Diesel powered 337

[hharney]

The Golden Hawk also is amazingly quiet -- another result of its original military design goals. The new Hartzell props provide lower noise signature and the engines are so quiet that it is said that it makes less noise on a take off roll than a Cessna 150 taxiing by on the ramp. Skymasters are usually noisy inside, so this will be welcome -- I don't know if the plane's ability to land nearly silently at midnight on a desert strip in the middle of nowhere half a world away is of interest to anyone, though....

TF Hawk said that the costs of operating the Golden Hawk Skymaster are extraordinarily low -- first, the engine maintenance is less than half of an IO-360 powered aircraft; second, the fuel is much cheaper than 100LL; third it burns less than half the fuel per hour and, when at altitude maybe even 1/4 the fuel; and fourth, it flies higher and faster TAS as a result, so you get there quicker. Based on that, the Golden Hawk is likely that your flying costs will go down by as much as $200 to $300 per hour or even more, depending on where you live and the price of fuel at your airport (I imagine that this conversion will be very interesting for European customers, where fuel prices are four to five times higher than they are in the USA).

Thinking about it, this means that if you fly 300 hours a year, the conversion will pay for itself in less than four hours as a result of the cost savings you will enjoy.

More to come.... I am arranging a phone call in the next week or so with one of the top team at TF Hawk, where I intend to confirm this and learn more yet, which I will pass on. When I discussed this with them, the company did state to me that the above is fairly accurate, though they're not confirming anything yet pending the launch of a new civilian conversion announcement on their website. They did confirm that they will deliver an aircraft in as little as six months from date of order and that they can handle up to six aircraft at a time in the shop. This is their first venture into the civilian market, despite nearly four years of development work underway for exclusive military uses, so they are excited about it.

[ngb1066]

Morne and Herb

Thank you for your comments. I can certainly see enormous benefits of diesel aero engines in terms of both performance and economy. I suspect that they are likely to be increasingly seen in GA. This applies even more in Europe than in the USA, in view of the stratospheric cost of 100LL avgas here.

The Golden Hawk project certainly looks very interesting and I will look out for updates on the TF Hawk website about their proposed civilian version of the aircraft. Herb - have you had your phone call yet with TF Hawk? I will certainly consider this option for the 337 I am looking for. My only reservation at this stage is engine power, which will be lower than currently available for any of the 337 varients. I imagine that this will not be a problem at altitude as diesel engines retain maximum power at greater altitude than the avgas fuelled equivalent, but in terms of take off performance do you consider the Deltahawk limit of 200 HP will be a significant factor? My concern is based upon operating from a relatively short grass strip.

Many thanks for your advice and information.

Neil

[robw]

We run a pair of 337s for aerial survey work and because of the huge problems getting avgas out here in Africa, we have been tracking both the alternative engine and alternative airframe possibilities for years.

First off, if HAWK are quoting $340k for their Skymaster conversion, I can’t see that they are going to get many takers. Adding in something between $100k and $200k for the basic aircraft means you are throwing around an investment figure above the half million mark and at the end of the day you still have a forty year old airplane no matter how well it has been checked out. For that sort of price you can buy a brand new out of the box Diamond DA42 twin diesel that offers comparable range and operating cost. It makes no sense.

Diesel does seem to be the inevitable way forward but (unfortunately) it is still early days. So far there have been only two certified engine manufacturers, Thielert and SMA, and they have both experienced massive technical difficulties in making their engines reliable. They do now seem to be getting on top of it but it would be naïve to expect any new manufacturer entering the market to instantly have a product that is problem free.

Of the two existing engines we much prefer the SMA. It was designed from the start as an aero engine as opposed to a converted car engine, it has been around for thirteen years, has a lower reliance on electronic wizardry and the major aerospace company behind it (Snecma) has stood solidly behind their warranties. One of the owners of a diesel 182 out here has had his engine replaced twice without quibble.

The SMA is also the closest potential fit to a 337. Compared to the IO360C it is 8” taller, 6” wider and 2” shorter without any sacrifice of horsepower. It weighs 100lbs more but this is largely offset by the lower sg of JetA and the reduced fuel burn. Some years ago we were informed by SMA that the tractor/pusher issue was not a design limitation but merely a matter of testing and certification but of course this carries a cost implication as well.

Cheap it is not. About $65k a pop the last time I looked. Throw in new props, mounts, instrumentation and multiply by two and you can’t be much shy of $180k before STC costs. A few years ago a firm in the USA quoted me $100k to do the STC work so there you are, back in the ball park of the HAWK price with all the same arguments against it.

It was a very smart move by TCM, or maybe it was the new Chinese owners, to buy the SMA technology. It could be they will be able to leapfrog over all the teething problems and they have the muscle and know-how to get a lot of engines onto the market quickly. Originally they were promising a certified, retrofittable 4 cylinder this year and a 6 cylinder in 2013. For which airframes they did not say and whether their plans will include the relatively small fleet of 337s remains to be seen but to my mind this is the only practical hope on the horizon.

[WebMaster]

I note in my iPad App for Oshkosh, that Delta Hawk has a booth. No idea what they will be showing. They are in booth 257, in the main aircraft display area.

Thanks Herb for pointing out the App.

[ngb1066]

Is there any further news from T F Hawk or Deltahawk? Both websites do not appear to have been updated for a while.

[Walter Atkinson]

Two things I don't see discussed about the diesels:

1) the HUGE hit they take in additional cooling drag which makes the fuel efficiency not nearly as good as the claims which do not take that drag into account.

2) the significant peak pressures which are transmitted to the prop in stress vibrations.

[ngb1066]

Originally Posted by Walter Atkinson

Two things I don't see discussed about the diesels:

1) the HUGE hit they take in additional cooling drag which makes the fuel efficiency not nearly as good as the claims which do not take that drag into account.

2) the significant peak pressures which are transmitted to the prop in stress vibrations.

Walter - The 235HP SMA diesel engine seems to have been operated successfully in the Cessna 182, so presumably the two problems you mention must have been addressed in some way. Do you have any further information on this?

[Walter Atkinson]

Originally Posted by ngb1066

Walter - The 235HP SMA diesel engine seems to have been operated successfully in the Cessna 182, so presumably the two problems you mention must have been addressed in some way. Do you have any further information on this?

"Seems" is the operative word in your post. The prop issue has been marginally addressed but the cooling drag issue has not been addressed at all. It's that pesky physics. For this reason, the BSFC(min) on the installation is nowhere close to the claimed number. The claimed BSFC of about .33 on a diesel is closer to .37 when the cooling drag is added in.

In my educated opinion, diesels will not offer the answer until and unless there is a serious breakthrough in combustion technology. That breakthrough is nowhere in sight on the horizon since the physics of chemical reactions is not likely to change. There will be, however, dozens of people/companies/concerns which will continue to try to make this happen for many years before finally admitting that diesels are covered by the laws of physics.

[Skymaster337B]

The best diesel fuel engines are turbines. However, a turbo prop Skymaster is so cost prohibitive. Avgas engines are here to stay...until the unelected EPA outlaws 100LL.

[ngb1066]

Originally Posted by Skymaster337B

The best diesel fuel engines are turbines. However, a turbo prop Skymaster is so cost prohibitive. Avgas engines are here to stay...until the unelected EPA outlaws 100LL.

It depends what you mean by best. Gas turbine engines have by far the best power/weight ratio, but the fuel consumption is poor other than in the cruise at altitude. Diesel engines are heavier but with generally better fuel consumption.

[CO_Skymaster]

I've been meaning to ask this question for awhile, since I have thought about replacing my engines with turbo diesels. If I did, I would probably replace them with the 210 HP rating on my current 1966 Skymaster or more. The TCM TD300 might be rated up to 250 hp. My Vne is shown as 220 mph (190 kts) on my airspeed indicator. I know some of the turbos and pressurized 337 can go faster (the Riely Rocket has speeds of about 250 kts). My question is about the frame of the Skymaster. Does the skymaster have to go though any structure reinforcement when faster speeds are normal or when more powerful engines are place in it? Except for the fussalge (the P-version will be different), are all other structual frame components the same for skymasters?

Karl

[wybenga]

In fact the opposite is true. Your Vne is limited to the top of the green arc, generally. But if you are indicating 165 knots at 6000 and still climbing at 2000 fpm or indicating 150 knots at 20.000 you are hauling buns.

Jack

[hharney]

The Super Skymaster with TSIO-520 rated at 310 hp has the same structural limitations as the standard 337 airframe that it was modified from. The advantages of the increased hp is climb. The higher speed at altitude is true airspeed but the calibrated airspeed is still within structural limits. The Super is about 20-25 kt faster at altitude with a cruise of about 220 kt TAS. The positive was 2500 FPM climb but the extra weight of the engines eroded the useful load terribly.

The 73 and newer airframes were substantially different from the pre-73 models. Cessna also changed the wing spar in the H model vs the G model. There were gross wgt increase mods but all landing weight requirements remained the same except for some proprietary STC's. I am not aware of anyone attempting to increase the structural load limits. It would be very expensive (if any possible) and there just isn't enough of an audience to justify it.

[Mayhemxpc]

I spoke with the Delta Hawk people at OSH. They are focusing on their smaller 160 hp engine which they say delivers the equivalent of 180 hp performance. No idea how they measured that. They seem to have a "pie in the sky bye and bye" attitude towards larger engines, and in particular the 337. TF Hawk was depending on Delta Hawk producing their engine according to its original program. (I know the president of TF Hawk.) As a result, even though they had everything else ready to go, they had to suspend everything because there was no engine, and no realistic delivery date for one. Sad.

That and they had very little in the way of solid interest from prospective buyers. Last I talked to him about that particular subject, the cost of a fully re-built TF Hawk O-2/C337 was not going to be that different than a Caravan. (The USAF has modified C-208's to launch HELLFIRE missiles for the Iraqi Air Force.)

Bottom line: A good idea has money attached to it. If they don't see enough potential sales interest, there won't be much development.

[CycloneSteve]

Has anything new happened since August?