Q: I would like to build a diesel RV. How soon might your "firewall forward" kit be available?
A: DeltaHawk is primarily in the engine business and does not plan to develop firewall forward kits. However, we are talking to companies who are interested in selling firewall forward kits, especially for RVs. Also,
it is our hope that builders of different aircraft will get together and develop mounts and firewall forward kits and share the information. DeltaHawk will do what we can to facilitate the sharing of information
among builders. We have already helped Cozy builders who are interested in DeltaHawk to get together.
Q: What will be the material of the exhaust pipes you supply?
A: All pipes we supply will be stainless.
Q: Is there provision for vacuum instruments?
A: Yes. There is a vacuum pump pad on the engine (and also a propeller governor pad).
Q: Does the V-4 have a crankshaft pulley which can be used for the alternator, air conditioning compressor drive, etc., or does it have only drive "pads"? Can the V-4 accommodate an automotive-type air
A: The alternator is up front and belt-driven from the crankshaft pulley. There is no spare pulley for a belt-driven air conditioner, however it would be feasible to develop an air-cycle air conditioner / air pump
system driven off one of the accessory pads.
Q: Are there provisions for additional "hard points" (similar to an automobile v-belt configuration) up front and/or especially at the rear for various belt driven accessories or backup systems? Or maybe a
rear starter/flywheel option also? I am looking into a front canard pusher aircraft and it seems to me that it might be advantageous to mount as much stuff as possible closest to the firewall for weight and balance
A: There are two pads on the accessory cover, driven at crankshaft speed, for a vacuum pump and a prop governor. They both can be used for other accessories, as they are on the anti-prop end of the engine. We have
already mounted the turbocharger and fuel pump forward of the engine mount (referenced for a pusher) to keep the center of gravity (c.g.) of the engine within 4.5" of the mounting point.
Q: Does the engine take a standard Lycoming mount?
A: No. The engine requires a unique bed type mount. Mounts will be developed as a part of aircraft-specific firewall-to-propeller packages.
Q: What is the weight and size difference between the 160 hp and 200 hp V-4 models? Do they use different batteries and starters?
A: The weight difference will probably be the weight of the intercooler and associated plumbing for the 200 hp model, ~15 lbs. Since they use the same block and other accessories, the size difference again will only
be the extra space required for the intercooler, approximately 12 x 12 x 3 inches. The two models use the same starter and battery.
Q: Have you approached aircraft manufacturers other than Velocity to develop installations?
A: A few have begun the planning process with us, and we will start work with others when we have all the systems in production status.
Q: Do you have any plans or projected plans to use the DeltaHawk engine(s) in helicopters which might require vertical mounting?
A: Yes, we do have such plans, and two such projects are nearing flight test.
Q: Have you tested the engine in the "tractor" configuration?
A: Yes. Our endurance test stand operates in the tractor configuration, and we have a Cessna 172 test aircraft. The engine has also been run on the test stand with a constant speed propeller.
Q: Is your engine suitable for an aerobatic airplane?
A: No. The main limiter right now is the turbocharger. "Gentleman's" aerobatics (no sustained negative G, no inverted, no snap rolls or spins) should be fine. We may investigate this in the future, but it
is not currently a priority.
Q: Will your engine mounts keep the engine in the same fore/aft position as existing engine installations, or is it reasonable to assume it could be moved to adjust weight and balance?
A: Appropriate engine mounts will be developed with the aircraft manufacturers for each new installation, to achieve the best balance of all the considerations such as weight and balance, propeller position and
cowling fit. In the Velocity installation, for example, the engine was moved farther aft from the firewall for weight and balance reasons. We then use a different length prop extension (shorter) than for a Lycoming
to keep the propeller in the narrow range that is suitable for that aircraft. Other items, such as battery and tanks, also can be placed so as to adjust weight and balance.
Q: Why did you choose a V configuration instead of opposing cylinders, as with the Renault, Continental, etc.? It seems that the V will be more difficult to fit under the typical cowling.
A: We chose the V configuration because it is compact and can be lighter than an opposed configuration. It is true that it is a more difficult retrofit in tightly cowled current aircraft, but for new aircraft designs
it permits a round cowling, which is actually more aerodynamic. Some propeller and new aircraft designers have said they love it. An inverted model is available for those who need a lower profile.
Q: We understand your engine will require a unique mount. Will the mounts be designed to attach to the same firewall hard points?
Q: Looking at your engine dimensions, a new cowl design should provide some distinct advantages (for an RV-8A installation). The problem will be the strong reluctance from us metal airplane builders to consider
making our own cowl. Will you offer a cowl as part of your firewall forward package?
A: We hope to develop a cowl source for different installations that could be made part of a firewall forward package, since we do not want to be in the business of building cowls for several hundred types of
airplanes. Ideally, we would help the RV factory people with a new cowl once they have agreed that our engine is acceptable to them, and they could supply it to those using the DeltaHawk. We have not yet begun those
factory discussions, since it would not be productive until the engine is fully tested and the configuration stable.
Q: What is the engine's heat rejection requirement?
A: 110,000 Btu/hr/100 hp from coolant and ~50.000 Btu/hr/100 hp from oil. About 15% of the total heat rejection is directly from the engine due to airflow through the cowling.
Q: What sort of cooling system are you using?
A: The current Velocity installation is a single radiator under the engine with one large belly scoop. However, our work on specing the cooling is not final, and each aircraft type will require its unique sizing and
placement. That will be part of our "firewall-to-propeller" packages.
Q: Would it be possible to use the fuel supply for cooling instead of glycol? In the case of a wet wing, the wing itself becomes a huge cooling fin and the fuel a coolant. Given the low heat rejection of diesels, 4-5
gallons of fuel should be sufficient. With any less than that in the tanks, any pilot would be operating at a very low power output to conserve the remaining fuel. The upside is that the radiator system would be
eliminated along with the associated cooling drag.
A: What you propose is potentially feasible if the aircraft type has enough heat rejection capability from the fuel tanks through the range of fuel loading (from full to low end-of-flight levels). In the Velocity
wing tanks, we do not (not even close). We would hope the designer would avoid circulating the fuel directly around the hot engine, though, and instead opt for a glycol/water to fuel heat exchanger!
Q: Conventional gasoline engines are prone to icing. Does the DeltaHawk have a similar susceptibility to ice-caused malfunction? Does it have an equivalent to carburetor heat?
A: There is no equivalent icing point in the two-stroke diesel. Fuel is injected directly into the cylinders.
Q: How do you address the problem of diesel fuel jelling at cold temperatures?
A: The fog point of Jet A (JP5) is - 40 degrees C, and Jet A-1 (European) is -47 degrees C. The jelling point is about 5-8 degrees C colder. Also, we have a fuel recirculation system which warms the fuel and fuel
filter so that water precipitates out in cold weather.
Q: So, what fuels are acceptable for use in your engine?
A: Acceptable fuels are Jet A, Jet A1, JP5, JP8, D1 and D2, which are all kerosene based. The high naphtha fuels (JP 4 and Jet B) are not suitable.
Q: Can jet fuel and diesel be mixed in the fuel tank (for example, when changing fuel used as temperature changes), or should one fuel be chosen and used forever.
A: Yes, the fuels can be mixed.
Q: Could you use heating fuel in your engine? I know this is not legal, but in a pinch could this be done?
A: It would not be recommended but if done, certainly use a lubricity additive.
Q:You have mentioned a using a lubricity additive when using Jet A. What is this additive and how much is used?
A: Although it may not be necessary, we think it is good insurance to use it. The product is usually added at the rate of one pint per 120 gallons (~1,000 to 1), and costs about $4.75/pint (~ 4 cents per gallon).
With the new pumps, ½ the normal rate is probably adequate for "insurance" purposes. This protects the injector moving parts and the pump piston. When we supply engines, the specification and source will
also be supplied. Any diesel shop carries it.
Q: How can you make do with only a single engine control lever? Don't you need to adjust mixture at some high altitude?
A: At a high altitude (above 18,000 ft) the fuel should be trimmed back. This can be done either by the pilot, based on indicated altitude and a chart provided by DeltaHawk, or automatically by an aneroid device
(pressure altitude sensor). Either way, it is the single lever, the fuel lever (or "throttle"), which is being adjusted.
Q: Considering that your engine does not have an ignition system or a mixture control, how is it shut down?
A: We stop a diesel by stopping fuel delivery. It is very crisp in its cutoff -- no after-running. The fuel lever connects to a "rack" on the fuel pumps through linkage, and we mechanically move the rack to
the delivery cutoff position. As a safety, we also have a mechanically (cable) controlled ball valve at the inlet to the fuel filter from the main tanks. This is also handy when it is time to change the fuel filter
(a thread-on type).
Q: Does the fuel injection system require a return fuel line or will it operate like a Bendix?
A: There is return fuel (about 25 gal/hr) that must go to a header or main fuel tank. You just need to be sure to draw from and return to the same tank.
Q: Is there any requirement for vent return to the fuel tanks, or is the header tank sufficient?
A: All the tanks need to be at the same pressure. The method to achieve this will be different for every aircraft. In the Velocity, for example, we have the vent for the header tank and the vents for the aircraft
fuel tanks all interconnected before exiting to the air.
Q: Why is flow through venting recommended in the fuel tanks?
A: It is required because of the different volatility of Jet fuel. Regular avgas, being more volatile, rapidly builds up a vapor level in the tanks which is too rich to be explosive. Jet fuel, being less volatile,
builds up so slowly that it may never get too rich. So the standard solution is to actively vent the tanks so that any time the aircraft is moving, or even facing into the wind if the vents are so designed, the
tanks are being kept below an explosive mixture level. This is most important in a hot, sunny climate.
Q: Please elaborate on the "flow through" fuel tank venting.
A: We can't be too specific on how to do it, because there are so many schemes with different aircraft. Here are the basic principles of the "why", which you will have to carry into your particular
installation. Most installations will bring air from a high pressure or ram pressure location into the top of the fuel tank(s). This originally allowed air in as fuel is extracted from the tank. In interconnected,
multiple tank systems, an equalization line is often used to keep a pressure imbalance from forcing fuel from one tank to another. If you have such a line, then a tee in that line will provide a convenient way to
equalize tank pressure with the header (return fuel) tank we use in the diesel installation.
Now, from that same line (or the header tank) continue to an overboard (low pressure) site. This will mean that air
flows into your tank(s), across the fuel and out the equalization line to an exit. The two things you must accomplish are:
1) equalize pressure in all tanks, including the return fuel tank, and
2) flow through of air from an inlet to the tank(s) to an overboard exit.
Additionally, the exit should NOT be to a confined space, such as the engine compartment, and it should be away from ignition sources. The place we use on our diesel Velocity is one of the cabin-air exit reverse
scoops on the lower surface of the strake. We'll provide a schematic in our installation instructions!
Q: The plans call for a ¼ inch fuel tank vent line. Will this small line provide adequate air flow
A: A 3/8 inch line would be better, as you are trying to supply more than make-up air for the fuel extracted from the tank and for a given pressure difference, you will get approximately three times more flow in 3/8
vs. ¼ inch line. If space is limited, a 5/16 inch line is a good compromise.
Q: When the tanks are full, the vent air supply line will be below the level of the fuel (wings angle up). This will prevent additional back pressure for the vent air supply and most likely will prevent air flow. Is
there still a need for positive tank venting when the tanks are full?
A: When the tanks are full, very little airflow is needed since the airspace is small. Just be sure the tank cannot drain through your vent line.
Q: Is there an issue when conditions prevent positive venting (plane parked in a hangar or not facing the wind)?
A: All of this venting is precautionary. The low vapor pressure of Jet A means it takes a long time or high temperatures to create a hazardous high fuel vapor fraction. It is still not hazardous without an ignition
source. There may be times when air/fuel mix in the tank space is dangerous, but these would be transient and as you fly you will vent the vapors. Gasoline tanks have similar transient dangerous mix periods, but
usually it is immediately after filling, and the mixture quickly becomes saturated and thus non-explosive. Gasoline tanks trap vapors to become "safe", and Jet A tanks vent to become "safe".
Q: I plan to install a pre-filter between my main tanks and the selector valve. Will the fuel flow be adequate?
A: We don't know the characteristics of the filter you are planning to use. Try a test by gravity draining through it and checking the flow rate. You should supply twice the engine's maximum requirement of 11 gal/hr.
So if each tank has a separate filter which can supply 11 gal/hr, you would be fine.
Q: What kind of fuel filter is used: 2, 10 or 30 micron element? I am excessive with this stuff and would like to have a 2 micron element near the engine and add a 30 micron filter on the tanks.
A: That sounds good. We currently use a commercial diesel fuel filter with 30 micron filtration) with a water drain, and a final fuel filter (3-5 micron) after the delivery fuel pump. A finer filter is okay as long
as it will flow ~ 20 gal/hr.
Q: How water tolerant is the engine? Diesel fuel has a significant water absorption characteristic. Will this lead us to JP fuel use only? If diesel fuel is used, will we need to pre-filter/separate it prior to
fueling the plane?
A: Both jet and diesel fuels have the potential to hold water in suspension. That's why we have the large filters. The main reason to use jet fuels would be the greater control in handling and distribution.
Q: Does your engine use an injector pump? A boost pump?
A: There is a delivery pump and four high pressure (20,000psi) mechanical injector pumps. We'll be recommending a boost pump for starting, especially under the condition of any air in the system (e.g. just after
installation or having run a fuel tank dry), or a large "head" (e.g. seaplanes with a high-mounted engine). The pump should be capable of delivering 30 to 40 psi. It will be OFF under normal operating
conditions. The main pump has its own internal delivery pump which puts 50-90 psi fuel to the injector pumps, which add the final pressure increase.
Q: Can I use #2 diesel instead of Jet-A?
A: Please see the April 22, 2005 issue of General Aviation News for the article by Ben Visser titled "Jet A vs. #2 diesel: Which is better?"
Q: Have you verified 200 HP output w/ the intercooler?
A: We haven't yet, but since we've gotten over 185 hp with the non-intercooled engine we know the intercooled version will produce at least 200 hp with no problem. We may be able to rate it for more.
Q: Have you built and/or run any V-8 engines yet?
A: No we have not. That's the next big R&D project.
Q: Have you run any inverted engines yet?
A: Yes, it ran for the first time July 2003. It is in testing now.
Q: Do you plan to develop an air-cooled model?
A: There are no such plans at this time. We believe the liquid cooling system is needed in order to moderate the rate of cooling. With no fixed air/fuel ratio or throttle plate, when you go to idle from a cruise
setting the engine combustion temperature drops dramatically.
Q: Do you have any feel for how long it might be before the V-8 version will be available?
A: The V-8 will probably lag one year behind the V-4.
Q: I understand they are not yet set in stone, but could you estimate the weight and size of your planned V-8 engine?
A: Reasonable guesses based on the current V-4 engine are a length of 42" and dry weight of 470 pounds (600 lbs fully installed). Engine frontal area (height and width) would be the same as the V-4. We also have
a V-8 "light" model in the plans that would come in under 500 pounds fully installed.
Q: Can you estimate what the weight and price would be for your 100 hp engine, if you develop it?
A: Best guess would be 150-160 lbs and $12,000 to $14,000. But that engine isn't as far along in our planning as the V-8.
Q: Why no plans for a 300ish horse V-6 DeltaHawk? It seems like it would be a natural for the Velocity XL... pretty close to max useable horsepower for the airframe without paying the weight penalty associated with
going to a V-8 (that could as easily produce 400 hp).
A: Maybe someday. But a V-6 would be an entirely new engine, not an evolution from the current design, with all the associated development time and $ costs. Hopefully the DeltaHawk V-8's power to weight ratio will
allow it to address most of the 300 hp applications.
Q: I want to build a Velocity XL RG. What is the displacement of your planned 300 hp engine? In France we can't have more than 7 liters or 427 cubic inches.
A: The V-8 will have a displacement of 404 cubic inches.
Q: Why are DeltaHawk engines suitable for industrial applications? Existing aviation engines are rarely if ever used for other purposes.
A: First, DeltaHawk engines are liquid cooled making them easily adaptable to most stationary and mobile applications. Second, the engine has far fewer parts than air cooled aviation engines and is designed for easy
service of components.
Q: What is the difference between DeltaHawk industrial and aviation engines?
A: Numerous parts and components necessary for weight reduction or compliance with accepted aviation practice will be replaced with less expensive industrial grade materials and parts. For example, aviation starters
will be replaced with commercial starters. Steel connecting rods may replace the titanium rods used in aviation engines. Aviation grade parts and fasteners will be replaced with industrial grade items where engine
reliability and longevity will not be affected.
Q: How much will these changes affect the price?
A: DeltaHawk industrial engines will be less expensive than the aviation version but priced higher than existing top quality diesel engines. They will be suited for applications where the completely unique features
and characteristics of DeltaHawk engines provide value which offsets the higher price.
Q: What is so unique about the DeltaHawk industrial engine compared to existing diesel engines?
A: It is the lightest, most compact compression ignition power plant available in today's market. A fully equipped engine (starter, alternator and radiator) will deliver up to ½ horsepower per pound out of 8 cubic
feet of volume. This is less than ½ the average weight of many diesel engines in the same horsepower class and a very dense overall power package.
Q: What type of applications need the special features of DeltaHawk engines?
A: Any application where a high horsepower to weight ratio, maximum endurance on a fixed fuel volume and/or multi-fuel capability is deemed necessary. This includes air-mobile equipment used by the military,
airlines, expeditions, drilling/pumping operations and forest services. Open ocean powerboats and racing yachts can improve their competitive position with DeltaHawk engines. Mobile and stationary equipment
operating in remote areas where gasoline is costly or unavailable will benefit from DeltaHawk's multi-fuel capability.
Q: What are some of the more notable technical features of the engines?
A: Each engine (V-4) has 3 standard accessory pads providing up to 10HP each. These accessory drives are coupled directly to the engine gear train and positioned to keep most driven accessories inside the engine’s
basic foot print. Models will be available that can be configured horizontally with the crankshaft above the cylinders or below the cylinders or with the crankshaft vertical, taking power from either end. Right or
left rotation is also available. Users have a choice of wet or dry oil sump.
Q: How will DeltaHawk industrial products be sold?
A: Dealers will sell, service and provide parts support in defined marketing territories.
Q: What is the engine warranty?
A: DeltaHawk industrial engines will be warranted for 1 year or 2000 hours, whichever occurs first.
Q: How does lubrication work for the inverted engine? Where is the sump?
A: The sump is internal to the engine, in the "V" between the cylinders on the inverted. The scavenge line comes out the side of the inverted engine instead of the bottom as in the upright.
Q: In most two-stroke engines, the problem is the lubrication of the piston because both beneath and above there is airflow. Normal gas engines "solve" this by putting oil in the gas, giving a disgusting
blue smoke out the exhaust. Larger engines have other solutions. Which is yours?
A: Lubrication in this engine is accomplished by the standard automotive or aircraft oil pump method. We do not draw air through the crankcase because it has oil in it. Additionally, the pistons are cooled by oil
jets, so there is no shortage of lubrication for the pistons.
Q: In regard to oil, you specify Delvac I. Can I use a different type of CD/CE grade diesel oil (a less expensive and more easily obtainable one)?
A: We are no longer specifying Delvac I. We are currently evaluating a Shell oil product and will prepare final recommendations from the data. The use of the specified oil is extremely important. Engines require
specific additive packages to survive, and aircraft engines even more so. There are books written and courses taught that discuss lubricant design... not a trivial subject. The wrong oil can cause ring sticking,
exhaust port fouling, bearing failure or corrosion. So oil specification is something we will be very particular about.
Q: Why doesn't the DeltaHawk engine have valves?
A: The advantages of no valves are less weight and manufacturing cost and a smaller size package. It is harder to design than an engine that has no valves but once the design is accomplished, it is easier to build,
has fewer parts and is cheaper to maintain and rebuild.
Q: What do you anticipate the service ceiling to be for the DH200V4 turbo?
A: The term "Service Ceiling" applies only to the airframe, not the engine. For the engine, we have flown the DH160V4 at FULL power to 18,000 feet MSL. We are estimating the "Critical Altitude"
(100% power) for the DH200V4 to be somewhere around 15,000 feet. We are estimating that the DH200V4 should get 60% power to 30.000 feet.
Q: How did you verify full power @14,500 MSL on the Velocity?
A: A chase plane was observing the climb. In a two-stroke diesel with excess combustion air being supplied for producing full rated power, the "smoke point" indicates when you no longer have enough air to
make that power. Up to 14,500, when that particular flight ended, the aircraft still had a clear exhaust. At that time, the engine rpm was 2650 at full fuel setting. (The critical altitude for the DH160 has since
been determined to be about 18,000 feet.)
Q: What are the advantages and disadvantages of the piston-ported design over an engine with valves?
A: The advantages of no valves are less weight and manufacturing cost and smaller size package. It is of course much harder to design than an engine with valves. Once that design is accomplished though, it is easier
to build, has fewer parts and is cheaper to maintain and rebuild. It should be equal in performance.
Q: Is this engine actually being designed to be run at 100% power 100% of the time?
A: It is being designed to be able to do that (e.g. the coolant system capability, etc.). Obviously, that is not how it would normally be flown. Further testing may of course dictate that 100% at 100% is not wise
long-term, but that is our design goal.
Q: Could you please provide some more basic information regarding stroke, bore and static compression?
A: Stroke and bore are both 4 inches. Static geometric compression ratio is 19 to 1.
Q: How many cubic inches is the cylinder displacement?
Q: What about climb/cruise figures for your diesel in at least one version of the Velocity to compare with the Lycoming IO-360 (200 hp) and the Franklin (220 hp)?
A: We will publish these numbers when we have them, after we have flown the engine. As we are currently flying an IO-360-powered Velocity RG, we have an excellent comparison platform. One thing can be projected now:
being turbocharged, the diesel engine should maintain full rated horsepower up to 16 to 18,000 feet. We estimate a maximum of 65% power at 30,000 feet.
Q: I was warned about the vibration potential in the event of fouled injectors or loss of compression on a cylinder. A friend recalled a diesel that lost a cylinder and the vibration was severe enough to crack the
transmission. Any experience with a failure of a cylinder?
A: Your friend may be thinking of a 4-stroke diesel rather than 2-stroke. Since the 2-stroke fires each cylinder on each propeller revolution, it behaves like an 8-cylinder in terms of vibration and power pulses.
We've intentionally shut down one cylinder, and above 1500 rpm it's hardly even noticeable (other than the expected power loss). One cylinder dropping out will not cause any significant vibration problem. Similarly,
we've run on two cylinders. They were on the same side of the engine and again the only noticeable change was in power. Losing two cylinders on opposite banks would, of course, make for a rough engine. We have not
tested that yet, but will before we're done.
Q: A very important safety feature of aircraft engines is their redundant electrical and ignition systems. Since a diesel doesn’t have an electrical ignition system, this is not a concern. However, if there is an
electrical system failure using a DeltaHawk engine, would it cause all injector fuel pumps to fail, or any other critical system to fail?
A: There are no critical systems dependent on the electrical system. Fuel injection and delivery from the tanks is by mechanical pumps. There is a backup electrical delivery pump, but it is necessary only for
Q: How would an operator verify engine performance when using a constant speed prop? Also, how would he/she know how to get a certain engine power setting (say 75%)? With no throttle valve, it seems that manifold
pressure would be of little help. I believe some turboprops are equipped with torque sensors in order to deal with this problem.
A: Torque sensors would be one way, but we are using fuel flow. It has a very linear relationship to power production. There will be performance tables supplied with the engine.
Q: What kind of prop governor and prop flange does the engine have?
A: The prop governor pad accommodates either a Woodward, Hartzell or similar governor. The propeller flange is an SAE 2L (like the Lycoming IO360).
Q: What are you planning to put on for a propeller? I know that horsepower is going to run around 200, but what about the torque from a diesel? It could rip the blades off the hub.
A: We have been flight testing a wood/composite propeller from Aymar-Demuth with good results. Several other composite constant speed props are in test or will shortly be in test. We are (and any user of any engine
should be) aware of the need to test a propeller with a specific engine. In the past, these tests have determined the "yellow arcs" where continuous operation is not recommended for a particular prop on a
specific engine. (Even changing the ignition system can invalidate some certified combinations.) Our goal is to have engine and prop combinations without yellow arcs if possible.
Q: Hartzell apparently has developed a special quiet prop for the anticipated TCM diesel. Could this prop be used with your engine?
A: We believe that the TCM diesel is projected to produce its rated power at 2200 rpm. If someone needed only 150 hp or so, they could limit our engine to running in that rpm range with that propeller to the same
effect. Our engine, however, is designed to produce its full 200 hp at 2700 rpm, which matches the other current engines out there.
Q: I would like your opinion regarding fixed vs. variable pitch propeller.
A: All of our testing so far has been done with a fixed pitch prop, an Aymar-Demuth wood/glass unit. We can turn it higher than the 200 hp IO-360 Lycoming on the baseline Velocity can. Our horsepower curve is flatter
than the IO-360 so we cross the propeller demand curve further out (higher rpm). In principle, with a given propeller you should have more takeoff thrust with the diesel. The rub of the fixed pitch prop comes when
you are at altitude and the diesel is still making 100%. At 10,000 ft the IO-360 without turbocharger is able to make about 65% while the diesel is at 100%. You have 70 more horsepower to drive your prop, and unless
you are climbing, it will allow an over speed. If you are happy with the cruise speed that redline on the engine gives you, simply pull back on the fuel lever (throttle) to maintain within rpm limits. The power is
then available for climbing when needed. If you want to use that extra power to go faster, you have two choices: get a prop with more pitch, or get a variable-pitch propeller. The first choice will lower takeoff rpm
and thus thrust, and the second lowers your bank account.
Q: For the design of a new generation of tow planes, the optimum propeller should have a diameter of about 3 m and run at about 1000 rpm. Do you think it would be possible to adapt or fix a gearbox on your engine?
A: It was not designed for a gearbox. There are no attachment points. It might be possible to use a transmission, as is done in marine applications.
STARTING / AIR SUPPLY:
Q: Please describe the engine start and air supply process.
A: The engine is both supercharged and turbocharged. A battery-powered starter with flywheel provides the initial compression stroke. (The engine is very quick-starting. Even when cool it turns only a few rotations
before firing.) The belt-driven supercharger (a positive displacement pump) provides the starting air compression, delivering air on the first rotation of the engine. Once the engine has achieved sufficient rpm, the
turbocharger comes online. The supercharger also provides "rescue power" in the event of a turbocharger failure (supplying approximately 50% power).
Q: Since compression ignition is used, what is used to stop accidental ignition should the propeller be moved for any reason? Especially since it is claimed the engine starts immediately when hot.
A: The prop must be turning at ~150 rpm or greater to start, for three reasons.
1) Fuel pump leakage past the delivery piston does not permit pressure to increase to the needed 3200 psi to open the injector
2) Leakage of air past the rings lowers the actual compression ratio below that needed for ignition.
3) The compressed air cools rapidly as it contacts the relatively cool piston and cylinder
wall. The heat of compression (~1100 degrees F) is what ignites the fuel.
In the engine cutoff position for the throttle, no fuel can be delivered to the engine. In case one inadvertently advances the
throttle and pulls the prop through, the above 3 reasons keep it from starting. It is virtually impossible to hand-prop this diesel.
Q: In a diesel cycle engine air is compressed in cylinders and then fuel is injected into this hot air. For this reason, at high altitudes, thin and cold air results in restart problems. How have you overcome this?
A: You are correct to be concerned about high altitude restart capability in diesel cycle engines. At some critical altitude, de-spooling of the turbocharger by reducing fuel flow (reducing "throttle") can
result in not enough heat of compression to ignite the fuel. Advancing the fuel lever will not restart the engine until the aircraft descends to a lower altitude where the air is denser. There are several approaches
to mitigate this phenomenon. One is to use a higher compression ratio to raise the critical altitude. Another is to limit fuel flow excursions by imposing a controller between the fuel lever and the engine fuel
pumps. It would control fuel based on atmospheric pressure and fuel lever position (an aneroid-based system). Liquid-cooled engines with thermostatic control help to keep the engine and thus the air supply warm,
improving ignition properties. Catalytic "hot spot" approaches may work to maintain ignition below normal uncatalyzed ignition effective compression ratios. A mechanical supercharger driven by the
windmilling propeller can provide additional charge density. Without getting too detailed, we use some of the above methods to raise our ignition critical altitude above that where most general aviation aircraft
fly. Until we complete flight testing we cannot give a precise altitude, but we expect it to be above 30,000 ft (~9,240 m). We have demonstrated shutdown and restart with a non-windmilling propeller at 14,000 feet.
Q: Does the supercharger have a clutch?
A: There is no clutch. The supercharger is for start and low power air; the turbo for high power. Unloading of the supercharger is automatic when the turbocharger output exceeds a pre-designed value. The supercharger
is then along for the ride. A bypass is also provided in the event of a supercharger drive failure.
Q: The idea of drawing air through the crankcase in a two-stroke is generally to get the inlet air pressure in synch with the piston movement. How do you accomplish this without drawing air through the crankcase?
A: We use a supercharger and an intake manifold that is always under pressure.
Q: What size battery is required to start the engine at below freezing temperatures?
A: We're currently using two B&C 12-volt 25 amp-hr batteries in series with a 24-volt starter. We don't have a final battery recommendation yet, but the above mentioned batteries we've used are fine. For cold
weather starts, the health of the battery is critical of course. We recommend plugging in the supplied block heater at temperatures below 40 degrees F (~4 degrees C).
Q: Just looked at the change about 28V only. My instrument panel is complete and tested with 14V. I have some devices the don't even have a 28V option. And I would have to re-wire the whole
system or start over. Is there some way to have both 14 and 28V or a converter for the panel?
A: Do not panic. We are flying with a hybrid electrical system in our test aircraft. The main bus is 28v and the heavy load items like gear motor and pitot heat and landing light (and starter) are on it. For the
avionics and the data acquisition computer there is a DC to DC converter installed that powers a 12v bus. These converters are TSO'd and come in various sizes up to 60 A. Theoretically you could run everything but
the starter off the converter, but it would be better to get the high load items on the main (28v) bus. If you do not like converters, there are schemes where two 12v batteries are switched to series for start and
then paralleled for charging and supplying the main bus. Hanging switching relays worry me with that approach though.
Q: What is the number of teeth (122 or 149) on the ring gear? The new Lycomings have 149.
A: The ring gear has 146 teeth and is 14.7" in diameter. The starter is the same as used with the Lycoming 122-tooth gear.
Q: How reliable is the supercharger, since it seems to be essential to the 2-stroke operation? What happens if it breaks?
A: We believe the supercharger will be very reliable. But if it breaks, what happens depends on when it fails. On the ground, the engine won't start. If an in-flight failure occurs when the turbocharger is online,
the engine will continue to run. If the failure was of the belt, the failure will probably be unnoticeable; a "frozen mechanical" failure would probably make enough noise to be noticeable. The only concern
would be that if the power is reduced too quickly and the engine stops, you could possibly not be able to re-start it with ram air. For that reason, we plan to have a sensor in the installation package to provide a
cockpit warning if the supercharger is not spinning, and our operator's instructions will provide procedures for no-supercharger landings. We will be thoroughly testing these situations in our flight test program,
SUPPORT AND SERVICE:
Q: If you guys have a mailing list, I'd love to get on it?
A: We don't send out general mailings. We try to put everything on our web site. Check it occasionally for updates. You may Email questions not answered on the website to the appropriate DeltaHawk contact.
Q: What are your plans for servicing the engines in the field?
A: A service cell will be set up at the company as soon as we sell engines. Additionally, we plan to develop service centers at existing repair facilities in various regions.
Q: Can you make a manual or installation guide available to people who are committed, but have to wait for delivery?
A: After we are sure there will be no more changes, we will do a manual. Meanwhile, we hope these Q&As will be helpful.
Q: Is your engine designed with the thought that at the end of the TBO the engine would be destroyed or rebuilt?
A: We expect at least one overhaul from the block. The crankshaft is (pending inspection) infinite life.
Q: Will the engines be shipped "pickled"?
A: Pickling will be available as an extra-charge customer-selected option. Standard delivery will be in a post-Dyno run condition with connection points plugged.
Q: Should I plan on putting in the "stock" speed brake on my Velocity fixed gear airplane? With a belly scoop for the radiator/oil cooler, I'm wondering if I will cut off the air flow?
A: Our pilot likes the speed brake on the Velocity. We fly a standard RG, and it helps the descent angle for approaches a lot. If you plan to use a constant speed prop, you may not need the brake, however, as the
prop at flat pitch provides considerable drag. Because the DeltaHawk diesel idles at a lower rpm (approximately 650), this also will help add "prop drag" for approaches. The disruption of airflow into the
radiator belly scoop is not a problem, as the speed brake is only deployed when power is retarded (as for landing). Not much heat rejection is required for this engine at the low power settings used for approach.
Q: Are you guys building the fuel cells in the strakes of the Velocity per plans? With the slightly heavier weight of kerosene and the increase in performance that you expect in fuel burn would it be prudent to
reduce the fuel capacity and help things out in the weight and balance area?
A: I would leave the fuel tanks as-is and just not top off if you don't want to carry the weight. I hardly ever top off my tanks -- I just carry the fuel needed for the mission plus reserves. The Velocity has very
good direct-reading fuel gauges.
Q: I assume you are planning on putting the battery in the rear of the Velocity?
A: No, the battery is located under the front passenger seat, just in front of the front seat support bulkhead.
Q: Will the engine(s) you submit for certification be identical to the engines we buy for experimental use? If so, will there be a way to demonstrate to the FAA that the engines in our experimental aircraft are
pending FAA certification? This could help in obtaining insurance.
A: Once the engine systems are all stable and into production, we will begin the certification process. All systems have been designed with certifiability in mind, so there are no known changes we will make on the
engines submitted for certification. Of course, during the certification process the FAA may require some changes. We will do our best to provide them as retrofits for earlier experimental engine purchasers, so that
once certification is achieved their insurers will view all the engines as coverable as "certified".
Q: Please elaborate on rebuilding the engine at TBO or whenever. Can the owner do it? What's involved in the estimated $4,000 cost? What's left out? What about injectors, i.e. maintain, rebuild, replacement cost, etc.
A: The engine is nonstandard and has unique and critical materials, testing equipment and procedures. We will not recommend owner maintenance or rebuilds. Our rebuild price projection is based on our current estimate
of the labor plus components that we anticipate having to replace. Nothing is "left out". There are very few parts in the engine relative to 4-stroke or even 2-stroke valve engines, and we don't anticipate
that the most expensive ones will require replacement at each TBO. The injectors can be rebuilt, and this is included in our rebuild estimate. If an injector fails between engine rebuilds but beyond the warranty, we
will provide injector rebuild service at a very reasonable price.
Q: I understand there will be a different scoop for engine cooling than the armpit scoops. Is it OK to assemble the cowling halves and work on the wing flange that holds the aileron controls on my Velocity?
A: I wouldn't recommend it at this time. We modify the cowling to fit the V-4 since it is 11" narrower than the IO-360, and the cowling flange will be wider.
Q: Is the boost pump mentioned necessary for the Velocity?
A: We currently recommend an electric high pressure delivery pump to purge air from the main pumps if there is ever danger of running a tank dry in flight. It also makes starting easier when the system has been
opened, as when changing a filter or other maintenance.
Q: For those of us who have already installed the cooler in the nose of our Velocity, can you provide suggestions on how the nose cooler can be incorporated into the cooling system?
A: If your nose oil cooler is installed, you can use it for cabin heat by running engine coolant to it as you would have run oil. It will be slightly more effective with water/glycol than with oil, due to the higher
specific heat of the coolant. If your installation is not complete, you may wish to delete the exit opening that was designed for the oil cooler mission, further increasing the heat available for your cabin and
removing one more exterior lump on your fuselage.