WWI Replica Safety

[Joe Perkel]

Originally Posted by Jeff Brooks

Joe,
With a modern engine, you have the higher prop speeds, which result in less propeller disc size. Less thrust is like an overgrossed aircraft ... not safe at all. For a seaplane, you will need that extra thrust just to break free from the grip of the water.

Jeff,

......And here you touch right on the issue that is bedeviling me in this project even at this early stage! It is the reason why I am very likely scrapping the notion of the bench seat trainer in favor of single.

The disk area, thrust, controllability issues, are all at the top of my list. This (performance), is the primary reason, why the rotary is so attractive!

We sure do get ourselves into a bit of a bind with these replica's do we not?

Come on Rotec!,..build me a bigger radial with a planetary reduction!!!

[RobW]

Joe,
Have you looked at the Russian M-14D engine? It is a version of the engine that has no reduction gearing... there is a little info on the Dr.1 thread... post #231 that may be of use.

rob

[Joe Perkel]

Originally Posted by RobW

Joe,
Have you looked at the Russian M-14D engine? It is a version of the engine that has no reduction gearing... there is a little info on the Dr.1 thread... post #231 that may be of use.

rob

Hi Rob,

It's a nagging issue (adequate power / thrust), that I try to shelve for the moment, but it keeps coming back at me from time to time. As Jeff points out, it's a significant operational and design safety issue, not to be casually brushed aside but, not to be obsessed over either this early in the game.

As a result of leaving it for a later time, no, I have not looked closely at the M-14D radial, and cannot come to any conclusions since I don't know much about them.

Briefly,...to "safely" attempt to match the original without grossly underpowering or exceeding design limits, I need to match 546 ft lbs of torque and 381 lbs dry weight as closely as possible. This was achieved with 130 hp @ 1,250 rpm and 102" propeller.

So far, what I have looked at either falls well short, or overshoots the mark by too much.

[Joe Perkel]

Originally Posted by RobW

Joe,
Have you looked at the Russian M-14D engine? It is a version of the engine that has no reduction gearing... there is a little info on the Dr.1 thread... post #231 that may be of use.

rob

Rob,

The M-14 looks to be a bit heavy and overpowered for this little kite! The 130 hp Clerget, was the maximum power upgrade done to the Baby.

A quick check of my notes, and I see that I identified the 220 hp version of the Continental W670 as the closest matching power-plant. It weighs in 30 lbs heavy, (dry I assume) and 525 lbs torque @ T.O. rpm (just 21 ft lbs short). I don't know what kind of prop it may swing.

I worry a bit about the age of these (perhaps unfounded, just gut), but in any case, determined to just take a "wait and see attitude." A pile of money and a premier overhaul shop, could hopefully allay any concerns in this regard.

I think off hand, I identified the Lycoming IO 390X, as the closest matching flat opposed for a pinched cowl Schneider, but not as close as the Continental radial, and for now, significantly more money for less performance matching.

Someday, when I finish the CAD model, I will try to determine the flat plate resistance of this aircraft, and try to compare that to an existing float plane / engine / prop combination.

[Joe Perkel]

Originally Posted by Flysafe

This brings up a very interesting discussion - the subject of fuel tank/system design and minimum quantities for flight. In the certified aircraft world there are specific requirements for design and test of fuel tanks and systems, fuel flow, unusable fuel and minimum fuel for flight, not so in the world of homebuilt aircraft. In many cases we find out the hard way what the minimum fuel for flight is. This is one critical area where we need to focus risk management. We need to design conservative, reliable, simple fuel systems and during the initial pre-flight engine runs determine minimum fuel quantities, unusable fuel values and any pitch/roll attitude limits for low fuel quantities. This requires some patient work, but is a very worthwhile investment in time and effort.

How would you propose doing this?

Meaning, ...what type of rig could be used to position the aircraft in these attitudes for ground testing at these power settings? Is this what you mean?

[Flysafe]

First, there are practical limits as to how this can be done. Specifically, we can only practically test the flow of fuel out of the fuel system into the carb/injection system. Trying to conduct a test with the engine running is not only impractical it is potentially unsafe. The engine/carb/injection system has pressure and flow rate specs that are published.

Essentially the activities would require determining the minimum fuel quantity at various aircraft attitudes (pitch & roll, conbinations) that ensures sufficient fuel delivery pressure and flow rate. Ideally tests need to be conducted with gravity feed and with electric pump assist and any other combinations based on the fuel system design. Testing parameters need to be limited by reasnoably expected aircraft attitudes. At the point when insufficient fuel delivery is achieved you can then also calibrate any guages and/or dipsticks.

The net result of all the tests will be knowing what fuel in the tank is unusable in best/worst case flight scenarios. This will also provide valuable information when determining aircraft range and endurance as well as determine if there should be pitch/roll limits for low fuel operations.

[Joe Perkel]

Originally Posted by Flysafe

First, there are practical limits as to how this can be done. Specifically, we can only practically test the flow of fuel out of the fuel system into the carb/injection system. Trying to conduct a test with the engine running is not only impractical it is potentially unsafe. The engine/carb/injection system has pressure and flow rate specs that are published.

Essentially the activities would require determining the minimum fuel quantity at various aircraft attitudes (pitch & roll, conbinations) that ensures sufficient fuel delivery pressure and flow rate. Ideally tests need to be conducted with gravity feed and with electric pump assist and any other combinations based on the fuel system design. Testing parameters need to be limited by reasnoably expected aircraft attitudes. At the point when insufficient fuel delivery is achieved you can then also calibrate any guages and/or dipsticks.

The net result of all the tests will be knowing what fuel in the tank is unusable in best/worst case flight scenarios. This will also provide valuable information when determining aircraft range and endurance as well as determine if there should be pitch/roll limits for low fuel operations.

I envision use of a fuel boost pump, used intermittently for T.O. and landing as you would in say,..a low wing Piper.

Would it be safe to say, that if one copies a particular fuel system configuration, for a given powerplant on a proven design, then this would go a long way towards ensuring an always adequate flow? This in addition to the FAA AC pubs.

Getting ahead of things here, have not looked at this issue in depth yet, but as you noted, it's a big one!

[Flysafe]

Jeff, I am not in agreement with your thrust quantityt argument as being a sole determinant in the safety equation for engine selection.

We are trying to manage two different risks when selecting an engine - thrust and reliability. While the original engine may address the thrust issue, the reliability of the power plant is a major consideration. Fuel and ignition system modifications may reduce some of the risk factors, but we must also consider the important issues of fundamental engineering design, material properties and the effect of age and poor storage on original engines as significant factors that contribute to the reliability and durability of an original engine.

We can mitigate the thrust risk by selecting the right power plant and the relationship between thrust and performance can also be managed. The risks associated with lower thrust, if not taken to the extremen, in many cases are limited to lower cruise speeds and longer takeoff runs. If managed with good pilot decision making the risk is easily manageable.

Although we can increase the inspection intervals to help address the reliabiility issue it certainly is not reasonably possible, due to the low numbers of original engines in service, provide us with the same level of certainty that a more modern power plant does. The severity of outcome of a power loss is very difficult if not impossible to mitigate, particularly if it occurs during critical phases of flight.

The pursuit of realism when building replica aircraft will always be a balance between accuracy and risk. If one is building a strictly static museum display aircraft the point is moot, but as one starts to look at flying the aircraft, taking it on cross country flights and conducting displays, the risk management equation moves more towards favouring engine reliability and durability than historical accuracy.

These discussions have no right or wrong, rather they have a spectrum of reasonable answers determined by the builders and pilots of these aircraft as to the operating environment and their individual acceptable threshold of risk. As long as this activity is done with a sound, reasoned risk evaluation to understand the probability of the risk and the severity of the outcome then the best solutuon will be acheived.

[Flysafe]

Joe, working from a known design MAY increase safety, but that asumes that the original design was well engineered and tested to start with. Additionally, unless you create an exact copy with every component and measurement being identical you cannot assume the same level of system performance.

The best way to address the issue is to design and build carefully and then carry out the tests to determine how well the entire system works and what are the limitations.

[RobW]

Originally Posted by Joe Perkel

Rob,

The M-14 looks to be a bit heavy and overpowered for this little kite! The 130 hp Clerget, was the maximum power upgrade done to the Baby.

A quick check of my notes, and I see that I identified the 220 hp version of the Continental W670 as the closest matching power-plant. It weighs in 30 lbs heavy, (dry I assume) and 525 lbs torque @ T.O. rpm (just 21 ft lbs short). I don't know what kind of prop it may swing.

I worry a bit about the age of these (perhaps unfounded, just gut), but in any case, determined to just take a "wait and see attitude." A pile of money and a premier overhaul shop, could hopefully allay any concerns in this regard.

I think off hand, I identified the Lycoming IO 390X, as the closest matching flat opposed for a pinched cowl Schneider, but not as close as the Continental radial, and for now, significantly more money for less performance matching.

Someday, when I finish the CAD model, I will try to determine the flat plate resistance of this aircraft, and try to compare that to an existing float plane / engine / prop combination.

Be sure you are looking at the M14D... not the M14P or M14PF... The M14D is the direct drive variant... if you take off the accessories it comes in close to 380 pounds. There are a couple of folks who are using the 14D as rotary substitute on Nieuports and such.

rob