I just bought a RAM 500, just wondering what kind of real-world fuel consumption figures you guys are getting...how much tankage I should plan for. I know it is dependent on throttle settings and flying style, but I want to just get an idea...

Im building a maverick and im putting about 70oz onboard,ive been told this should be fine for 7/8 mins safe flying time. I am test running mine tomorrow night, I will post the exact cosumption tomorrow night if the isn't a definative answer by then.

jason

The standard BobCat fuel system is an advertised 1.75 liters. I've never measured it. I get 10 to 11 minutes total run time. I set my timer for 6:40, start it just before TO, and fly till it goes off. This give me time for one quick go-around if needed.

The guy I got it from had it in a Hotspot and said he got 10 minutes of flying time out of a two liter tank. Two liters would be 65 ounces, right? He may be a little optimistic, or the hotspot does not need much throttle. Or he is talking about flying the tank out, which is not really realistic.
I would feel more comfortable with more flying time, as the seven minute mark is sometimes the point at which my knees stop shaking and I start enjoying the flight!
Actually, I like to fit big tanks into my models. Call me a frequency hog. I just have always thought that most problems with models happen during the takeoffs and landings, so the longer I am airborne, the longer I can avoid those two particualar problems!
But, the additional tankage to feed a turbine for the kind of duration I like may translate into quite a few pounds of extra weight. No free lunch...
How much tankage would I need to carry to get ten minutes and some safety margin? This is the full auto-start version, so I guess I can spend less time on the ground putting the hatch on and stuff...
Curtis
Tony...one more thing...
Would it be convenient for you to measure the wing-root tanks of the Bobcat, dimensions, not capacity? I am building a Mick Reeves Venom, and he shows two British windsheild-wiper fluid tanks, and the bobcat tanks might be a lot neater if they will fit....
If you cannot get to them, it's no big deal. I'm not that far along yet...

Easytiger,

I have two sets of Bobcat Tanks built in the shop right now. Tell me exactly what dimensions you need and I will measure them for you.

David Reid

Maximum length, width, height, and the minimums. Don't kill yourself, or go out and buy a micrometer or anything, just a general idea. They have a constant taper, right?
How are they mounted?

The 500 uses 6 oz./min. at WOT. Taking into account that fuel consumption is GENERALLY linear with thrust output, half throttle (6lbs.) would be 3 oz./min. Remember that RPM and thrust are not linnear. Half throttle is probably 130-140k. It all really depends on your flying style. I personally like long flights also. So safely, 70-80 ounces would give a 10 minute safe approx. flight time. Put it wherever it fits!!! Happy landings,

Tony's taxi and flight times indicate to me that the way Tony is operating his Ram 500 he is burning very close to 9 oz a minute.
I do know, cause I measured them the Bob Cats main tanks will hold 39 oz of fuel each. That's 78 oz divided by let's be conservative and calculate 8 minutes of throttled up flight time that equals = 9.75 oz per minute. Tony figures his total run times at about 11 minutes including taxi etc. It looks like to me the Ram 500 @ full throttle burns about 9 oz a minute minimum!
Lee ------

overall length 7"

Width small end 4.5" Depth here is 2"

Width Big end 7.5" Depth here is 2.5"

It is not really a constant taper but pretty close

Lee, you're not taking into account that I still have fuel left. I always have to pump a fair amount out of the tanks to empty them. I don't like running out of fuel, so I always land with a fair amount left.

I think I probably pull 10 to 12 oz out of the fuel tanks at the end of the day. So that means, if you're numbers are correct, that I burn 66 to 68 oz of fuel in 11 minutes of run time. That's an average of 6 to 6.2 oz/min. Those who have watched me fly the BobCat know I'm not off the power much.

RAM has always used an average flight to show fuel burn. So that 6 oz/min # is pretty close to what I'm getting.

Sure is nice to get a lot of flights off that 5 gallon can with the 500/BobCat.

I have my 500 in an Avonds Rafale, and my flights are 5 min max with 50 oz of fuel on board. There is usually some left when I land, but not much. The Rafale is not a fast plane, so I usually run pretty close to full throttle. I figure I am burning at least 7 oz per minute, maybe more.

I don't have a Ram 500, but if I did a test would be in order. It's got to be easy for someone to do. You know a measured, known, exact fuel amount in a little tank and let her rip! Then all of the guessing will be dispensed with----I'll bet a lot of fellows would really like to know what the Maximum fuel burn is so they could flight plan from that info --------I flight plan 11oz a minute with my P-80 and I never burn it all of course-------
Tony,
I could guess within 2 gallons the fuel burn on my C-182, it was a game of sorts, how close could I get to what I would pump back into the tanks starting from full tanks.
A lean fuel mixture, and I mean lean(white clean soot) @ 9,500 ft MSL cruse, 20 inches of manifold pressure and 22 hundred RPM one day I burned only 9.7 gallons of fuel per hour (actual lapse time not tach) form El Paso Int. to APA Centennial --- 4 hours 10 minutes lapse time, takeoff to touch down and I pumped 40 gallons back in the tanks ------- that was a perfect smooth ride the whole way not a ripple -----even through New Mexico very unusual-----
Lee -------

One thing I don't like is sales talk, I like to know what the heck something really does. Light aircraft manufactures were always the best (worst) at doing that. When I see averages quoted or this new safety feature or more baggage room or more payload (same airframe) someone's just stretching the numbers to look better to someone who doesn't know the difference. Puffing like that always comes back to haunt the unit. The first thing I key on is what is mentioned that is supposed to be better, I assume that is usually where the stretching of the facts are.
Lee ------

Thank you so much, David. That's just what I needed.
Lee, I'm not sure if letting the 500 rip at full bore gives any more accurate a figure than the factory's average of six ounces per flight. Somewhere inbetween is probably a reflection of what I would get.
As far as Cessna or RAM or Range Rover factory mileage figures, well, we all know that they are based upon rather idyllic conditions. But, if you only drive at a steady 55 on smooth roads, using very smooth ankle movements on the pedal, well, maybe you WILL get those numbers...
I don't think Tony is upselling his figures, I think he really gets that, but he is very familiar with his aircraft, and he's probably a better, smoother pilot than myself. I don't feel sales pressure from Tony, I think he reps the companies that he does because he actually uses and likes the stuff. Really.
Seems like I should plan on seven ounces a minute or so, as neither of my two aircraft are going to be as clean as a Bobcat...

This all brings up the discussion of fuel consumption in any model. In my opinion the best way to figure on this is to actually measure it while flying the model. Take for example the Tony's Bobcat..... He knows he has X number of ounces on board, and he sees the factory published fuel consumption. PLanning with that information he sets his flight timer to 5 minutes, hee lands taxis back and checks remaining fuel. He is not even into the hopper yet. He knows the hopper is 20 oz so he adds 30 seconds to his timer for the next flight. When he lands he has used about 2 oz out of the hopper so he knows he can increase his flight time by another 30 seconds and still be safe, and have enough fuel for a go around. The full throttle tests that Lee suggests could also give you a good starting point for fuel capacity sizing.

I think Tony's numbers are close to real world figures.

Gsmurfs comments are right on. For simlilar thrust, fuel consumption remains linear not only on one engine, but from similar from engine to engine. If you want to see the math, look at Schrecklings Turbine Bible, Chap 4&5.
The JetCat ECU spits out pretty accurate fuel consumption/run. I only have to spool my P-120 to about 75-80 K to get 12 lbs thurst. At that RPM, I burn 6-7 oz/min. I routinely fly my HotSpot agressively for 6 min flight time, and 9:30-10:00 min total run time and I burn 1900-2000 cc or about 65-70 oz. After comparing my fuel consumption to another fellow flying a 500 on a HS, it is nearly identical, since he has to be at full throttle to match my performance at 2-3 clicks about 1/2 throttle.

RPM vs fuel consumption is not linear. For our turbines, fuel consumptions begin to approach exponential, rather than linear increases above 125,000 RPM. That's why full scalers try to cram the biggest, most fuel efficient (hi-bypass turbofans) into their planes, and spin them at as low an RPM they can.

Since engine prices are coming down, it seems to makes more sense to get a P-120, or RAM 1000, or SimJet 3000, to power your BC, Roo, or HotSpot, since you can loaf these engines along at 78-80 K and EGT's around 450C, and still do 160 MPH It's RPM and temps that really influence time before overhaul.

Tom

I agree with everything Tom said except for one point, the weight of the engine and system. A RAM 500 is about 1 to 1 1/2 pounds lighter then a RAM 1000, P-120, etc. My BobCat weighs 17.5 pounds with the 500 and a monokote covered wing and stab. And the take-off weight is a lot less with the smaller fuel supply. This gives me a much lighter BobCat then the XL's I've seen. And since it's the same wing the loading is significantly less. Which all translates into a nimbler plane. Maybe it's my pattern background but I like that.

But then it's all probably a sales pitch.

On the Grey Hog I have 72 oz per engine, (two RAM750F's) and have my timer set to count down 10 minutes. Count down starts upon gear retraction and as soon as I hear the buzzer I imediately set up for landing. One flight here in Denver I made three go arounds before finally landing and lost one engine as I was taxing back!! Talk about luck!!

I could see where a 750 throttled back might burn fuel at a similar rate to a 500 going full tilt...but since I own the 500, not the 750, it's a moot point for me...
Actually, one of the planes I am building is a Mick Reeves Venom. RCJI had a three part review, and they actually flew it with both setups. First with a simjet(I think...anyway, something in the 750 class) and then with the 500. With the 500, by the time all was said and done, the airplane was four pounds lighter at takeoff, and the reviewer seemed to like the model a lot more.

In the end, lighter is ALWAYS better. If not, why do they make high performance engines? Why buy a Jett 50 if you can just stuff in a 60 instead? Because all the weight adds up.
I went through this with DFs a lot...why not just put a 91 into every 45 sized model? Because the same plane two or three pounds heavier could be a very different model.

If I HAD a 750, though, instead of the 500, I would be using that.
Dean, your Hogs look great. I have seen them fly on video, DF and turbine. What a nice, forgiving aircraft. Looks like fun to fly.
I've done that same dumb trick a couple of times on an Me110 twin. Ran out one engine while taxying back. It will only taxi in circles then...

Just finished stripping all the Byron guts out of my JD Models Crusader, will beef it up and put in the 500. What a pain, as I spent thirty hours last week re-installing all the DF stuff after a crash...
Sorry, wrong picture.

I'm still curious how much fuel the little Ram "can" burn Maximum. Can / "will" anyone quote that figure? Seems to me if we know the worst case, all else will take care of it's self.
Tony, I was not trying to imply you were trying to sell anything, quite the contrary. I am sure you are quoting exactly what you experience using the product. I know you wouldn't say anything that wasn't what you had experienced. Maybe my calculations are off a little, but I truly would like to know how much the Ram 500 "can" burn, not how much it doesn't. No two people fly in the exact same manner, longer taxi times, go a rounds, size of landing pattern etc., etc., the only one fact that will remain very close to exactly the same is the Maximum amount a motor can burn. With that real world information everybody can then plan there flight times and fuel tank sizes accordingly, and not be disapointed cause they have to land just when there legs are began to stop shaking!
Lee ------

Lee, I could go do a test, but it will only be valid for the conditions during the test. Temp, pressure, humidity, will all vary the results significantly. Since I have no way of correcting for the conditions, it wouldn't mean much.

I flew my MiG for about 6 months at my location, which is at about 2,400 feet, average temp 80 to 90. Got my timers set and got used to the thrust. I was a happy camper. Then I went to Whidbey in 2000 for their rally. Sea level, 60 degrees. The increase in thrust was great! Almost ran it out of fuel on the first flight.

What DavidR described is how I do every new jet/engine. Go with short time and check how much is left. Really no reason to go overboard here. 78 ounces gives me adequate flight time. If you want longer, put in bigger tanks.