small engine?
 

i am working on building my own plane and wanted an rc glow engine for it. Wingspan is 26in. What should i get?

RE: small engine?
 

If you could provide wing area and your best guess at the "all up weight" when completed someone may be able to give you a better answer. At 26 inches your in the right forum. but depending upon the two stats above you could be anywhere from a Cox .020 to an OS .10 Is the plane being designed for sport flying or training? Speed or lazy floater?

RE: small engine?
 

Hi panzertank,
These guys are quite the willing helpful bunch but I'll give you a TIP....WE are addicted to pictures[sm=wink_smile.gif]:D

RE: small engine?
 

I have a related question about engines, what is a good engine loading figure for a 1/2a? Don't mean to steal the thread, but any data may aid in the main post as well.

It is a term I know little about.

RE: small engine?
 

By engine loading are you referring to the prop size?

If that is what you are asking, it depends on the engine, fuel, and what type plane you need to prop. Many seem to gravitate to the APC 5.7x3 or the 6x2 for modern hi-revving .061 glows. A diesel generally swings a larger prop. A Cox reedie uses from 5x3 to 6x3, depending on porting, etc.

If you have a specific engine in mind, let us know. I'm sure someone has flown it. :D

George

RE: small engine?
 

Good size for a 26"?

I'm gonna guess ... 049 SureStart.
Change the prop to fit the mission.

If you can take a guess as to the area, or post a plan even a cellphone camera pic of a napkin with your plan, the gang here can crunch all the engineering with you. You gonna use a bunch of sheet balsa or a whole bunch of stick. You going for speed or relaxing simple loop/roll. Some will even help fit engines to the blue FFF planes :)

Or take the shortcut: We look at a similar plane and see what worked on it.

RE: small engine?
 

GCB;

This is somthing I have just read about, and usally use the trial & error method. The engine loading is stated in Ounces per C.I. displacement, and is based on the model's specs and size of the engine.

It would add to the post in this forum.

RE: small engine?
 

Here's a general guideline for glow sport flying.

Power Loading
(oz. per cubic inch displacement)

300+ .........Sunday Flyer
250-300 ..............Sporty
200-250 ...............Racer
Below 200.......Holy Cow!


Weight of plane in oz / cubic inch displacement = Power Loading
or
Weight / Desired Power Loading = engine displacement

RE: small engine?
 

dieFluggeister;

Thanks for the data. So, is this right across the board, all classes, or will it vary with size of aircraft model?

The loading for a .60 would still follow the base figures you posted? Am not to keen on this yet, but it would help in placing a engine in a model.

A model I just did shows a Wing loading of 8.37 Oz sq Ft, and a engine loading of 387.7 Oz/ C.I. So sport you show in the data, this one is a 41" span.

RE: small engine?
 

Remby - it is just a rule of thumb or a comparison between similar models and a guide to determine an appropriate engine size. Keep in mind that airfoil, wing loading, airframe drag etc. will have a huge effect on performance of the model as a whole. It remains pretty true for larger sized models too.

Your example model looks like it is a glider/trainer with the light wing loading and light power loading. Is that right?

RE: small engine?
 

dieFluggeister;

Yes, sorry, the model I gave the basic specs for is a Carnad. I found out about the engine loading questions from working the C.G. placement, and came across the term. Your discription fits this model as a slow flyer, sport type. The model I built is called the Lazy Duck,and was scaled down to fit a wing that survived another plane. I found a program that did the C.P./C.G. , and the engine loading questions were found out about with the program.

Over 400 / C.I. then is a brick, I guess. Thanks, your discription helps a lot!

RE: small engine?
 

Well it would be a brick with a high wing loading but yours is below 9oz / sq ft. If you have a high lift airfoil you may have a neat little motorglider! I would expect long shallow climbs and maybe even some thermalling! The smaller canard wing may stall at lower speeds though! [X(]

For instance I have a Dynaflite Wanderer glider, and with a cox .049 power pod. It gives me some ridiculous power loading figure of well over 600! As a sport plane that would suck, but as a glider it is graceful with big spiraling climbs. Any more power is overkill for what the plane was built for. On the other hand I have a little pylon racer with a power loading of 153! But it would fall out of the sky with anything more than 300 because the wing loading is high for a small model (around 20oz/sq ft).

So just use the figure for comparison. The numbers given work for sport flying but must be adjusted when you are talking about gliders, racers, scale, etc.

edit sp.

RE: small engine?
 

dieFluggeister;
Your description is correct, and I consider this a powered glider type of flying model. The carnad's front wing is quite large, so it really helps in the lift area, and it is a clark-y airfoil, so it should fly quite well. I built it to haul a digital camera setup.

I will update this perhaps in it's own thread, I did not intend to steal panzertank's thread here, but thought it would add to this post he started here. Thanks!

RE: small engine?
 

I've seen those numbers before somewhere and I've never quite understood how to use them...
There are so many things that affect how a plane will fly and is designed to fly. And why would merely the size of the engine be any reliable measure of the power output, maximum thrust might be a better measure?

Perhaps one can used it the other way around instead. Lets say you have a sunday flyer design and want to know what engine size to go for, then you have a rough guide by using 300+ (anything less would be overpowered). If instead you want to impress you mates with a speed design then you should aim for <200 :D

RE: small engine?
 

I agree with Mr Cox.
The power loading chart really is only relevant when working with watts or horsepower, not engine size. Some 1/2A engines are 3 times more powerful than others.
How each engine is propped further complicates the matter, because that becomes the final developed HP.
A 26 inch span model with 130 sq inches will normally come out weighing somewhere between 7 and 12 ozs if outfitted with 1/2A sized equipment [2 servos] and depending on construction techniques. The lighter, the better...anything over 12 ozs [at this size] will not very well. Most guys here who have written about scratch built planes in this size range have had no problem building them at about 9-11 ozs and they fly tremendously.

RE: small engine?
 

Finally finished the wing. It is 26in long with a fully symetrical airfoil and 0 dihedral. The plane is generally going to be a little heavy. In the following pictures you can see the wing compared to a screwdriver and the partially assembled fuselauge

RE: small engine?
 

Looks like a Sure Start would be perfect. Four servos? Needs a throttle ring, or is it setup along more functions?

Low aspect ratio, for sure. It would help once the tail group is on, to get a better visual of the layout.

RE: small engine?
 

Only three servos. Didn't build ailerons into the wing. No choice now to put them in