Rocket Racing League

Chris Hall wrote:



Well, LOX and LN2 are things that average graduate students can easily
learn how to handle, yet I think I'd rather trust my life to civilian
airport personnel than a run of the mill graduate student. :-)


Although you could get LOX at a military facility, getting it at
Jamestown Airport is going to be difficult- I'm pretty sure you could
get the alcohol by distilling the blood of some of the cropduster
pilots, but even that would take specialized equipment. :-)
Seriously, having odd propellant needs for your aircraft is definitely
cut into its sales potential.
You could operate it like the BD-5J as an airshow attraction though.

Pat

Pat Flannery wrote:

Although you could get LOX at a military facility, getting it at
Jamestown Airport is going to be difficult...

Well, it's not like 100-LL just flows out of the ground there either.
Just truck in the LOX, the same as with any fuel.

As far as the racing goes, the artist renderings all show planes
belching long flames out the back, but realistically, these planes
would be using burps of thrust to climb out, then their built-up speed
and kinetic energy from a gliding dive to run most of the course as
gliders, saving their fuel as much as possible. That's not the
turn-and-burn jet racing they tried at Reno. This is most like the old
FAI class F-3-B radio control electric powered glider racing. They
changed the class designation, I dunno what they call it now, but the
planes have very powerful electric motor systems and folding props. At
launch, they climb out at more than 45 degrees alpha, until they reach
a certain altitude, within a limit of something like one minute run
time. When the timer starts, they kill the mortor, any use of motor
after that point costs them time added to their total. They then do a
speed laps task running laps between two sets of gates/ground sighting
devices until they run out of altitude or finish the requisite number
of laps/time. They can leave the course to gain altitude by
thermalling, but they dare not use motor runs except in emergencies. At
the finish, still gliding, they pass thru/under a limbo style gate,
then land. it's very impressive to watch, takes masterful mamagement of
your ships' energy state, (like what Bob Hoover used to do in his Twin
Commander) and drove advances in the hobby relating to battery and
motor performance, airframe design and construrction techniques, and
airfoil development/optimization. Its an international contest.

Jake McGuire wrote:

The wing loading on an Me-163 is pretty close to conventional light
aircraft, so landing speeds oughta be pretty low, and the L/D ratio is
probably going to be a bit better as well, due to the aerodynamically
clean design and the lack of an aircooled engine and stopped propellor
up front.


I checked up on this Eric Brown touched down on his first Komet flight
at around 115 mph, so a minimum landing speed is probably around 100 mph.
That would be considerably lower in the composite replica Komet, but
there's a downside to the low weight; any increase in drag is going to
cause the speed to bleed of faster in the replica than in the actual
aircraft.
So once your landing gear comes down, you are going to start losing
velocity fairly quickly.



For one thing, the retractable landing gear means that drag will go up
after it's lowered, so at that point you are pretty well committed to
landing.



What's preventing you from firing the engine again and going around?


That would be the obvious solution, but it means keeping some
propellants on board for a possible aborted landing, and that means more
weight, a steeper glide angle, and a higher stall speed.
It also means touching down with LOX and alcohol on board, and while
they aren't hypergolic like the Komet's propellants, the possibility of
rupturing part of the LOX tankage or feed lines in a rough touchdown
could lead to injury to the pilot if it came in contact with him. Of
course if the propellants mix inside the airframe and there is the
slightest spark....



The real Me-163B suffered from another landing problem- once it reached
low altitude, it had a severe problem with floating in ground effect
which made a precision touchdown difficult (pilots were killed or
injured by having the aircraft float past its intended landing point
onto rough ground - retractable underwing spoilers helped, but it was
still tricky to land)



Of course, having conventional telescopic landing gear vs. a fixed skid
means you don't need to really grease it on in order to not break your
back, and the absence of hordes of marauding P-51s means that you can
enjoy such luxuries as landing on an honest-to-god runway. And then
once you don't have to assume crash and breakup on landing, and don't
have hideously toxic propellants, you can actually carry the fuel to go
around if needed.



Since XCOR's replica would share the same aerodynamics as the Me-163,
this problem could manifest itself also. I don't know what happens in
regard to going into ground effect with the gear lowered, but I suspect
it ends in a stall at very low altitude.



Why? Just like any other airplane, come in at 50% over stall velocity
(the Me-163's wing loading isn't THAT high), flare, and land.



That was the problem with the Me-163; you'd do that, open the wing
spoilers, and the plane would come down to within a few feet of the
ground and just float in ground effect till the speed bled off enough
that it would settle to earth.
Being tailless it behaves differently than an aircraft with a horizontal
tail fin.
Trying to raise the nose to decrease speed and make it touch down drives
the outer trailing edge of the swept wing closer to the ground, where it
comes in contact with the ground effect pressure area and starts to
rise. The thing becomes a WIG vehicle during final approach.
On the other hand, once the pilots got the hang of that strange
touchdown behavior it was supposed to have really superb flying
characteristics.



Considering the airframe will be pretty light weight, something along
the lines of the Microturbo engine used in the BD-5J should be powerful
enough to get it airborne. I've seen one of those things, and they move
like a raped ape- although it can reach 320 mph, its small size makes it
look like it's traveling a near-sonic velocity.
The motor doesn't weigh much (84.88 pounds), and on the BD-5J is fed by
a pair of small unobtrusive side-mounted NACA scoops:
http://www.bd-micro.com/FLS5J.HTM
You'd probably need a bigger engine for the Me-163, but still it would
be doable.



The BD-5J, like most Jim Bede creations, is well known for falling out
of the sky and killing pilots with alarming frequency. And the Me-163
had an installed thrust of around 4000 lbf, which is about 10 times
that put out by the Microturbo in the BD-5J.



Yeah, but the XCOR variant wouldn't be carrying anywhere near that fuel
load or engine thrust I assumed- it was supposed to be a hobbyist
replica rather than a full-blown point defense interceptor wasn't it?
You go up the FAA and tell them you want to make something rocket
powered that can do around 590 mph and climb at 11,000 feet per minute,
and they might give you the green light- you tell hem you want to start
producing these things for sale and they might be have some concerns.


While I agree that the Me-163 as previously built left much to be
desired as an operational aircraft, the BD-5J is one of the few things
out there that's worse.



I don't think they've had quite the pilot attrition rate they had with
the Me-163 with the BD-5J; they lost more Komet pilots in takeoff and
landing accidents than they did to combat, and that's fairly unusual for
an aircraft in wartime.
I can see why the crash on occasion; the one I saw was one of the
Budweiser airshow ones, and the pilot did a very low altitude flight
down the length of the runway at over 200 mph- it was only after I saw
the size of the aircraft that I realized he'd had been at around ten
feet altitude!

Too bad they couldn't find any buyers, but it looks like their modified
EZ-rockets might actually be going into something resembling serial
production.



What these motors might be very usable for is a built-in JATO system for
aircraft (assuming you have access to LOX). You can see all sorts of
uses for a reusable rocket boost system for aircraft that doesn't
require you to lug around heavy JATO bottles in poorly developed areas.

Pat

Henry Spencer wrote:


Until it becames a frequent thing, almost certainly the way you'd fill up
would be from one of the same tank trucks that supply the hospitals, with
the hose handled by the same guy who does it for the hospitals. When the
airports start having permanent facilities for it, yeah, the crews would
need a bit of training for it, but that'll come with the equipment.


I doubt that there is ever going to be a big demand for rocket planes at
airports- the whole concept has a lot of shortcomings compared to
turbine propulsion, starting with inferior flight duration for the same
weight of propellants.
These will remain airshow curiosities and high-end novelty toys for the
rich at best.
They just aren't a rational approach to civilian aircraft propulsion no
matter how safe you make them, which is why the were quickly superseded
by the turbine engine during the 1950's.
You could certainly reach a higher altitude with one than with a turbine
engine (although from a surface takeoff that might be an iffy
proposition due the the weight and bulk of propellant tankage you would
have to drag along), but that really doesn't seem to be a very salable
commodity except in some sort of novelty passenger use.
Has anyone looked into the effect the rocket motor is going to have on
the runway when the aircraft rotates for take-off?
Noise is also going to be a problem.





Considering the airframe will be pretty light weight, something along
the lines of the Microturbo engine used in the BD-5J should be powerful
enough to get it airborne. I've seen one of those things, and they move
like a raped ape- although it can reach 320 mph, its small size makes it
look like it's traveling a near-sonic velocity.



A number of years ago, I saw an aerobatic display by a BD-5J at an
airshow. The impression of lightning speed was indeed very strong...
especially compared to the C-5 that was also there.


I saw a C-5 coming in for landing at Fargo- it looked like it was moving
at about 25 mph. You almost get scared that it will fall out of the sky
on you it appears to be moving so slowly.

Pat

Alan Anderson wrote:


Well, it's not like 100-LL just flows out of the ground there either.
Just truck in the LOX, the same as with any fuel.



Again, this sounds like something for a plane used at a airshow- it
shows up on its trailer, they attach the wings, fuel it from their
LOX/alcohol tanker, and wow the crowd. National demand for that sort of
aircraft is going to be ten or twenty tops.
If you use them for racing then you have to have odd rules for them, as
they are going to have a very limited flight duration.
If they had something they could do better than a jet it would help, but
I can't think of what it would be.
A surplus MiG-21 could blow them clean out of the water if it ever raced
against them.

Pat

D. Orbitt wrote:

They can leave the course to gain altitude by
thermalling, but they dare not use motor runs except in emergencies. At
the finish, still gliding, they pass thru/under a limbo style gate,
then land. it's very impressive to watch, takes masterful mamagement of
your ships' energy state, (like what Bob Hoover used to do in his Twin
Commander) and drove advances in the hobby relating to battery and
motor performance, airframe design and construrction techniques, and
airfoil development/optimization. Its an international contest.



For radio control this would be fun and could be done for a reasonable
cost on the part of the contestants; but for manned flight it would be a
pretty obtuse sport, probably of limited crowd appeal due to the short
duration of the whole race.
Now unlimited jet trophy races- that would be fun! The Harrier's VIFF
allow to round the pylon tightly, but that Foxbat is going to be a
terror on the straight-away! :-)

Pat

Pat Flannery wrote:
I checked up on this Eric Brown touched down on his first Komet flight
at around 115 mph, so a minimum landing speed is probably around 100 mph.
That would be considerably lower in the composite replica Komet, but
there's a downside to the low weight; any increase in drag is going to
cause the speed to bleed of faster in the replica than in the actual
aircraft.

Aren't you arguing two paragraphs ahead that the Komet is excessively
clean and floats down the runway forever? Is this consistent?

So once your landing gear comes down, you are going to start losing
velocity fairly quickly.

How quickly? Even with extended landing gear, the Komet still probably
had an L/D over 10.

That would be the obvious solution, but it means keeping some
propellants on board for a possible aborted landing, and that means more
weight, a steeper glide angle, and a higher stall speed.
It also means touching down with LOX and alcohol on board, and while
they aren't hypergolic like the Komet's propellants, the possibility of
rupturing part of the LOX tankage or feed lines in a rough touchdown
could lead to injury to the pilot if it came in contact with him.

But the XCOR replica would have had real landing gear. No dolly to
take a funny bounce and hit the airplane on takeoff, or to fail to
separate. Actual shock absorbers, so you could land with an
appreciable sink rate. Brakes that you can apply or not as you see
fit! Directional control during the landing rollout!

I don't think that you're appreciating just how big of a difference
that makes.

Of
course if the propellants mix inside the airframe and there is the
slightest spark....

Which hasn't been as excessive concern with the EZ-Rocket, or any of
the other rocket-powered aircraft that have been built before. Purges,
firewalls, leak checks... it can all be done.

Yeah, but the XCOR variant wouldn't be carrying anywhere near that fuel
load or engine thrust I assumed- it was supposed to be a hobbyist
replica rather than a full-blown point defense interceptor wasn't it?

Nope. XCOR was actually promising ENHANCED performance. No armament,
clearly.

-jake

Pat Flannery wrote:
Alan Anderson wrote:


Well, it's not like 100-LL just flows out of the ground there either.
Just truck in the LOX, the same as with any fuel.



Again, this sounds like something for a plane used at a airshow- it
shows up on its trailer, they attach the wings, fuel it from their
LOX/alcohol tanker, and wow the crowd. National demand for that sort of
aircraft is going to be ten or twenty tops.

So? That's actually higher than Xcor thought the demand was going to
be. No one was envisioning fleets of hundreds of these things.

If you use them for racing then you have to have odd rules for them, as
they are going to have a very limited flight duration.

The typical heat of the Reno Air Races lasts less than ten minutes.
Fuel consumption is not likely to be a problem.

If they had something they could do better than a jet it would help, but
I can't think of what it would be.
A surplus MiG-21 could blow them clean out of the water if it ever raced
against them.

Unclear. The MiG-21 has a slightly higher thrust-to-weight ratio, but
a much higher wing loading, and delta wings aren't known for their
great efficiency at high lift-to-drag ratios. Not to mention that it's
unlikely that a race class would exist that allowed both the MiG-21 and
the Komet replica, so the point is largely moot.

The Xcor Komet replica was not intended to replace the 777 in mainline
revenue service; it was marketed as an expensive toy. Too expensive,
it turns out, at five million dollars, but that's what it was always
supposed to be.

-jake

Jake McGuire wrote:

Pat Flannery wrote:


I checked up on this Eric Brown touched down on his first Komet flight
at around 115 mph, so a minimum landing speed is probably around 100 mph.
That would be considerably lower in the composite replica Komet, but
there's a downside to the low weight; any increase in drag is going to
cause the speed to bleed of faster in the replica than in the actual
aircraft.



Aren't you arguing two paragraphs ahead that the Komet is excessively
clean and floats down the runway forever? Is this consistent?



Komet puts down a skid- that's not much extra drag. XCOR was going to
put retractable gear on theirs, and that would be a lot of drag compared
to the skid.
the big problem here is that Lippisch was primarily a glider designer,
and he designed the Me-163 as a rocket boosted glider to some extent. A
glider designer instinctively wants to get the best glide ratio
possible, so the aircraft was very clean aerodynamically, and handled
exceptionally well while gliding. But all of its aerodynamics were
designed for something that probably would weigh far more than a modern
composite replica would in its landing configuration with its
propellants expended. So I don't know what effect that would have on its
landing characteristics.



So once your landing gear comes down, you are going to start losing
velocity fairly quickly.



How quickly? Even with extended landing gear, the Komet still probably
had an L/D over 10.



Yeah, but tires and landing gear doors are going to generate a fair
amount of turbulence compared to the skid.



That would be the obvious solution, but it means keeping some
propellants on board for a possible aborted landing, and that means more
weight, a steeper glide angle, and a higher stall speed.
It also means touching down with LOX and alcohol on board, and while
they aren't hypergolic like the Komet's propellants, the possibility of
rupturing part of the LOX tankage or feed lines in a rough touchdown
could lead to injury to the pilot if it came in contact with him.



But the XCOR replica would have had real landing gear. No dolly to
take a funny bounce and hit the airplane on takeoff, or to fail to
separate. Actual shock absorbers, so you could land with an
appreciable sink rate. Brakes that you can apply or not as you see
fit! Directional control during the landing rollout!

I don't think that you're appreciating just how big of a difference
that makes.



True, landing would be a lot less bumpy than a Komet, it's just the LOX
gets me a little queasy.



Of
course if the propellants mix inside the airframe and there is the
slightest spark....



Which hasn't been as excessive concern with the EZ-Rocket, or any of
the other rocket-powered aircraft that have been built before. Purges,
firewalls, leak checks... it can all be done.


Their approach on EZ-Rocket was smart- keep the two propellants as far
apart as possible
however if you want the Komet to look right, both end up inside the
airframe.



Yeah, but the XCOR variant wouldn't be carrying anywhere near that fuel
load or engine thrust I assumed- it was supposed to be a hobbyist
replica rather than a full-blown point defense interceptor wasn't it?



Nope. XCOR was actually promising ENHANCED performance. No armament,
clearly.



In that case you'd be lugging a hell of a lot of LOX and alcohol along-
what would the propellant cost per flight be?
You've still got the limiting mach number for that airframe design to
deal with, so your speed can't go much beyond 600 mph.
and an engine powerful enough to get that sort of performance might
wreak havoc on a runway as the aircraft heads for take-off; that's okay
at a military airfield where things are taking off on afterburner- but
how about a civil airport that may have asphalt runways? You might set
the runway on fire during takeoff.
But since they apparently aren't going to build it, this whole
discussion is somewhat moot.

Pat