DG-808J self launch motorglider

[Bob Carlton]

Hello fellow aviators,

Desert Aerospace is pleased to announce the first DG-808J motorglider powered by twin PBS TJ40 engines. It is a blast to fly. Here is a link to more information:

https://www.dropbox.com/s/b7m3j9tz85ga0w8/DG%20808J%20report.pdf?dl=0

The second DG is in the shop now for conversion.

Also of note...as of a few days ago, we finally won a decade-long battle with the FAA. Pilots of turbine self-launch motorgliders no longer require any special authorization. It's been a long fight and we had to play hard ball to get them to understand their own rules, but we finally got it.

[Dave Nadler]

Congratulations! Looks nice.
Why two motors this time??

PS: My presentation wasn't so much about safety as reliability. They're
only unsafe when you trust it, and don't always fly to be safe when it
fails...

[2G]

Don't get too excited - Bob clearly states that this ISN'T a motorglider, but a motorized airshow glider. There is a BIG difference.

Tom

[Mark Mocho]

> Don't get too excited - Bob clearly states that this ISN'T a motorglider, but a motorized airshow glider. There is a BIG difference.

Incorrect. The Salto with the TJ-100 is solely an airshow glider. The DG-808J does everything that the piston/propeller DG-808C does, but uses a pair of turbines to self-launch, retract and then proceed as a sailplane. Just like a Schleicher or Schempp-Hirth motorglider.

[youngbl...@gmail.com]

On Tuesday, December 6, 2022 at 6:20:15 AM UTC-5, Mark Mocho wrote:
> > Don't get too excited - Bob clearly states that this ISN'T a motorglider, but a motorized airshow glider. There is a BIG difference.
> Incorrect. The Salto with the TJ-100 is solely an airshow glider. The DG-808J does everything that the piston/propeller DG-808C does, but uses a pair of turbines to self-launch, retract and then proceed as a sailplane. Just like a Schleicher or Schempp-Hirth motorglider.

Why don't you motorglider guys just call them Non-Binary gliders? Old Bob, The Purist

[Mark Mocho]

Why two motors this time??

The TJ40 is rated at 40 DaN (89 lbs.) of thrust. That is insufficient for self-launching. Two engines are enough even at high altitude airfields on hot days with water ballast.

[Dave Nadler]

But why not the same single engine as used on some of the other
projects? Too big?

[Mark Mocho]

> But why not the same single engine as used on some of the other
> projects? Too big?

Definitely too big. The TJ100 is 10.5 inches in diameter and about 22 inches long. While that would fit inside the fuselage (assuming the engine bay door opening is wide enough), there is virtually no room for the extraction mechanism. Also, since it has an oil tank and recirculating oil system, it must rest horizontally in the engine bay. With a two-seat glider like the Arcus, this is not a problem, but a single seater is just a bit too small. Also, the price on the TJ100 is over twice as much as a PAIR of the TJ40s.

[Eric Greenwell]

Congratulations, and thank you for your perseverance. It's another stepping stone to
keeping glider requirements "real" - connected to the actual situation.

Your article was interesting and informative, but I have to offer an important correction
to a statement in it:

"What other group of aviators (or any other sport) suggests that a post-flight inspection
after every flight is critical to find things that broke? I’ve seen broken mounting bolts,
broken case bolts, stripped drive belts, and numerous other vibration/stress-induced
failures. These are way too common."

I think you were referring to piston powered self-launchers, but you didn't explicitly
state that. I think it's important to note that Schleicher Wankel powered self-launchers
do not require a post-flight inspection, and none of the owners do one, because it is a
very smooth running engine that does not cause things to unscrew, strip, crack, break, or
fall off like most of the two stroke engines used in the other gliders.

It is also worthwhile noting that, in addition to the Wankel powered gliders, that there
are hundreds of self-launchers that are also vibration free: electric powered sailplanes.

--
Eric Greenwell - USA
- "A Guide to Self-launching Sailplane Operation"
https://sites.google.com/site/motorgliders/publications

[jfitch]

It's an impressive achievement, though perhaps there is a little hyperbole in the description. In addition to the Wankel not falling apart after every flight, the statement "..but suffice to say, it will outperform any other motorglider..." does not seem to be true, based on the stated numbers.

[Mark Mocho]

hundreds of self-launchers that are also vibration free: electric powered sailplanes.

I am aware of only two types of electric self-launchers: the Pipistrel Taurus Electro and the Alisport Silent Electro. There are also the "Birdy" and the GP Jeta, but neither seems to be in actual production.

[Mark Mocho]

Congratulations to Bob & Mark on another successful build!

Nick- I can't take much credit for the DG-808J. The engineering and construction were done by Bob Carllton, Min Tang and Grayson Hardy of Desert Aerospace.

[Charlie M. (UH & 002 owner/pilot)]

On Tuesday, December 6, 2022 at 11:37:47 AM UTC-5, Mark Mocho wrote:
> hundreds of self-launchers that are also vibration free: electric powered sailplanes.
> I am aware of only two types of electric self-launchers: the Pipistrel Taurus Electro and the Alisport Silent Electro. There are also the "Birdy" and the GP Jeta, but neither seems to be in actual production.

Production?
Well.....one off, "UH's" ASW-24e converted from gas to electric. I have about 100 flight hours in 2022 in it.
It has been self launched (I haven't done that yet) and I have done "saves" to altitude (testing and real) as well as self retrieve.
I have traces on Skylines if you want to see. I can tell you the flights. A real save and self retrieve were both at Newcastle this year.

As to this thread, guessing my old IPad OS and browser won't let me open the link.

[Eric Greenwell]

On 12/6/2022 8:37 AM, Mark Mocho wrote:
> hundreds of self-launchers that are also vibration free: electric powered sailplanes.
>
> I am aware of only two types of electric self-launchers: the Pipistrel Taurus Electro and the Alisport Silent Electro. There are also the "Birdy" and the GP Jeta, but neither seems to be in actual production.
>

The MiniLAK, Ventus 3 FES, and many other FES gliders (which includes the Silent Electro)
can self-launch. The newer mast style designs, like the AS34 and JS3RES are all
self-launchers. There are still Antares gliders flying (I think nearly 100 were produced),
and let's not forget the ones added to the fleet by people like Hank Nixon. It all adds up
to "hundreds".

[R]

Congratulations Team Desert Aerospace. Perhaps another ‘ Chairman Award’ along with others will be coming recognizing the Team achievements. Can’t help but think of Elon Musk and his drive to Achieve. Bob, Desert Aerospace’s History continues.

Jet powered gliders certainly have a place in aviation and records have shown that the pilot, not the engine, is by far the weakest link. I have the greatest confidence in my Astra engine (ASH-31) and do not adhere to Nadler’s ‘fly with fear’ philosophy and believe more emphasis should be on pilot’s preparedness, procedures, and high maintenance standards. Then …. fly with confidence.

I always post-flight my engines, wipe off the bugs, kiss them good night, a pat on their mufflers.
Yin and Yang,,,,,,,works for me.

R

[Chris]

What is the cost of the conversion?

[Mark Mocho]

> What is the cost of the conversion?

I don't know.

Contact Bob at Desert Aerospace for more information.

[Mark Mocho]

Schleicher Wankel powered self-launchers
do not require a post-flight inspection, and none of the owners do one, because it is a
very smooth running engine that does not cause things to unscrew, strip, crack, break, or
fall off like most of the two stroke engines used in the other gliders.

Really? You might ask Keith Essex about that. This summer, I helped him remove his ASH-32 Mi engine to attempt to replace three broken case studs. We got two out, but the third was rather uncooperative. The engine had to go to Rex Mayes at Williams Soaring for a more extensive teardown.

[Squeaky Squeaky]

Very nice, I added your DG-808J motorglider to my book, "Mary, Monkey, Sun, Tree and Penis Whoreshippers, Part A."

[Dave Nadler]

On 12/6/2022 11:37 AM, Mark Mocho wrote:
> I am aware of only two types of electric self-launchers:
> the Pipistrel Taurus Electro and the Alisport Silent Electro.
> There are also the "Birdy" and the GP Jeta, but neither seems to be in actual production.

There were maybe 75 electric-powered Antares built.
I flew mine ~1400 hours, but some hints on why I disposed of it:
https://nadler.com/public/2020_AlmostSoaringReport/2020_DavesAlmostSoaringReport.html

And yes, this one got post-flight inspections...

[jfitch]

You really cannot condemn all of the Austro Wankels on that basis. A limited range of serial numbers was built with improperly heat treated bolts. There is no evidence that engines outside of that range, or those engines - once the correct bolts are installed - have any problems. I know of no operational failures as a result of the broken bolts, they were observed on normal inspections. The engines have their own set of problems, but vibration induced failure isn't generically among them.

[Craig Reinholt]

> The MiniLAK, Ventus 3 FES, and many other FES gliders (which includes the Silent Electro)
> can self-launch. The newer mast style designs, like the AS34 and JS3RES are all
> self-launchers. There are still Antares gliders flying (I think nearly 100 were produced),
> and let's not forget the ones added to the fleet by people like Hank Nixon. It all adds up
> to "hundreds".
> --
> Eric Greenwell - USA

On a bit of a tangent.
I wonder if we should term a glider "self launch" only if it can launch ballasted at full gross weight at an airport @ 1500' (pick a reasonable altitude other than sea level) above sea level at a reasonable climb rate?
Can some of the FES systems get in the air on their own steam minus ballast? Yes of course. However, maybe we call those systems "strong sustainers"? Something to ponder.

[Matthew Scutter]

Getting ready to self-launch for the 5th day in my ballasted 'strong sustainer' I guess. https://www.weglide.org/travel/1387

Congratulations to Bob/Desert Aerospace. The DG808J looks great.

[Eric Greenwell]

Were you looking for vibration related problems? That was what Bob mentioned, and what I
addressed. If not vibration related, what were you looking for?

Eric

[Dan Marotta]

I doubt it'll out perform my Stemme...

Climbs at 800 fpm
Cruises at 140 KTAS at 18,000'
Burns around 4 gph in cruise
30 gallon fuel capacity (no water ballast)
600-800 NM range at cruise
50:1 glide as a sail plane
Carries 2 people

Starts like an airplane, just open the three cowl flaps and the
propeller dome with the push of a single lever, turn on the pump switch,
apply the choke, and turn the key. Electrically operated landing gear.

Requires a glider rating with self launch endorsement to fly.

I've flown mine for almost 1,000 hours and will sell it in the next year
or two at a very attractive price.

Having said all of the above, I think Mark and Bob have done a terrific
job (as always) in putting this thing together. I hope they sell a
bunch of them!

Dan
5J

[Eric Greenwell]

I'm willing to accept the manufacturer's designation, and leave it up to the customers to
decide how much self-launch performance they need. We already do that with glide ratio,
wing loading, flaps, and other performance features. After all, the recreational pilot
launching unballasted from a Florida airport isn't going to need the same performance that
a OLC or record seeking pilot requires to fly from Ely in the summer.

The MiniLAK (LAK 17B FES) can self-launch ballasted to MTOW. There may be others, but the
Silent and Mini are the only ones I know very much about.

[John Ackerson]

Congratulations Bob!
Please bring one to the SSA convention in Reno in February. I would love to see and talk to you about it.
John

[Dave Nadler]

Yes, and....

> If not vibration related, what were you looking for?

Signs of hydraulic, electrical problems. Loose bits in engine bay.
Leaks, burning smell, etc.

[Mark Mocho]

> Signs of hydraulic, electrical problems. Loose bits in engine bay.

> Leaks, burning smell, etc.s, and....

You know, the usual stuff with motorgliders and powered aircraft. I usually just have to worry about mouse turds and spiders in my glider. Used to have to worry about snakes, until I started hanging it 12 feet off the floor.

[George Haeh]

If there's a snake inside, it's either pursuing rodents or digesting same.

[2G]

On Tuesday, December 6, 2022 at 3:20:15 AM UTC-8, Mark Mocho wrote:
> > Don't get too excited - Bob clearly states that this ISN'T a motorglider, but a motorized airshow glider. There is a BIG difference.
> Incorrect. The Salto with the TJ-100 is solely an airshow glider. The DG-808J does everything that the piston/propeller DG-808C does, but uses a pair of turbines to self-launch, retract and then proceed as a sailplane. Just like a Schleicher or Schempp-Hirth motorglider.

Wrong, a motorglider is PRIMARILY a glider with an auxiliary engine. This is PRIMARILY a powered aircraft that was converted from a motorglider. In other words, you would not use this machine to launch and then shut down the engine for the vast remainder of the flight.

Tom

[Mark Mocho]

> Wrong, a motorglider is PRIMARILY a glider with an auxiliary engine. This is PRIMARILY a powered aircraft that was converted from a motorglider. In other words, you would not use this machine to launch and then shut down the engine for the vast remainder of the flight.

Incorrect (again). This is intended to be used EXACTLY as a self-launch, retractable engine motorglider, with the capability of extending the turbines at any point in the flight. It does EXACTLY what your ASH-31 Mi does, but with a different power source. Read the report again, it states this clearly. If you get past the first couple of paragraphs that describe the airshow Salto, which IS a glider that uses a turbine throughout the performance, you might notice that the engines are retractable, extendable and restartable and are installed in a reasonably high-performance 18-meter sailplane. It might be too much to ask, but you should consider that maybe YOU are not the "expert" in this particular discussion.

[Bill Tisdale]

On Monday, December 5, 2022 at 6:03:51 PM UTC-5, Bob Carlton wrote:
> Hello fellow aviators,
>
> Desert Aerospace is pleased to announce the first DG-808J motorglider powered by twin PBS TJ40 engines. It is a blast to fly. Here is a link to more information:
>
> https://www.dropbox.com/s/b7m3j9tz85ga0w8/DG%20808J%20report.pdf?dl=0
>
> The second DG is in the shop now for conversion.
>
> Also of note...as of a few days ago, we finally won a decade-long battle with the FAA. Pilots of turbine self-launch motorgliders no longer require any special authorization. It's been a long fight and we had to play hard ball to get them to understand their own rules, but we finally got it.

Congratulations Bob! A long hard fought battle.
I remember being in one of your original "ground classes" at the SSA Convention years ago with the Bonus Jet and your plans for that.
I look forward to seeing the DG-808J at the next SSA Convention.
Bill

[2G]

On Friday, December 9, 2022 at 9:15:30 PM UTC-8, Mark Mocho wrote:
> > Wrong, a motorglider is PRIMARILY a glider with an auxiliary engine. This is PRIMARILY a powered aircraft that was converted from a motorglider. In other words, you would not use this machine to launch and then shut down the engine for the vast remainder of the flight.
> Incorrect (again). This is intended to be used EXACTLY as a self-launch, retractable engine motorglider, with the capability of extending the turbines at any point in the flight. It does EXACTLY what your ASH-31 Mi does, but with a different power source. Read the report again, it states this clearly. If you get past the first couple of paragraphs that describe the airshow Salto, which IS a glider that uses a turbine throughout the performance, you might notice that the engines are retractable, extendable and restartable and are installed in a reasonably high-performance 18-meter sailplane. It might be too much to ask, but you should consider that maybe YOU are not the "expert" in this particular discussion.

Wrong, AGAIN - the description CLEARLY states that the engines can't be retracted and are fixed in place.

Tom

[Mark Mocho]

> Wrong, AGAIN - the description CLEARLY states that the engines can't be retracted and are fixed in place.

OK. Now you are just being stubborn, and possibly displaying OBTP symptoms.

WATCH THE VIDEO!

https://www.dropbox.com/s/a0csxezkny23roa/DG808_retract_extend_2022_07_18.mp4?dl=0

[Mark Mocho]

Holding my breath, waiting for 2G to admit he is wrong.

[AS]

On Monday, December 12, 2022 at 7:06:51 AM UTC-5, Mark Mocho wrote:
> Holding my breath, waiting for 2G to admit he is wrong.

Please don't, Mark! You will die and I am planning on having a beer with you at the brewery this summer! ;-)

Uli
'AS'

[Mark Mocho]

> > Holding my breath, waiting for 2G to admit he is wrong.
> Please don't, Mark! You will die and I am planning on having a beer with you at the brewery this summer! ;-)
>
> Uli
> 'AS'

Well, OK then! That sounds like a better option than waiting for something that probably won't happen. 2G is about as likely to admit he made a mistake as a member of the Flat Earth Society acknowledging the existence of GPS. By the way, did you ever notice that the Flat Earth Society and "Front Electric Sustainer" share the same three-letter acronym? Just sayin'...

[youngbl...@gmail.com]

Please do us all a favor and not compare me with 2G, AKA, DH. DH has a long history of showing symptoms of electrical shock therapy, as we say down South, "That Boy Just Ain't Right. OBTP

[2G]

On Tuesday, December 6, 2022 at 6:41:22 AM UTC-8, Mark Mocho wrote:
> > But why not the same single engine as used on some of the other
> > projects? Too big?
> Definitely too big. The TJ100 is 10.5 inches in diameter and about 22 inches long. While that would fit inside the fuselage (assuming the engine bay door opening is wide enough), there is virtually no room for the extraction mechanism. Also, since it has an oil tank and recirculating oil system, it must rest horizontally in the engine bay. With a two-seat glider like the Arcus, this is not a problem, but a single seater is just a bit too small. Also, the price on the TJ100 is over twice as much as a PAIR of the TJ40s.

That must be a different glider than the DG808J Bob wrote about, which includes this quote:

"Its engine is not retractable"

which is what I relied on.

Tom

[2G]

How is the new airfield search going, PottyMouth?

[Mark Mocho]

"That must be a different glider than the DG808J Bob wrote about, which includes this quote:"

"Its engine is not retractable"

Tom, if you had actually bothered to read the report, you would have seen these two statements, which clearly define two entirely different aircraft:

"The most famous of these is my Salto airshow glider powered by a PBS TJ-100 turbine which produces 250 pounds of thrust. It was built
specifically for airshow aerobatics, not soaring. It is a glider like a NASCAR Toyota Corolla is a Corolla. Its engine is not retractable."

"The DG808J has two TJ40's mounted side by side when extended. They rotate one above the other to retract."

Maybe if you read the whole thing before firing the cannons, you wouldn't look like a (insert suitable description here.) You could perhaps minimize the effect by actually admitting you were incorrect, but I don't think that is in your nature.

.

[Martin Gregorie]

IIRC *that* comment applied to the jet Salto, not the DJ-808J: one of the
videos about the 808J clearly showed its engine mount pivoting 90 degrees
and retracting.

Both gliders were referenced in the same post, though I did wonder what,
if any, relevance the Salto had in a post about a about a modified DG 808.


--

Martin | martin at
Gregorie | gregorie dot org

[Mark Mocho]

> Both gliders were referenced in the same post, though I did wonder what,
> if any, relevance the Salto had in a post about a about a modified DG 808.

The reference is simply to give a bit of credibility to Bob Carlton's experience with jet powered gliders. Specifically, Bob has converted a total of eight gliders to turbojets. (Alisport Silent with two AMT 450 turbines in 2004, Salto with non-retract PBS TJ-100 in 2008, TsT-14 Bonus with retractable PBS TJ-100 in 2010, four Schempp-Hirth Arcuses with retractable PBS TJ-100s in 2016-2018, and now the DG-808 with two PBS TJ-40s in 2022)

Other than that, the reference to the Salto appears to have been successful in demonstrating the stubbornness, lack of comprehension and poor reading skills of some obtuse individuals

[Hank Nixon]

Salto reference provides perspective on the prior experience Bob has with projects of this type and I see that as useful.
Not his first rodeo.
UH

[Martin Gregorie]

On Tue, 13 Dec 2022 06:15:53 -0800 (PST), Hank Nixon wrote:

> Salto reference provides perspective on the prior experience Bob has
> with projects of this type and I see that as useful.
> Not his first rodeo.
> UH

Fair comment, though I'd have included a link to a piece about the Salto
rather than weaving it into a write-up that was primarily about the DG808
because that would be less likely to be misunderstood.

[Mark Mocho]

"I look forward to seeing the DG-808J at the next SSA Convention."

Unfortunately, the DG-808J will NOT be at the SSA Convention because Bob Carlton will be performing at the Australian International Airshow.

[Chris Esselstyn]

On Monday, December 5, 2022 at 5:03:51 PM UTC-6, Bob Carlton wrote:
> Hello fellow aviators,
>
> Desert Aerospace is pleased to announce the first DG-808J motorglider powered by twin PBS TJ40 engines. It is a blast to fly. Here is a link to more information:
>
> https://www.dropbox.com/s/b7m3j9tz85ga0w8/DG%20808J%20report.pdf?dl=0
>
> The second DG is in the shop now for conversion.
>
> Also of note...as of a few days ago, we finally won a decade-long battle with the FAA. Pilots of turbine self-launch motorgliders no longer require any special authorization. It's been a long fight and we had to play hard ball to get them to understand their own rules, but we finally got it.

Looks like another Desert Aerospace amazing project. I particularly like how the turbines rotate 90 degrees for extension and retraction. I believe this is the first 18-meter ship to self-launch with turbines. Congratulations Bob, I can't wait to see it at Reno or Oshkosh.

[2G]

I don't think it will see much of a market in Europe.

Tom

[Mark Mocho]

> I don't think it will see much of a market in Europe.

Correct. Noise restrictions in Europe pretty much eliminate turbines as self-launchers. Jet sustainers are OK, but ground engine runs face scrutiny.

[krasw]

On Thursday, 29 December 2022 at 13:59:15 UTC+2, Mark Mocho wrote:
> > I don't think it will see much of a market in Europe.
> Correct. Noise restrictions in Europe pretty much eliminate turbines as self-launchers. Jet sustainers are OK, but ground engine runs face scrutiny.

Main issue here is WHY. Why would you want a jet self laucher? What are the advantages? Disadvantages are certainly plenty. I agree that market has to be microscopic for something like this, no matter where.

[Mark Mocho]

> Main issue here is WHY. Why would you want a jet self laucher? What are the advantages? Disadvantages are certainly plenty.

Advantages:
1- Reliability. (When using a properly designed and purposed engine)
2- Lack of vibration.
3- Low drag. (Small engine profile and operation with engine bay doors closed)
4- Ease of starting. (Extend engine(s). Switch to "ON.")
5- Lower thrust line.
6- Shorter cool-down period.
7- Ease of shutdown and retract. (No propeller alignment necessary)
8- High cruise speed. (Up to 120 knots or more)

Disadvantages:
1- Cost
2- Fuel consumption
3- Noise

I am sure you will come up with more perceived disadvantages, but these are the ones I consider relevant.

[John]

A few more advantages I thought about.
1- sounds so cool on flybys
2- fulfills my personal dream to fly a jet someday.
3- safety, by maintaining a great glide ratio and much more range with engine out,
4- maintenance, easy to remove and light and cheap to ship it for repairs and maintenance.
5- low weight addition to airframe especially with fuel in the wings helps with better climb rate.
6- much easier to upgrade when newer better turbines are available.


I would love to purchase a Jonkers JS2 without the sustainer jet. Then I would have Bob Carlton work his magic with the twins for self launch capacity.

[krasw]

How does the ground roll compare to proper self-launching DG? Published low climb rate and jet's low static thrust indicates that might be an issue. Easy maintenance is certainly a plus when you double your chance of engine trouble by having 2 engines.

[Mark Mocho]

"How does the ground roll compare to proper self-launching DG? Published low climb rate and jet's low static thrust indicates that might be an issue."

Try reading the DG-808J report linked in the original post:

https://www.dropbox.com/s/b7m3j9tz85ga0w8/DG%20808J%20report.pdf?dl=0

"Takeoff is accomplished by simply pushing the throttles forward to 100%. Takeoff acceleration is slightly less than with the prop, but the acceleration never slacks off. There is considerably less pitch/power coupling due to the engines' lower thrust line. Liftoff is normal, but instead of climbing as slow as practical as you would with the piston/prop system, stay in ground effect until 70–85 knots is reached before beginning the climb (jets like more speed).

The initial climb will be excellent! Our tests have all been done during summer in Moriarty at a field elevation of 6200’, giving us density altitudes of 8000’ to 10,000’. Even up here, we’re seeing over 500’/minute climb at 80 knots indicated."

Yes, the initial takeoff roll is slow (like trying to accelerate your car from a standstill in fourth gear) but as noted, it just continues to accelerate faster and faster. A propeller moves a large amount of air at a relatively low speed and acceleration starts out fast but drops off as speed increases. Jets move a smaller amount of air, but REALLY fast, and acceleration continues to increase through the takeoff.

And I don't consider 80 knots with a 500 fpm at 6,200 ft. MSL on an 8,000 ft. density altitude day to be a "low climb rate." It is definitely better than a "stock" DG-808. That's why the owner of the second DG-808 is making the switch.

Your statement about doubling the chance of engine failure by having two engines is an exercise in statistics. It's like saying that no engines mean no engine failures. Both statements are true, but with no failure incidents to cite, you could also say that two engines are twice as reliable as one, and infinitely more reliable than none.

[Dan Marotta]

How would the larger jet engine work in a DG-1001T?

Asking for a friend. No, really!

Dan
5J

[Bob Carlton]

On Tuesday, January 3, 2023 at 8:03:03 AM UTC-7, Dan Marotta wrote:
> How would the larger jet engine work in a DG-1001T?
>
> Asking for a friend. No, really!
>
> Dan
> 5J

Dan, I am speaking with the DG1000T owner (I assume the same one). It will come down to the size/shape of the engine bay of the sustainer engine.

[Dan Marotta]

Same owner. He just emailed me about your upcoming visit.

Dan
5J

[Darren Braun]

> Disadvantages:
> 1- Cost
> 2- Fuel consumption
> 3- Noise

The oil is costly also. And JetA is not available at a surprising number of airports.. looking around recently some are 100LL only(i.e. can't assume that just because there is fuel, they would have both). Not sure if you can use diesel on these engines.
Darren

[krasw]

On Tuesday, 3 January 2023 at 16:05:44 UTC+2, Mark Mocho wrote:
> Try reading the DG-808J report linked in the original post:

I did, but could not find a word about ground roll.

[Mark Mocho]

> I did, but could not find a word about ground roll.

Well, except for the statement about slower initial acceleration. There are no numbers for takeoff roll distance or clearance over an obstacle, as we did not measure these. But I don't recall seeing any numbers for the piston/prop version either, so it would be difficult to make an honest comparison anyway. And the comparison would be irrelevant, as "factory" numbers would probably be taken at or near sea level on a cool morning with an unstated wind condition.

Maybe at some time in the future it will be possible to do a direct comparison between the turbine-powered DG-808J and a piston/prop DG-808C. That will depend on whether there is an available DG-808 to do a test at the same runway on the same day in the same conditions. Otherwise, guessing at takeoff numbers is useless.

But it is clear that you want to believe that the turbine DG has "worse" performance, so I will save you the time. It probably is not as good. But by how much? We don't know.

Happy now?

[kinsell]

I know one jet owner who has jetA available at his home airport, and the
FBO won't sell it to him.

[Eric Bick (DY)]

Section 5.2.3 of the DG-808C Flight Manual has takeoff performance tables for 18 and 15 m configurations. As Mark states, they are noted as being at sea level, dry asphalt runway, engine/prop/glider in "proper" condition, and no wind. Also a statement that dry grass will increase roll 10-15%. For those at places like Moriarty, those numbers are not useful other than as a best possible performance. What we want to know is how it takes off at 6200' MSL, density altitude 8-10 kft. Since I now have an 808C, piston driven, maybe Mark, Bob, the J owner(s) and I can coordinate a day/time this spring to do a comparison such as Mark indicates. With the igc traces we now all generate, doing a takeoff comparison (1 s recording interval, observer to verify liftoff point) should be straightforward. Time to altitude (say 2kft AGL) will also be interesting as the J has a different climb profile from the piston drive.

[Wallace Berry]

On Tuesday, December 6, 2022 at 11:27:10 AM UTC-6, Charlie M. (UH & 002 owner/pilot) wrote:
> On Tuesday, December 6, 2022 at 11:37:47 AM UTC-5, Mark Mocho wrote:
> > hundreds of self-launchers that are also vibration free: electric powered sailplanes.
> > I am aware of only two types of electric self-launchers: the Pipistrel Taurus Electro and the Alisport Silent Electro. There are also the "Birdy" and the GP Jeta, but neither seems to be in actual production.
> Production?
> Well.....one off, "UH's" ASW-24e converted from gas to electric. I have about 100 flight hours in 2022 in it.
> It has been self launched (I haven't done that yet) and I have done "saves" to altitude (testing and real) as well as self retrieve.
> I have traces on Skylines if you want to see. I can tell you the flights. A real save and self retrieve were both at Newcastle this year.
>
> As to this thread, guessing my old IPad OS and browser won't let me open the link.

Beautiful electric conversion on that 24! By the way Charlie, Happy New Year. I had a great time flying and conversing with you at New Castle. Hope to see you at the races this coming season!

[Bob Carlton]

I'd like to thank Mark for stepping in with answers to questions on this forum while I've been busy. Also thanks to those who have posted valid questions and support of our efforts. Thanks to all for not turning this thread into a discussion of the jet Caproni ;o)

In general, here's what it boils down to. Every aircraft is just a bunch of flying compromises. Whether piston/prop, electric, jet, tow plane, nuclear or whatever, each launch method will have its pros and cons. We realize the jet glider isn't for everyone, but having flown nine different PBS turbine powered aircraft over 15 years, in all conditions (hot, cold, high altitude, dry, pouring rain, aerobatics), having been the POC for all of them, and all of the SubSonex builders, I can attest to their simplicity and reliability. The vast majority of failures of aircraft systems (all aircraft, not just motorgliders) are related to vibration. (Imagine if airliners were still using radial engines.) Turbine engines run smoother than any other options. Even electric aircraft must deal with the flight loads of a large spinning propeller. Even if the turbine glider uses a bit more runway on takeoff, once airborne, the low drag of our turbine installations provide a huge safety margin in the unlikely event of a double engine failure (the DG808J can climb on a single engine). As both Mark and I have stated, any performance numbers we generate up here at 6200 ft MSL and with near 10,000 ft density altitude can't be compared to the sea level, standard atmosphere numbers in flight manual.

Jets and props produce thrust differently. A propeller is a constant power device (engine horsepower). As airspeed increases, thrust decreases - a lot. It's like having a car with only first gear. This can be mitigated somewhat by using a variable pitch (constant speed) propeller, but you still only get about second gear, maybe third, given enough horsepower. A jet is a constant thrust device (actually thrust can increase with speed, but not in the speed range we fly our gliders). More like a car with fourth gear that auto switches to fifth or sixth if you go fast enough. This is why the DG808J can climb at relatively higher speeds. 65 knots is good, and so is 90 knots. And why once you're at a higher speed, you can reduce thrust and continue to climb well. A comparison of static thrust of propeller vs. jet is not a very useful comparison.

So...are there disadvantages to the turbine self launch glider? Sure. They are thirstier, louder, and (if retro-fitted to an existing glider) more expensive. However, from a safety standpoint (and safety is our number one priority, right?), they offer simpler operation, fewer moving parts, lighter weight, lower vibration, lower drag when extended, engine bay doors closed with engine extended, higher climb speed, higher climb rate, higher cruise speed, twin engines with independent systems, internal starter/generator, no belts, jet fuel is lower volatility, easy engine/component replacement, parts on the shelf or available overnight (US). The list goes on.

Owners of other motorgliders can often point to one or two 'mine is better' parameters, and each single parameter will have its vocal champions, but overall, I think we've struck a pretty good balance of flying compromises, especially if safety really is a concern.

I would like to take Eric Bick up on his idea of a fly-off. We can compare the prop DG to the jet DG in the same conditions. I'd say we compare takeoff distance, time to 2000' AGL(normal thermal climb), 4000' AGL (wave climb), and time to a turnpoint 10 miles away (reaching a convergence line early in the morning), then time to lose 2000' with engine extended, but not running (just to be fair, I'll kill both engines in the jet since it can still climb on one). We could also include the Stemme in this fly off if Dan is up for it.

Blue skies,

Bob

[Dan Marotta]

Great write-up, Bob! ...And I'd love to take part in that test!

It will be interesting to see how the turbocharged four stroke engine
compares to the normally aspirated two stroke. Unfortunately, I don't
have any numbers about power to weight ratio to compare my glider with
Eric's.

I'm also interested to compare to your jet in flight, especially since
I've hyped it to a friend who's considering switching his two-stroke
engine for one of your jets.

Dan
5J

[Eric Bick (DY)]

On Thursday, January 5, 2023 at 5:04:59 PM UTC-7, Dan Marotta wrote:I’m in.

[Bob Carlton]

Reply to kinsell: Why won't the FBO sell your friend jet fuel? Curious if they would sell him 100LL? My guess is they don't want to dispense any aviation fuel into gas cans, especially improperly labeled gas cans. I have had this problem at a couple of FBOs years ago. I was always able to show them the aircraft, the aircraft flight manual fueling instructions, and my pump system with sealed quick disconnects and finally convince them. I now have a 26 gallon welded aluminum transfer tank permanently installed in my truck. Somehow that doesn't raise as many flags. Technically, at least here in the USA, and at a publicly funded airport, I don't think they can refuse to fuel a registered aircraft in accordance with its operation manual.

[kinsell]

I believe he showed up with jerry cans, and the FBO was not happy with
the fuel handling. This was another glider conversion to jet
self-launcher, I'm sure you know him:

https://youtu.be/U6t0BdoVRU8

[Dan Marotta]

That looked like Salida, CO...

Dan
5J

[kinsell]

Well, it wasn't Salina KS. Wasn't Salina UT either. Yep, must have
been Salida CO!

Breakneck acceleration achieved with a downhill, downwind takeoff.

[Dan Marotta]

...And breakneck down wash off the east end of the runway!

I have towed and been towed both directions at KANK. Great place for
soaring.

Dan
5J

[krasw]

On Wednesday, 4 January 2023 at 17:35:29 UTC+2, Mark Mocho wrote:
> But it is clear that you want to believe that the turbine DG has "worse" performance, so I will save you the time. It probably is not as good. But by how much? We don't know.
>
> Happy now?

I do not want to believe or guess, I try to base my opinions on facts. That's why I asked for them. I see 808J as a niche product for those operating at very high density altitudes and long, hard runways, not minding trading water ballast to Jet A-1 ballast, or those that simply want to fly jet. No doubt the installation and technology is as state of the art as currently possible. I wish all the best for the project.

[Charlie M. (UH & 002 owner/pilot)]

Hank gets the credit for the conversion, I just try to fly it well. See ya at the races.

As to this thread, new iPad, thus can see the links. Interesting looking system. Curious, in the inflight retract/extend, why crack open the spoilers? Is this needed, for minimum door open speed, or something else?
Would be neat to see it in person, but I’m east coast so not likely.

[Mark Mocho]

"Why don't you motorglider guys just call them Non-Binary gliders? Old Bob, The Purist"

The DG-808J is clearly a Non-Binary glider, as it has 2 jet engines. If it was "Binary," we would have to say it has 10 engines.

[2G]

On Friday, January 13, 2023 at 2:58:40 AM UTC-8, Mark Mocho wrote:
> "Why don't you motorglider guys just call them Non-Binary gliders? Old Bob, The Purist"
>
> The DG-808J is clearly a Non-Binary glider, as it has 2 jet engines. If it was "Binary," we would have to say it has 10 engines.

Maybe PottyMouth can find a jet towplane.

Tom