Raptor Aircraft

Tufts 24” long also seem a little unorthodox.
You are of course correct, but if we're going to point out what's unorthodox, both in the subject and in the analysis and suggestions from vultures' row, we're going to need a bigger server.

Nauga,
WDTSFAL - still
 
Too bad he couldn’t have done a wind tunnel test prior to getting this far and having to do redneck testing in the field.
 
Too bad he couldn’t have done a wind tunnel test prior to getting this far and having to do redneck testing in the field.

...Or continued with testing the scale RC model as numerous folks suggested...
 
Too bad he couldn’t have done a wind tunnel test prior to getting this far and having to do redneck testing in the field.
Or maybe build a scale model and test the full range of flying characteristics. :sosp:
 
Too bad he couldn’t have done a wind tunnel test prior to getting this far and having to do redneck testing in the field.

Don’t need no stinking wind tunnel. Computer sim says it’ll be rainbows and unicorns.

 
Too bad he couldn’t have done a wind tunnel test prior to getting this far and having to do redneck testing in the field.
You want redneck? Get a few leaf blowers or a fan boat and put er by a smoldering leaf fire.
 
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Too bad he couldn’t have done a wind tunnel test prior to getting this far and having to do redneck testing in the field.
There is no magic in wind tunnel testing that will provide valid data with someone with little experience or assistance building the models and running the tests. It is easier to spend more time and money in a wind tunnel collecting bad data than by using some of the common mass-market analytical methods. TLAR backed up by sound engineering is often good enough for for airframe design at this level rather than placing absolute trust in tools and methods without the skill or knowledge to identify flaws.

None but the most sophisticated wind testing and subscale model testing would identify many or even most of the issues this design faces, including power and cooling, control surface hinge moments, aeroelasticity, and so on...

Nauga,
who's so fast he can generate bad data in half the time
 
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That’s what it looked like. No aerodynamicist but I think his tufts are just showing the obvious.
I could be mistaken, but I've always assumed that there's a science behind where the tufts are placed, as opposed to just "hmm, yeah I might stick a few here" - there's also apparently no consideration for the considerably interference a gopro is going to have to the airflow just directly upstream of the intake
 
None but the most sophisticated wind testing and subscale model testing would identify many or even most of the issues this design faces, including power and cooling, control surface hinge moments, aeroelasticity, and so on...
Somewhere back in the last 37 pages I had asked if he had done any of this, and someone directed me to his RC plane video. I'm wondering how often do (successful) homebuilt designs get sophisticated testing like that? For some reason I would have assumed most, if not all, do and did (at least for Vans, Velocity, the Lance designs) but maybe not? Presumably though those guys also didn't (and don't) operate in a vacuum either shutting out all outside advice. The VK-30 was pretty unconventional, did Cirrus guys of yonder do windtunnel tests?

Peter really could have benefited from building a good relationship with the Wasabi people and letting them help bring this thing across the finish line (which may be yet still very far away)
 
Most or all of the individual problems can be attributed to the bigger umbrella issue, which is PM’s complete refusal to listen to people with far more experience and/or specialized expertise. If they say anything he doesn’t want to hear and/or that he thinks he has a more innovative solution to, they are discarded. For that reason, he could have access to the latest testing methods and equipment, but would likely still discard any data that was “inconvenient.”

This man has one of the most narcissistic personalities I’ve had the experience to watch. It’s sad.
 
A 200hp Lycoming weighs 330 pounds. A 200 HP outboard weighs 500. They also enjoy the luxury of an unlimited supply of cold water for cooling, and through thermostats, get to operate at a constant temp, reguardless of load or rpm. Something an air cooled motor can't enjoy so you can't get the benefit of tight tolerances and precisely controlled fuel/air ratios. The environment they operate (Cylinder head temps, oil temps, air inlet temps, etc) in is very controlled and varys little. Now look at an aircraft engine, Air inlet temps go from 100 deg to the negative numbers routinely every flight. Oil temp vary with load on every climb and decent. Same for CHT and EGT. So, if you want the modern advancments of a marine engine in an aircraft, you need to make it water cooled, have a large enough cooling sysem and water load to cover all situations, and constantly varying thremostats and poppet valves to maintain temps, and never fly where air temp is going to vary much, like what your typical outboard sees its whole life.
I understand, the weight is the big thing. My main point (perhaps poorly illustrated) was that there are other designs out there that stay at one power setting for most of their life that continue to see small design improvements with each update year after year, even if it's just incremental improvements in fuel burn, etc.

I'm sure the numbers exist out there, but I'm, lazy to Google it and go down that rabbit hole. But the large PW Wasp radials and Wright Cyclones were probably the epitome of piston technical capabilities, and are contemporary to Lycoming/Continental. I understand the maintenace is a whole other matter, but strictly speaking, for a fuel burn/power perspective how do those giants compare to the engines driving our planes? Those big engines also had high volume of production and commercial interests as well as industry competition to be as good as possible. Is a DC-7/Constellation "more efficient" than a PA28?
 
Does tufting right up against the prop give you any information except yep...prop works! Cover the whole damn plane not such small areas. You know at least some air is getting where it needs but you don't know if there's turbulence 12" from the scoop
Yeah, it's almost like confirmation bias. But a tuft inside the inlet "hmm, yeah, air is going in here!"

I would have expected something more like this:
upload_2020-10-17_18-28-51.png
^granted, that's from MIT.. so not exactly the same "tier" of design
 
Somewhere back in the last 37 pages I had asked if he had done any of this, and someone directed me to his RC plane video. I'm wondering how often do (successful) homebuilt designs get sophisticated testing like that?
Building an RC model of a yet-to-be-built prototype is not 'sophisticated' in and of itself. Models most of us are familiar with would be appropriate for fixed-surface (wing, canard, verticals) sizing and basic geometry and balance at best. Models that would have even a slim chance at identifying the problems people are harping about here are beyond the capability of most average modelers and airplane homebuilder. Configuration-specific controllability characteristics are at least understood well enough to know how to scale a model to represent them, but achieving that scaling is challenging, even moreso as the scale decreases. Predicting handling qualities, aeroelasticity, power/propulsion integration, and cooling issues? Not a chance, at this scale; not from a model, not from a wind tunnel test (in and of itself), and not from X-Plane or any other linear estimation tool.

It's easy to sit back and armchair engineer this with "he should've done this and that," but in reality most of the suggestions are just as far off the mark as what has been done. I don't hold much hope for success, but I also understand the magnitude of the problems.

Nauga,
and his scaling laws
 
I would have expected something more like this:
Why?

Here's an image of a KC-135 winglet with tufts. Were they wrong to only tuft the winglet? I mean, if they knew what they were doing shouldn't they have tufted the whole airplane? (facetious question for those not following the thread)
Winglet_with_attached_tufts_of_an_KC-135A.jpg


Nauga,
scoped
 
Why?

Here's an image of a KC-135 winglet with tufts. Were they wrong to only tuft the winglet? I mean, if they knew what they were doing shouldn't they have tufted the whole airplane? (facetious question for those not following the thread)
Winglet_with_attached_tufts_of_an_KC-135A.jpg


Nauga,
scoped
True, but but had Peter been part of the KC-135 winglet design I feel like he would have just randomly stuck three or four pieces of yarn on instead of neatly organizing them out like that
 
Outboard engines operate 3 feet away from a unlimited source of great cooling. Aircraft engines don’t get that luxury!
 
True, but but had Peter been part of the KC-135 winglet design I feel like he would have just randomly stuck three or four pieces of yarn on instead of neatly organizing them out like that
What you feel he might have done has no bearing on what is actually required. What was the goal of his tuft test and how many did he need for a conclusive answer? There are cases where I can tell what I need to know with a single tuft. You might know it as a yaw string but the principle is the same.

Nauga,
who don't need a weatherman to tell which way the wind blows.
 
Outboard engines operate 3 feet away from a unlimited source of great cooling. Aircraft engines don’t get that luxury!
Yeah, 120mph forced through a air-to-water radiator is real ineffective . . . Cooling systems for modernized aircraft engines aren't exactly in the realm of rocket science.
 
So, let me be the devils advocate for a moment. If he was going to listen to what everyone else says, then wouldn’t he end up with a plane just like those already designed? If you’re going for something different, don’t you need to do things differently?

I don’t really think that, but I wonder if he does.
 
So, let me be the devils advocate for a moment. If he was going to listen to what everyone else says, then wouldn’t he end up with a plane just like those already designed? If you’re going for something different, don’t you need to do things differently?

The only thing meaningfully different here is his engine choice. Otherwise, it is a fat Velocity, poorly executed.

Point is, the high performance planforms are fairly well established after 75 years of Post-WWII GA development. Peter picked one of the viable options. After that...
 
I could be mistaken, but I've always assumed that there's a science behind where the tufts are placed, as opposed to just "hmm, yeah I might stick a few here" - there's also apparently no consideration for the considerably interference a gopro is going to have to the airflow just directly upstream of the intake

I have not designed an airplane but I have designed a few sails. You put tells where your interested in knowing what the air is doing. There are certainly areas where tells are hardly necessary. I don’t think a tell belongs on the inside of his air scoop. But I would make sure the flow path a long way in front of it is well understood.
 
I could be mistaken, but I've always assumed that there's a science behind where the tufts are placed, as opposed to just "hmm, yeah I might stick a few here" - there's also apparently no consideration for the considerably interference a gopro is going to have to the airflow just directly upstream of the intake

I think the wing placement positions makes sense because you want to determine the extent of span wise flow. He elected to not go with vortilons and it’s yet to be determined if that was a good decision.

Now tufting the aft cowling around the upper inlet and lower outlet, I think just shows the obvious. He’s getting undisturbed airflow back there and I would have assumed that. Some Velocities have used VGs on the upper cowling but that was for NACA vents. I haven’t heard anything definitive on if they worked or not. The simple fact is, piston pushers run a bit hot on the ground and some on climb out. That’s why I’ve got two oil coolers on my Velocity. Without the benefits of a tractor config pushing air into a cowling or plenum, it’s just the way it is. Of course if Peter would have stuck with Lyco or Conti, these problems would’ve already been worked out. Gonna be some serious cooling teething pains in the Raptor’s future.
 
How (in the specific case of a low RPM, constant speed engine) would higher compression help?

From Thermodynamics course years and years ago I recall that the efficiency of an internal combustion engine is strongly related to the compression ratio. I believe the benefit is not small. I think that all modern cars use much higher compression than in the past due to the demand for better fuel use. Achievable through knock detection and amelioration.
 
From Thermodynamics course years and years ago I recall that the efficiency of an internal combustion engine is strongly related to the compression ratio. I believe the benefit is not small. I think that all modern cars use much higher compression than in the past due to the demand for better fuel use. Achievable through knock detection and amelioration.

Absolutely. Our challenge is that low revving engines with big cylinder volumes are not good candidates for high compression. The cylinder volume is so large the fuel burn may not complete (move from the plugs all the way through the cylinder volume) before the heat and higher pressure from combustion in the cylinder detonates the remaining fuel on the unburned side of the flame front. That's why we're stuck with relatively low compression rates, even using 100 octane fuel.

Bikes with high revving engines and tiny cylinder volumes have compression ratios in the low teens these days, and that works for them on 93 octane fuel.
 
The simple fact is, piston pushers run a bit hot on the ground and some on climb out. That’s why I’ve got two oil coolers on my Velocity. Without the benefits of a tractor config pushing air into a cowling or plenum, it’s just the way it is.

Maybe instead of coolant tanks in the nose, he’d be better served with putting one or more oil coolers up there? And install one or more fans to supplant airflow during ground operations?
 
Maybe instead of coolant tanks in the nose, he’d be better served with putting one or more oil coolers up there? And install one or more fans to supplant airflow during ground operations?
Well, the problem with oil coolers or radiators is that they require airflow to be effective. There's only so much cooling you can do when sitting at idle. Adding an electric radiator fan would be more effective I'd think.
 
Well, the problem with oil coolers or radiators is that they require airflow to be effective. There's only so much cooling you can do when sitting at idle. Adding an electric radiator fan would be more effective I'd think.

DUCTING air to the radiators/coolers would be the first step. His radiators and oil cooler are basically just sitting in the engine compartment. There's no airflow through them.
 
Since we talked about outboards, interesting story:

About 10 years ago I bought 1960s flat bottom aluminum jon boat. It came with a rusty home made trailer. Attached to the partially rotten but functional plywood transom was (is) a 1956 Evinrude 10hp. It starts on the 2nd pull every time, even sitting after 2 years.

I bought the setup from a 20 something who fished with it for 4 years. The first thing I did as the new owner was drain the lower unit for a lube change. Got my glass spaghetti sauce jar so I could see if there was any water in the old lube. I open the plug and out comes a clear thin liquid. Waiting for lube. Nothing but water comes out of the lower unit.

Great. I bought a POS. Time to drop the lower unit for inspection. Opened her up. Not a single speck of corrosion to be found. Shiny shaft and gears (otherwise I guess water would have been rusty). Wow, they made these things well.

Looked around for a lower unit gasket kit and very surprisingly found that NAPA could get me one. Put it back together and all’s well.

One of the funnier things to me, as a guy in the environmental business - this thing takes a 1:24 mix. It has a 6 gallon fuel tank. That means I dump an entire quart of motor oil into the fuel tank for every 6 gallons. I really always laugh when I fuel it. Then I laugh some more when I pull away from the boat ramp, in my own oily fog of exhaust. Then giggle a little more at not only the smoke plums behind us, but the oily rainbow sheen in the water behind us.

Maybe it’s not tuned right. Maybe it is. But imagine what the fishing holes looked and sounded like with these old Evinrudes. Throwback...

Back to aviation now.
 
DUCTING air to the radiators/coolers would be the first step. His radiators and oil cooler are basically just sitting in the engine compartment. There's no airflow through them.
But again, ducting does little of anything for a pusher configuration when not in motion. There's no airflow to go through the ducting, lol. If you've ever dealt with older sports cars like the Corvettes, many of the high-hp models tend to overheat if they sit in traffic at idle. The radiators are small and steeply-angled (to fit in the narrow front end), they don't do well cooling a 427 in 95 degree heat. Once moving, they do just fine.

The Raptor certainly needs ducting/baffling, but it's not going to do a ton for idling on the ground or run-up.
 
The Raptor certainly needs ducting/baffling, but it's not going to do a ton for idling on the ground or run-up.

The heat load isn't high at idle, taxi, or run-up either and the aircraft has a nice low pressure area at the cooling exits. I think it would be fine at idle, with ducted air. There's no sane reason to have it the way it is. Force the air to flow where you want it - through the various radiators. Don't give it an option. This is fundamental stuff and is executed well in every aircraft I've ever looked at. With one exception. ;-)
 
You make it sound so cheap.

Exactly. Who hasn't done that?

Seriously, on construction sites where they take down a lot of trees, they often use forced air burning to hold down the air pollution that comes from running a fire at an overly rich (oxygen starved) mixture.
 
So what’s happened with his cooling system since this run up? He said instead of pumping cooling water thru his heat exchanger, in the aircraft it’ll be diesel fuel. Could that be the reason? Also, I believe he has 2 fans beneath the radiator pulling air thru at isle. Is that correct? Just doesn’t make sense how he did several run ups with oil temps not getting above 215 but yet he now has cooling issues.

 
Why do a liquid intercooler, when the systemS weigh more and the liquid becomes “heat-soaked”? Why not air-to-air?
 
So what’s happened with his cooling system since this run up? He said instead of pumping cooling water thru his heat exchanger, in the aircraft it’ll be diesel fuel. Could that be the reason? Also, I believe he has 2 fans beneath the radiator pulling air thru at isle. Is that correct? Just doesn’t make sense how he did several run ups with oil temps not getting above 215 but yet he now has cooling issues.
I’m not sure the fans he used on the test stand were actually installed in the plane.
 
I’m not sure the fans he used on the test stand were actually installed in the plane.

Thats what I was thinking. I’m wondering if he thought just the air being pulled into that upper inlet would be enough cooling air thru the radiator.
 
Since we talked about outboards...

Outside of Tallahassee, FL resides the Tallahassee Automobile Museum.

Lots of stuff other than cars, including a very large collection of antique and classic outboard motors. Never been “into” outboards, but some of the examples there were fascinating examples of engineering.

Worth a trip.
 
Since we talked about outboards, interesting story:

About 10 years ago I bought 1960s flat bottom aluminum jon boat. It came with a rusty home made trailer. Attached to the partially rotten but functional plywood transom was (is) a 1956 Evinrude 10hp. It starts on the 2nd pull every time, even sitting after 2 years.

I bought the setup from a 20 something who fished with it for 4 years. The first thing I did as the new owner was drain the lower unit for a lube change. Got my glass spaghetti sauce jar so I could see if there was any water in the old lube. I open the plug and out comes a clear thin liquid. Waiting for lube. Nothing but water comes out of the lower unit.

Great. I bought a POS. Time to drop the lower unit for inspection. Opened her up. Not a single speck of corrosion to be found. Shiny shaft and gears (otherwise I guess water would have been rusty). Wow, they made these things well.

Looked around for a lower unit gasket kit and very surprisingly found that NAPA could get me one. Put it back together and all’s well.

One of the funnier things to me, as a guy in the environmental business - this thing takes a 1:24 mix. It has a 6 gallon fuel tank. That means I dump an entire quart of motor oil into the fuel tank for every 6 gallons. I really always laugh when I fuel it. Then I laugh some more when I pull away from the boat ramp, in my own oily fog of exhaust. Then giggle a little more at not only the smoke plums behind us, but the oily rainbow sheen in the water behind us.

Maybe it’s not tuned right. Maybe it is. But imagine what the fishing holes looked and sounded like with these old Evinrudes. Throwback...

Back to aviation now.


Racing older air-cooled two stroke motorcycles was an interesting learning experience in compression rations, oil/gas ratios, carburetor jetting, and cylinder head design. I normally raced using 34:1. One of my fellow racers did an experiment, to see how much oil they could get in the gas and still make power. They got down to like 18:1, but had trouble fowling plugs. Running it on a dyno, the bike was making more power. They guessed that it was because the oil helped the rings seal better and keep the heads and piston tops cooler. Of course, the jetting had to go up to deal with more oil in the fuel...

Getting heads milled to modify the squish-bands on a 2stroke means you could run higher compression ratios as the thin layer of fuel/air on the outsides of the piston top prevented detonation. Fun stuff.
Good book that covers two strokes, in case anyone's interested: https://www.amazon.com/Two-Stroke-Performance-Tuning-Bell/dp/1859606199
He also wrote a pretty good book on 4stroke engine tuning.
 
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