CG" Period, there are too many variables



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RE: Float length - 6/6/2010 5:54 AM   
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Status: offline 		Alasdair, thanks for documenting your scientific method.

Back to your comments about Catalinas: Years ago I worked with a former PBY pilot. He regaled me with stories of how it took both pilots rocking the boat with the elevator to get up on step with smooth water. When they were in the harbor it was common to send a couple of destroyers out to stir up the surface so the PBYs could take off.
Scale PBYs suffer also from inadequate step depth. I'm pretty sure the full-sized ones used a vented step to get some air in there to help break suction.

Scale only 4 me: We agree that there is a broad widow of "what will work". Float incidence seems to be more critical than other parameters. If the nose is too low, the plane rides up on the nose and becomes unstable just about takeoff speed. If the nose is just a little lower than that, the plane can porpoise. There's about a 5-degree "happy range", then if the nose is too high, the plane won't rotate.
I remember an older gentleman showing up at our pond with a Senior Telemaster with the noses of the floats massively too high. He said he had never flown it and wanted some help trying it out. I offered to tweak the incidence of the floats...he had an extension strip attached to the rear hard points to make the tail higher. He did not want me to adjust it. We did the "high-speed boat" trick with it for several minutes, finally doing figure-8s back and forth over its wake and got it in the air. After landing, I asked again if he would like for me to tweak it so it would take off. He said, "nope, it seems fine to me" , and he left and never came back. Meanwhile my Senior tele would take off in 6 feet reliably. ( But I liked taking off at about 1/3 power, making long, graceful liftoffs)

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RE: Float length - 6/6/2010 8:10 AM   
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Status: offline 		Interesting, all the difference of opinions about floats. Twenty years ago, I followed the Cunninghams instructions and never had a problem. I'v e built at least half a dozen float planes and still fly most of them once a week. It's been several years since I've read his column in Model Airplane news, but the one I kept is in the October, 1991 issue. I t told me all the basics of model float design.


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RE: Float length - 6/6/2010 8:13 AM   
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RE: Float length - 6/6/2010 1:34 PM   
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Status: offline 		JimCasey, Thank you. I have more from the following month, but I start with tests on floats designed like those on hugho's red model, with the underside angled up from step to bow end.

I started designing floats based on the full size ones in the photo, on a Piper Cub at Jack Brown's seaplane base in Florida. Note that the bottom ahead of the step is parallel to the top for a bit, maybe a quarter of the total length.
Here is a bit of my next magazine article, dealing with that. Plus some systematic tests of float angle.

I tried a new design of floats on my latest PeTe design, the 46" span version with the OS 10. Until now, all my floats have had the planing bottom ahead of the step parallel to the top, but not this pair. This time I took someone's advice from a magazine article and angled the bottom up at 3 degrees. The photo will give the idea. They worked adequately into wind on choppy water, but when I tried them in calm weather the aeroplane behaved quite differently.
It was a real dog, refusing to take off and just squirreling about on the water like an ugly duckling. I tried changing the float angle, a wedge at the step, 30% nitro in the fuel. No good.
I decided to change the floats rather than the engine, since I recently discovered to my surprise that floatplanes can manage with remarkably little power. I went back to my normal float design and the model is directionally stable and will now run straight hands off. If the up trim is set it will take off by itself without pulling back on the stick as well, just like its three big brothers (56", 66", and 76" span). My advice is to make the floats with the bottom just ahead of the step parallel to the top and to the aircraft's datum line as that seems to work best.

Step position
The next obvious trial was to move the step too far forward, so the whole float mounting was unscrewed and re-attached with the step ahead of the CG. I put it in the water, opened the throttle and off it went. There were no problems taking off, or flying around, flying some aerobatics, or with circuits or touch and go landings. After burning off 10 oz of fuel I brought it in and cut the engine. As it glided to a stop in front of me the model leaned back until the tail slowly dipped into the water. All-right PeTe, point taken! The buoyancy is too far forward.
I took off the 45" floats and fitted a 36" pair which barely extended as far forward as the prop, with the step correctly placed. At rest in the water the floats were low in the water, betraying that they were meant to support 6 pounds, not 8. On calm water they threw up more spray initially as engine power pulled the nose down, until the model was up and planing. But on choppy water the model would sometimes surge forward and the prop would take a great bite out of the next approaching wave, creating a cloud of spray. Usually the engine recovered from the shock, but sometimes it would stop in protest. Not enough buoyancy forward.
Angle of Dangle
I was told, and I always tell others, mount the floats parallel to the datum line! But what if you don't?
On PeTe 10 the angle of the floats could conveniently be changed from level to five degrees either way in three increments. There are two ways of looking at this. Either you look at the model flying, with the nose of the floats angled either up or down. Or you sit it on its floats and say that the nose of the aeroplane is angled up or down relative to the floats. Since you sit it down before you try to fly, I'll refer to the second option.
I lengthened the rear float attachment to angle the nose of the aeroplane down by 1, 3 and then 5 degrees. In each case the model took off and flew fine though, especially on the last trial with the nose down at 5 degrees, the engine tended to pull the front of the floats down into the water creating excess spray. However, with a little speed the hydro-dynamic and aerodynamic forces lifted the float fronts, the model planed beautifully (directionally stable) and lifted off a treat. The handling was fine with just a little down trim needed. On landing the aircraft came in with the floats held nose up out of the way and when it hit the water and decelerated it pitched nose down onto the floats, which kills the lift and removes any thoughts it might have had about bouncing or porpoising.
Next the floats were angled the other way by up to 5 degrees, so that the aircraft sat nose up on the water. At 3 degrees the model would no longer track straight, but planed along chasing imaginary rabbits like a puppy in a field. It seemed that aerodynamic forces were lifting the tail to a level attitude, and that shifted the planing point from the step to the front of the planing surface, producing instability. However flight was achieved after a difficult take off.
While I was increasing the nose up sit to 5 degrees there was a sharp increase in the wind, producing a chop on the water. The exaggerated nose up sit of the model prevented take off, or rather, the plane leapt off the water far too soon and immediately cartwheeled back in. Several times. Eventually I gave up and hand launched. The model flew around well enough but it looked very odd and did not seem quite as stable in flight as normal. A touchdown on the water was attempted, and despite the nose down hang of the floats, was accomplished without incident.
To check that the refusal to take off was not attributable to the sudden rise in wind and rough water, the floats were returned to their usual angle and another take off was attempted. This time the model lifted off easily and cleanly from the water despite the rough surface.
So what have I learned?
1. If the floats are right excess power is not necessary, but power could compensate for other faults.
2. Put the step just aft of the CG, but it is not critical with excess power available.
3. Float size is not critical on calm water.
4. On rough water 10% of the float length ahead of the prop is a great help.
5. With the floats level on the bench, rig the model level (or slightly nose down).
6. A nose up sit (on the bench) produces planing instability and makes take off unexpectedly difficult.
7. Waterplane flying is always fun.


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(in reply to JimCasey)
       Post #: 21

RE: Float length - 6/6/2010 5:11 PM   
JimCasey



Posts: 1930
Score: 115
Joined: 3/4/2002
Last Login: 5/21/2013
From: Lutz, FL, USA
Status: offline 		Alasdair, Thanks again for your scientifically documented observations.

Further to your conclusion #4, 1/3 to 1/2 of the prop diameter of float length in front of the plane of the prop contributes to successful beaching. If the prop is in front of the noses of the floats, it can be damaged on shoreline obstructions.

The real beauty of this discussion illustrates two points. (1) my contention that the "rules" are just guidelines, and (2) Most floats can work, and there are symptoms and remedies for poor water handling.

Thanks for your comment "that floatplanes can manage with remarkably little power". The "Everybody knows" that I have always disputed is that you need to bolt a turbo cosworth or some such drastic overkill to the front of a Kadet senior if it has floats. My experience is that if the floats are sized and rigged properly the plane will need no more power than if flying from wheels. Light weight helps. Ever since i used my first pair of foam floats I have used nothing else. They are only marginally heavier than wheels, and contribute very little more drag. (Floats have more frontal area, but are more aerodynamic than a wheel. corollary: it is reported that the wing of a 747 contributes about the same drag as a 1" steel rod the same length. )

_____________________________

Jim Casey/Seaplane Nerd
http://www.smilesandwags.com/Floats.html

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(in reply to alasdair)
       Post #: 22

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