Advice on motor glider wanted - FES - Jet - Engine

Before you buy a jet powered glider, consider the noise level. Our neighbors would shut down our Gliderport if we allowed them to use their engines in the area.

Tom

At 19:35 10 December 2016, wrote:
Before you buy a jet powered glider, consider the noise level. Our
neighbors would shut down our Gliderport if we allowed them to use their
engines in the area.

Tom


Never thought of that, thought with them being so small they would not be
noisy. Was intending to use it away from the airfield but good point.

On Friday, December 9, 2016 at 9:00:05 AM UTC-5, J W wrote:
Seeking advice for a cheapish motor glider but a good investment is
more important.

Was considering the newer types like the 13.5 metre Mini LAK, Silent 2
and HPH Shark.

Concerned that there are very few registered and certified in the UK so
may not be a good investment?

Like the idea of short span, low weight, carbon fibre construction as I’m

not so young and will be flying from rough grass strips. Fly for fun and
not in to competitions.

Would consider electric sustainer but think an engine or jet will be
preferable for range, allowing time to explore mountains and wave.

Suggestions welcomed, Thanks.

I'm new to these jet engine sustainers but I'm interested as well. I have a few major concerns: From what I can gather, they have limited run times, like 10 minutes. Also nobody seems to be saying what the TBO is on these little jets. It might be as low as 50 hours but I'm not sure. And, what is the overhaul cost and therefore, what is the hourly cost of operation?

I believe the overhaul time is 25 hours, at least for the HpH gliders.

On Tuesday, January 3, 2017 at 9:21:45 AM UTC-8, Doug B wrote:

I'm new to these jet engine sustainers but I'm interested as well. I have a few major concerns: From what I can gather, they have limited run times, like 10 minutes. Also nobody seems to be saying what the TBO is on these little jets. It might be as low as 50 hours but I'm not sure. And, what is the overhaul cost and therefore, what is the hourly cost of operation?

The HpH ones run as long as you have fuel left - maybe 30-40 mins at a reasonable power setting. Time to overhaul is 50 hours, which at the rate I use mine is going to be somewhere between 10 and 20 years. Cost is said to be a few hundred euros - it's basically looking at the bearings.

Paul


On Tuesday, January 3, 2017 at 6:01:16 PM UTC, Jonathan St. Cloud wrote:
I believe the overhaul time is 25 hours, at least for the HpH gliders.

Jets are cool, no doubt, and highly reliable, but they're very noisy
and, at the speeds gliders fly, very inefficient. I don't know how they
cost compared with a Wankel or piston engine, but I wouldn't have one.
The novelty will wear off.

My $0.02...

On 1/3/2017 10:21 AM, Doug B wrote:
On Friday, December 9, 2016 at 9:00:05 AM UTC-5, J W wrote:
Seeking advice for a cheapish motor glider but a good investment is
more important.

Was considering the newer types like the 13.5 metre Mini LAK, Silent 2
and HPH Shark.

Concerned that there are very few registered and certified in the UK so
may not be a good investment?

Like the idea of short span, low weight, carbon fibre construction as I’m

not so young and will be flying from rough grass strips. Fly for fun and
not in to competitions.

Would consider electric sustainer but think an engine or jet will be
preferable for range, allowing time to explore mountains and wave.

Suggestions welcomed, Thanks.
I'm new to these jet engine sustainers but I'm interested as well. I have a few major concerns: From what I can gather, they have limited run times, like 10 minutes. Also nobody seems to be saying what the TBO is on these little jets. It might be as low as 50 hours but I'm not sure. And, what is the overhaul cost and therefore, what is the hourly cost of operation?

--
Dan, 5J

The inefficiency comes from simple single stage turbine without bypass and low operating temperatures (compared to real turbofans).

On Wednesday, January 4, 2017 at 3:48:53 PM UTC, Dan Marotta wrote:
Jets are cool, no doubt, and highly reliable, but they're very noisy
and, at the speeds gliders fly, very inefficient. I don't know how they
cost compared with a Wankel or piston engine, but I wouldn't have one.
The novelty will wear off.


Noise can certainly be an issue, and you wouldn't want to use them much near your home site. But for us glider pilots, efficiency is not a big issue (we don't use it enough to worry). However, they have a very distinct advantage over a piston or wankel, and that's the lack of drag when you extend them.

That means that your commit height is much lower - people I know with conventional engines have to start them above 1000 ft AGL (some use considerably higher) and be downwind on a suitable landing area in case they don't start. With a jet, there's effectively no extra drag, so waiting until 500 ft AGL is perfectly feasible - or you can be further away from the field. That's the difference between completing a flight and not doing so, surprisingly often.

For me, at the moment it's a toss up between jet and FES - though I suspect within a few years FES will win out as battery technology gets better.

Paul

One problem I've seen is getting low away from a landable area following
flight in very cold air, e.g., wave. Whereas my Stemme has very little
increase in drag during engine start, and it starts quickly and
reliably, there's a requirement not to use much power until the oil
temperature reaches a certain level. Even with cowl flaps closed, that
can take 5 minutes or more to achieve. Fortunately, with power just
above idle, the Stemme has little to no decent.

Having flown turbojets in Alaska and turbofans in the lower 48, I don't
recall any cautions about oil temperature, though good sense should
prevail. There should be enough temperature for oil to circulate. The
jets would start and run just fine at -40 deg F.

On 1/7/2017 11:31 AM, Paul Ruskin wrote:
On Wednesday, January 4, 2017 at 3:48:53 PM UTC, Dan Marotta wrote:
Jets are cool, no doubt, and highly reliable, but they're very noisy
and, at the speeds gliders fly, very inefficient. I don't know how they
cost compared with a Wankel or piston engine, but I wouldn't have one.
The novelty will wear off.

Noise can certainly be an issue, and you wouldn't want to use them much near your home site. But for us glider pilots, efficiency is not a big issue (we don't use it enough to worry). However, they have a very distinct advantage over a piston or wankel, and that's the lack of drag when you extend them.

That means that your commit height is much lower - people I know with conventional engines have to start them above 1000 ft AGL (some use considerably higher) and be downwind on a suitable landing area in case they don't start. With a jet, there's effectively no extra drag, so waiting until 500 ft AGL is perfectly feasible - or you can be further away from the field. That's the difference between completing a flight and not doing so, surprisingly often.

For me, at the moment it's a toss up between jet and FES - though I suspect within a few years FES will win out as battery technology gets better.

Paul


--
Dan, 5J

On Saturday, January 7, 2017 at 9:31:46 PM UTC+3, Paul Ruskin wrote:
On Wednesday, January 4, 2017 at 3:48:53 PM UTC, Dan Marotta wrote:
Jets are cool, no doubt, and highly reliable, but they're very noisy
and, at the speeds gliders fly, very inefficient. I don't know how they
cost compared with a Wankel or piston engine, but I wouldn't have one.
The novelty will wear off.


Noise can certainly be an issue, and you wouldn't want to use them much near your home site. But for us glider pilots, efficiency is not a big issue (we don't use it enough to worry). However, they have a very distinct advantage over a piston or wankel, and that's the lack of drag when you extend them.

That means that your commit height is much lower - people I know with conventional engines have to start them above 1000 ft AGL (some use considerably higher) and be downwind on a suitable landing area in case they don't start. With a jet, there's effectively no extra drag, so waiting until 500 ft AGL is perfectly feasible - or you can be further away from the field. That's the difference between completing a flight and not doing so, surprisingly often.

For me, at the moment it's a toss up between jet and FES - though I suspect within a few years FES will win out as battery technology gets better.

Isn't FES already better?

According to reviews, 30 kg of batteries and 30 kg of jet fuel both seem to provide about 90 miles or 1 hour of range. FES provides more thrust/climb rate, is instant starting, non-smelly/mess, much quieter, the motor is lighter. Liquid fuels take minutes to refuel rather than hours, but that's probably not a limiting factor for a recreational glider. LIPO batteries may be a bit more likely to immolate themselves than liquid fuels but the risk is pretty low with both and you do have insurance and a parachute I hope :-)