Engine Suggestions for SPADXIII ?

Does anyone know of a suitable modern replacement engine that will fit in the mounts of a SPADXIII? Or are there any actual authentic reproductions that will work as the Hispano-Suiza is no longer manufactured?

The dynacam would be ideal, but not sure it is still in production. Smaller and lighter than the Hisso, but with almost dead on the same torque, and a little higher horsepower, at the same RPM. That is the key. It is, like the Hisso, a high torque low rpm engine. None of those are around nowadays. Practical effect: your SPAD would have virtually identical performance as did the original with its Hisso, but will do it much more reliably with a lot less maintenance. Gearing a modern engine down does not accomplish that purpose. Downside is its relatively expensive, assuming its even still available. Lighter weight is easy to address. Just add ballast and it will return your SPAD to its original balance. Depending on how you do it you might even be able to save some weight and still maintain the balance.

[Brad]

Actually one would think that a modern V8 or even V6 with an appropriate reduction drive would do nicely.

[William]

Joe,
Although the Hisso is no longer manufactured it is one of the easier to find originals. We encounter them and Liberty engines much more often that what we want to find. Reliability is always an issue. My opinion (just that) is if you are building the airframe for "accuracy" an original Hisso could be more appropriate. If you are building for safety/reliability go with one of the suggested modern engines.
Regards,
William

Originally Posted by Brad

Actually one would think that a modern V8 or even V6 with an appropriate reduction drive would do nicely.

Doesn't work that way. The modern engines provide the horsepower, but not the torque of the original. No matter how much you gear that engine down, all you are doing is reducing rpm. Gearing will allow you to develop your engine's full horsepower at lower rpm. You do not, however, and cannot, increase an engine's torque by gearing. It has what it has and you better be ready to dance with the one you brung. The dynacam was a low rpm, high torque engine that made it an ideal, if expensive, option for WW1 replicas.

Responses much appreciated - if anyone knows of websites, sources or vendors, please feel free to share - Not going for "museum piece" here - safety and reliability #1 concern.

[hank jarrett]

Pardon me while I back away from Matt on this one. I don't want to get splattered by all the "less than charitable" responses.
I'm afraid you are absolutley WRONG on the torque issue. When you gear an engine down the torque at the prop DOES go up as RPM goes down. Think of the gears as levers wrapped in a circle and you will see what I mean. As the lever gets longer (larger gear) the moment arm increases and the torque goes up. What DOESN'T go up is the ENGINE torque. It's an easy thing to get confused on but if torque didn't go up as RPM goes down (for the same engine RPM) there would be no reason to put transmissions in cars. It's the same for props. Gear drives reduce RPM and raise torque for higher static thrust.

[Brad]

Originally Posted by Matt Witt

Doesn't work that way.

I have to disagree... the definition of HP is:

HP = torque x rpm /5252

This is a formula that holds true, no matter if you are turning 1 RPM or 1,000,000 rpm...

The modern engines provide the horsepower, but not the torque of the original.

Agreed, on this point at least.

No matter how much you gear that engine down, all you are doing is reducing rpm. Gearing will allow you to develop your engine's full horsepower at lower rpm. You do not, however, and cannot, increase an engine's torque by gearing.

This is where we part ways. Gearing is used for precisely that reason- to increase the torque at the device that is doing the work, such as a wheel or a prop. (In the case of the prop it is ALSO used to allow the engine to develop peak power while keeping the prop tips subsonic.)

Referring back to the formula HP = torque x rpm /5252, you can see that to keep the HP the same, if the rpm is cut in half, the torque must be doubled for the formula to work. Note that this ignores "mechanical loss" caused by the drag of belts, gears, bearings, etc.

It has what it has and you better be ready to dance with the one you brung. The dynacam was a low rpm, high torque engine that made it an ideal, if expensive, option for WW1 replicas.

Please don't let the terms confuse you. In a direct drive situation, the torque is important. In a reduction drive situation, you should consider the HP and torque at the operating RPM, and how much you will reduce the RPM by, and use that to compare the torque figures. Whoever told you that reducing the RPM with a reduction drive doesn't increase the torque at the prop has mislead you gravely. The formula doesn't lie.


One thing that MUST be said about automotive conversions is that auto engines are not generally designed to be operated at thier rated HP for long periods of time- those are peak HP figures. One MUST make sure the engine is capable of sustained output at the needed power level- this generally means the kind of modifications that racers use. You can't just bolt in a Chevy 350 from the salvage yard and go flying. Attention has to be paid to the oiling system, cooling, etc to be sure it is all suited to the sustained output you want. Aircraft engines are designed and rated to use 75-100% of their rated power sustained over time, where auto engines aren't.

Brad

[Tedders]

Arrrrggghhh! Don't you guys subscribe to W.WY.1 Aero? This topic's been addressed by numerous writers and aeroplane buffs. Here is the latest:
August, 2004; Issue No 185, pages 67 & 68.
In this, Doe Blomberg writes how he and his team have taken a Chevrolet .292 six-cylinder truck motor and, by teaming it with a planetary gear reduction unit, have reduced the RPMs and increased the torque. They used a copy of a German prop for a Mercedes (that's the power unit they're trying to replicate for W.W.1 aircraft builders) and it swings great. See the article for Mr. Blombergs explnantion about hp, torque, conversions, and longevity.

PS: They hope to replicate other engines, '...If the interest is there.'

Oh, man!

Fly laughing
Tedders

[Brad]

Originally Posted by Tedders

Arrrrggghhh! Don't you guys subscribe to W.WY.1 Aero? This topic's been addressed by numerous writers and aeroplane buffs. Here is the latest:
August, 2004; Issue No 185, pages 67 & 68.
In this, Doe Blomberg writes how he and his team have taken a Chevrolet .292 six-cylinder truck motor and, by teaming it with a planetary gear reduction unit, have reduced the RPMs and increased the torque. They used a copy of a German prop for a Mercedes (that's the power unit they're trying to replicate for W.W.1 aircraft builders) and it swings great. See the article for Mr. Blombergs explnantion about hp, torque, conversions, and longevity.

PS: They hope to replicate other engines, '...If the interest is there.'

Oh, man!

Fly laughing
Tedders

No, I don't subscribe to WWI Aero.

One of the guys (Troy Wright) on the Aerodrome builders list (different group, nothing to do with us on here) is doing the same thing with a Ford inline 6 though. I'm working on (yes, it is MUCH smaller) a reduction for my 4A084 (ABOUT 40hp at 3500 RPM) to get the prop RPM to about 2000. That puts it in the same range as a Model A Ford conversion like they use on the Pietenpol- 40 hp at 2000 RPM.

The 4A084 will swing a 52 or 54" prop (sorry don't know pitch) at 3300 or so RPM direct drive... I will be swinging something like a 74x40 at 2000 RPM, producing over 2x the thrust. Top speeds will be very similar, but I'll have a shorter takeoff and better climb.