Power House power?

[Joe41]

Hi all, :) could some one help me with working out the best E-power for a planned fullsize Powerhouse?

I have some motors but I'm open to suggestions,
Possible motors available at hand:
Cobalt 05, 2.5:1 g/b
AXI 282010
AXI 412018

If I can get a ball park size I might even restart another old project and build an LRK motor for it.

I suppose the real question is what sort of performance am I looking for to copy the original?

Cheers Joe

[Gerald]

I think most of the original .60 size sparkers of the period when the Powerhouse first appeared (1938) were rated for about 1/5 hp. So that would be equivalent to 150watts. A geared cobalt 05 or 15 would be in that ballpark. Not much power for an 84" span model is it?

[Joe41]

What a good place to use up all those unused abandonded brushed motors! heh heh :)

I've just come across this OT econversion with a speed 700 & 8cells http://www.flyelectric.com/setuppowerhouse.html

What a great looking model!

Joe

[vintage1]

what sized prop wold those old sparkers have swung? I am mindful of something I read where a geared motor was then applied to a second belt drive to swing a massive prop at 'count the blades' RPM...

[Joe41]

For the PowerHouse the old write up recommends a Foster with an 18" prop with a 12 -14" pitch.

This site http://www.theplanpage.com/Months/2101/phpt1.htm has a great read and plans on the Powerhouse. Also this site http://www.iroquois.free-online.co.uk/phouse.htm has more stuff on the Power House.

enjoy Joe

[Ian Easton]

I was talking to Sal Taibi yesterday (the designer of the Powerhouse).

He's alive and well and still flying frequently - he still competes too!

Ian

[Joe41]

Cool :) what's he fly now? betya it's not one of them new fang dang turbine jobs. :D
Joe

[vintage1]

well a quick adapation of my black magic motocalc setup suggests that if you can get total gearing on the astro 05 to something like 6:1 (add a belt drive on it?) that on 3s LIPO will swing a 20x12 prop at something like 3000 RPM. About 4.5lb of thrust and 34mph pitch speed.

Drawing about 30A, dropping to 25A or so at 25mph.

I have been playing around modifiying an old Tom Hunt belt drive, and I would say that it might be possible to make a 6:1 drive if you can source belt drive parts.

Gordon Tarling pointed me at Davall in the UK, for a possible source of pulleys and belts.

I think that would be my choice. Or put a standard belt drive on the outrunners. The 2820/10 with 3.6:1 looks like it would be a possibility - but of course the case diameter would again make it a custom job.

[Ian Easton]

My Black Magic flys great with a 480 geared 2.33:1 and with 8-1600ma Nimh I get 20-25 minute flights. But then my Black Magic is no where near 4 pounds. If I remeber correctly it's around 2 pounds.

Sal Taibi is still flying all those good old designs.

[tim hooper]

The 2820/10 with 3.6:1 looks like it would be a possibility - but of course the case diameter would again make it a custom job.

Vintage,

Ernie Thorpe has been experimenting with gearing a 2820/10 for use with sailplanes, using his own gearboxes;

http://www.rcgroups.com/forums/showthread.php?t=176360

If anyone can make a custom-made gearbox, it's Ernie!

tim

[Joe41]

Just in case antone can't find the second part to the Powerhouse write up here it is http://www.theplanpage.com/Months/2101/phpt2.htm it mentions that for the test flight have the engine 'just ticking over' or run it as slow as you can! :eek:

I might just conmvert mine to rubber powered and cut back on the winds :rolleyes:
Joe :)

[Tim Trick]

Joe,

I am not familar with the Powerhouse, but I have converted a Ben Buckle Junior 60 to AXi 2820/10 on 7 x KAN 3000 NIMH cells with a MA electric wood 12x8 prop.

Static thrust was measured on a test rig as 1126 grams at 32.6 amp draw (volts drop to 6.7). The Junior 60 flies very nicely at an AUW of 1780 grams (3.9 lbs). I can float around the sky very happily in traditional style with flights of 25-30 minutes.

If the wing loadings of the Powerhouse are anything like that for a 3.9 lb Junior 60, then the AXI 2820/10 on direct drive will have no problem (in fact my Junior 60 is somewhat overpowered and will climb steeply at about 50 degrees at full grunt - but that is not really the name of the game is it?)

An Axi 4120/18 would probably pull the Powerhouse vertical and put Burt Rutan's attempt at the X prize to shame - a bit over the top! (I am putting one in a 1:7 scale PC6 Porter and will be pulling nearly 900 watts from it!)

Cheers

Tim

[Joe41]

Tim, your probably right, going by the original 1939 write-up the target weight for the Powerhouse is 4 1/2 lbs, which includes medium batteries? and the Forster motor swinging an 18x10 prop so I guess the rpms would be way down.

I currently have two sets of wings (about 20 years old) and some partial fuz, there is lots of opportunity to shave off weight.

The 2820/10 it is then, on 8 cells 12x7 prop.

Joe

Joe

[Tim Trick]

Joe,

I have been looking into the powerhouse and notice on another Aussie site showing kevin Johnson's full size powerhouse at 2.1 m span and 2.5 kg weight.

I had some problems balancing my Juni0r 60 due to the fact that the 2820/10 weighs 161 grams (compared to the heavier motor/gearbox specified in the original kit design) and the 7 cell battery pack was as far forward as was possible whilst still staying within the fuselage! - had to move the wing back 9 mm to achieve good C of G.

If you plan to go to the same size, then you will be on the upper limit of the 2820/10 - a 2820/12 with 14 cells would be a better bet - especially if you need more battery weight up front to help balance the plane.

If you don't want to go up to a new motor, then maybe the 4120/18 maight not be bad idea after all if you need more weight up front. Trouble is that you really need a minimum of 16 cells for this motor and then your overall weight begins to spiral again (motor weighs 320 grams, 16 cell pack of KAN 3000 mah NIMH for example is in the region of 996 grams!).

Tim

[Joe41]

Tim, would the power house fly with say 60w per lb? I really don't know what power levels these things are supposed to run at.

Should be able to get 400w from the 2820/10, @ that weight that's about 75 plus watts per lb.

5.5 lbs, If I get rid of most of the ply and the engine bearers I reckon the weight will come down some, also Kevin Johnson is using s 700BB (about 350grams plus a g/box ??grams) he's starting to get a little on the porky side,, then again the P/house has 1126 sq in of wing area,,,,, must be able to get the weight down somehow, the original was 5 and a bit lbs with floats!

BTW have you been to Bob Holman's site? http://www.bhplans.com/index

Joe

[Tim Trick]

Joe,

From my experience with the Junior 60, the quoted requirement of 40-50 watts per pound for ROG seems to work with quite a margin. My Junior 60 weighs 3.9 lbs (1780 grams) and has an INPUT power of 208 watts at full rpm. She is airborn from a rough grassed strip in about 7 metres (25 feet) at full power.

I have tried taking off at half (approx 14 amps draw) and she will also do that, but needs nearly 20 metres take off run, climbing very sedately. At half rpm take off, the INPUT power was then approx 112 watts at then 29 watts per pound!

I generally fly around at half to 1/3 throttle (between 7-14 amps) without loosing height, which is around 58-112 watts input-15-29 watts per pound!

Bear in mind that a full size Powerhouse of dimensions similar to what Kevin has made will have a greater drag value and more power would be required for flight than that for my junior 60.

Neverthless, with your quoted wing area of 7.8 square feet and an AUW of 5.5 lbs, the wing loading of approx 11 oz/square foot is very light and you should be able to take off and fly very slowly.

Pulling 400 watts out of a 2820/10 (10 cells needed) is right on the limit of the motor and speed controller and probably would not be required to get in the air-check out the modelmotors site for specs on the 2820/10:

http://www.modelmotors.cz/index.php?id=en&nc=produkty.

I have found that the static thrust measurement program on the EStar website has proven to be quite accurate when compared to tests I have made with numerous props at different speeds:

http://www.estarmodels.com/

And for general motor choices I looked at the Macxim motor site and their calculation method to choose motors also gives some ideas to play with:

http://www.rc-aero.com/biz/maxcim/guide.html

Cheers

Tim

[Tim Trick]

Joe,

I tried the link you mentioned, but but unluckily received an error messaage saying the site could not be found.

Tim

[Joe41]

Thanks for your help Tim, much appreciated, lots of food for thought. :)
BTW try this now http://www.bhplans.com

Joe

[vintage1]

A vintage model should stay in the air with a fairly efficient 10-15w/lb or so. Teh rest of the power is all in the rate of climb.

Leaving aside all inefficiences a watt is .7375 foot lb per second. That is one watt will get a .7lb model to climb at 60 feet per minute.

I regard 240 fpm as an acceptable climb rate, so thats 4/.7 watts per lb. About 6W per lb excess over what the plane needs to fly level.

If the plane glides at say a 1 in 10 slope, then it needs one tenth of teh weight times the speed in feet per second times the watts, to stay up.

So say its a pound, it needs 1/10th pound thrust, and that times - say 25mph (36.67fps) gives us 3.667 foot pounds per second, or almost exactly 5W (per lb)

So 11W per pound output from a well matched prop is what you need to fly a fairly clean old timer at sensible 25mph speeds.

With a 50% efficient motor and a 50% efficient drive train, thats 44W/lb.

Wth an 80% efficient motor and 50% efficient drive train, that's 27.5W/lb.

Thats what a brushless can do :)

At 5lb, I'd say a speed 600 at 250W would be MORE than adequate.

And even a 480 class brushless - a well deep geared mega 16/15 on a BIG prop - could probably do an acceptable job.

[dr.E]

I have an 84 inch Powerhouse it was kitted by Midway and in the mid 80's Flying Models mag did a nice review of it. I fly it with a geared Astro 25 on 16 cells and a 12x8 prop.

Motor options would be:

Astro 25 geared
Astro 40 marine geared (little hotter than the sportwind but not as crazy as the FAI)
Mega 30-2 3:1 gear

Keep it simple and cheap

[benlo2d]

My Powerhouse flies with authority with the following:

Astro FAI 15 4.62:1 Superbox
18X10 Zinger 3800 RPM
10x GP3300's
38 A at full throttle

cruises at about 1/3 stick. flight times of around 10 min if no
thermals around.
Ben

[Joe41]

Thanks for the input everyone, well the AXI 412018 is going back into the P40, (13 x 8 & 20 x 3300's), so I'm going to play with either the 6turn cobalt (a bit of an amp hog though) & 2.5:1 inline box (11 -12" prop), 8 cells ,,, or the AXI 2820/10, 11 - 12" prop, 10 cells,,, or if it's not too difficult to mate up, the 2820/10 + 2.5:1 g/b 10-12 cells, maybe 13-15 prop.

Gotta finish building the plane first! :)

Joe

[Tuomo]

I just ordered me powerhouse plans. The idea is to power it with 10-12xGP2200 or GP3300 nimh setup. The motor will be Flyware direct drive to avoid the complexity and noise of a gearbox.

How do you install the drive batteries to your oldtimers? I have my background in competition sailplanes and I do care so much about slightly changing the structure or looks. I was planning to build a separete battery opening to the bottom of the fuselage. removing the wing for a battery change/charge is a pain.

Better ideas?

BTW A comment to the (rather old) discussion about using a Axi 2820/10 in a powerhouse. I am really interrested in teh results. As stated below this pushes the performance of the motor to the max. That would be ok for a 10 second climb in a sailplane...

It is also wise use grossly oversize controllers in this kind of applications. In many cases the controller is actually working harder when running at half power. In the F5X classes where the limits are really pushed no one even dreams of running their motor at reduced setting, it is on/off.

[50+AirYears]

That Forster mentioned was an ignition .99. You'd probably want a geared or outrunner power plant that could swing at least the 15-6 at the 6000 rpm figure, but might be better with a 16 to 18 inch prop in the 5000 to 6000 range.

Those OT planes were pretty draggy, with lots of frontal area and underchambered airfoils. Need lots of disc area, not RPMs.