10/23 Raptor Video

[BBerson]

Or, he may be looking at all of the other suggestions such as replacing both turbos. Or the entire engine or whatever.
What good is just trying one turbo if that negates the mission purpose?

 

[flywheel1935]

What good is just trying one turbo if that negates the mission purpose?

As the Raptor in its current state is unlikely to ever reach an altitude where the cabin need pressurization, (or even close) then why bother with the second turbo, as the Audi engine designer has recommended (several times) & I guess he knows a 'bit more' than PM ?

 

[Kyle Boatright]

Or, he may be looking at all of the other suggestions such as replacing both turbos. Or the entire engine or whatever.
What good is just trying one turbo if that negates the mission purpose?

He's got aero issues and engine issues. Making the engine run cooler and generate more power will help his flight test program and might allow him enough test flight time to figure out his aero problems. He's gotta start somewhere, because he's made very progress since the airplane was "ready to fly" in August 2019.

 

[poormansairforce]

What good is just trying one turbo if that negates the mission purpose?

It might just save his life...kinda important!

 

[cblink.007]

Formula 1 Race cars use a greenish airflow fluid in testing ( at speeds over 200mph) to see what the air is doing, guess its water based as its cleaned off before the race. As it exists there must be a supplier somewhere.

We use a healthy amount of flourescent fluids in test events. Green, orange and red work great.. Always a challenge to mount the release tubes without compromising flows. Sometimes I do not envy our instrumentation boys!

 

[rbarnes]

Marc Z,

What would have happened if the trim spring that broke, had broken in flight ?

 

[BBerson]

He's gotta start somewhere, because he's made very progress since the airplane was "ready to fly" in August 2019.

Well, the experts think he should "start over". Only he can decide what step is important to his goal each day.

 

[BBerson]

It might just save his life...kinda important!

I didn't say he shouldn't fix the turbo. I am saying he could make two turbos work together correctly now.
"nuff said" (to quote Jeff)

 

[poormansairforce]

I didn't say he shouldn't fix the turbo. I am saying he could make two turbos work together correctly now.
"nuff said" (to quote Jeff)

Gotcha, I thought you were looking at it the other way.

 

[pictsidhe]

Or, he may be looking at all of the other suggestions such as replacing both turbos. Or the entire engine or whatever.
What good is just trying one turbo if that negates the mission purpose?

Replacing both turbos with correctly sized ones will be a lot of work. The LP turbo needs to be much, much bigger. It isn't going to fit without moving a lot of stuff around.
Switching to a single turbo will allow safer low altitude flight testing. One of his existing ones would be a huge improvement over his current setup. Yes, to a higher altitude, too. But not the mission altitude, either.

 

[Marc Zeitlin]

Isn't the hinge line on the Raptor offset further than on most (all?) of the Rutanesque designs, possibly accentuating this characteristic?

Most, and possibly all, yes. The VariViggen's elevator hinge line was pretty far below the bottom surface of the canard/elevators, so there was substantial area increase with TE down motion there as well, but the planes seemed to have flown decently. So could this make the pitch sensitivity higher? Maybe, but I think it will depend more upon the specifics of the pitch actuation system (friction, moment arms, motion ratio) than the hinge line. With VE, LE, COZY, etc. planes, the side stick's motion is very small, BUT since one can rest their arm on the armrest and use only wrist motion to move the stick, you have pretty good fine motor control. I don't believe the Raptor's stick is manipulable in the same way, since it slides in and out, so you have to move your whole arm to manipulate it. Fine motor control is harder that way.

 

[HomeBuilt101]

Marc said>The downwash from the canard is ALWAYS impinging upon the main wing, reducing it's effective AOA, within the span of the canard - this is a known phenomena and slightly reduces the efficiency of canard aircraft. There are most certainly times in which the tip vortices of the canard are impinging upon the main wing, particularly at slow speeds and high AOA's (when the vortices are the strongest). In none of these aircraft does that impingement (and I include the planes with open wheel wells with the gear extended - Velocity RG, Berkut) cause oscillatory behavior either in pitch or roll.

I have always looked at these aircraft and wondered if the downwash of the canard would affect the main wing.

Yes the airplane "looks" good with the canard up so high on the nose...however it might be best if the canard was installed lower on the fuselage so as to keep the disturbed airflow out of the way of the main wing...

 

[Dantilla]

Never enough time to do it right.
Always enough time to do it again.

 

[Marc Zeitlin]

What would have happened if the trim spring that broke, had broken in flight ?

Good question. On the canards with the GU and/or Roncz airfoils, the aircraft (theoretically) trims itself to about 125 KIAS. A couple of folks have tested this on purpose and they do seem to have found that the self-trim IAS is somewhere in the 110 - 140 KIAS range. So that's where OUR canard aircraft want to fly, if you remove the trim springs. This implies that IF the trim spring disappears, cruise isn't so much of a problem but the aft stick force to slow down for landing would certainly be substantial, and you wouldn't want to have to pull that hard for very long (but it IS doable).

Where does Raptor want to fly with no trim? An aero analysis could probably predict approximate "elevator zero hinge moment" IAS, but I'm going to guess a WHOLE lot faster than 110 - 140 KIAS, given what Peter said about how much trim force he was using at 80 KIAS or so, with the CG nowhere near the front limit.

So then the question is, how much force (sans trim) is necessary to maintain the 75 - 80 KIAS landing speed that he used in the first flight. No clue. If it's 10 - 15 lb of pull, it might be possible for the pilot to deal with it for the 30 seconds it would take to land. If it's 50 lb., well, that's a different story - you're essentially wrestling with the plane at that point, and the landing wouldn't be pretty.

 

[Marc Zeitlin]

I have always looked at these aircraft and wondered if the downwash of the canard would affect the main wing.

And it does. I've got a crude and introductory presentation on Canard Aerodynamics here:

http://cozybuilders.org/Oshkosh_Presentations/2019_Columbia-Canard_Aero.pdf

and on page 20, I discuss the downwash issue. Note that all of the graphics were stolen from the references shown on Page 33.

I'm quite sure that a real aerodynamicist would find fault with some parts of the presentation, but it was introductory for a bunch of pilots at a canard fly-in - not an aero convention .

Yes the airplane "looks" good with the canard up so high on the nose...however it might be best if the canard was installed lower on the fuselage so as to keep the disturbed airflow out of the way of the main wing...

As Billski pointed out earlier, the downwash effect extends upward and downward to a approximately a full span-width of the airfoil that's creating the downwash, so with a 12' span canard on a COZY MKIV, I'd have to mount the canard 6' above or 6' below the main wing for it to have essentially no effect on the trailing airfoil.

For what should be fairly obvious reasons, that's not going to happen and isn't possible (and it's why the notion that moving the airfoil up or down a few inches will effect the main wing, on these types of aircraft, doesn't pass the smell test).

 

[pictsidhe]

I'd imagine that spring rate makes quite a difference to the handling. Any articles on that?

 

[BBerson]

As the Raptor in its current state is unlikely to ever reach an altitude where the cabin need pressurization, (or even close) then why bother with the second turbo, as the Audi engine designer has recommended (several times) & I guess he knows a 'bit more' than PM ?

Are you saying remove the second turbo? Andreas said "get rid of the first turbo"
Which turbo bleeds air to the cockpit?

Sorry if this was covered before, the focus seems to have turned to turbo issues again today.
It seems to me that PM may have originally needed and received some engineering help to design the complex turbo and pressurization system. Is that true or not?

 

[Jet787]

He may not be "ignoring", but rather trying one thing at a time? (as some suggested)

Then he should fix his cooling issue first.

 

[TarDevil]

Are you saying remove the second turbo? Andreas said "get rid of the first turbo"
Which turbo bleeds air to the cockpit?

I wonder if it matters which turbo.

It seems to me that PM may have originally needed and received some engineering help to design the complex turbo and pressurization system. Is that true or not?

Good question; if true, it was poor advice.

 

[rv6ejguy]

No, Peter matched the turbo components on his own after reading the online tutorial and spreadsheet from Turbonetics (intended for SI engines, not CI engines BTW). He failed to grasp the concepts of density ratio and compressor inlet flow at altitude and even the most fundamental aspects of staged turbos where the 1st stage compressor is ALWAYS larger than the 2nd stage. He argued with me on YT when I pointed this out a couple years ago and said I needed an education and should read the Turbonetics site... He of course had no idea about turbine matching either.

In a nutshell, he chose inappropriate turbos for the intended mission. Only the 2nd stage compressor is in the ballpark. The 1st stage compressor is half the size it should be (needs a 95-100 mm wheel) and both turbine sections are too small.

I'd add that his intercooler setups are way too small to dissipate the required heat loads at the 7+ pressure ratios he will need to run to make 350hp at 25,000 feet. This assumes they are properly ducted too, which they are not. The intercooler heat load up there will approximately equal the coolant heat load. He could have taken a clue to look at the size of intercoolers used on production aero diesels- huge. Diesels require much higher manifold pressures than SI engines to make the same torque and hp, consequently compressor discharge temps will be much higher than on an SI application.

I don't believe he consulted anyone to review his pressurization system design either.