Comparing new turboprops with industrials

June 10 2013 - Ivan G Rice

In the previous part of this series, the author wrote about the commercial use of single shaft engines that used natural gas as fuel. In this concluding part, he reveals the surprise element – the activation of the TU 95 H for surveillance service – and explains how it compares with the jet engine-powered B-52.

There have been a number of other applications of the Russian TU 95 15,000 HP engines. They have been used to power the Zubr-Class LCAC large air-cushioned landing craft of Soviet design, the world’s largest hover craft known. Each craft uses five of the large turboprop engines. There are currently nine of these hover craft ships in active services today. In 1972, another application has been for the A-90 Orlyonok, a Russian ground effects vehicle. This half-ship and half-plane, flies close to the water – a few meters up, to capture the ‘ground effect’ during takeoff and landing. It can fly to an altitude of 9,800 feet. The plane/vessel was retired in 1993.

Another plane using this engine is the four-engined cargo, the Antonov An-22. Recently, a bigger turbofan engine, the An-124, has been replacing the old turboprops. This plane has a maximum speed of 400 MPH.

The surprise element

Here comes the surprise – the TU 95 H was retired 15 years ago, but when Russian President Vladimir Putin re-assumed office in 2008, he activated the TU 95 H once again for surveillance service. The plane was put back into service a few years ago, and now flies to various places around the world.

The TU 95 Bears have recently been seen a number of times around Japan, around Guam, off the US west coast and near Alaska. It is reported that the Bears were spotted as late as the 28th of April this year, flying near Alaska. After radar picked up the two planes, US F-22s were dispatched and the pilots confirmed the presence of the TU 95 Hs. However, the Russians have never entered our territory and have kept to the international air spaces. What a surprise!

B-52s vs. TU 95Hs 

The US B-52s and the Russian TU 95s were both originally designed and built to carry atomic bombs in the early 1950s and both are still in service today – quite a parallel. However, there are some differences in places. The B-52s were jet engine-powered while the TU 95s were turboprop-powered. The B-52s were about 100 MPH faster than the TU 95s at cruise speeds. The B-52s dropped several bombs during the Vietnam and Persian Gulf wars. However, the TU 95s have not dropped bombs in a war but for the one largest atomic bomb ever dropped as a test.

The B-52 has had a number of engine improvements and model changes incorporated and probably the TU 95s have also had engine improvements made. The TU 95s had a number of different airframe models including a civilian passenger transport that carried 250 passengers across Russia, and Japan. The B-52 has never been used to transport civilians as a passenger plane. The Hanoi Taxi was a different plane (Lockheed C-141C Starlifter).

The TU 95 is scheduled to be used until the year 2040. Likewise, the B-52 is expected to be used for another 20 years. These two airplanes have been great achievements for both the US and Russia. It is reported that Russia produced over 500 of the ‘Big Ivan’ TU 95 Bears. The TU 95 is extremely noisy, far more than the B-52, due to the transonic prop tip speed. Books on the Russian TU 95 Bear are listed on Amazon.com, which includes technical books, and one on the never-acknowledged defection of one TU 95 to Canada.

New turboprop engines

Now let us return to the two new turboprop engines under test for new regional airplanes. The cycle efficiency of each of the two new turbines is expected to be about 36 percent. The new Solar Taurus 70 - 10,310 HP @ 34.8 percent (1994), Siemens SGT 300 - 11,000 HP @ 34.6 percent (2011) and Man D & T GT 6 - 9,253 HP @ 34.0 percent (2012) are three units to compare, as listed in the catalog. The two new aero engines should have an efficiency that is a more than these values. The 36 percent is only an estimate based on the published data and considering the size and year of introduction. The exhaust temperatures should be around 900o F, but no data is available yet to give any exact figures. Likewise, exhaust flows are not known at this time.

The key to the industrialization of these new gas turbines depends, to a great extent, on the availability and cost of natural gas fuel over the full market area. Here in Texas, and across the US, the supply and cost of shale-produced natural gas looks promising for many years. It must be remembered that not all aero engines make the cut to be converted for the industrial market.     

There are a number of places where the new 6000 to 8000 HP gas turbines can be applied considering size, efficiency and other factors. Some of them are railroad electric locomotives, natural gas pipelines, electric power generation, off-shore drilling rigs and production platforms, gas stripping plants, chemical plants, refineries and ships.

Ivan G. Rice, past chairman of the South Texas Section of ASME (1974 - 75), and the ASME Gas Turbine Division (now IGTI) (1975 - 76), has authored many articles and ASME papers on gas turbines, inter-cooling, reheat, HRSGs, steam cooling and steam injection. He is a Life Fellow Member of ASME and Life Member of NSPE/TSPE.