Lack of speed

[Darrin Tolleson]

I have a 1966 PA 30B C/R and the fastest I have seen so far is about 140 KTS at 2000' with 75% + power. I normally see 130-135 KTS ind from 3000'- 9500'. I have various speed mods on the acft, but the speed isn't even close to what I think I should be able to achieve (150ish). Does anyone have any ideas that may help increase my speed.

Thank you

[MULEFLY]

Darrin.... that does sound quite doggy... by chance to you have a defective air speed indicator? To make sure I would do a airspeed check with the following and GPS

http://www.pilotfriend.com/calcs/calcul ... ulator.htm

At least that will give you a solid base line of your current performance and you can see the effects as you work to improve it.

Secondly, send me your email address at jim dot covington at inwave dot com. I have some articles that I'll gladly forward to you.

Hans has the fastest twinco in the fleet... I believe he has demonstrated 181.6 kts... 209 mph. I have a PA39 and I file at 165kts (full gross weight 3,800 pounds) ... depending on load I frequently see more than 170 kts... (with Robertson STOL mod).

All the best!
Jim

[Jay]

I'd start with rigging.

Jay

[N3322G]

Darrin,

I noticed this is your first post. Welcome to the Maintenance Forum. We all help one another here.

Jim has a good thought on the air speed gauge - just had mine overhauled as I felt as though we were landing too fast - even though the airspeed gauge said differently. Wrote about it in the June Flyer in Comanche Care, Part 2. Very happy with Air Parts of Lock Haven for this work. I also learned a static check is required after the R&R of this gauge.

Please post what path you take and the results.

Hope this helps.

[md11flyer]

Darrin:

First of all a stock PA 30 should clock in at least at 160 knots true. From your speeds are you giving us indicated airspeeds?
If so, convert them over to true and you will probably be in the ballpark. With most of the speed mods and fresh paint, my PA-30B
has just been clocked using GPS at near gross, at 65% power at 7000 ft, at 170knots. At wide open throttle 75%, ROP lightly loaded,
I have seen 175 knots.

Do the check over again with the GPS or if you don't have one, a willing radar operator can give reasonable ground speeds for the cardinal points.
135 knots at 75% power is in my opinion not possible for the PA-30,except if it is dragging the gear in the slipstream.
That being said jack the bird up and see if the gear tucks nicely into the wells . (there is a item in the maintenance manual about this check as well)

Gary

[Darrin Tolleson]

Thank you for the quick responses. The airspeeds that I mentioned were indicated airspeeds; the GPS seems to back up what the airspeed indicator is indicating. I have a true airspeed wheel on the airspeed indicator as well, I do not believe I have seen over 145 - 150. And that is a guess because the number on the true airspeed indicator cannot be seen because the window does not go that low on the airspeed indicator. The true airspeed window starts about 135 KTS I believe. I have seen 160 KTS on the airspeed indicator on descents and over 200 KTS gnd speed once again on a long descent with a tailwind. I will take a look to see if the landing gear is hanging down. And I plan on checking the rigging on my annual in November.

When I was flying and it didn't matter what altitude I was cruising at, it felt as if the plane was being held back or flying around with a drag chute behind it.

I will keep you posted.

Again, thank you all for the quick and useful responses.

[N3322G]

Darrin, that's helpful info - speed mods, if poorly installed or loose can also create rather than reduce drag but based on your description, my vote (or guess) would go for gear drag or poor rigging. Please post what you discover. Thanks.

[Jay]

I would break out an E-6B, old fashioned whiz wheel or electronic, and get a handle on your actual true airspeed plus do the multiple course GPS check before I spent much more effort on troubleshooting.

Jay

[David Pyle]

Here's a simple test. While at rest observe that the retracted flaps both align the same way with the fuselage bottom. Then see if the ailerons both align with the flaps. It is not so important that they line up with the wing tips (which never quite match). If this works out look at the yoke to see if it is in the neutral position. To the degree that aileron trim tabs are deflected is a clue that in flight one or both ailerons are misaligned which can slow the airplane.

There are other rigging issues but this is easy to check. A drooping gear will do it and loose gear doors will do it and even the passenger door fit can do it. Poor and pealing paint can do it. Usually if it flies straight and level hands off its not too serious.

Some may argue, but some airplanes come from the factory slower and there is no way to fix it. Is there anything different in the history of your TC? Ever wrecked and rebuilt? That could do it...

[Jerry Mazza]

I have a 1970 Twinco and on mine the dial for the true airspeed is in MPH, while the indicated is in knots. At altitude (around 8k) i usually indicate around 150 kts but shows an indicated of 190 mph which is approximately 165 knots. I do have alerion and flap gap seals, the Lopresti speed spats, Johnston wingtips, Roberston STOL, Loptesti WOW Cowls, and the Miller nose and dorsal fin and the Araphoe sloped windshield. I used to own a stock Twinco and I would routinely get around 145 kts true. I agree a sagging gear seems likely. Also, be sure that your manifold pressure gauge is reading correctly as well as you tachometer. Aircraft Spruce sells an inexpensive optical tachometer checker that you can use from the pilots seat to verify your Tach. The maniflod pressure gauge can be checked by comparing it to ambient pressure with the engine off and compensating for altitude. You take the altimeter setting and either add 1'' of pressure or subtract for every 1000 feet above sea level. It has been a long time, and I can't remember exactly how to do this. Anyone else remember the calculation? Also, do you seem to bwe producing full power on takeoff?

[Jerry Mazza]

By the way, what has Hans done to get sucha fast plane???

[David Pyle]

What the instruments show is less important than what your GPS tells you in various wind conditions. However, do qualify the gauges...A/S ind. can be checked at an avionic shop, the hand held RPM may not work in a twin and manifold ind. is likely correct.

Hans is a magician and Jeff is his protege. Don't even try...

[Hansmeister]

Dear Jerry,

The answer is just about everything that I can think of. I've written a number of tech articles that probably Jim Covington has forwarded to you.

The short list is: 1) rigging, 2) gear tight in wells, gear door set for 1/8" at 9 pounds, 3) cowl baffle seals very tight and all holes plugged, 4) the usual speed mods, 5) some additional mods that I have developed.

My current cruise speed going to Lost Wages a few months ago was at 9500 at cruise power, with a true of 209 mph per the Aspen.

The first 10 knots are easy, and the last 10 are very difficult, and easily lost if the plane is not properly maintained. For example, one year going to the Reno races, I was only seeing 200 true. Where did my speed go to? Well, after cleaning my K&N air filters after 5 years, I got 5 mph back. It's the little things that count.

[steen]

Darrin,
I fly a '66 CR also and I used to file and make 170knts TAS. Now at mid-time engines i file and make 165 knts and don't really quite make that. As the engines
age I believe they put out less power at the same old MP/RPM settings. How many hours are on your engines?
Engine nacelles are many times the highest drag on the airplane....we have two.....a lot of potential drag. The cowl seals must be very tight and all openings
plugged to direct the cooling airflow properly. This is a commonly overlooked item and is crucial to the Twinkie getting that last 5-10 mph it is capable of.
Steen

[N3322G]

Darrin,

As I pre-flighted for today's flight, I noticed the alternate air door knobs were just a little out so I pushed them in - which made me think of another thing that can slow you down. Are your alternate air doors all the way closed? This is a check item on annual but my experience is, that it frequently does not get done - search on that item in this Forum and you'll see some examples. The Service Manual is explicit on the adjustment and the manual is online at this website under the Tech Tab.

Look forward to hearing what you do and what the results are.