Hi everyone,

I have presently the Desser AeroClassic 21/8.00-6 tires and cruise at around 85-90mph. How much speed loss do I have to expect with the 26" and 29" Airstreaks? My gross weight is 1300lbs and I can't decide if I want to go 26" or 29". My hangar neighbor has some 29" Airstreaks he is planning on putting on a CH-801 and these tires look huge. Anyone having first hand experience with the Airstreaks?

I went from 6.00-6 to the 26" AirStreaks and lost a few MPH (3-5). I can't be more exact than that since I replaced the gear legs, brake calipers, etc. at the same time. I also did not install the gear leg fairings so it was hard to figure what the lose was from just the tires. I put the fairings back on the other day but haven't done a speed test yet.

I went from 8:00's to 26" Airstreaks on my S-7, and then finally manned up and went to the 29" Airstreaks. I was somewhat surprised to find the 29's so much more cushier then the 26's, they hold a lot more air is why I guess. My advice is don't mess around, go right to the 29's, go big or go home! That said, even the 26's will be MUCH better then what you have now, and worth every penny.

In the middle of all this I also went from the very clean stock Rans single leg spring gear to Cub style gear. I have fully faired the new gear. Bottom line is my top speed has dropped from around 115 to 105. More importantly, as I never fly at my top speed, I can still fly economically at 85 to 90, though even that is faster then I usually go unless I need to get somewhere. My fuel burn seems to have gone up a bit when cruising faster, maybe 1/4 GPH or so, hard to tell there. The increase in utility is so much greater, and the bumps so much easier on the airframe, I feel this is a fair trade off and would do it again in a heartbeat.

Thanks for the replies. I think courierguy convinced me to go 29".

8.00x6 to 26's on my champ, maybe a few mph difference, barely noticeable

8.00x6 to 31s on my Citabria I lost 2 kts. Hardly noticed.

Given drag increases with the square of velocity, at your speeds it's unlikely to be much of a concern. In a faster aircraft doing 130kt + you might expect to lose a more significant ammount.

Battson wrote:Given drag increases with the square of velocity, at your speeds it's unlikely to be much of a concern. In a faster aircraft doing 130kt + you might expect to lose a more significant ammount.

Yes, one "advantage" of having a slow airplane!

I went up last night and did a little ridge soaring (and chasing some turkey buzzards around) with throttle almost down to idle, much less then usually needed for sustaining flight. Didn't shut down as I wanted the heater and the lift just wasn't strong enough. At 45-50 mph the added drag of the big tires is probably pretty minor, but it always strikes me as comical as hell to be ridge soaring with those big old tires hanging out in the slipstream, like what's wrong with this picture?!

courierguy wrote:At 45-50 mph the added drag of the big tires is probably pretty minor, but it always strikes me as comical as hell to be ridge soaring with those big old tires hanging out in the slipstream, like what's wrong with this picture?!

The only thing wrong with the picture that I can think of is that you didn't post a picture.

The laws of nature being what they are (for every action there is an equal & opposite reaction), those bigger tires are draggier and there is a price to be paid-- whether it's apparent or not. More drag + more power = same speed, kind of the ohm's law of drag. While it may be true that you're not seeing much reduction in speed with those bigger tires at the same cruise rpm, it's likely that you're using more power to achieve that rpm. Hard to tell with most airplanes equipped with fixed-pitch props since they don't usually have a manifold pressure gauge. Only way to tell would be by the fuel burn, or maybe measure how much throttle knob is sticking out of the panel.

Good point fro sure Hotrod, and I have noticed that when on XC's and bumping it up a bit more then usual. In my case that means closer to 4 GPH, maybe even (gasp), as much as 4 1/4 GPH then 3 1/4, near as I can tell maybe 1/4 to 1/2 GPH more burn at "speed" (for me) with the Cub style gear AND the 29's. then before with a cleanly faired single leg spring rod gear and 8:00's. Bumping around slow, like today, over 4 hours mostly at 45 to 65 with a bit of 85 to 90 MPH, it appears pretty much the same though I'm sure it has to be a bit more. Point being, if a pilot is all about going fast as possible all the time, keep the small tires for sure. But if playing around on off airport stuff, go big as possible/affordable (money and fuel burn).

Todays adventure: 8800' LZ, to put those mts. in the background to scale, what a great weather day! This site I have landed before, on 8:00s, just a little earlier though I landed another and there was a cluster of rock hard ant hills mixed with cantalope size rocks that made me glad I had the 29's, insurance

hotrod150 wrote:The laws of nature being what they are (for every action there is an equal & opposite reaction), those bigger tires are draggier and there is a price to be paid-- whether it's apparent or not. More drag + more power = same speed, kind of the ohm's law of drag. While it may be true that you're not seeing much reduction in speed with those bigger tires at the same cruise rpm, it's likely that you're using more power to achieve that rpm. Hard to tell with most airplanes equipped with fixed-pitch props since they don't usually have a manifold pressure gauge. Only way to tell would be by the fuel burn, or maybe measure how much throttle knob is sticking out of the panel.

I was with you right up until fixed pitch.
Having a fixed pitch prop means RPM varies with power. Unless I'm forgetting something... There could conceivably be a very very suble difference because of the efficiency of the prop at different airspeeds, but it'd be small.