Sport_Pilot

This is a college team and the engine would likely belong to the school and possibly be displayed and unused long after the competition.

Sport_Pilot

I don't think the rules have a budget, and if they didhow would they enforce it?I also think a budget of $1,000 would be way too slim. If your school has a $1,000 buget then maybe they should try for the Micro class because I think it too slim even for the regular class.

Sport_Pilot

I think you should shoot for maybe 40 pound of payload and 15 pounds of plane or less with two engines. That would put you right at the 65 pound limit. Rethinking this the fuel counts as payload and they supply 15% nitro fuel so the engine should be designed around that. Notice I said designed, as I see no restriction in asking someone to design an engine. That alone may bust your $1,000 budget.

hsukaria

Talk about misplaced priorities!!!! Maybe the engineering department should get some money from the over-bloated athletics department!![:@]

It seems that this competition would need an engine that can swing a big prop to pull such a heavy load. No mention of speed in the competition rules. So, either gearing the engine down, or tuning/modifying the engine to swing a big prop would help. I hear the Kangke SK (SK50) engines are especially tuned for that purpose. I plan on getting an SK90 in the future as a substitute for 4-strokes.

jaka

Hi!
One of the most powerful .46 two strokes on the market today is the ASP/Kyosho GX .46. Can handle large props much better than any Rossi.40 or .45.
Runs good on 0-5% nitro if one of the head shims or both are removed.

victorzamora

Sport_Pilot, you're fantastic for having read the rules.  I'm not on the team, so I haven't thoroughly read the rules.  I'm asking because I'm the only senior that has much R/C experience and I'm leading my own team and have no intention of worsening my workload.  I'm just trying to help out my fellow Hokies.

MJD

My Feedback: (1)

The Jett .46 is known, versus alleged, to be a total powerhouse and for this event I can't see why it would not be a killer if allowed to spin up on a larger diameter lower pitch prop - 11x4 for example. And it is set up to run on 15% nitro fuel as madnated in the rules. The FISE version will spin a 10-6 at 16.5k or better, I can't see why it would not achieve about that on an 11-4. 16.5k translates to a pitch speed of a bit over 60mph. How fast do these payload lifters need to fly to get off the ground?

victorzamora

I'm sure 60mph would be plenty fast.  I'm in another collegiate design competition that flies electrics.  We fly 60-70mph on our speed missions and like 50mph on our heavily-laden missions.

bpbrinson

Jett is the best choice, hands down. The other fact in favor of Jett is the fact you can contact Dub Jett personally and he can advise and build/tune to specific needs. http://www.jettengineering.com/

Don't waste your time with cookie cutter mass produced engines and I have know Dub to "sponsor" projects such as yours.

Hope this helps
Brooks

AMB

you may want to consider an OS 46AX with a Davis Diesel diesel conversion head you have about a 30% increase in power over glow and can swing a larger diameter prop and fuel economy much better, thus less fuel needed, weight saving
an aircraft on the order of the telemaster would be in order for weight carrying martin


this is assuming a limit of .46 on engine size

MJD

My Feedback: (1)

[link=http://www.rcuniverse.com/forum/fb.asp?m=1364541]Jett .46 post[/link]

A few supporting comments there.

It might indeed be wise to consult with Jett on this application. According to the above report, this guy's sport .46 is turning an 11-4 at 16,200. That's pretty serious power, but worth seeing what Jett has to say about setup and prop choice. All I will add to that is that pay attention to prop pitch, and let the engine spin up in its powerband. Dragging an aircraft through the air at a specific speed requires a specific amount of power. In the case of a loadlifter, your maximum payload depends on - with the design of the aircraft being fixed once built - how much power you have available. IOW adding weight requires either an increase in airspeed (which requires more power) or an increase in angle of attack at the same speed (more power again). Transmitting the engine power efficiently, i.e. minimizing losses, depends on prop choice. As a general rule and don't hold me to the math, you'll want a pitch speed just a few percent higher than the target airspeed. This will be a good sign that you are not wasting excessive amounts energy by spinning prop blades at too high an angle of attack.

The 11-4 has lots of blade area and will generate gobs of pull, and if these load lifters really do fly in the 50mph range, then since the theoretical pitch speed is just slightly higher, i.e. in the 60mph neighborhood, this is probably about the right choice. Using 6" pitch for example, and holding it back is how you waste horsepower, since it means the prop blades are running at an excessive angle of attack all the time. The best setup has the prop blades working in their most efficient regime which means looking at rpm and flight speed, and choosing the pitch of the prop to suit based on target rpm and using the diameter/blade area that lets the engine spin there.

After saying all this, it is worth knowing that the pitch number on most props is not bang on - either rounded to the nearest integer or not measured in true (actual aerodynamic) pitch. So in the end the final incremental improvements come down to trial and error.

Handy tool:

[link=http://www.rcpro.org/rccalc/PitchSpeed.aspx]Pitch speed calculator[/link]

[babbling mode off]

mustange1

My Feedback: (11)

These engines are sreamers and they are very strong AVIASTAR


.46 2 Stroke Glow Engine


Modern design combined with state of the art computer-driven machinery and superior metallurgy to create the finest 2 stroke model airplane engines.

For instance, the connecting rods use the same aluminum alloy as found in some full size aircraft engines. Crankshafts are one piece hardened Cr steel. A specially developed "KK" bronze alloy is used for the conrod bushing which allows it to withstand high RPMs. Cylinders are made of a special heat treated Cr steel alloy to insure a hard and true cylinder that will not distort at high temperatures. Piston rings (1.2 - 2.0 in3 engines) are made of the same steel alloy as found in some racing motorcycles. The .46 in3 is true ABC construction. All engines contain high quality dual ball bearings.


Of course, the carburetors are of a twin needle design for the best balance between power and fuel consumption. O-rings are used at all critical points to eliminate any possible air leakage. There's no lapse of power throughout the transition, making this a popular choice for aerobatic flying.

Sig recommends 10% Nitromethane Champion Glow Engine Fuel with castor blend. Power ratings listed were obtained with FAI fuel (0% nitro) on a hot summer day with 85% relative humidity.

Included with the SIG Lt-40 RTF. Some other popular airplanes for this engine include SIG Sealane BIY, SIG Kadet Senior BIY/ARF, SIG Four Star 40 BIY/ARF, SIG smith Miniplane BIY, SIG Somethin' Extra BIY/ARF, SIG Rascal Forty ARF, SIG 1/5 Scale Piper J-3 Cub BIY, SIG Sun Dancer 50 ARF, SIG Mayhem 40 ARF.
Specifications
Displacement .46 in3 ( 7.53 cm3 )
Bore .886 in ( 22.5 mm )
Stroke .756 in ( 19.2 mm )
Practical RPM 1 900 to 16 000
Weight
Ex. Muffler 13.4 oz ( 378 g )
Power 1.66 hp at 16 000 rpm
Shaft Size M 7x1
Muffler included

2walla

My Feedback: (10)

I read the rules- If you are talking about using a 46 u are probably going to be competing in the advanced class- this isnt a max weight competition but delivery of a 3 lb payload via a FPV system and cooperation between the pilot and the FPV observer that is to direct the pilot to the target.... You are only lifting three pounds.. So the key to winning will be in a good writeup combined with good flight performance.. That means you need something reliable and you will probably want to PRACTICE with the pilot/observer team a bunch.. Sound engineering writeup, a simple trainer, good reliable engine.. and practice...practice...practice.. will take home the prize... I would use a 3 channel plane that flys well- and is stable..-converted free flight design probably...Slower flying and simpler the better... Just get an OS or a Magnum, or an ENYA if you can find one... You don't want to get something too exotic and you don't need a lot of power to lift 3 lbs...

If entering the weight lifting you are restricted to a 61 OS or Magnum... I would suggest researching what a "control wing" is and its advantages are for a payload competition.... I wouldn't offer you any more than that as it could be construed by the rules as a violation and soliciting receiving help/advice from an model expert or professional engineer..

bpbrinson

Just did some quick calculations and a 11x4 APC turned at 16,200 Rpm is making almost 12 lbs of thrust static. That would power a 24 lb airplane quite well with a climb at over 30 degrees. That is a power/weight ratio of .5 to 1 and full size aircraft often fly at less than .25 to 1. I am sure Dub Jett could cut the porting and tune the muffler to do better than that, rpm or even a bigger prop.

Brooks

bpbrinson

Ok, never mind........ should have read the rules

victorzamora

2walla, if you're talking about circulation control: that would be AWESOME to get to do.  However, it's not really worth it on an aircraft of this size....even though it's something all of us have been drooling over since our first fluid mechanics course.

Sport_Pilot

I would agree which is why I suggested Fox. Jett has also made custom engines for low speed and high torque. He had a CL stunt motor that would pull stumps.

Sport_Pilot

While they turn very large props the diesels do not have more power and thus a glow engine timed for lower RPMor a gear reducer would work better.

Sport_Pilot

Uh Oh. My son is an AE at Georgia Tech! I don't think they compete in the SAE competition though. Still I'm going to have to think twice about giving advice here on out!

Sport_Pilot

I don't have the rules in front of me now, but I thought there were 4 flights and one was a 3 pound drop and at least one other was heavy lift.

victorzamora

Well, I know for a fact that Georgia Tech DOES compete in the AIAA Design, Build, Fly competition....and that's MY competition.  This'll be five year and 6th plane that I've worked on.  4th year and 5th plane.  GT has no hope against me!

MJD

My Feedback: (1)

Gear reducers are not allowed. 15% nitromethane glow fuel is provided so no diesels.

Not quite sure how timing an engine to turn large props slower is of any benefit for this application because it will, in the end, sacrifice much needed horsepower. Pulling a 24lb aircraft with gobs of wing at sufficient airspeed requires power and a good dose of it. We're not talking about a scale biplane at 8lb that stalls at 15mph here. A low timed engine with a big prop would be nice for such a model, sure. Good for C/L stunt models too, lots of pull, airspeed limited and lots of downline braking. Good for a sport model where you don't want to listen to a screaming engine. But the only way to get a bunch more power from a 2 stroke engine of fixed displacement is rpm. The engine can only aspirate a fixed volume of fuel/air mixture per revolution. Power is a rate of doing work. Therefore, to do more work per second you must burn more fuel per second, which means you need more intake cycles per second = rpm.

I'm talking about a wide blade fine pitch prop on the .46, not a pylon prop at 25k here. Such a prop is the aerodynamic equivalent of gearing down. It has a fair amount of blade and disc area, and will generate heaps of thrust at low airspeeds. While Jett might make stunt motors with gobs of torque - relatively speaking - I guarantee you they do not produce the same horsepower as the sport engines timed for peak power in the mid to high teens. Just because you can put a bigger prop on a varient of the same engine without meltdown does not mean it is better for every application.

hsukaria

Like I said, you should go get some funds from those over-paid bloated athletics departments. Watch out from now on, Sport Pilot will give you the wrong advice on purpose. But we all know the best school is Texas A&M!!!!

jeffie8696

Maybe you can port and polish that AX , together with a tuned pipe

2walla

My Feedback: (10)

http://m.youtube.com/?reason=8&rdm=2...%3DnC1iqmuWIu4


At the Reynolds number a model within the rules size restriction is operating at circulation control would be impractical. Take a look at the video and pay attention to the controls. Throttle and the ability to rotate each wing panel few degrees around the axis of the center of lift to induce a bank with a spring to retunn to neutral. There was a writeup in sport aviation back in the 70's on its merits. Won't stall - wont takeoff if over its maximum lifting capability based on the available thrust/airspeed. (A powered parachute operates on the same basic principle.). With a bit of basic calculation on the power available and the selection of the right airfoil/aspect ratio wing it would probably be unbeatable. It also takes the pilots skil/pilot error out of the equation.