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Top Flite Cessna 310 posted

Old 02-21-2007, 11:33 AM
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Default RE: Top Flite Cessna 310 posted

Yes, prop range and rpm are the only indicator when comparing engines of different design. Think of a pickup with a 325 hp gas engine and another with a 250 HP diesel. The Diesel will out pull the gas but run out of steam at high rpm. Torque for the diesel may be over 400 where the gas engine only has 270 or so. This is where gearing comes into play (or prop size in this case).

If you want to use a twin, look into what type/size single engine plane is flown with the engine you are interested in. What would be the equivalent 2 stroke? If it is a .46, you are golden.

Mark
Old 02-21-2007, 11:38 AM
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Default RE: Top Flite Cessna 310 posted

Wasabi,

Two Saito 90 twins or two Saito 100 twins would be plenty enough power to fly this plane. I'm still toying with the idea of the 90 Twins myself.

Last night I took the valve covers off one of the 90's and placed it inside one of the nacelles. With the valve covers off I can get the engine far enough inside the nacelle that the prop drive hub sticks out about 3/8". This means that if you were to cut the holes to clear the covers, you would have to remove them to install the nacelles then put them back on after the nacelle is in place. It's doable for sure but require cutting holes in the RIGHT places so it looks neat.

The last time I flew my GP Spacewalker with the Saito 90 twin I changed from a 14x6 Master Airscrew to a 13x7 APC. I got 9800 rpm out of it. HP Thrust says 8.35 lbs of thrust and 1.344 HP. I know this program isn't exact but it gives you something to compare.

Bob
Old 02-21-2007, 11:47 AM
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Default RE: Top Flite Cessna 310 posted

Bob,

Do you have a formula to determine thrust? My rough numbers say to get an engine which only turns 9.8k to the same top end speed as one turning 15 (6 pitch) you would need a 9 pitch prop. I figure the 90T can turn an 11x10. This may be a nice solution. Slowing down will need major flaps though.
Old 02-21-2007, 11:51 AM
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Default RE: Top Flite Cessna 310 posted

Found on Horizon's site:

Saito 4-Stroke Myth

4 strokes lack power.

Mike McConville flies a Midwest AT-6 powered with a Saito 170 R3 radial. According to Mike, "This was true when 4-Strokes were first introduced to RC in the early 1980s, but today 4-strokes provide extraordinary power. Because they produce more torque than 2-strokes, "4-stroke power" has a unique feel. The models fly at a more constant speed, go up with a more authoritative feel and come downhill slower". Pete Goldsmith chimes in on this one, too: "I absolutely agree about the torque. What 4-strokes lack in top end horsepower, they gain in torque. Why is torque so cool? Well, you can turn big props, generating more propeller efficiency and hence gain more thrust. A side product of this is that bigger loaded props turn less RPM and that is the best way to keep noise down. Plus, with lower RPM and more propeller efficiency, the engine will have a better fuel efficiency. The lower RPM is also better for life span of the engines and the life span of glow plugs.
Old 02-21-2007, 12:03 PM
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Default RE: Top Flite Cessna 310 posted

10000 RPM is about max on the twin.

You'll get plenty of speed but only 4 lbs of thrust. Not nearly enough to fly this.

Bob
Old 02-21-2007, 12:53 PM
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Default RE: Top Flite Cessna 310 posted

In keeping apples to apples....
I see that a OS .55 will accept a 12X7 or 8, and 13X6 or 7 @ 17,000 RPMs
A staito 90 or 100 twin will spin a 12X8 or 14X6 @ 10,000 RPM.

The prop sizes seem comparable. but the RPMs are way different. My understanding of hoursepower is that there is a function of time involved. Specifically RPM.. revolutions per minutes. I had heard that if you doudle the speed of the engine, you double the hp. True?

So, is prop size the final indicator of power and can engine speed be ignored as long as we can spin the prop according to mfg's claims?

Bobby (somewhat confused) Wasabi
Old 02-21-2007, 01:06 PM
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Default RE: Top Flite Cessna 310 posted

Bobby,

The larger question is "is the manufacturer telling you the whole truth?". They will list the props an engine will turn and then follow with the max RPM and HP rating. What they generally don't tell you is which prop was used for that measurement, how much nitro was in the fuel and if the engine was on the ragged edge of blowing up. I found the following by doing a Google on the 55ax and RPM.
>>
After 1/2 gallon of break in time on the OS 55 AX I have some numbers:

On 15%, Just off peak, slightly rich. 50* air temp.
11x6 Scimitar = 13,000 rpm
12.25X3.75 APC = 12,100 rpm
13X6 APC = 9,850 rpm
13x4 cleaned up wood Pro Zinger = 10,400 rpm


http://www.rcuniverse.com/forum/m_51...122675<<
Old 02-21-2007, 01:13 PM
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Default RE: Top Flite Cessna 310 posted

Bobby,

Actual numbers from an OS .55 on a Cessna310, 10,800 RPM with a Master Airscrew, 2-Blade, 13x7

10,900 with a master Airscrew 3 blade 12x6, much less speed.

Bob
Old 02-21-2007, 02:19 PM
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Default RE: Top Flite Cessna 310 posted

Meesh
Speed? do you mean aircraft airspeed?

If I am swinging a 13X7 at lets say 13000 rpm and I am swinging the same prop at 10,000 rpm, am I getting less "work" from the slower turning engine? If my thinking is correct it would seem to me that to get the same thrust from a slower turning engine I would need at least more pitch and/or dia.

While we are at it, Does anybody have a understanding of relationship between prop dia/pitch/ no of blades, disc/power loading for a 20lb C-310? I guess we have a benchmark using a .46 and .55 two stroke
Old 02-21-2007, 02:46 PM
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Default RE: Top Flite Cessna 310 posted

wasabi757

I've done some calculations;

Cessna 310 LIFT CALCULATOR

C1 0.0267 lift coefficient
D 0.075 LB/CU FT
V 55 MPH
A 7.38 SQ FT area
L 22.35 LB lift

Estimated thrust to overcome drag at 72 mph, 150 alt, 70 degF ~ 1.2552 pounds

Propeller

v=72 mph air speed
rpm=10800
2 blade
pitch 6
dia 13"
Thrust 1.3795 (pounds per engine) dynamic

Think this is correct and I hope it helps.
Old 02-21-2007, 02:48 PM
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Default RE: Top Flite Cessna 310 posted

Yes. Aircraft speed

10,800rpm with a 2 blade 13x7 (can do with the .55 OS) produces 9.56 lbs of static thrust. Multiply that times 2 and you get a pretty decent thrust to weight ratio. 19 lbs moving a 20 lb plane, Oh Yeah! That equates to 71.59 MPH

Bob
Old 02-21-2007, 03:31 PM
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Default RE: Top Flite Cessna 310 posted

What would the thrust be using a engine that turns 10,000 rpm's turning 14X 6 prop? ( Satio 90 twin)
Old 02-21-2007, 03:38 PM
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Default RE: Top Flite Cessna 310 posted

It will only turn about 8900-9200 with that prop.

8900 is 8.74 lbs of thrust but only 50 MPH

9200 is 9.33 lbs of thrust at 52 mph
Old 02-21-2007, 03:43 PM
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Default RE: Top Flite Cessna 310 posted

My propeller selector program sez (static) 1s 9.1665 pounds per engine and at 72 mph air speed 0.9436 pounds per engine (dynamic).

@10,000 rpm!
Old 02-21-2007, 03:52 PM
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Default RE: Top Flite Cessna 310 posted

The best way is to try it. The 90 Twin won't turn a 14x6 at 10000 rpm.

I've never seen two thrust/speed programs come up with the same data.

Bob
Old 02-21-2007, 03:55 PM
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Default RE: Top Flite Cessna 310 posted


ORIGINAL: Meesh

It will only turn about 8900-9200 with that prop.

8900 is 8.74 lbs of thrust but only 50 MPH

9200 is 9.33 lbs of thrust at 52 mph
Saito claims 14X6 as their benchmark prop however there is no referance to how fast the engine will turn that prop, just that 10,000 is the upper limit of engine speed (red line?)
Bottom line is that it would apear that the Saito 90 and 100 are too low in the beans department, not to mention that they weigh twice what the OS 55 weigh !
Old 02-21-2007, 04:21 PM
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Default RE: Top Flite Cessna 310 posted

Guys, give me your take on the Saito 72-AAC seems like it might be ok with slightly mor beans then the OS 55
Bobby (still confused) Wasabi
Old 02-21-2007, 04:37 PM
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Default RE: Top Flite Cessna 310 posted

http://www.horizonhobby.com/Products...ProdID=SAIE072
Old 02-21-2007, 08:01 PM
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Default RE: Top Flite Cessna 310 posted

Mike B. - i used a putty knife like you and fuel tanks went in great.

Next question - The 4 nacelle dowel pins and the 2 wing pins - which end goes in and which end sticks out? The ends are not the same.

Bob
Old 02-21-2007, 08:11 PM
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Default RE: Top Flite Cessna 310 posted

Bob,

The ends with the grooves go into the wing and the epoxy fills the grooves and locks them in.
Old 02-21-2007, 09:56 PM
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Default RE: Top Flite Cessna 310 posted

Wasabi, my take on this is that any pair of 4 strokes in the 60, 70, or 80's range would fly this airplane, maybe marginally with the 60's, but the 70's, or 80's should be no problem. I seriously thought about a pair of Saito 82's which I'm sure would yank this baby right off the ground, the issue is whether you want to cut holes on the side of the cowl to accommodate them, in my case I decided against it. Another thing to think about is the overall fit and clearance in the stock mount without surgery to the firewall since the carburator and air intake are located in the rear of these 4 strokers.
Old 02-21-2007, 11:05 PM
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Default RE: Top Flite Cessna 310 posted

Ouestion are gear doors like a P51 the door closes when the gear is down? If they stay open with gear down a jomar is not nessary. Just use a push button air switch on the retract servo to close doors and not have to use a extra retract valve . Dan Avilla
Old 02-21-2007, 11:44 PM
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Default RE: Top Flite Cessna 310 posted

Thanks Rick.

Bob
Old 02-21-2007, 11:48 PM
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Default RE: Top Flite Cessna 310 posted

Dan,

The 310 main inner doors operate like the Mustang, that is, closed when the gear is down. The 310 has fully mechanical gear with pushrods and bellcranks, with a gear reduction motor to drive the linkage. The doors are on a differently timed bellcrank to allow the open and close cycle during the LG transit. The nose gear doors are open when the gear is down, and there's a linkage that's driven from the NG to close them. The early Cessna 411, 421 etc had this setup as well. They all went to electro-hydraulic in the last versions I believe.

Note that the Beech Bonanza, Debonair, Baron, Travel Air and T-34 also have mechanical linkage driven by an electric motor, and cycle the inner doors this way.

Stan
Old 02-21-2007, 11:50 PM
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Default RE: Top Flite Cessna 310 posted

Orvel - I'm putting Saito 82's in mine. Been working all day trying to figure out how to attach throttle to servo. As you said - carb is in the rear. After trying several things, the only way I see it can work is to mount the engines upside down. This way the throttle hooks up per the plans, and the cowl only needs to be cut on the bottom.

I have other planes with inverted 4 strokes and do not use glow plug drivers. I've never had a flame out. I don't think inverted 4 strokes are as susceptable to flame outs as inverted 2 strokes. If there is a problem, glow drivers can always be added.

Bob

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