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How much power?

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Old 07-09-2010, 12:03 AM
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20hdstd05
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Default How much power?

Hi Everyone
This is my first post so I hope I have put it in the correct place.I have been in and out of RC for many years and have always built from kits.I am currently building an old Bud Nosen 8’ jenny.This is the largest plane I have ever built.My question is this.What power should I use?The kit was originally for a 60 two stroke.I was going to put a 91 four stroke on it but after talking to some of the guys at the Warbirds over Oklahoma in May they led me to believe that would never be enough.I have not finished it yet so I don’t know what its weight will be.Is there a general rule of thumb for how to power your plane if the weight and wing area is known?I have made a few modifications to the wing setup to make it easier to transport so I am sure it will be heavier than originally designed.I have always used the power recommended for what ever kit I was building (mostly 40 powered).
I know this is probably a deep subject but any input would be helpful.
Thanks
Steve
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Old 07-09-2010, 06:09 AM
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Default RE: How much power?




Welcome back Steve.

What do you think it will weigh ???
8 ft wing span ? Any pics you can share ?

Bob
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Old 07-09-2010, 06:48 AM
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Default RE: How much power?

Hi Steve-

Glad to have you back in the hobby!

Everyone has an opinion on the power issue. Without knowing the approximate final weight any estimate is questionable at best and there are many variables such as the altitude you fly at, the wing area and potential drag of the aircraft and, of course, the weight. For a biplane at sea level, I use the rule of thumb that a .60 four stroke will fly a 6-7 pound plane, a .90 four stroke a 9-10 pound plane, a 1.20 four stroke a 12-14 pound plane etc. 10 to 1 more or less. This may be slightly too much power but I'd rather have an excess and control the throttle and the extra weight up front in a bipe never hurts. If I were forced to venture a guess on your Jenny I'd pick something like a Saito 1.00 or the new OS 1.10 FSa.

Let us know what you go with and how it works out!
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Old 07-09-2010, 07:40 AM
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Default RE: How much power?

I don't know that bipe, but I always use the rule better to have too much power then not enough because you can always throttle back. I would run a Saito 125A to compensate for the extra drag on takeoff and landing.
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Old 07-09-2010, 07:54 AM
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Default RE: How much power?

A jenny will certainly fly on the power recommended, even if the recommendation was made years ago.

Also, a biplane isn't going to respond to extra power like other planes will. They've got extra drag and it often just absorbs extra power.

A 90 four cycle is certainly going to fly the Jenny decently and sound good doing it.
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Old 07-09-2010, 10:09 AM
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Default RE: How much power?

Those Nosen planes were designed when there were no gas engines avaliable. 60 size engines are going to make you crazy with that plane; it will fly it but it will have to be 0 wind and it will drag around the sky like an overweight 1/2a powered glider. 28-30cc gas with the appropriate mods to make it strong at the engine. A bigger engine will not make it go faster but it will allow it to climb when you need too. I remember one as a kid; it was beautiful, a master piece. It took 3 circuts over the field to get high enough to stop sweating a dead stick; that summer got to see my first ducted fan plane, it drug around the sky at the edge of stall too.
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Old 07-09-2010, 10:13 AM
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Default RE: How much power?

Good points made.The arf kits we buy now are designed to have a lot of weight up front so i fly four strokes in them,sounds nice.
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Old 07-09-2010, 09:26 PM
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Default RE: How much power?

The "real" Jenny's were no powerhouses. A .90 would probably be scale-like and maybe even a .60 if you build light. Most R/C models of late are powered out the giggie. If you build it with full flying and landing wires you may wish for that extra oomph, though.

You never hear a pilot complaining that they had too much power available.
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Old 07-10-2010, 12:31 AM
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Default RE: How much power?

You do often hear pilots complain about their planes being too heavy or using too much fuel though.

It sounds like the guys on here are steering you in the right direction, but in the end it's the weight of the plane that will determine what engine you need.
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Old 07-10-2010, 06:10 AM
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Default RE: How much power?

Steve,

Consider a couple of factors. If you complete the Jenny with covering before you make your engine choice, you can get a good idea of how much engine weight will bring it in balance. Why mount a 90 4-stroke AND 2 lbs of lead on the firewall. An 8 ft. span bipe can probably handle a very wide range of engines. For me, I would start with a G-26 Zenoah (I am a gasser).

Second issue is prop diameter. As said before, a 60 2-stroke was the big engine of the day when the Nosen design came out. My guess is it's 12 or 13 in. prop will look all wrong. Back to the G-26, you can mount a 16 or even 18 in. prop and I bet it will look much more appropriate. If you have 2 in. of ground clearance with whichever prop, you have more than enough.

Have fun with it!

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Old 07-10-2010, 07:01 AM
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Default RE: How much power?

Hey snap i have the equivilent to the g26 in my lawnmower! and that sound annoys the hell out of my neighbours
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Old 07-11-2010, 03:31 AM
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Default RE: How much power?

OF,

To REALLY annoy your neighbors, pull that engine out of your lawnmower and put it in an airplane and start flying it overhead. Now that would get them going!

The G-26 with standard muffler is not bad at all. There are some small aftermarket mufflers that are another story. I have one on a Quadra 42 and I hate it.

Bedford
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Old 07-11-2010, 05:59 AM
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Default RE: How much power?

I'd agree with the 90-120 class four stroke crowd, it would give the plane a nice scale like flight & sound. A 2-cycle (gas or glow) would sound aweful IMHO

good luck
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Old 07-11-2010, 07:20 AM
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Default RE: How much power?

Any of the current gasoline engines of 18 to 30cc would be ideal. A Zenoa G26 would be excellent. You will want a little weight up front and the gasoline powered engines are so very fuel efficient that you can get by with a tank as small as 8 ounces and still get 20 minute flights.
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Old 07-12-2010, 02:04 AM
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Default RE: How much power?

Having a couple of Bud Nosen planes myself, I would recommend a 1.20 four stroker or a 26cc gas engine. If you install a .90 four stroker you would have to fly close to WOT, you would actually use up more fuel in a .90 at WOT than a 1.20 four stroker at 2/3 throttle and they will fly the same. That is why I use 1.20 for stroker in my quarter scale Cubs and the like. I leisurely fly for about 20 minutes on less than 16 oz of fuel at 1/2 to 2/3 throttle.
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Old 07-13-2010, 11:51 PM
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Default RE: How much power?

Thanks guys

Sorry I did not respond sooner but I was out of town. Sounds like I need to pile every thing on a scale and get a estimate on my weight. I should be able to do that a get close to an empty weight. Should I do that without an engine and then plug in different engine weights to get a total weight? Seems thats all i can do seeing as how i dont have a stock of engines laying around.

I am a slow mover nowdays so I will post the weight when I get it but it may be a few days. I dont have any pictures yet but will take some when i get closer to getting it finished.

Thanks to everyone for all the information

see ya later
steve
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