UAV's and endurance

[blue9]

I have always wondered how the uav's get their endurance.
The predator can fly for more than 40 hours. I have a 2 meter sailplane with a small 4 stroke, but even with a large tank, it seems the limit is around 2 hours. I know that we are talking about full scale, but even so. Just wounder if they have any special features.

[spitfiremk9]

I have always wondered how the uav's get their endurance.
The predator can fly for more than 40 hours. I have a 2 meter sailplane with a small 4 stroke, but even with a large tank, it seems the limit is around 2 hours. I know that we are talking about full scale, but even so. Just wounder if they have any special features.

Blue9, you need to get that four stroke running on regular Gasoline/petrol ( I am assuming its a glow motor ) then you'l see a big reduction in fuel consumption

[c_matt92]

A lot of your high endurance UAV's have fuel cells in the wings. Also, I agree on the gasoline engine comment.

[tekrunner]

A lot of your high endurance UAV's have fuel cells in the wings. Also, I agree on the gasoline engine comment.


Would you please elaborate on these fuel cell systems? Anyone have more info on them?

[tekrunner]

Would you please elaborate on these fuel cell systems? Anyone have more info on them?


I guess I should elaborate. Are there any systems available. Anything I can buy to test the concept? I found a small science kit where you build a hydrogen fuel cell car, perhaps that'd be a start.

[Gary Mortimer]

I think Matt means the wings are full of fuel, not the new fuel cell tech.

They have big fuel tanks!!

[EddieWeeks]

This plane has the best endurance of them all..

1.1 gallons in 6.5 minutes !!!

Nothing can beat that !!!... hahah

Eddie

[blue9]

Her is the specs for the Mq-1 predator

General characteristics

* Crew: 2 (one pilot and one sensor operator)
* Length: 27 ft (8.22 m)
* Wingspan: 48.7 ft (14.8 m (dependent on block of aircraft))
* Height: 6.9 ft (2.1 m)
* Wing area: 123.3 sq ft[41] (11.5 m²)
* Empty weight: 1,130 lb[42] (512 kg)
* Loaded weight: 2,250 lb (1,020 kg)
* Max takeoff weight: 2,250 lb[42] (1,020 kg)
* Powerplant: 1× Rotax 914F turbocharged Four-cylinder engine, 115 hp[42] (86 kW)

Performance

* Maximum speed: 135 mph (117 knots, 217 km/h)
* Cruise speed: 81–103 mph (70–90 knots, 130–165 km/h)
* Stall speed: 62 mph (54 knots (dependent on weight of aircraft), 100 km/h)
* Range: >2,000 nm[43] (3,704 km, 2,302 miles)
* Service ceiling: 25,000 ft [42] (7,620 m)


And the max endurance is 40hr +
But i suppose it has a very large fuel thank, and that's all there is to it.

[c_matt92]

Fuel cell just means a way to store fuel, not just hydrogen like many people think. The tanks that I have seen held 91 octane gasoline and were made of a bladder of some sort.

[spitfiremk9]

Fuel cell just means a way to store fuel, not just hydrogen like many people think. The tanks that I have seen held 91 octane gasoline and were made of a bladder of some sort.
Yes, you can put fuel bladders in the wing or fus, basically, they are just petrol tolerant plastic bags that mold themselves to shape once filled, you would be surprised how much fuel you can get in a tight place!

[Apep]

Yes, you can put fuel bladders in the wing or fus, basically, they are just petrol tolerant plastic bags that mold themselves to shape once filled, you would be surprised how much fuel you can get in a tight place!

ATL has some nice bladders.

[aperture]

I expect that these carbon fiber wings do not have bladders, but are sealed wet wings. Bladders are old technology.

As to endurance, at high altitudes flown, the engine can be leaned considerably to save fuel. From memory, I recall an Insitu designed UAV crossed the Atlantic ocean, using only 1.5 gallons of fuel. I'm sure that high altitude prevailing winds helped to speed the plane along too. Also from memory, an Insitu Integrator design carries only about 7 gallons and is said to be able to fly for 24 hours.

ken

[blue9]

Another factor that i might have forgot, is that just hovering takes very little amount of power. Perhaps as low as 5-10 hp. So comparing the situation with my family car, which has a similar power plant is wrong.

[RCAV8R13]

I expect that these carbon fiber wings do not have bladders, but are sealed wet wings. Bladders are old technology.

As to endurance, at high altitudes flown, the engine can be leaned considerably to save fuel. From memory, I recall an Insitu designed UAV crossed the Atlantic ocean, using only 1.5 gallons of fuel. I'm sure that high altitude prevailing winds helped to speed the plane along too. Also from memory, an Insitu Integrator design carries only about 7 gallons and is said to be able to fly for 24 hours.

ken
Very accurate info Ken, well done.
We did one more trick with the Aerosonde, besides converting the 4 stroke to gas. We did not mix the oil with the gas. This allowed us to run pure gas through the cylinder. With a 4 stroke we would have had to dilute the fuel with 5+% oil (as apposed to the standard 2% for a 2 stroke).

Kip

[Nimski]

The endurance problem is one that I have faced for a while in the design of my UAV. In this case however I think the disadvantage is that I'm using an electric power system and the efficiency of batteries these days in terms of Wh/Kg is overshadowed by that of most types of fuel. That and the fact that you lose fuel as you burn it, but the batteries always remain for you to carry (unless you're thinking of jettisoning depleted poisonous Li-Po batteries all over the place).

[airmcn_3]

The endurance problem is one that I have faced for a while in the design of my UAV. In this case however I think the disadvantage is that I'm using an electric power system and the efficiency of batteries these days in terms of Wh/Kg is overshadowed by that of most types of fuel. That and the fact that you lose fuel as you burn it, but the batteries always remain for you to carry (unless you're thinking of jettisoning depleted poisonous Li-Po batteries all over the place).


Ya probably not a good idea, defiantly the down side of electric power.

[gkamysz]

Very accurate info Ken, well done.
We did one more trick with the Aerosonde, besides converting the 4 stroke to gas. We did not mix the oil with the gas. This allowed us to run pure gas through the cylinder. With a 4 stroke we would have had to dilute the fuel with 5+% oil (as apposed to the standard 2% for a 2 stroke).

Kip

Why did you need to run 5% oil? I heard of others using 2% in Saitos for UAV applications.

Greg

[spitfiremk9]

Why did you need to run 5% oil? I heard of others using 2% in Saitos for UAV applications.

Greg
Greg
2% is fine, this is a standard mix with a quality synthetic oil, I strip and inspect all my motors after 20hrs run time.
I used to run 100ll Avgas and mix a little stronger for longer duration

[gkamysz]

Was that in a four stroke RC engine? I'm just curious why the Aerosonde people found they needed 5% oil. Enya four stroke have steel cylinders without chrome, and I'm pretty sure this is the case with the 1.20 I was going to try a crankcase lube system, but I have to consider where the weight penalty balances, probably right around 1 gallon fuel load.

Greg

[spitfiremk9]

Greg
I think there is quite a lot of misinformation floating around regarding certain projects
My preferance is to start from scratch and document everything
I only use Saito engines now but I have used Yamada (YS), Enya and OS and have converted most sizes from .2cuin to 1.8cuin

[RCAV8R13]

Let me clarify. We never mixed the oil and gas on the Aerosonde. We estimated that we would need 5% oil because with a four stroke the fuel does not go through the crankcase first. I know Maynard Hill worked very hard to find the right oil that he could mix with his fuel (If I remember at the time he was using Coleman white fuel) and he got his mix down to 6%. We never bothered, we went straight to a separate oiling system.

Kip

[spitfiremk9]

Kip
Who was the Guy that designed the injection system on Aerosonde, I can't remember his name and its bugging me

[picooZer]

Can't you get quite a fair range with a glider?

With a glide ratio of 1:15 (not including thermals) and with 5 climbs to 1000 meters couldn't you easily get a range of 75km? That's more than enough for me.

[matttay]

This paper below is pretty comprehensive, and in the intro goes into good detail why something like a Cox 0.01 TD could be a good starting point for UAV power. The TD 0.01 could be good for 15W or so, with a Brake-specific Fuel Consumption of about 5 grams of fuel per WH produced. Of course, a range of larger engines were also made, so the 15W is really the lower bound.

The paper is impressive. Don't miss it.

http://www.lib.umd.edu/drum/bitstream/1903/4216/1/umi-umd-4031.pdf

[Gary Mortimer]

Thats a great paper matttay, I have always wanted a Cox engine and that combined last weekend with a visit to a free flight event where there were loads. Means I almost have to buy one now!!!

[Airboatflyingshp]

Check out with the vintage and free flight guys for which cox is the best and what to avoid........ they also did diesel conversions for them, the little bigmigs might also be worth a look.

[Gary Mortimer]

Truth be told it could only be the Cox 049 the thing I always wanted when growing up!

Just need an excuse ;-)

The only advantage of getting older is that you can, if cash allows buy that toy.

[gkamysz]

5000g/kWh is awful, but unavoidable in that size, especially on methanol and nitro.

Greg

[matttay]

Yes, 5 isn't great. LiPo is around 7g/wh or 142 wh/kg. And the ~10W or so that you could harvest might keep something shy of a pound aloft.

If you moved up to a 0.020 or 0.049 how would BSFC improve? The paper suggests things could get better fast--1200 wh/kg, or an order of magnitude improvement over the TD 0.010. But where is that cross over? I also don't remember enough chemistry to know how glow fuel differs from liquid hydrocarbon. But it looks like the paper covers that.

[gkamysz]

When you talk about methanol/nitro fuel you automatically give up 50% or more of the possible BSFC compared to petroleum based fuels. Improving BSFC of little engines is difficult. I've measured some reasonable figures for four stroke engines in the 8cc range. I'm working on improving performance.

Greg

[Airboatflyingshp]

PAW motors, http://www.eifflaender.com/enginepics.htm compare the performance but Enya do a 4 stroke deisel now........ might that not give longer range, what if it was attached to an efficient reduction gear drive as well?

[RCAV8R13]

Kip
Who was the Guy that designed the injection system on Aerosonde, I can't remember his name and its bugging me
I don't know who designed the injection system. The last guy I remember working on engines for the Ausies was a brilliant fellow named John Jeng. Perhaps he did.

Kip

[spitfiremk9]

When you talk about methanol/nitro fuel you automatically give up 50% or more of the possible BSFC compared to petroleum based fuels. Improving BSFC of little engines is difficult. I've measured some reasonable figures for four stroke engines in the 8cc range. I'm working on improving performance.

Greg

Greg
Are you using Walbros or the standard carb? Have you experienced the dreaded icing yet?