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108'' PBY Power System

Old 03-22-2008, 05:27 PM
  #1  
daviator
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Default 108'' PBY Power System

We're building a 108" PBY. Finished weight with retracts about 20lbs. Had some fun with small arf electrics lately and am very impressed with performance. Now the big question. What power system will get my scale Pigboat in the air? The plans call for 60 -80 2cyc. The plan designer (Novack) uses O.S 91 4cycs. My calculations for electric conversion don't look promising because of the limited propeller diameter. I've only got 13'' between prop shaft centerlines.
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Old 03-23-2008, 02:02 AM
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Originally Posted by daviator View Post
We're building a 108" PBY. Finished weight with retracts about 20lbs. Had some fun with small arf electrics lately and am very impressed with performance. Now the big question. What power system will get my scale Pigboat in the air? The plans call for 60 -80 2cyc. The plan designer (Novack) uses O.S 91 4cycs. My calculations for electric conversion don't look promising because of the limited propeller diameter. I've only got 13'' between prop shaft centerlines.
Hi, This Towerpro 3520-07 motor Should work Nice for you, on 5 Cells, Equall to a 60 size 2 stroke nitro, with a 13x6.5 apc prop or 11x 8-- 3 blade if you need the room, about 850 WATTS on each motor, for a total of about 1700 WATTS.

http://www.hobbycity.com/hobbycity/s...?idProduct=666
read the feed back on this motor at Hobby City, If Buying over seas, use Paypal, its cheap insurance, you will get your money back, just incase.

http://www.uce-bestbuy.com/views.asp?hw_id=530



http://www.hobbycity.com/hobbycity/s...idProduct=4130
5 cell lipo 4100Mah


and a 80 AMP ESC
http://www.hobbycity.com/hobbycity/s...idProduct=4315



and a UBEC, if using 4 cells or more, you need to use a UBEC.

http://www.hobbycity.com/hobbycity/s...idProduct=2160



Hope that helps, Chellie

Last edited by CHELLIE; 03-23-2008 at 11:43 AM.
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Old 03-23-2008, 07:25 AM
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13" between the shafts? - so a max prop diameter would be 6.5" ? Less really because you dont want the tips that close.

How were they running OS91 4cycl's on 6" props? Even 4 blade 6" props wouldnt load up a 91 I wouldnt think.

Did you mean you had room for 13" props like Chellie proposed?

That IS going to be a challenge trying to get enough thrust from 6" props to get a 20 lb plane off the water.

Even Chellie's suggested setup would be marginal I'm afraid.

Id guess that plane would want more like 100-150 watts per pound minimum to ROW, so your going to want 2000-2500 watts peak to get off the water. It takes a good bit more power to take off from water than land.

Once your in the air it will take a lot less to keep it there.

No offense Chellie, but no way would I trust a project like this to that cheep stuff from Hobby city.

Your going to need to pump a 1000 watts thru each motor so they need to be efficient. The cheep stuff just doesnt survive at hi power levels very long due to inefficiency and over heating. Not to mention that plane is going to be too nice and waaaaaay too much work to risk it on cheep stuff.

IF you really only have room for 6" props, your probably going to have to go with inrunners to get enough rpm, efficiently, to produce the thrust you need.

If it was me, Id start with two of the new Medusa 36-60-1100 V-2 motors and run them on twp 12S1P A123 packs. They are very very nice motors for the money and very efficient.

The MOTORS will be efficient but the 6" props turning at 40K will NOT be efficient at all - and noisy as heck!

Still, that should put you in the 1000-1200 watts per motor range. The motors are rated to 920 watts and thats a conservative rating, but you'll still want to use good throttle management.

If you have room for 12" props then Id go a different route and use an outrunner like the Hyperion Z4035-10 or similar. It should get you close to 1000-1200 watts on a 12" prop and 12S A123's.

With that power system you should get good takeoffs and be able to cruise for an easy 8 minutes or more.

Good luck!

Larry
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Old 03-23-2008, 07:31 AM
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If it's 13" between the shafts, you should be able to run up to 12" props provided the motors will swing them and they clear everything else. That will leave 1" clearance between the tips. Remember you only count half of each prop between the shafts.
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Old 03-23-2008, 07:46 AM
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Silly me! - One tooooo many juice packs tnight

I should have known something was wrong - 100" span and 6" props???

Larry
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Old 03-23-2008, 08:09 AM
  #6  
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Originally Posted by Larry3215 View Post
Silly me! - One tooooo many juice packs tnight

I should have known something was wrong - 100" span and 6" props???

Larry
That apple juice will do it every time.
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Old 03-23-2008, 10:14 AM
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Originally Posted by Larry3215 View Post
13" between the shafts? - so a max prop diameter would be 6.5" ? Less really because you dont want the tips that close.

How were they running OS91 4cycl's on 6" props? Even 4 blade 6" props wouldnt load up a 91 I wouldnt think.

Did you mean you had room for 13" props like Chellie proposed?

That IS going to be a challenge trying to get enough thrust from 6" props to get a 20 lb plane off the water.

Even Chellie's suggested setup would be marginal I'm afraid.

Id guess that plane would want more like 100-150 watts per pound minimum to ROW, so your going to want 2000-2500 watts peak to get off the water. It takes a good bit more power to take off from water than land.

Once your in the air it will take a lot less to keep it there.

No offense Chellie, but no way would I trust a project like this to that cheep stuff from Hobby city.

Your going to need to pump a 1000 watts thru each motor so they need to be efficient. The cheep stuff just doesnt survive at hi power levels very long due to inefficiency and over heating. Not to mention that plane is going to be too nice and waaaaaay too much work to risk it on cheep stuff.

IF you really only have room for 6" props, your probably going to have to go with inrunners to get enough rpm, efficiently, to produce the thrust you need.

If it was me, Id start with two of the new Medusa 36-60-1100 V-2 motors and run them on twp 12S1P A123 packs. They are very very nice motors for the money and very efficient.

The MOTORS will be efficient but the 6" props turning at 40K will NOT be efficient at all - and noisy as heck!

Still, that should put you in the 1000-1200 watts per motor range. The motors are rated to 920 watts and thats a conservative rating, but you'll still want to use good throttle management.

If you have room for 12" props then Id go a different route and use an outrunner like the Hyperion Z4035-10 or similar. It should get you close to 1000-1200 watts on a 12" prop and 12S A123's.

With that power system you should get good takeoffs and be able to cruise for an easy 8 minutes or more.

Good luck!

Larry
Hi Larry The PBY is a big flying GLIDER 2, 3520-7 on 5 cells, will almost rip the wings off that plane Take care, Chellie

Last edited by CHELLIE; 03-23-2008 at 10:45 AM.
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Old 03-23-2008, 10:15 AM
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Originally Posted by Larry3215 View Post
Silly me! - One tooooo many juice packs tnight

I should have known something was wrong - 100" span and 6" props???

Larry
YOU BETTER SHARE what your Drinking Larry and it better not be PRUNE JUICE Chellie

Last edited by CHELLIE; 03-23-2008 at 10:56 AM.
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Old 03-23-2008, 10:24 AM
  #9  
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A Little more info on the PBY

http://groups.msn.com/rcmodelsflying...electrics.msnw

5. PBY-5A Catalina. (1999) 1/12 scale Span 100 ins. Wing area 1350 sq in. Airfoil Eppler 195 with NACA droop outboard. Length 63 in. Weight with sixteen RC-1700 cells is 147 ozs giving wing loading 15.7 oz / sq. ft. Motors are Master 550 can motors, (similar to Speed 600) with Master Airscrew 3.0:1 gearbox driving Master Airscrew 11 x 8 three blade props. Motors wired in series with differential power for water steering. Props turn 5,200 RPM static at 19 amps giving 46 ozs thrust. Six channels provide for retractable landing gear (own design) and retractable tip floats. Excellent performer off water as well as land. Hull is 1/32" ply and fuselage sides’ 1/16 balsa covered with silkspan and nitrate dope for water resistance. Flies at 33 watts / pound. April 2001, motors changed to Magnetic Mayhem with 2.5:1 gearboxes, same 11 x 8 three blade props. Much better performance with 6,000 RPM at 22 amps static giving 60 ozs thrust. 40 watts / pound.

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Old 03-23-2008, 10:27 AM
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The twin 3520-7 on 5 cells , with a 13x6.5 or 11x8 3 blade prop if you need the room, will give about 16 LBS of thrust combined, more than enough thrust 3.7v x 5 = 18.5v x 600kv = 11100 RPM on a 11x8 - 3 blade prop should do it 11 x 8 three blade props. Much better performance with 6,000 RPM

Last edited by CHELLIE; 03-23-2008 at 10:54 AM.
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Old 03-23-2008, 11:08 AM
  #11  
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Originally Posted by daviator View Post
We're building a 108" PBY. Finished weight with retracts about 20lbs. Had some fun with small arf electrics lately and am very impressed with performance. Now the big question. What power system will get my scale Pigboat in the air? The plans call for 60 -80 2cyc. The plan designer (Novack) uses O.S 91 4cycs. My calculations for electric conversion don't look promising because of the limited propeller diameter. I've only got 13'' between prop shaft centerlines.
Build it lite for electrics or you may need to go nitro, as its going to get expensive to buy the electric power system to power it, Take care, Chellie


the inexpensive power system I mentioned will cost.
2- motors -----------$ 60.00 to 70.00 @ 30.00 to 35.00 each
2- 5 cell lipos ------- $170.00 @ 85.00 each
2- ESC --------------$ $100.00 @ 50.00 each
1- UBEC--------------$12.00
total for an inexpensive power system is about $352.00 and it goes up from there,
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Old 03-23-2008, 07:05 PM
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Hi Chellie - no I dont share my special recepy cranapple juice - your on your own!

His model weighs 20 pounds - more than twice the weight of the one you referenced. Thats what concerns me. I also suspect that is the glow weight and by the time you convert it the all up weight may easily hit 21-22 pounds.

It would probably stay in the air on 500 watts once it was up. Its the water take off Im concerned with. You need enough "juice" to get it up on step and moving along nicely.

Take two identical water planes (or boats) where one weighs twice what the other does and it will take more than twice the power to get it off the water. You will have well over twice the water drag to contend with.

Once its off - you can throttle back and cruise at a much lower throttle, but your still going to need a lot more "cruise power" with double the wing loading.

Im sticking to my power recomendations

Larry
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Old 03-23-2008, 07:41 PM
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Originally Posted by CHELLIE View Post
Build it lite for electrics or you may need to go nitro, as its going to get expensive to buy the electric power system to power it, Take care, Chellie


the inexpensive power system I mentioned will cost.
2- motors -----------$ 60.00 to 70.00 @ 30.00 to 35.00 each
2- 5 cell lipos ------- $170.00 @ 85.00 each
2- ESC --------------$ $100.00 @ 50.00 each
1- UBEC--------------$12.00
total for an inexpensive power system is about $352.00 and it goes up from there,
I agree it IS going to be pricey - I think its going to be even more than you do. No way would I trust a big scale model to cheepo stuff.

2 motors - Hyperion Z4045 Outrunner Motor $149 each = $300 total
24 A123 cells @ $15 each plus DIY pack building supplies = $ 380.00
2 ea Castle HV85 = $178.00 ea = $356.00
1 UBEC (the real one not the imitation clone) = $49.00
misc conectors, wire, bits and pieces = $ 50.00
A123 DIY zip charger = $ 15.00

Total = $ 1150.00

Believe me, I do understand the temptation to buy the Hobby Citty "stuff". (I almost said "cheepo junk" again, but I resisted ).

The price difference is huge - especially on large, hi power projects.

However, IMO, thats the worst possible project type to try to save money on by using Hobby City "stuff".

This is a kit, not an ARF. Its going to take a LOT of time and effort to get together. Not something Id want to risk to the HC "stuff".

Its also a large, heavy model. If he looses it due to an equipment failure, it can do some serious damage.

The specs from Hobby City are always exagerated, more often than not grossly so, and the quality is directly proportional to what you paid for it (if your lucky) and the service is fair at best to non-existant more often.

In my experience (beta testing and with "stuff" guys in my club bring to me to get working) and based on the reports Ive seen - the hi power "stuff" is even worse than the regular "stuff".

On top of that, ..... never mind. Im not going to go on about the other reasons NOT to buy from Hobby City

Ofcourse, thats just me and my silly old opinion.

I know Im in the minority when it comes to buying from Hobby City etc. They would have long been out of business if they were a vendor from the US or any country that had any kind of consumer protection, truth in advertizing, copy right infringement or fair business laws.

Even being in China, they have had to change thier name at least twice in the last 2 years that I know of

Larry
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Old 03-24-2008, 04:19 PM
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Default PBY power

Gentlemen, Thank-you for the advice. Just want to confirm that I will only be able to run 2, 11''+ props due to distance between prop shafts. The finished weight I originally posted was a glow powered 91.o.s setup with retracts but I would like to be able to fly off the water . The extra juice would certainly be benificial. Hobby Lobby has an AXI system c/w speed controller. The online calculator suggested numerous combinations .Would this be a resonable set-up ?
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Old 03-24-2008, 06:10 PM
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Originally Posted by daviator View Post
Gentlemen, Thank-you for the advice. Just want to confirm that I will only be able to run 2, 11''+ props due to distance between prop shafts. The finished weight I originally posted was a glow powered 91.o.s setup with retracts but I would like to be able to fly off the water . The extra juice would certainly be benificial. Hobby Lobby has an AXI system c/w speed controller. The online calculator suggested numerous combinations .Would this be a resonable set-up ?
Post a link or details of what they are recomending.

Hobby Lobby recomendations tend to be on the low side of the power range. They want to keep the price down as low as possible. Its generally what I would consider marginal - but there are exceptions.

Need to see the details.

What weight are you expecting to come in at? If you only deduct the retract system you might save .5 to .75 pounds or so including wheels?

The final all up weight is the key to coming up with a flyable power system.

Larry
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Old 10-11-2009, 12:13 AM
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So, rather than post anything new - I think I'd like to continue where this left off 18 months ago. I find myself in the EXACT same position, and as long as I've been on wattflyer, I do respect your opinion Larry.
However, my cheap nature and some TGY AerodriveXp experience has me looking at the 42-50 650kv here:
http://hobbycity.com/hobbycity/store...idproduct=7069

I'm thinking master airscrew three bladed 12x8 (plans showing scale 12" prop) on 6S lipo.

As far as weight, if you make it scale it will add up. I hope to come in under the suggested 20lbs from the reference material, I've read a few that were 3-4 pounds over. The retracts, if CJM are used, are about 2.5 lbs alone. I'm hoping to make some myself a bit lighter (not using castings)

I was hoping to get close to 1200 watts per side to match a modern hot .91 4cyl
6S + 60A = 1332Watts = 1.78HP

Larry states 150W/LB to ROW, which would mean 3KW total on 20 lbs, and I don't see that happening on a 12X8 based on the numbers I found - maybe I should be looking to high KV inrunners? On the plans I should be able to fit 13" three bladed, if I have to.

However the 12" prop is a real limit, and I think I can hit 1KW easy enough on the three bladed. The above motor was all HC seemed to have to make those numbers. Thoughts?
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Old 10-11-2009, 03:48 AM
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I dont have experience with the 42-50 but I do with the 42-60. In 6 cell with a 14x7 three blade I was drawing in the 50-60 amp range for 1200-1300 watts and 10lbs of pull. Based on the numbers I got with the larger motor your numbers look about right. The SK is a great motor by the way. My 42-60 was going strong untill I decided to plant it a few inches under the ground and I currently fly a 64" Extra on a 50-65 SK and it performs very well.
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Old 10-11-2009, 04:26 AM
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If you want more power, then you need a higher kV motor or more cells.

Im running an 750 kV inrunner motor on 6S A123 packs and a 13x6 2 blade prop. Im generating about 1350 watts. Thats roughly equal to a 5S lipo pack and a 12x6 3 blade. The motor Im using is a Medusa inrunner - 36-70-750.

Medusa is out of business but a large efficient inrunner in the 600 kV range weighing around 340 grams or more should do ok on a 12x6 3 blade and give you roughly those same numbers.

Of course, thats assuming its a relatively efficient motor. If you buy a cheepo you will need to up-size so it can handle the extra heat generated from a lower efficiency.

Edit: That motor from hobby city is only 230 grams. I seriously doubt it will last long at its rated power out or even close to it. You need to run a much larger motors if your going to be in the power range you are shooting for. The Medusa is waaaaaay more efficient than any Hobby City motor and even being 1/3 larger it runs quite hot at 1300 watts - even with outstanding cooling. The Medusa uses quality hi temp magnets and wire. The Hobby City motors do not.
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Old 10-11-2009, 04:34 AM
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A 650KV will give in the 15,000 rpm range at WOT. Thats not enough for a 12x8? Sure looks good to me. And the efficiency on those SK motors is pretty dang good in my experience. Not all of us can afford Hacker motors at $180 a pop. Thats typically about what I spend on a whole system from HC and I have had zero problems. You have to realize that HC is a low cost option for those of us without deep pockets, and that doesnt mean its all "cheepo" crap. Please dont take offence, I just dont like it when people bash what I fly because I cant afford the "nice" stuff.
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Old 10-11-2009, 06:00 AM
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Originally Posted by scatsob View Post
A 650KV will give in the 15,000 rpm range at WOT. Thats not enough for a 12x8? Sure looks good to me. And the efficiency on those SK motors is pretty dang good in my experience. Not all of us can afford Hacker motors at $180 a pop. Thats typically about what I spend on a whole system from HC and I have had zero problems. You have to realize that HC is a low cost option for those of us without deep pockets, and that doesnt mean its all "cheepo" crap. Please dont take offence, I just dont like it when people bash what I fly because I cant afford the "nice" stuff.
Sorry, I get a little carried away on the Hobby City thing I admit. The word "cheepo" is derogatory so I will apologize if I offended you.

However, the comments about QC and over all quality and efficiency stand. No way is ANY Hobby City motor even in the same ball park with a Hacker motor efficiency wise or quality wise. Thats just a fact and not intended to put you down in any way. They are not very efficient motors and the specs are exaggerated.
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Old 10-11-2009, 06:29 AM
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I didnt mean to make a big deal out of it Larry...it just sucks being a poor college student with a wife and three kids. The wife and kids part is awesome...just not the broke part. I was not offended at all, just standing up for the cheepo stuff I put in my planes. I understand the quality issues and just prepare myself for the fact that I might get something that just plain doesnt work. As I said I guess I have just been lucky so far, but I am realistic about what I am buying. Now back on point. Given the quality and efficiency differences, I believe the 42-50 will work quite well in this application, especially if your wing loading is close to the 16 oz/ft CHELLIE quoted earlier in the thread.
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Old 10-11-2009, 06:31 AM
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Take a look at what a more efficient motor can do for you.

Lets take my setup as one point. The Medusa is running somewhere in the mid to hi 80% range on this setup depending on which calculator you use. Lets say 85%.

That Turnigy motor at full power will be lucky to hit 70%

So the Medusa at 1350 watts input in wasting about 15% as heat or about 200 watts is going into heating the motor. That leave 1150 watts to turn the motor.

When I drop the Medusa down to the 1100 watt range its efficiency goes to a little over 90%. That means 110 watts into heat and 990 going to the prop.

The Turnigy at 1100 watts and say 70% efficiency to be generous - which it wont get close to in practice - will be wasting 330 watts as heat leaving 770 watts to turn the prop. Its 1/3 smaller mass means it will run way way hotter than the Medusa with 3 times the power going into heating the motor.

On top of that the Medusa will fly longer in the air and come down cooler and last longerat the same power usage on smaller packs and still have a much higher peak power output.

You can get at least some of those benifits just by going with a larger motor. The bigger size will run more efficiently at the higher power levels and give you back some of those benifits.

Pushing too small a motor too hard just doesnt pay off well at all.
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Old 10-11-2009, 06:35 AM
  #23  
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Originally Posted by scatsob View Post
I didnt mean to make a big deal out of it Larry...it just sucks being a poor college student with a wife and three kids. The wife and kids part is awesome...just not the broke part. I was not offended at all, just standing up for the cheepo stuff I put in my planes. I understand the quality issues and just prepare myself for the fact that I might get something that just plain doesnt work. As I said I guess I have just been lucky so far, but I am realistic about what I am buying. Now back on point. Given the quality and efficiency differences, I believe the 42-50 will work quite well in this application, especially if your wing loading is close to the 16 oz/ft CHELLIE quoted earlier in the thread.

I understand where your coming from all to well! Been there and done that! 3 girls later....

I should probably check the wing area numbers, or I will regret this statement - I think Chellies wing loading calc is very optimistic. If he is at or above 20 pounds he will probably be well into the low to mid 20oz/ft range.
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Old 10-11-2009, 06:40 AM
  #24  
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I was too conservative. At 1350 sq inches thats about 9.4 sq ft.

If he is at 20 pounds thats 320 ounces. That works out to 34 ounces per sq foot!!!

If he ends up at the hi end of his range that could easily put him at 40 ounces per foot!!

Thats in a different class altogether.

Keep in mind that the power required to take off from water is far more than that needed to ROG. It also goes up even faster on water as the weight increases than on the ground.

It may not take much to KEEP it in the air but getting it up there is going to require some oomph
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Old 10-11-2009, 06:43 AM
  #25  
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your right...thats 16 oz/sqft at 9lbs. So he'll be in the 30 oz/sqft range at 20 lbs :
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