DA42-VI (jet boost)

Any DA42 related topics.

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baldesk
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DA42-VI (jet boost)

Post by baldesk »

I absolutely love nearly every aspect of my DA42-VI. Two things that would make it the perfect aircraft for me...

1-Reclining rear seats to keep backseat passengers more comfortable on long trips
2-Faster cruise speeds...

Here is a crazy and fun thought exercise! :scream:

I know my fellow DA42 owners would love to pickup an extra 50-60kts when flying at FL180 in smooth air where indicated airspeed affords us a healthy gap to Vne.

Imagine an otherwise unmodified DA42 that converts the 'GA' button on the throttles to an 'afterburner' toggle switch that deploys the PBS TJ-100 jet that is also used on Sonnex aircraft (must-see demonstration https://youtu.be/e6QJf83Oe3w?t=2m). Now imagine throttling smoothly up to to 250 kts TAS! Thrust from the jet could be managed in parallel with the existing fly-by-wire throttles, but with an automatic step-down to keep your DA42 'Diamond-Jet' below Vne. Jet-A could be supplied from the existing fuel system. For safety, you would want to systematically police the minimum altitude AGL for deployment (e.g. > FL050), restrict deployment to safe airspeeds (e.g. between 120-160 kts indicated), and require straight-and-level flight as a pre-requisite to deployment. You would also want to auto-retract/stow the jet at a pre-determined altitude to return the DA42 to its certified flight characteristics for a safe approach and landing.

To keep this a fun mental exercise, I have not calculated the incremental fuel burn, which I acknowledge could be a showstopper. Assuming 100 lbs. of thrust was sufficient (???), I calculate incremental fuel burn around 20gph, for a total fuel burn of 36gph-ish.

The ~$60K USD PBS TJ-100P weighs only 38.8 lbs., produces 281 lbf., and is rated for a windmill start within 7 seconds. Pretty incredible! https://www.pbs.cz/en/products/aerospac ... pbs-tj100p. They have smaller jets that weigh less, burn less fuel, and are less expensive. The key question is how much thrust is required increase the airspeed of a 4,407 lb. DA42 to 250kts TAS at FL180?

Wahoo!
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TimS
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Re: DA42-VI (jet boost)

Post by TimS »

At that point, just drop the draggy diesel engines and switch to these:
https://www.pbs.cz/en/our-business/aero ... -pbs-tp100

Same company, but more efficient than the turbojet.

While were at it, maybe a couple of PT6-67s....

Tim
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Rich
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Re: DA42-VI (jet boost)

Post by Rich »

Just so you know - flutter onset is a function of TAS/Mach Number, not IAS or CAS.
2002 DA40-180: MT, PowerFlow, 530W/430W, KAP140, ext. baggage, 1090 ES out, 2646 MTOW, 40gal., Surefly, Flightstream 210, Orion 600 LED, XeVision, Aspen E5
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neema
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Re: DA42-VI (jet boost)

Post by neema »

I'd rather have 200 hp Deltahawk engines hung on the plane. Even the 180 hp engines would make a dent in the ASI.


-They're lighter, maybe 100 lbs less apples to apples (some speed gain there)
-Much smaller frontal area, so the cowling has much less drag (some speed here too)
-you gain useful load (doesn't pertain to speed, but nice)
-Only slightly higher fuel consumption (a negative)
-the claim for 180hp model was to hold max power to at least 15,000' (better than the Austro's can manage)

2x Austros will make max power of 80-85% at FL180 depending on temps. That's 269 - 286 hp and with max RPM.

2x 180hp Deltahawks will make, let's say 90-95% power at FL180, so 324 - 342 hp.

BSFC claims are everywhere, but I've seen as low as .39. That's 19.9 gph at 95% power.

To summarize: 50-60 hp more horsepower, always on tap and in a lighter, less draggy package than the factory offering should give you a... 15 knot boost? Say you get 210 KTAS. At FL180, that's 159 knots indicated. 8 knots into the green arc. Imagine where you'd be at 8000'

It'd never happen for one blaring reason: G1000 engine instruments controlled by Diamond

The 200 hp model would make even more sense on the 62.
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Re: DA42-VI (jet boost)

Post by Antoine »

baldesk wrote: Sun Feb 28, 2021 8:04 pm I absolutely love nearly every aspect of my DA42-VI. Two things that would make it the perfect aircraft for me...

1-Reclining rear seats to keep backseat passengers more comfortable on long trips
2-Faster cruise speeds...

Assuming 100 lbs. of thrust was sufficient (???), I calculate incremental fuel burn around 20gph, for a total fuel burn of 36gph-ish.
Lol, I bite! Power = thrust x speed. 100 lbs = roughly 430 N and 80 m/s TAS I calculate roughly 50 HP.
If your Austros were still making 100 HP a side at altitude, you’d add 50 HP to the 200 HP starting point.
Speed increases with the cube root of power increase. You get 7.7% speed increase.........😳 but certainly a very cool sound!

Shall we look at these reclining rear seats again 😂 ?

I am sure my good friend Tommy will soon chime in and offer a more pragmatic way of talking in mach without the use of a turbojet !😉
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