RV-8 Fastback Aerodynamics

[DanH]

Actually I kinda agree with Andy, but I'm building a fastback anyway. The reasons are mostly practical. And you can't just say 'fastback" since there are two varieties. Personally I don't think the slider fastback has any practical advantage compared to a tip-over.

In the context of speed, two advantages for the tip-over; better sealing at the canopy perimeter (reduced leakage drag) and reduced canopy drag due to the one-piece bubble. Raymer suggests canopy form factor drag is increased by 40% with a seamed two-piece canopy.

However, speed considerations pale compared to the Missus Factor. Most of us are happily paired with lovely ladies of a certain age. A lot of those ladies have a very practical problem with RV entry and exit; it's hard to be graceful when there's nothing good to grab. The relocated roll bar assembly is a huge handhold.

[jferraro17]

"However, speed considerations pale compared to the Missus Factor. Most of us are happily paired with lovely ladies of a certain age. A lot of those ladies have a very practical problem with RV entry and exit; it's hard to be graceful..."




Great, not only does he build with the skill of an artist, now he puts us to shame by writing with the prose of a Pulitzer Prize winner. Dan H....Renaissance Man/Silver-Tongued Devil


Joe

[PRIME]

Originally Posted by Andy_RR

I'd love to, except I refuse to make my -8 a fast back since I'm the only person in the world that finds them ugly, try-hard and me-too. (no disrespect intended).

You're not completely alone... I too prefer the standard -8 appearance. I guess i'm a "D model" kinda guy...

[RV8RIVETER]

Originally Posted by Andy_RR

I'd love to, except I refuse to make my -8 a fast back since I'm the only person in the world that finds them ugly, try-hard and me-too. (no disrespect intended).

You are not the only one after all. I greatly prefer the look of the std 8 over the fastback, might as well build a rocket. To each his own, as they say.

[SHIPCHIEF]

Ugly was early WWII Italian fighters. They had a bubble canopy on a hunchback fuselage to give ultimate pilot visibility.
Funny how successful fighters soon followed the practice....minus the ugly.
I'm OK with fastbacks, Kent Paser did the ultimate expiriment by fastbacking his already built standard Mustang II and documenting the resultant change.
So I build toward completion, a long and grinding road. Maybe after a few years I'll take some tips from Kent's fine book; "Speed with Economy".

[dedgemon]

D model also.

[zspivey]

Originally Posted by DanH

In the context of speed, two advantages for the tip-over; better sealing at the canopy perimeter (reduced leakage drag) and reduced canopy drag due to the one-piece bubble. Raymer suggests canopy form factor drag is increased by 40% with a seamed two-piece canopy.

However, speed considerations pale compared to the Missus Factor. Most of us are happily paired with lovely ladies of a certain age. A lot of those ladies have a very practical problem with RV entry and exit; it's hard to be graceful when there's nothing good to grab. The relocated roll bar assembly is a huge handhold.

I have never cared for the look of the fast back. In addition to demonstrating a golden tongue, Dan has shown us another reason for the fast back. If it eliminates the draft on the neck of the afore mentioned lovely ladies, I would consider the ugly fast back.

[Jetj01]

As one who thinks Fastback -4's and -8's DO look much better, mostly becausew they get rid of that bulbuous giant canopy look on the -8 especially, with no loss of pilot headroom, another BIG benefit for the Fastback is the considerably larger cubic foot area of the rear baggage compartment. While -8's in general have adequate baggage space with the front and rear baggage areas, adding the Fastback mod makes for a higher baggage space-more room in the veritical-because of the higher bulkheads. In my -4 Fastback I can put in standard sized airline overhead bags in the aft baggage compartment. Also, on X-C flights, my wife brings a pillow and can lean her head back on the aft cockpit Fastback bulkhead and 'sleep' her way to our destination.

Yes, I vote they are better looking but also more practical. I can't say for sure aerodynamically they are more efficient, but the old axiom "Form follows function" would seem to apply, at least for me

Ugly???? I don't think so: http://img33.imageshack.us/img33/3724/n88xl0341.jpg

http://img695.imageshack.us/img695/6756/n234jj.jpg


Tailwinds!

[L.Adamson]

Originally Posted by Jetj01

As one who thinks Fastback -4's and -8's DO look much better, mostly becausew they get rid of that bulbuous giant canopy look on the -8 especially,

IMO, the D model P-51 Mustang with it's full bubble canopy, was one of the best looking aircraft ever designed. It's my all time favorite, and happily I had a friend who owned one. Therefor, I was able to have the pleasure of riding in a 1944 P51D as a passenger where the fuselage fuel tank once resided.

However, I also think the full canopy on the 8 is out of porportion with the rest of the aircraft. The 8 is just much smaller than a P-51D, yet we're cramming two people in it. I too, prefer the looks of the fastback. However, the "standard" 8 and full canopy, still emulate the look of the P-51D from certain angles. I guess that's what counts!

L.Adamson ---- RV6A (fastback by original design)

[Scott Hersha]

Fastback probably only refers to appearance for all practical purposes. Jon and I have nearly identical RV-8's as someone here said and mine is 2-3 knots faster, but the 'nearly' needs clarification. I have a Whirlwind 200RV prop and electronic ignition. Jon has the Hartzell blended airfoil prop and 2 mags. Mine weighed in about 45 pounds lighter than Jon's on the same day - mostly because of those two items just mentioned. We have the same stuff in our panels, same upholstery kits, similar paint jobs. Weight is partly responsible for the speed difference, and electronic ignition may account for something too, because in our speed comparison, we were in loose formation with wide open throttles, and about 2550 RPM. Asthetics should be the main reason you want a Fastback. It's a matter of taste. Some of us like blondes, some like brunnetts. Don't ask your wife to relate to this because they are more practical. And there are advantages and disadvantages practically speaking with a Fastback compared to the standard canopy. Visibility is the major winner in the practicality area in a Fastback. Entry/exit is also easier - in both seats. Baggage area behind the back seat is bigger and easier to load. Being able to easily access the behind the panel area is wonderful when you need it. You probably won't need it very often - maybe never - after you're done building, so I wouldn't weigh that advantage too heavily. If you like to work with fiberglass (I don't mind it), then you'll have fun with the Showplanes kit. It was easy to work with because it's so well made and if you know what you're doing, or are willing to learn through practice, you can get a truly tight fit all the way around. But let me warn you about the air blowing down your wife's neck. It still happens unless you seal it somehow. My canopy lays down very tight on the turtledeck. I can barely get a fingernail under it when it's sitting on the ground. When you're airborne, there's enough lift on top to open up a very small area and that's all it takes to get a small amount of ice cold air moving vertically down the back bulkhead between the fiberglass and metal. It's very easy to seal though. I used foam weather seal from Lowes that is sticky-backed and it fits snugly between the fiberglass/honeycomb aft canopy bulkhead and the metal turtledeck bulkhead when closed (I stuck it on the aft side of the fiberglass bulkhead). When you are building the canopy, you bond this bulkhead in place by clamping it to the metal turtledeck bulkhead bulkhead with small wood spacer blocks (1/2" I think), and then 'glue' it to the canoppy frame with epoxy/flox by lowering the frame down onto it. This leaves a space after it's glassed in that is the best place to seal this area. A similar situation exists up front too - also easily sealed with soft foam.
Disadvantages to a Fastback? Appearance if you don't like fastbacks. Taxiing - you loose the cool looks of a fighter pilot after a formation arrival at an airshow with your arm hanging over the side waving at the crowd.... I can still do that (left side only) with my canopy in the taxi position but it doesn't look as cool. Temperature - wise it is cool though because in the taxi position you get a really good blast of fan-forced air through the cabin (hang on to your hat!). You sacrifice visibility while taxiing though. In the taxi position, the glareshield/canopy front blocks the bottom of your field of view and you need to sit taller in your seat to see clearly over the nose. This may be do to seat cushion geometry. I tried to make my canopy as low as possible for appearance purposes. I didn't like the 'bulbuous' look of the canopy and kept trimming and moving the canopy forward until I had the look I liked. I still have plenty of head room (I'm 6'1") and I can see straight over the nose normally with no problem, but with the canopy in the taxi position, I have to stretch a bit or do some zig-zagging. I may drill an intermediate hole/taxi position to give me more vis and less air. I'll 'sperriment with that next spring. If there's anything about this you don't like, don't do the Fastback for 3 knots. I don't think it's worth that.
Am I happy with my Fastback? I love this airplane. I fly formation with several other RV-8's (Cincinnati River Rats) and when we are sitting on the ground, I just look at mine and I'm so happy I did it this way. In my opinion (the one that counts), I have the best looking one by far... The formation visibility is incomparible too.

Scott
RV-8 FB