HobbyKing.com New Products Flash Sale
Reply
Thread Tools
Old Feb 06, 2013, 11:26 PM
Registered User
United States, MD, North East
Joined Apr 2011
280 Posts
No problem, this is what I got from the evo rep... Hope it was not confidential or anything lol - he never said not to share!
chemnut842 is offline Find More Posts by chemnut842
Reply With Quote
Sign up now
to remove ads between posts
Old Feb 06, 2013, 11:57 PM
Zor
Suspended Account
Ontario,Canada
Joined Feb 2007
9,742 Posts
Quote:
Originally Posted by chemnut842 View Post

No problem, this is what I got from the evo rep... Hope it was not confidential or anything lol - he never said not to share!
The graphs bring up an interesting situation.
Note that the maximum power takes place at 11,500 RPM

So a propeller selection should be such to obtain that RPM.

I believe that many fellows think that more RPM is more power.
It is not so due to the drop in torque at the higher revolutions.

We can still play with diameter and pitch depending if we are looking for speed or for rate of climb.

The fuel usage would also maximize at that rpm and the performance curves (graph) would vary with the carburetor in use.

Zor
Zor is offline Find More Posts by Zor
Last edited by Zor; Feb 07, 2013 at 12:05 AM.
Reply With Quote  (Disabled)
Old Feb 07, 2013, 04:10 AM
Registered User
Issus's Avatar
Joined May 2012
225 Posts
Very interesting graph, do you know what units the torque is in?

Does that motor come with the ignition system?

The recommended prop is only 13x8 as a max, but it is running at a higher RPM that our 16x10 we currently have i guess... We are also way overpowered by most peoples standards

Is one of the RCG 15cc motors any good? http://www.hobbyking.com/hobbyking/s...HP_1_54kw.html

I tend to try to avoid horizon hobby...
Issus is offline Find More Posts by Issus
Reply With Quote
Old Feb 07, 2013, 09:22 AM
Registered User
United States, MD, North East
Joined Apr 2011
280 Posts
Quote:
Originally Posted by Zor View Post
The graphs bring up an interesting situation.
Note that the maximum power takes place at 11,500 RPM

So a propeller selection should be such to obtain that RPM.

I believe that many fellows think that more RPM is more power.
It is not so due to the drop in torque at the higher revolutions.

We can still play with diameter and pitch depending if we are looking for speed or for rate of climb.

The fuel usage would also maximize at that rpm and the performance curves (graph) would vary with the carburetor in use.

Zor
It is starting to look like a "too hot, too cold" kind of situation. The 20cc motor would fly the plane around at 30-50% power, which is probably outside of its best efficiency, while the 10cc motor may have to be at 80-90% power which may end up using as much fuel at the 20cc at 30-50% power (or slightly better, who knows..).

A 15cc motor keeps getting mentioned - so maybe that is the ticket... I am getting even further away from what I have experience with - but Saito has a line of 4-stroke gasoline engines. I think the FG30 (30cc) has a strong pump in its carb, but the smaller ones do not... not 100% on that... But they have a 14cc a 17cc and a 21cc 4 stroke that is gasoline - they are just quite expensive..

Quote:
Originally Posted by Issus View Post
Very interesting graph, do you know what units the torque is in?

Does that motor come with the ignition system?

The recommended prop is only 13x8 as a max, but it is running at a higher RPM that our 16x10 we currently have i guess... We are also way overpowered by most peoples standards

Is one of the RCG 15cc motors any good? http://www.hobbyking.com/hobbyking/s...HP_1_54kw.html

I tend to try to avoid horizon hobby...
I also wondered what the units for torque were, but never cared enough to ask the rep; but I do know that it comes with an ignition module. I do not have experience with the RCG 15cc, nor have I read much about them. On paper it looks like it would be a good fit, but I would go search for that particular motor in the "engines" subsection of the fuel section. There has to be a thread on that motor buried in there somewhere... That way you can see what others have experienced before buying.

Good luck! I hope you get it figured out, its always hard trying to nail it right on the first try...
chemnut842 is offline Find More Posts by chemnut842
Reply With Quote
Old Feb 07, 2013, 10:26 AM
Zor
Suspended Account
Ontario,Canada
Joined Feb 2007
9,742 Posts
Units of torque

I also have been concerned that in the graph the torque units are not defined. Torque is measued in pounds-feet (force-distance).

If the units used are pounds of force and feet then the formula is _ _ _

Torque = HP x 5252 divided by the RPM.

Looking at the graph at 11,000 RPM and at 15,000 RPM

We have _ _ _

1.14 x 52 52 / 11000 = 0.5443 lb ft _ _ _ graph shows 6.4
and
0.9 x 5252 / 15000 = 0.3151 lb ft _ _ _ graph shows 4.0

Units ratio at 11,000 is 11.76
Units ratio at 15,000 is12.69

Could the graph torque be in units of oz-inches ?
or newtons-centimeters ?

More figurations needed. I may work on it.
Any help out there ?

Zor
Zor is offline Find More Posts by Zor
Reply With Quote  (Disabled)
Old Feb 07, 2013, 01:45 PM
Zor
Suspended Account
Ontario,Canada
Joined Feb 2007
9,742 Posts
For anyone inerested

Attached is a calculation subject to verification by any math wizard.

Personally I still do not know the units used in the torque values.

Zor
Zor is offline Find More Posts by Zor
Reply With Quote  (Disabled)
Old Feb 07, 2013, 07:13 PM
Registered User
United States, MD, North East
Joined Apr 2011
280 Posts
Quote:
Originally Posted by Zor View Post
I also have been concerned that in the graph the torque units are not defined. Torque is measued in pounds-feet (force-distance).

If the units used are pounds of force and feet then the formula is _ _ _

Torque = HP x 5252 divided by the RPM.

Looking at the graph at 11,000 RPM and at 15,000 RPM

We have _ _ _

1.14 x 52 52 / 11000 = 0.5443 lb ft _ _ _ graph shows 6.4
and
0.9 x 5252 / 15000 = 0.3151 lb ft _ _ _ graph shows 4.0

Units ratio at 11,000 is 11.76
Units ratio at 15,000 is12.69

Could the graph torque be in units of oz-inches ?
or newtons-centimeters ?

More figurations needed. I may work on it.
Any help out there ?

Zor
I took the figure you came up with (.544 ft*lb) and checked it. That math looks perfect - I got the same answer through the same formula you used, just rearranged a bit differently ( HP = (2*pi*ft-lb*RPM/33000)). After converting that to in-oz I came up with 6.53.

So I guess it is in in*oz...
chemnut842 is offline Find More Posts by chemnut842
Reply With Quote
Old Feb 09, 2013, 06:52 AM
Jim in the Desert
United States, NM, Las Cruces
Joined Aug 2007
1,263 Posts
What a great thread. Subscribed.
cloud_9 is offline Find More Posts by cloud_9
RCG Plus Member
Latest blog entry: Drill Sizes
Reply With Quote
Old Feb 12, 2013, 10:41 AM
Registered User
Tucson
Joined Nov 2009
1,062 Posts
Remember, with the gas planes the tubing is stiffer, and the clunk may not bend down to the front of the tank. You will need to leave some fuel in the bottom of the tank when you make your landing run. Especially a steep descent to land will bring all the fuel away from the rear clunk, and you will be sucking air. Get an oversize tank, and don't plan to use all the gas in it.
wuest3141 is offline Find More Posts by wuest3141
Reply With Quote
Old Feb 12, 2013, 02:36 PM
Zor
Suspended Account
Ontario,Canada
Joined Feb 2007
9,742 Posts
Something I did

Quote:
Originally Posted by wuest3141 View Post

Remember, with the gas planes the tubing is stiffer, and the clunk may not bend down to the front of the tank. You will need to leave some fuel in the bottom of the tank when you make your landing run. Especially a steep descent to land will bring all the fuel away from the rear clunk, and you will be sucking air. Get an oversize tank, and don't plan to use all the gas in it.
I installed the fuel tank so that the rear is lower than the front even at a steep (high angle) approach trajectory.

That would work for both glow fuel and gasoline.

Zor
Zor is offline Find More Posts by Zor
Reply With Quote  (Disabled)
Old Feb 12, 2013, 11:23 PM
Registered User
United States, MA, West Bridgewater
Joined Mar 2002
193 Posts
I am curious as to why you need such a fuel capacity if you have to land all the time to refill the pesticides?
GMPheli is offline Find More Posts by GMPheli
Reply With Quote
Old Feb 12, 2013, 11:50 PM
Registered User
kerwin50's Avatar
winston mo
Joined Oct 2006
7,539 Posts
WOW that DLE 20 is a gas hog.
I've got a DLE 30 and I get 30 minutes easy on a 16 oz tank flying a 30cc MX
kerwin50 is offline Find More Posts by kerwin50
Reply With Quote
Old Feb 12, 2013, 11:56 PM
Registered User
kerwin50's Avatar
winston mo
Joined Oct 2006
7,539 Posts
BTW stay away from the RCG 15 if you want a dependable plane. The satios drink alot of gas and just don't perform as well as the DLE.
If you want a 20cc motor look at the OS 20cc gas
kerwin50 is offline Find More Posts by kerwin50
Reply With Quote
Old Feb 13, 2013, 07:49 AM
Registered User
United States, MA, West Bridgewater
Joined Mar 2002
193 Posts
To me, this thread looks like it could be terror related. In the first post the op says:

"I have a project where I need long endurance, a couple of hours at least and electric is going to be far too expensive in batteries and weight to be able to do it."

Then a little later he says:

"The 20cc consumption figures are also really nice to have as we're looking at building a sprayer with a 4m wingspan and 8m of sprayer boom + pump, chemicals, etc - obviously with a limited amount of pesticide you cant fly for very long, but it does allow for planning"

It makes no sense, unless he is not telling us the truth. It is our responsibility to watch for these things. I would not help this guy anymore unless he comes up with a good reason for the duration. I would report this thread to a moderator if I knew how
GMPheli is offline Find More Posts by GMPheli
Reply With Quote
Old Feb 13, 2013, 10:51 PM
Registered User
United States, MD, North East
Joined Apr 2011
280 Posts
Quote:
Originally Posted by GMPheli View Post
To me, this thread looks like it could be terror related. In the first post the op says:

"I have a project where I need long endurance, a couple of hours at least and electric is going to be far too expensive in batteries and weight to be able to do it."

Then a little later he says:

"The 20cc consumption figures are also really nice to have as we're looking at building a sprayer with a 4m wingspan and 8m of sprayer boom + pump, chemicals, etc - obviously with a limited amount of pesticide you cant fly for very long, but it does allow for planning"

It makes no sense, unless he is not telling us the truth. It is our responsibility to watch for these things. I would not help this guy anymore unless he comes up with a good reason for the duration. I would report this thread to a moderator if I knew how
I do not think one needs to state a reason for needing/wanting longer duration. Its a UAV..... enough said.....

If you are going to invest the time, effort and money into building something like what you have quoted above - you have to do the legwork and make darn sure your power system and endurance are up to the task at hand. Asking questions is a great way to do that!
chemnut842 is offline Find More Posts by chemnut842
Reply With Quote
Reply


Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Discussion Recomendation 20CC Gasser devilbomber Engines 43 Jun 22, 2012 08:44 AM
Sold 20cc Gasser roncannell Aircraft - Fuel - Engines and Accessories (FS/W) 5 Dec 02, 2011 08:34 AM
Discussion RCGF 20cc Gasser Doclove524 3D / Fun Fly Fuel Planes 2 Jun 19, 2011 10:00 PM
Found want to trade TT .91 FS + cash for a 20cc gasser Why Not...? Aircraft - Fuel - Engines and Accessories (FS/W) 6 Jul 13, 2010 01:22 AM
Question Needed- Fuel consumption numbers, very low fuel consumption engine for small UAV UAVproject Engines 9 Dec 15, 2007 06:13 PM