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ArjayS(at)aol.com
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 Posted: Mon Jul 19, 2010 9:14 am Post subject: More LoPresti Data |
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Hi Guys!
Please allow me to add to the data set. First, let me tell you I'm a fan of the Jaguar cowl and of AU Country. I told Gary so at the convention. There are so few guys out here working on Grumman parts and we need to appreciate what it takes to get those products to market. I mentioned we originally designed a complete cowl but the market size and the ownership of the company was in question at the time, so we chose discression (as the better part of valor) and produced the Nose Bowl. I REALLY appreciate all Gary has had to do to get his design approved and to market. He's a good guy and when we spoke at the convention he agreed, we certainly don't do this for the giant financial reward. We do it because we're compulsive and passionate and making something better.
Please don't take the following responses personally. They are just data points. They merely reflect what we have measured over time and what we know.
Thanks!
Rj Siegel CEO/LoPresti Aviation Engineering
Gary, In reference to Arjay's email copied below. I've discussed the testing you mentioned to me some time ago with several people. That is your temperature testing of the air in the induction where you found no heating from the cylinders at cruise speeds.
There is an increase of 4 to 6 degrees F due to adiabactic heating of the induction air relative to the ambient air. There is about a 20 degree F increase over abient air temp with the stock induction system.
I just wanted to confirm that I remembered your results correctly. That is you found no increase in the air temp from the cowling entrance to the induction entrance at the rear of the baffles. That is correct right?
No, actually we found about a 26 degree F rise.
I would wager that the NACA used in LoPresti design actually yields a lower manifold pressure than the stock induction and not any cooler temps.
Nope we measured a lower temperature then stock.
Also not taking the induction air from the plemun leaves more air to cool the engine and oil.It is well known and recorded in the NACA literature that a NACA scoop is a very poor design for use where RAM is desired such as in an induction where it was shown that up to 30% pressure loss occures. A pitot type inlet is best. But taking the air off of a heated air source through a simple cut hole is worse. That is why we changed it to the NACA duct. I own both a LoPresti nose bowl and a Jaguar Cowl. I purchased the LoPresti years ago when it was the only option. I also owned another Tiger with the LoPresti. I did a lot of researching other owners of the LoPresti and found that all but one found no speed increase. Most said that the engine temps were lower and more even. One person Stu Morse, who is a racer, who, although he did not have just before and just after numbers, thought the LoPresti added 2 or 3 kts and helped in cooling both CHT's and oil temps. Glen Hadley who's Tiger I owned did have before and after flight tests and said he found no speed increase but also said cooling was improved. Most people can't flight test well-Racers have to be able to to improve their aircraft.
Stu is a sharp guy and an accomplished racer. You make another valid point, that racers pay strict attention to very small increments because those improvements are what really win or lose the race.
Just to be clear, there really is no common ground between the LoPresti nose bowl and the Jaguar cowling. They are 2 completely different things and the LoPresti in no way comes even close to the benefits of the Jaguar. One of the things I like about the Jaguar is that it retains the stock induction location. I had already proven that this is good for 3/4 - 1" of manifoild pressure increase over the stock AG5B location.
The AG5B is not the same as the stock tiger the AG5B is not as good as the original design. (Which of course shows up in the slower speeds of the Aircraft).
>From all the flight testing I have done over the years I have learned that it is quite difficult to repeat flights with the same conditions. It is also difficult to quantify 2 or 3 kts difference in speeds due to mods.
That's a very important point. We takes so many test flights my head hurts. The data set needs to be large enough that you can be certain the results are repeatable. However, if you know what you are doing you can indeed measure small increments. It's just hard. [quote][b]
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Discover
Joined: 26 Feb 2007
Posts: 429
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| Posted: Mon Jul 19, 2010 3:00 pm Post subject: More LoPresti Data |
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Okay Arjay,
Just spent the afternoon flight testing with a temp probe in the induction entrance. I flew for 45 minutes in all 4 ordinate directions. Here are the results:
OAT INDUCTION RPM
88 89 2730
The difference is 1degF
The greatest difference I could achieve was on the ground after the flight sitting running at 1360 down to 670RPM for 10 minutes where the temp difference was 11 degF
I would be very interested to take you up on the offer you made to Cliff and have you show me how you get a 26 degree difference in cruise flight.
I'd also be interested in seeing your Thermo calcs which support your adiabatic numbers....
I would still be willing to make a wager.
How about you?
Your Fellow Grumman Enthusiast,
Ned
Here is a picture of the temp probe installation:
[img]cid:777BF0100E284FD6BDDABA0C7B6BECB3(at)JULES[/img]
| Quote: |
Gary, In reference to Arjay's email copied below. I've discussed the testing you mentioned to me some time ago with several people. That is your temperature testing of the air in the induction where you found no heating from the cylinders at cruise speeds.
There is an increase of 4 to 6 degrees F due to adiabactic heating of the induction air relative to the ambient air. There is about a 20 degree F increase over abient air temp with the stock induction system.
I just wanted to confirm that I remembered your results correctly. That is you found no increase in the air temp from the cowling entrance to the induction entrance at the rear of the baffles. That is correct right?
No, actually we found about a 26 degree F rise.
I would wager that the NACA used in LoPresti design actually yields a lower manifold pressure than the stock induction and not any cooler temps.
Nope we measured a lower temperature then stock. |
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teamgrumman(at)YAHOO.COM
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| Posted: Mon Jul 19, 2010 3:35 pm Post subject: More LoPresti Data |
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| | - The Matronics TeamGrumman-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
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