Speed mod report.

EdFred

Taxi to Parking
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White Chocolate
I've owned my Cherokee for almost two years, and once I got a grasp on the power that was actually being delivered to my engine, I have always got 117-118 KTAS with it. Whether I was heavy, or light, hot or cold, I would always true out at 177-118. After waiting for a month (!) to get my plane back from annual, and having the knots2U flap seals, aileron seals, stabilator seals, wing root fairings, and flap hinge fairings installed, I got to take it up today after the Great Lakes Aviation conference.

After a more thorough than normal preflight, it was time to climb inside and see how it handled. Temperature today was just above freezing at the surface with 00000KT and SKC. My dad (230lbs) was in the right seat next to me, and I was about 1/2 full with fuel. Rolled on the power, headed down 30 and let it lift off the runway. Pitched for Vy and watched a 1300 fpm climb up through 3000'. Maintained nearly 1000 fpm with a 30 degree bank as I spiraled all the way up to 8500'. Ok, climbs real well, but I am going to attribute some of that to the cold smooth air. Let's see what my airspeed ends up being.

I call up Grand Rapids approach and let them know I will doing some manuevering over Hastings. I get my transponder squawk, increase power to 75%, and roll into a heading of 270. The air is as smooth as I have ever felt it, and I check the Garmin 430 for my ground speed. 102 kts. Hmmm, this isn't what I paid for. I turn left to a heading of 180 and get my second reading. 138 knots. This is better, let's see what 090 gives me. Roll out of my turn onto my 090 heading, level out, and check the ground speed. 148 knots. That's a nice wind out of the northwest. One more heading to check out and I get a reading of 112 knots at 360. (102+138+148+112)/4
125kts at 8500, -8C, 30.41" Hg, 2650 rpm.

Pulled the power, put in a 30 degree bank, and spiraled back down. Cancelled radar services with GRR, and let local know where I was. Ok, now lets see how all these mods affect landing. Wow. It lands sloooooooow. I have never had that much nose up trim set in before, and I've flown on colder days and been lighter than this. First time landing, it floated quite a bit, more than I thought it would, even though I expected some float with the less drag, but not this much. Flew two more patterns with a slower airspeed each time. I would say that I can land this at least 5-7 knots slower than I could before.

I can land with less airspeed, and can get a faster cruise. Tell me how this is a bad thing? So far, I'm happy with the investment.

Next up, wheel pants.
 
N2212R said:
That's a nice wind out of the northwest. One more heading to check out and I get a reading of 112 knots at 360. (102+138+148+112)/4
125kts at 8500, -8C, 30.41" Hg, 2650 rpm.

I hate to deflate your euphoria, but that method of calculating TAS isn't accurate when the wind is strong (stronger the wind the worse the error). There is a formula involving 3 headings 120 degrees apart, but the answer is a bit more complicated than averaging the speeds. To prove my point consider a wind equal to the TAS. If one heading happens to be directly into the wind then you get the following four groundspeeds:

0
2*TAS
1.41*TAS
1.41*TAS

The average of these four speeds is 1.207* TAS, IOW the estimate is almost 21% high. In your case the error will be smaller, but it could easily be a significant part of your 8 Kt improvement. My guess at this point would be that you're off by about 4 kt so you still got a 4 kt improvement which IME is fairly hard to come by with bolt on's.
 
Ah, but lance I didn't have a gain in speed in three directions. I had a gain in speed in 2 directions and a loss in speed in 2 directions. In your example you had me gaining speed 3 times, and losing it once, hence the error average. I was +/- 23 knots in the E-W and +/-13 in the N-S.
 
Ed, thats great. I know you'll enjoy the extra speed. I think i gained (by book 20kts by real world 10 kts) by my mods.
 
I'm sure cold weather may have helped, we will see what my TAS calculations come out to be as I fly it in different conditions.
 
Not with the weather here being forecast as it is. Rain/snow mix on 28th and 29th
 
Ed, relax. Its still a Cherokee. If you want a true speed mod, get a Grumman. :D
 
Anthony said:
Ed, relax. Its still a Cherokee. If you want a true speed mod, get a Grumman. :D

Yeah, an F-7F TigerCat or perhaps a BearCat....
 
If you want to get an accurate average TAS based on GPS groundspeeds, try this site. BTW, you also need to get a strobe tach to be sure your tach is reading accurately and that you're really producing only 75% power. Tachs as old as yours often read 100-150 RPM low.
 
Henning said:
Yeah, an F-7F TigerCat or perhaps a BearCat....

Or Northrop F-5, Tiger. Oh, BTW, Northrop is now Northrop-Grumman. :)
 
Ron Levy said:
If you want to get an accurate average TAS based on GPS groundspeeds, try this site. BTW, you also need to get a strobe tach to be sure your tach is reading accurately and that you're really producing only 75% power. Tachs as old as yours often read 100-150 RPM low.


Two steps ahead of you, Mr Levy. Remember last year when my Lycoming was able to turn more RPMs than anyone had ever heard of? (I could fly it S&L at full power at 2500' and get 2900 RPM out of it.) We'll we strobe tested it, and it was reading ~200 RPM high. So last year I yanked it, and put in a non mechanical tach. Retested, and it matches exact. (Well at least within 5 RPM since mine only displays to the nearest 10) So, I am sure of the power setting. Unless of course my engine is producing more than 180HP that it is supposed to be producing, in which case I wont complain.

After putting in the numbers on the site you recommended, I got a TAS of 124kts.
 
Ed, my very uneducated guess is that you probably won't know the real effects unitl you have flown the bird for a few months in varying conditions and then you will "just know"
 
AdamZ said:
Ed, my very uneducated guess is that you probably won't know the real effects unitl you have flown the bird for a few months in varying conditions and then you will "just know"

That's kinda what I am thinking, too. Even so, it *seems* like they helped. The climb is what kinda impressed me.
 
N2212R said:
Two steps ahead of you, Mr Levy. Remember last year when my Lycoming was able to turn more RPMs than anyone had ever heard of? (I could fly it S&L at full power at 2500' and get 2900 RPM out of it.) We'll we strobe tested it, and it was reading ~200 RPM high. So last year I yanked it, and put in a non mechanical tach. Retested, and it matches exact. (Well at least within 5 RPM since mine only displays to the nearest 10) So, I am sure of the power setting. Unless of course my engine is producing more than 180HP that it is supposed to be producing, in which case I wont complain.

After putting in the numbers on the site you recommended, I got a TAS of 124kts.
Ed, I was also impressed, right off the bat, by the climb rate you mentioned.

124kts w/o wheel fairings? That is very encouraging. I hope it proves out in the long run, and I can't wait to hear what you get with the fairings in place.
 
SCCutler said:
Ed, I was also impressed, right off the bat, by the climb rate you mentioned.

124kts w/o wheel fairings? That is very encouraging. I hope it proves out in the long run, and I can't wait to hear what you get with the fairings in place.

I want to see a couple of certain Tiger owners heads explode if wheel pants get me another 7 knots or so. :yes:
 
N2212R said:
I want to see a couple of certain Tiger owners heads explode if wheel pants get me another 7 knots or so. :yes:

Seven? Lets see, that will put you up to 131 knots and I get 135 knots in my Tiger. I've never heard of wheel pants adding seven knots to a Cherokee unless you put a Merlin or something in there. :)

Besides I am removing my ADF antenna (huge drag) and the steps on both sides. That should get me another 10 or 12 knots easily. :D
 
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I'll sacrifice the 4 knots to be able to get in and out of a 1500' grass. You mean the steps aren't on a MEL ?? Ooooh, off it comes! And tape...I'm going to run a line of tape over all the rivets, reducing drag even more. That should get me another 15-20kts.

:D

(I;m not sure how much the pants will help, but Scott says he lost (or maybe he was 'zaggeratin') 10kts when his came off. 10 kts gets me to 134. hehe
 
N2212R said:
I'll sacrifice the 4 knots to be able to get in and out of a 1500' grass. You mean the steps aren't on a MEL ?? Ooooh, off it comes! And tape...I'm going to run a line of tape over all the rivets, reducing drag even more. That should get me another 15-20kts.

:D

(I;m not sure how much the pants will help, but Scott says he lost (or maybe he was 'zaggeratin') 10kts when his came off. 10 kts gets me to 134. hehe


Keep dreamin Ed. When I put wheel pants on my Cherokee it actually went slower! :rofl:
 
N2212R said:
I'll sacrifice the 4 knots to be able to get in and out of a 1500' grass. You mean the steps aren't on a MEL ?? Ooooh, off it comes! And tape...I'm going to run a line of tape over all the rivets, reducing drag even more. That should get me another 15-20kts.

:D

(I;m not sure how much the pants will help, but Scott says he lost (or maybe he was 'zaggeratin') 10kts when his came off. 10 kts gets me to 134. hehe
Ed, I know I was supposed to keep this a secret. But I ma very weak. And so, here is your secret, exposed to the world and everyone. Sorry.
 

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LMAO Spike, that is the funniest thing I have seen in a looooooong time.

Looks like something that A.C.M.E. would supply.
 
N2212R said:
LMAO Spike, that is the funniest thing I have seen in a looooooong time.

Looks like something that A.C.M.E. would supply.

Well, Ed, there are so many Tiger boosters, I just felt like we needed a little engineering assistance for the Cherokee gang.

And besides, real pilots spin their finger in the air to trim.
 
SCCutler said:
Well, Ed, there are so many Tiger boosters, I just felt like we needed a little engineering assistance for the Cherokee gang.

And besides, real pilots spin their finger in the air to trim.

Uh, my trim wheel is between the seats.
 
N2212R said:
Uh, my trim wheel is between the seats.

Oh.

Sorry.

(walks off whistling innocently...)
 
If y'all want to compare 180 Cherokees to Tigers for speed, you can compare the unmodified aircraft, or you can compre Ed's modified Cherokee to a Tiger with a full array of "Mean" Gene Plazak's speed mods for the AA-5 series, including low-drag wheel pants and a number of fairings. I think you'll find that equally modified, the Tiger retains its substantial speed advantage.
 
Ron Levy said:
If y'all want to compare 180 Cherokees to Tigers for speed, you can compare the unmodified aircraft, or you can compre Ed's modified Cherokee to a Tiger with a full array of "Mean" Gene Plazak's speed mods for the AA-5 series, including low-drag wheel pants and a number of fairings. I think you'll find that equally modified, the Tiger retains its substantial speed advantage.

Plus, it's a convertible!

But, is there a "CRAP GAP" system available for the Tiger?

---

Uh Oh, I just researched STCs, and found out Tigers have a similar technology! It's called the Grumman Rocket Assisted Booster Acceleration Supplementation System (or, "GRAB ASS" for short).

Back to le drawing board!
 
SCCutler said:
But, is there a "CRAP GAP" system available for the Tiger?

Now, the SRB is a nice idea, but can only be used once. And, I think some of us have seen that CriCri that used model turbine engines, so I was thinking, why not mount some of those model turbine engines on the Cherokee gear strut, then you can have sustained boost.

http://www.bvmjets.com/turbine/turbine_power.htm
 
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