10/23 Raptor Video

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TFF

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The owner of that plane started a thread right after it happened. The thread if I remember was more about how to make it survive as is than section the power out as it should have been. The video is lagged by a couple of months. As bad as that electrical was, that’s a much easier fix than the CG. It either has to be nose heavy to fly a passenger or it needs to be fixed. The way that tail pops up is just a count down until it noses over on takeoff. Sleep at the wheel will be another prop strike.
 

Victor Bravo

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One of the people I am privileged to have met is Norm Howell, an Edwards TPS graduate and was also the very brave young fellow in the front seat of an F-4 Wild Weasel on the very first trip "downtown" into Baghdad in 1991. Truly among the best America has to offer, an incredibly nice guy, built a Q-1 Quickie, EAA Chapter member, etc..

Someone asked him, as a trained test pilot what was the most disappointing airplane you ever flew? The answer... "P-51".
 

TFF

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Sure but we want to know why. I know some Vietnam pilots who love their RVs and some who put up with it because they can’t afford more. Some don’t want to go backwards and some wanted what the childhood dream was. Usually you can group them to their love on when they were exposed to aviation first.
 

rv6ejguy

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I do worry that his niche is becoming aircraft no one else wants to deal with. And P-51s aren’t really friendly for the shade-tree weekend pilot. People need to be thinking long and hard about what they’re willing to accept before buying or building these aircraft.
I have multiple customers with Titan T51s and some Stewart S51s. These all use automotive engines, gearboxes and are electrically dependent. There is nothing wrong with those things if done right but more things to go wrong if not done right. There has been quite a number of forced landings on these aircraft where the fan has stopped turning for various reasons. These aircraft demand more maintenance skills than many owners have. Lots are sucked into the idea of flying a cool P51 replica, erroneously thinking it will be as reliable and simple to maintain as a 172. Guaranteed it won't be.

The same goes for complex designs like Raptor. This will require a lot more maintenance hours than something like an RV-10- even if the powerplant, drive and systems were as reliable as typical aircraft stuff. I'm pretty sure most new builders/ owners with stars in their eyes don't think of such things and it may bite them down the road.

Most airplanes with auto engines and gearboxes are not the favorite things for many A&Ps to dive into. In fact, if you can't do the work yourself, you may find it hard to locate someone to wrench on your new pride and joy.
 
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PPLOnly

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I have multiple customers with Titan T51s and some Stewart S51s. These all use automotive engines, gearboxes and are electrically dependent. There is nothing wrong with those things if done right but more things to go wrong if not done right. There has been quite a number of forced landings on these aircraft where the fan has stopped turning for various reasons. These aircraft demand more maintenance skills than many owners have. Lots are sucked into the idea of flying a cool P51 replica, erroneously thinking it will be as reliable and simple to maintain as a 172. Guaranteed it won't be.

The same goes for complex designs like Raptor. This will require a lot more maintenance hours than something like an RV-10- even if the powerplant, drive and systems were as reliable as typical aircraft stuff. I'm pretty sure most new builders/ owners with stars in their eyes don't think of such things and it may bite them down the road.

Most airplanes with auto engines and gearboxes are not the favorite things for many A&Ps to dive into. In fact, if you can't do the work yourself, you may find it hard to locate someone to wrench on your new pride and joy.
Yup. I try to stay away from airplanes that historically had a team of people on the ground to care of them after each flight.
Even modern aircraft like civilian C-130s suffer from bad economics due to trying to convert the manpower a military can throw at maintenance into a civilian structure.
 

malte

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Yup. I try to stay away from airplanes that historically had a team of people on the ground to care of them after each flight.
Even modern aircraft like civilian C-130s suffer from bad economics due to trying to convert the manpower a military can throw at maintenance into a civilian structure.
Funny story to pick up on this: German Army Helicopter training uses EC-145 helicopters maintained by Airbus on a contract. The responsible guy said he calculated the necessary manpower for military maintenance of these helicopters. He would need at least three times the manpower for the same job due to structures and other military necessities (drills, structure, work orders, hierarchy, shifts, manoeuvres, material storage and purchase processes...). I think you can maintain a military aircraft cheaper than the military does, but still it would be far more than what a design made for maintenance and long usage would cost.

Back to the Raptor:
I agree, keeping the ship into the air for 40 hours with just one emergency doesn't prove anything. I also agree that financial / commercial goals diverge from engineering / piloting sense quite often. Furthermore, the Raptor has been his life for a very long time now. Throwing that away and accepting his personal defeat by physics is really, really hard. Not everyone is easily up to the task.

But as any entrepreneur will tell you: fail fast and fail often. Only with letting go of dead stuff, you make room for working stuff. I wish him to be able to accept that and take another clean sheet approach with all the lessons learned. Including listening to his experts. This project is crap, but it does not need to be.
 

speedracer

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One of the people I am privileged to have met is Norm Howell, an Edwards TPS graduate and was also the very brave young fellow in the front seat of an F-4 Wild Weasel on the very first trip "downtown" into Baghdad in 1991. Truly among the best America has to offer, an incredibly nice guy, built a Q-1 Quickie, EAA Chapter member, etc..

Someone asked him, as a trained test pilot what was the most disappointing airplane you ever flew? The answer... "P-51".
I used to race with Norm Howell at the R.A.C.E. air races and you're right, a very cool guy. He had a very nice and fast Long EZ. He put me into second place at the Copperstate Dash (304 NM, Apple Valley, CA. to Coolidge, AZ.) He was visiting one of the races with his girlfriend's (now his wife) Mooney. After the race I departed behind him and caught up. When I got along side of him I said "Norm, look left". He said "You might be faster than me but I burn more gas than you".
 

lelievre12

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Being Australian and in Asia, I only know metric, so how close is 3,700 ft and 127kts to the advertised 27,000 ft and 300kts?

Pretty darn close I gather from your excitement ...
I know this has turned into the 'hate PM' group but its worth being objective on how close this project is to speed goals. CheapRacer says Raptor will need 8 times more horsepower to make the fabled 300 knots at 30,000 feet. This is simply not true. At 30,000 feet the calibrated airspeed needed on a standard day is around 187 KCAS. Given that Raptor has already demonstrated around 140 KCAS in level cruise flight the project is around 47 knots shy of its target in raw power terms. It would take an accurate L/D curve to know how much additional power it would take Raptor to make 187 KCAS but as a rough guide lets consider a Cozy IV.

1624639728864.png

At 140 KCAS the Cozy IV drinks around 6 GPH and at 187 KCAS /7000 ft it needs just under 10 GPH. Or in other words the Cozy IV needs 50% more power to make 187 KCAS than 140 KCAS. If the Cozy was turbo'd and could maintain same power at altitude it would also do 300 knots at 30,000. If we apply the same rule of thumb to Raptor it is clear that if Raptor can attain 140 KCAS on 65% cruise power it should make 187 KCAS on 100% power.

Based on the videos we have seen so far Raptor is not far from these numbers. PM is orbiting at around 65% and is maintaining around 130 KIAS reliably. That is close to target. So its ridiculous to assert that Raptor would need 8 times more power to make 300 knots at 30,000 feet. It doesn't. It probably has enough power now to do it if only it could maintain 100% continuous power at any altitude.

The issue of 300 knots at 30,000 feet is more about the present Raptor engine being unable to stay cool enough to maintain max continuous and the questionable compound turbo/intercooler design being able to operate effectively or at all at 30,000 feet. However these problems are not moonshot difficult to solve and as RV6EGUY and others have said, simply removing one turbo and refining the cooling could get gross weight speed performance close enough to target to be credible.

So the Raptor could be as fast as predicted. However it is certainly too heavy to make its distance/pax goals. However that issue is for another post.
 

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rv6ejguy

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Max cruise at FL250 is likely to be closer to 230-250 KTAS. It's never going to FL300. Using only a single turbo stage will limit it to under 20,000 feet like all the other turbo diesels out there. Simply can't develop the PR required with a single stage on the diesel.

The intercooling drag will be huge at the required pressure ratios up there as I discussed in my video on this topic and it will require a substantial increase in coolant heat rejection capability as well, over what it has now. More drag still.

No way it's going 300 KTAS the way it sits now. Lots of what ifs with a complete re-design. Of course it could be made to perform much better than now. Millions more and years down the road.

A Lancair IV-P trues about 290KTAS with a real 350hp engine, a way smaller wing, way less frontal area, less weight and a lower Cd. Raptor going 300 KTAS. No way.
 
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Voidhawk9

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I know this has turned into the 'hate PM' group but its worth being objective...
It is a fallacy to believe that because someone disagrees with someone else, that they hate them. Please do not conflate the two (although it has become very popular to do so).

Raptor has to date been unable to get even close to 10,000ft, let alone 30,000, so the argument is kinda moot.
 

lelievre12

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A better first order rule of thumb:
Power2=Power1*(Vel2/Vel1)^3

i.e 140 to 187 kts ==> 2.4 times as much power
Sorry but drag increases with the square of speed not the cube.

The correct 'rule of thumb' is Power2=Power1*(Vel2/Vel1)^2

ie 140 to 187 knots ==> 1.78 times power. Or put another way in this very simplistic analysis you'd need 56% power at 140KCAS to make 187KCAS at full power. Not that much different from the Cozy test data.

Of course as RV6EJGUY says, the chance of Raptor ever making 100% power at 30,000 feet is not very likely. Certainly not with one turbo. However its not impossible at least in concept as the Jumo 207 Diesel could do it and had a ceiling of 49,000 feet. Just take a turbo-supercharger the size of a small bus to make the needed 87" MP.

1624668275355.png
 
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AdrianS

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Sorry but drag increases with the square of speed not the cube.

The correct 'rule of thumb' is Power2=Power1*(Vel2/Vel1)^2

ie 140 to 187 knots ==> 1.78 times power. Or put another way in this very simplistic analysis you'd need 56% power at 140KCAS to make 187KCAS at full power. Not that much different from the Cozy test data.
Wrong wrong wrong.

Drag force is a function of v^2.

Power = force times velocity.
So power is a function of v^3
 

rv6ejguy

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The Jumo 207 had 2 stages of compression. Impossible to generate 87 inches Ab at 49,000 feet with a single stage centrifugal compressor- even today. That would be about a 20 to 1 pressure ratio. Realistically, with modern compound turbos and 2 stages, you can develop PRs of around 10-12 to 1.

2.4 X the HP is correct to go from 140 to 187 knots. 1.336 cubed. Not sure where 1.78 comes from?
 

mcrae0104

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Given:

\( P=TV \)
\(T \propto V^2 \)

therefore

\( P \propto V^3 \)

Next,

\( \frac{P_2}{P_1} = \frac{V_2^3}{V_1^3}\)

and therefore

\( {P_2} = P_1 \frac{V_2^3}{V_1^3} = P_1 ( \frac{V_2}{V_1} )^3 = P_1 ( \frac{187}{140})^3 = 2.38 P_1 \)

...which is the long way of saying @N91CZ and @rv6ejguy are correct.
 
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