iron eagel

Only if I could come up with 20 to 1 thrust to weight, but I think I would have to use hydrogen and Lox for fuel.

combatpigg

My Feedback: (3)

Inching forward......

I keep running into little details that I've never had to handle before, but working with these materials long enough gives you insight for how you might do something differently or better next time. Same goes with knowing where it pays to spend time and where it doesn't. I used to spend a lot more time with the molds, but by the time you apply2 or 3 or 4 layers of 4 oz cloth, the surface prep is meaningless. Just make the mold dimensionally correct and under cut it where you want extra thickness, like in the spinner area.

Mike Connor

My Feedback: (5)

The engine cowling looks great but the servo setup reminds me of something HighPlains said not long ago. The shape of the tail end of a turd is just as important as the front end (not a quote).

combatpigg

My Feedback: (3)

A teardrop shape would be better. I've got an old article from way back that analyzed the differences in drag when they went about cleaning up an old jalopy for the Salt Flats. This was even before there was formal drag racing. They used to buy those surplus WWII teardrop fuel tanks and make car bodies out of them.

iron eagel

Boy you have got a lot done in the past couple of days!
Looking good.
I am sure HP will have something to say about the those servo covers.

HighPlains

My Feedback: (1)

You need "Canoe" covers.

http://cafefoundation.org/v2/pdf_cafe_apr/RV-4.pdf

2nd page photo bottom of page.

Good article on a fast homebuilt.

combatpigg

My Feedback: (3)

HP, My computer doesn't do PDFs.......but are you talking about a flexible boot? A custom boot could be cast.....some how.

Wiggy

HP,

The link is not working for me. It says, "Forbidden You don't have permission to access /v2/pdf_cafe_apr/RV-4.pdf on this server."

Wiggy

iron eagel

Here is a link to the site HP was talking about lots of useful information on this site.

http://cafefoundation.org/v2/main_home.php
or
http://cafefoundation.org/v2/tech_lib.php


By the way CP if you can download and install the firefox browser it reads pdf's also photoshop will open pdf's so you can view them.
The free version of acrobat is not all that big of a download and should run on any computer, it should only take a few minutes even with dial up, well worth the effort...
You just might have gotten a bad download when you last tried, that is why I stopped using the dreaded internet explorer years ago.
I used to use netscape for years, then switched over to firefox a much superior browser then what comes with windows.

Mike Connor

My Feedback: (5)

I was able to right click and save the PDF file to my hard drive. Attached is the photo on the bottom of page two.

combatpigg

My Feedback: (3)

Thanks Mike.

I can visualize the forward area of the pushrod fairing being a semi rigid epoxy/glass bubble that tapers as it extends to the rear. It could come to a point in back where the sides meet, leaving a opening for the pushrod to poke through. The push rod would need to be cycled through it's travel before the trailing edge of the boot could be defined.

HighPlains

My Feedback: (1)

The covers on the RV-4 wing cover over the pivot points of the aileron hinges. So the front half is affixed to the wing, and the back half to the aileron surface. When the aileron moves the back half is moving inside the front half, with enough overlap that it is always covered at extreme movement of the surface.

The photo on the right is the tailwheel assembly he used during his speed attempts. About the size of a roller skate wheel. The taper rod to the wheel is fairly aerodynamic due to its tilt relative to the air (gives an elliptical cross-section).

iron eagel

Thanks for the explanation on how the canoe covers work HP, I had heard of them but never knew the exact setup or function.
edit to add:
Up until recently I had never gotten all that concerned with extreme speed, or drag reduction other than the basics, not being a racer.
I really want to thank you for sharing your knowledge with us!

HighPlains

My Feedback: (1)

Most RV-4's are redlined to 210 mph. However Harmon took the basic design, put in an engine with 50% more displacement and called it the Harmon Rocket - good for about 230 mph. Van was not an outright supporter, though he did sell the majorty of the components for it.

Along came Dave Anders. He took a basicly stock RV-4 and made very minor changes (basicly added a turtledeck to replace the bubble canopy. He built it as light as possible, lost a bunch of weight (helped the climb for CAFE scoring), and spent most of his effort around the engine.

In light planes, a large portion of the total drag is from cooling the engine. Most light plane engine installations are about as bad as it gets in terms of drag. Big openings in the front, poor air management inside the cowl, and a few square corners to let the air out. Anyway, it can be as much as 15 to 20% of the total airplane drag.

On top of that, he did the normal hotrodding things to the engine - higher compression, running at higher rpm than the standard 2700 for the Lycon 360, and special prop. Anyway, it was estimated to be pulling 225 to 230 hp instead of the standard 180 or 200 (depending on carb or fuel injection). Still, he should have been pretty slow compared to a Harmon Rocket with 270 to 300 HP.

So with all the things he did, he ended up with a top speed of just over 250 mph. So he did a bunch of things right.

HighPlains

My Feedback: (1)

Also noticed that the photo shows the covers and the reflection of the covers (bare AL), so the cover is half as big as it looks at first glance.

iron eagel

I had read about that RV years ago I did not put 2&2 together until you mentioned the cooling work he did, it was an amazing accomplishment.
I just re read that article a few minutes ago, an inspired effort!
I got a kick out of the comment that to better it, they felt that only a purpose built airplane would be required...
I know a few guys who have cleaned up the cooling setups on their planes, not for speed, but to improve the mileage or fuel use (well if they got a few more knots out of it at cruise, so much the better, but that wasn't the main goal).
Still it is pretty wild to have a home built that punched such a hole in the sky.
I have a buddy who wants to build an rv the only thing putting him off is all the rivets.
Still Van's still produces some excellent airframes that I think are well worth the effort.

You are right that polished Al makes it look a lot bigger, I love that shop photo!

To bad I am stuck to the ultralight or sport categories nowadays, I was going to build a Velocity it had the range and payload capacity that was perfect for a touring plane for me.

combatpigg

My Feedback: (3)

How about this for an exhaust outlet?

iron eagel

I would imagine it would get awfully messy pretty fast, is that also an exit for the cooling air?
I not sure that is an optimum shape to insure good airflow, although I like the idea...
Typically anything that departs for a circular or elliptical shape is not real good for airflow.
Although were that will be in an area of negative pressure that may not be a real issue.

Mike Connor

My Feedback: (5)

I am not aware of any rules saying the exit has to be round. Unless the pipe sticks through that crack it would be messy.

combatpigg

My Feedback: (3)

I can deal with the mess, but having the fin meltdown during a run would suck. [X(]

iron eagel

If you are using that as a cooling exit as well as the exhaust outlet it should stay cool enough to avoid meltdown.
It would come down to how much heat the fin has to dissipate and the time it would be heated.
Do you have any idea what temperature of the exhaust gas runs?
Worst case you have to extend a bit of tube through a relived area in the fin, and build out the fin enough so you could run the tube out with out physical contact occurring.

HighPlains

My Feedback: (1)

NACA ducts may void that observation.

The expansion of the gas cools it. ? is, does it expand enough 2B cool?

I'm not sold on having an internal pipe*. What is the current thinking in CL speed?

* Reason being the increase in surface area with airflow over the pipe and the inside and outside of the pipe cover being a lot of drag. Unless you restrict the airflow a lot.

combatpigg

My Feedback: (3)

I'm not sold on the idea, but thought it was worth a shot. This model does have it's share of surface area. I've given thought to lopping the top of the fin off a little, but I'm just going to leave it for now. I'll leave the plane raw fiberglass and try different things with it.
The last time I looked at a C/L speedster the pipe hung out a fair amount.
High aspect ducts are restrictive, but if the tail is to be used as an exit I'll have to guess at a working compromise.

Mike Connor

My Feedback: (5)

My experience is that anything that interferes with the exhaust exit could cost rpm. Even a short but oversize exhaust deflector cost me a couple hundred rpm on one of my Jetts with a standard tuned muffler.

iron eagel

I did forget about NACA inlet and outlets as far as their shape and function, I did not even consider them as a possible solution in this case.

I do know that if you cool the exhaust pipe it cools the exhaust reducing the volume a bit so that it in essence is like having a larger exhaust.
I think that was part of the reason that car exhaust mufflers now are typically as far back as they can put them they are more effective when the exhaust is a bit cooler.
I have recently seen a few piped exhaust that were fabricated with CF but I would imagine they are using a high temp epoxy for this sort of item.

High aspect ducts typically are very restrictive but I have used one or two which used have a nozzel structue as an exit and they do seem to work fairly well.
But these were not used in anything with a top speed even close to what you are shooting for.